# β24: A discrete, cascoded, fully-differential power amplifier



## amb

I just posted my latest project, basically a β22 on steroids, as a dedicated speaker amp, with a few new twists thrown in:

HeadWize: DIY Workshop > β24: A discrete, cascoded, fully-differential power amplifier

 Have a look!


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## d-cee

nice, but way out of my depth

 nice looking graphs though


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## joneeboi

Interesting, as I JUST had the thought last night of building a speaker amp for downstairs.

 Come on, d-cee, where's the fun in life if you don't involve yourself in projects that are way over your head? 
	

	
	
		
		

		
		
	


	




 Colour me hooked. I'll be following along closely.


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## 00940

Very nice amp. 
	

	
	
		
		

		
		
	


	




 How much power is dissipated at iddle in the output stage ? (I couldn't find any figure in your text)


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## Ferrari

Thanks for the exciting news amb !
 I will sit back with a fresh cup of coffee and have a close look at the schematic and the circuit descriptions.
 Starting from the already excellent β22, it should undoubtly resulted in a great amp.


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## johnsonad

Ti, thanks for another outstanding amp! This is what I've been looking for


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## aamefford

Ti, this is great! I am early in my DIY career (but well into my mechanical engineer career...). My goal is to work my way up to the Beta22 and then find a nice speaker amp to build. By the time I'm ready, your Beta24 will likely be well tested and built. I'm stoked!


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## MoodySteve

WOW!!! I'm very excited about this project...and I think it'll be a great first foray into loudspeaker power amps (no one offers the quality of documentation and real-time support that AMB Audio does).

 Guess I'll have to make some loudspeakers to go with it...δ24 anyone???


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## naamanf

Sorry about my wallet. Looks like I know what I am doing when I get these B22s finished


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## asebastian0

Wheeeee! Another tasty treat, looks good amb!


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## rsaavedra

WOW!!!!! Great graphs! Ok this is officially my next DIY project, finally a top-notch DIY 100w speaker amp to build.


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## Polaris111688

Extremely impressive figures. I really like the slew rate of 290V/us. I'll be looking into this in the future for sure.


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## borisov57

Wow. Cooool. That is also true balanced amplifer for headphones from input to output. But volume control must be elsewhere and gain should be lower. AMB roules.


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## sbyers77

I need to graduate and get a job so I can spend money on stuff like this.


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## rsaavedra

Just realized that I had saved this bookmark for another possible DIY speaker amp candidate, also 100w into 8 ohms. I wonder Amb if you might know about it, and might want to share some assessment or comparison with the Beta24. Is this a worthy competitor of the Beta24?

 Would like to know your thoughts on differences in maybe ease/difficulty of build, ease/difficulty in finding components, sensitivity to component matching, differences in features, measurements, even differences in size, heatsinking needed, things like that.

 In any case I'll most likely try to build two Beta 24 monoblocks, but would highly appreciate your comments on this one anyway.


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## OverlordXenu

Is it an integrated or a pure speaker amp? Sorry if it was mentioned before, I didn't notice it.


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## 00940

considering it will be driven to full power with a common cdp output (2.8Vrms) and can be driven by an unbalanced input, it just needs a pot to become an "integrated".


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## Nebby

Wow that's exactly what I've been looking for! I'll be waiting patiently for it


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## dBel84

Quote:


  Originally Posted by *00940* /img/forum/go_quote.gif 
_considering it will be driven to full power with a common cdp output (2.8Vrms) and can be driven by an unbalanced input, it just needs a pot to become an "integrated"._

 

afraid not..... quoting AMB from headwize

 "AMB, is there any problem with driving the B24 directly from the source( with source selector and atten) as a integrated amp?"

 "masantos, As I said in the first post, the amp has low-ish input impedance and must be driven from a source with low output impedance. If you put a volume control directly before the input of this amp, the volume pot will become a high impedance source at anything except maximum volume. Typically, the volume control is before a flat-gain or buffer stage in the preamp in a speaker rig."

 another superb project, thanks for sharing amb..dB


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## johnsonad

It was interesting to read on the other site how Ti's idea was actually a patent of Nelson Pass. Great minds think a like but at different times 
	

	
	
		
		

		
		
	


	




 I'm glad to see that Mr. Pass has given the okay to go ahead with this project and the rest of us are excited to put it to use! Thanks again Ti!


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## amb

Quote:


  Originally Posted by *rsaavedra* /img/forum/go_quote.gif 
_Just realized that I had saved this bookmark for another possible DIY speaker amp candidate, also 100w into 8 ohms. I wonder Amb if you might know about it, and might want to share some assessment or comparison with the Beta24. Is this a worthy competitor of the Beta24?_

 

Yes, I've seen that circuit before, Kevin Gilmore linked to it in a post at one point. I've not done any detailed analysis of it so I can't really say much, it looks to be well thought-out. It has many more parts than the already-complex β22 or β24. I've used those Sanken ring-emitter transistors in a previous project and they are quite good, but they might be difficult to source from a worldwide perspective, and the market is rife with counterfeits. I try to steer clear of some of the more exotic Japanese BJTs, which also tends to become obsolete, leaving perfectly good designs out to dry, not to mention my preference for the reliability and well-behaved thermal characteristics of MOSFETs.


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## 00940

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_afraid not..... quoting AMB from headwize

 "AMB, is there any problem with driving the B24 directly from the source( with source selector and atten) as a integrated amp?"

 "masantos, As I said in the first post, the amp has low-ish input impedance and must be driven from a source with low output impedance. If you put a volume control directly before the input of this amp, the volume pot will become a high impedance source at anything except maximum volume. Typically, the volume control is before a flat-gain or buffer stage in the preamp in a speaker rig."

 another superb project, thanks for sharing amb..dB_

 

Hum, yeah, you're right, I stopped reading too early. 
	

	
	
		
		

		
		
	


	




 On the topic of the preamp still, do you get better distortion results when the amp is driven by a balanced source ?


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## rsaavedra

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Yes, I've seen that circuit before, Kevin Gilmore linked to it in a post at one point. I've not done any detailed analysis of it so I can't really say much, it looks to be well thought-out. It has many more parts than the already-complex β22 or β24. I've used those Sanken ring-emitter transistors in a previous project and they are quite good, but they might be difficult to source from a worldwide perspective, and the market is rife with counterfeits. I try to steer clear of some of the more exotic Japanese BJTs, which also tends to become obsolete, leaving perfectly good designs out to dry, not to mention my preference for the reliability and well-behaved thermal characteristics of MOSFETs._

 

Thanks Amb! I knew I had gathered the link from Head-fi, but wasn't completely sure. That counterfitting issue of that key component in the other amp confirms my first thought, so the β24 it will be.


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## ppl

Everything Old is New again Cross coupled Amps have been around for quite a while Consider reading www.next-tube.com/articles/cci/cci_EN.pdf - the Reasons are the Same reduced High order harmonics


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## Crowbar

Quote:


  Originally Posted by *ppl* /img/forum/go_quote.gif 
_Everything Old is New again Cross coupled Amps have been around for quite a while Consider reading www.next-tube.com/articles/cci/cci_EN.pdf - the Reasons are the Same reduced High order harmonics_

 

Are you sure? It's not just about being cross-coupled, but in such a way that distortion from one side appears in phase on the other side. I simulated a few cross-coupled amps two years ago and not all show this behavior (inject a pulse with a voltage source somewhere along the path on one side after the differential pair, and on some such as Gilmore's Blue Hawaii and the Pass-derived Aleph-X amps it appears on both outputs).


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## amb

FYI. I posted an update:
HeadWize: DIY Workshop > β24: A discrete, cascoded, fully-differential power amplifier


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## infinitesymphony

I know it's still fairly early in development, but is there any estimate of final build cost?


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## amb

No estimate of cost yet. As you are surely aware, the electronic components of the build is only a portion of the total cost. Items such as headsinks, casing, and other mechanical stuff would affect the actual cost greatly, and everyone's build will be different.

 As a reference-class uber-amp, you know that it won't be cheap.


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## naamanf

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_\

 As a reference-class uber-amp, you know that it won't be cheap._

 

My wallet trembles in fear and anticipation


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## MrMajestic2

Quote:


  Originally Posted by *naamanf* /img/forum/go_quote.gif 
_My wallet trembles in fear and anticipation 
	

	
	
		
		

		
		
	


	


_

 

My wallet just commited suicide.


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## amb

A sneak preview: 3D rendering of β24 PCB

 For high-res version click here.







 - One channel per board
 - Board size 7" x 4.5"
 - 4 copper layers
 - Silkscreen on top side
 - Soldermask on top and bottom sides
 - Flexible off-board MOSFET heatsink schemes
 - 8 onboard Panasonic TS-HA 1500uF 100V capacitor bank for output stage


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## TheRobbStory

Welp, I'm salivating.

 I just moved into a huge apartment in DC that's just BEGGING for a solid speaker setup!


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## Ferrari

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_A sneak preview: 3D rendering of β24 PCB

 For high-res version click here.

 - One channel per board
 - Board size 7" x 4.5"
 - 4 copper layers
 - Silkscreen on top side
 - Soldermask on top and bottom sides
 - Flexible off-board MOSFET heatsink schemes
 - 8 onboard Panasonic TS-HA 1500uF 100V capacitor bank for output stage_

 

Thanks for sharing !
 Your excellent works are highly appreciated.


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## fierce_freak

Beautiful work, amb...expensive looking, too 
	

	
	
		
		

		
		
	


	




 (to build)


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## ferds

WOW nice work... Cant wait..


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## mofonyx

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_afraid not..... quoting AMB from headwize

 "AMB, is there any problem with driving the B24 directly from the source( with source selector and atten) as a integrated amp?"

 "masantos, As I said in the first post, the amp has low-ish input impedance and must be driven from a source with low output impedance. If you put a volume control directly before the input of this amp, the volume pot will become a high impedance source at anything except maximum volume. Typically, the volume control is before a flat-gain or buffer stage in the preamp in a speaker rig."

 another superb project, thanks for sharing amb..dB_

 

Ideally, the B22 preamping the B24?


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## Crowbar

amb, how did you create the 3D rendering?


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## heatmizer

Eagle3d and Povray I believe.


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## amb

Quote:


  Originally Posted by *heatmizer* 
_Eagle3d and Povray I believe._

 

Yup...


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## amb

Silkscreen: light grey
 Top layer: red (signals/ground plane)
 Inner layer 1: grey (high current V+)
 Inner layer 2: navy blue (high current V-)
 Bottom layer: blue (signals/ground plane)

 Overlap of top/bottom layers: violet
 Overlap of inner layers: light blue


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## d-cee

I see what you did there


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## Crowbar

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_I see what you did there_

 

You're doing it wrong.


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## DaKi][er

Really? 4 Layers? It's hard to tell with the real low res and compressed picture but surely you should be able to design it in only 2 layers, I'm yet to see any through hole board that couldn't be done in 2 layers and still be a good layout at the end


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## d-cee

Quote:


  Originally Posted by *Crowbar* /img/forum/go_quote.gif 
_You're doing it wrong._

 

Sorry






 Anyway... back on topic!

 Is that the production layout amb? or are more changes expected to be made?


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## n_maher

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_Is that the production layout amb? or are more changes expected to be made?_

 

It's the prototype layout, upon which initial testing will be done. I think we're a good ways from seeing the production pcb's, which is as it should be.


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## amb

Quote:


  Originally Posted by *DaKi][er* /img/forum/go_quote.gif 
_Really? 4 Layers? It's hard to tell with the real low res and compressed picture but surely you should be able to design it in only 2 layers, I'm yet to see any through hole board that couldn't be done in 2 layers and still be a good layout at the end_

 

Yes, it's 4 layer. The placement of parts is as logical as I could make them (which correspond to the schematic almost exactly) with very short and direct traces. I want a relatively compact board, but given the large number of parts I have to pack them in fairly tight (which helps distances too). Add the requirement to put the output devices at the edges for off-board heatsinking, plus the onboard capacitor reservoir banks, there just isn't enough room for the large/fat high current V+ and V- areas that I also want to put in.

 Adding two internal layers for V+ and V- neatly solves this problem without compromising parts placement and signal routing. The incremental cost of the extra layers isn't too bad considering the nature of the amp.

 Oh, and yes, I'm still playing with the layout -- this is definitely not the production version.


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## rsaavedra

Looks great!!! Keeping an eye on whenever you nominate your production version Amb.


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## amb

If there are no further comments, I'm going to order prototype boards based on v0.6:

HeadWize: View Post [DIY Workshop > β24: A discrete, cascoded, fully-differential power amplifier]


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## amb

Prototype PCBs based on v0.6 have been ordered, ETA is April 11. To keep the price down, I ordered 20 boards (for ten amplifiers). If any of you would like to be early prototypers please PM me.


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## amb

A sneak preview... my front and rear panels.


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## naamanf

Wowser Ti! Very nice.


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## n_maher

one word...

 [size=medium]*WOW!*[/size]


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## thrice

Very nice indeed!


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## TheRobbStory

Holy crap, Ti. My Jaw's on the floor!


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## Pars

x2!

 Note to self... floor doesn't taste good, pick up jaw...


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## BradJudy

Wow - you went hardcore on this one. Very high-end professional look.


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## n_maher

My only suggestion (after looking at the pics more) would be to change out the silver XLR's for black units. That would tie in better with the IEC and fuse since the silver of the XLR doesn't match the chassis (or doesn't appear to).


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## holland

I would use gold to tie in with the other jacks. Allow the IEC and fuse to be called out separately. I say, I would, but in reality, I wouldn't because I don't care about aesthetics much since it would be hidden behind a cabinet. However, if I did, I would. 

 Edit: Very nice plates, amb. I mentioned it at headwize, but forgot to do so here.


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## TheRobbStory

Quote:


  Originally Posted by *holland* /img/forum/go_quote.gif 
_I would use gold_

 

Funny you should say that. I intend to build mine into a machined block of solid gold. It is going to be <i>so</i> baller


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## Ferrari

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_A sneak preview... my front and rear panels._

 

Good to see some pieces of "The Master Piece" in the make. 
	

	
	
		
		

		
		
	


	



 Excellent work, Ti !


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## Crowbar

I like the heavy duty construction, but why do you have handles on the back? LOL


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## amb

Quote:


  Originally Posted by *Crowbar* /img/forum/go_quote.gif 
_I like the heavy duty construction, but why do you have handles on the back? LOL_

 

I estimate the overall weight of this amp to be north of 70 lbs, having handles on both ends allows two people to carry it.


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## MrMajestic2

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_I estimate the overall weight of this amp to be north of 70 lbs, having handles on both ends allows two people to carry it._

 

So its a portable amp then


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## amb

Quote:


  Originally Posted by *MrMajestic2* /img/forum/go_quote.gif 
_So its a portable amp then 
	

	
	
		
		

		
		
	


	


_

 

Only for those with strong arms!


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## BradJudy

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Only for those with strong arms! 
	

	
	
		
		

		
		
	


	


_

 

And very long power cords.


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## swt61

Holy Crap! Those plates are gorgeous!


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## luvdunhill

knowing you amb, I'm sure you have plans for how the case will be assembled. Care to share them? Specifically going from a two panels and two heat sinks, to an assembled case.


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## penger

wow. nice case work!


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## n_maher

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_I estimate the overall weight of this amp to be north of 70 lbs, having handles on both ends allows two people to carry it._

 

Wow, and here I thought that my 65lb monster would be the heavy-weight around these parts. 
	

	
	
		
		

		
		
	


	




 I can't wait to see the finished product, Ti, it already looks like you've once again raised the bar for the rest of us.


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## holland

70lbs, eh? That's quite heavy. Might I suggest some casters in the back. My power amp has that, and it helps quite a bit to tilt up the front a bit to adjust the position on the rack, particularly if I need to pull it out to twiddle around with the rear panel.


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## amb

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_knowing you amb, I'm sure you have plans for how the case will be assembled. Care to share them? Specifically going from a two panels and two heat sinks, to an assembled case._

 

It's basically a Hifi2000 Pesante Dissipante 4U 300mm case with the optional 10mm panel. But I replaced the rear steel panel with another 10mm panel, added a reinforcement plate to the bottom, added more reinforcement/support bracketry inside and will replace the steel top cover with a clear 4mm Perspex one so you can look inside.


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## Ferrari

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_It's basically a Hifi2000 Pesante Dissipante 4U 300mm case with the optional 10mm panel. But I replaced the rear steel panel with another 10mm panel, added a reinforcement plate to the bottom, added more reinforcement/support bracketry inside and will replace the steel top cover with a clear 4mm Perspex one so you can look inside._

 

amb, you have done something with that HiFi2000 Pesante Dissipante enclosure.
 It makes me thinking of a Dutch guy (not me 
	

	
	
		
		

		
		
	


	




) making the enclosure for his pre-amp mainly out of 12mm thick copper plates,
 which finally resulted in ~50Kg pre-amp. 
	

	
	
		
		

		
		
	


	




VERSTERKER DER VERSTERKERS


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## amb

Just a quick snapshot of my β24 chassis configuration. As you can see, the β24 and σ22 board for each channel are mounted to the heatsink on each side. The big Plitron transformer and a smaller SumR transformer, as well as the bridge rectifiers and solid state relay are mounted to a 4mm thick aluminum plate which is then bolted down to the bottom of the case.


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## Beefy

OH......MY......GOD......

 That is just...... unbelievable!


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## rsaavedra

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_



_

 

WOA! Awesome job Amb!


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## Covenant

There's something strange about this hobby. I dont own speakers, I live in a small apartment, all my listening is done via headphones...

 And yet, i see these pics that AMB is taking, lick my lips, and immediately start thinking "I wonder if any builders will offer to make these professionally..."


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## Polaris111688

Holy.... Crap.....

 Absolutely stunning work, AMB.


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## n_maher

Quote:


  Originally Posted by *Covenant* /img/forum/go_quote.gif 
_And yet, i see these pics that AMB is taking, lick my lips, and immediately start thinking "I wonder if any builders will offer to make these professionally..."_

 

I'm sure they'd think about it till they realized the near 5 figure price tag that might be required to make it worthwhile. 

 Fantastic work as always, Ti.


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## holland

where'd you get the toroid covers?


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## amb

Quote:


  Originally Posted by *holland* /img/forum/go_quote.gif 
_where'd you get the toroid covers?_

 

I did not get the "covers" separately. These are encapsulated/potted and magnetically-shielded toroids, and were manufactured that way.


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## d-cee

Quote:


  Originally Posted by *holland* /img/forum/go_quote.gif 
_where'd you get the toroid covers?_

 

I think the audio transformers are encapsulated so that's how they look. at least from Plitron

 edit: beaten by amb.


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## Ferrari

amb, you've beaten me on the progress of this beauty by far, looks very professional ! 
	

	
	
		
		

		
			




 I see that you manage to mount the β24 board with output MOSFETs on that 4U heatsink, was it much of a problem due to limited space? Do you have to cut on the side brackets a bit?

 The β24 and σ22 boards on mine are mounting (almost) similar to yours, only different is that the σ22 doesn't have on-board heatsinks. The output MOSFETs of the σ22 are mounted on the same large heatsink as the β24.
 (I'm using 300mm x 300mm heatsink)


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## amb

Quote:


  Originally Posted by *Ferrari* /img/forum/go_quote.gif 
_amb, you've beaten me on the progress of this beauty by far, looks very professional ! 
	

	
	
		
		

		
		
	


	


_

 

LOL, it looks close to completion but I still have a _lot_ more to do.

  Quote:


 I see that you manage to mount the β24 board with output MOSFETs on that 4U heatsink, was it much of a problem due to limited space? Do you have to cut on the side brackets a bit? 
 

No, I chose not to cut the brackets. There is enough room without doing that, even though the MOSFET and Caddock resistor leads have to be bent back some to reach their PCB holes:


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## Ferrari

Very neat solution !


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## TheRobbStory

Quote:


  Originally Posted by *Covenant* /img/forum/go_quote.gif 
_There's something strange about this hobby. I dont own speakers, I live in a small apartment, all my listening is done via headphones...

 And yet, i see these pics that AMB is taking, lick my lips, and immediately start thinking "I wonder if any builders will offer to make these professionally..."_

 

Ha, I'm in the same boat. I'm a thousand miles away from my speakers, yet I've been lusting over this project since its inception. I ordered a set of prototype boards and the first round of parts yesterday. I 'finance' most of my projects by spreading their construction out over time.

 In this case, this helps me both financially, and educationally. I've got plenty of time to do homework. 

 Right now I'm in the process of sorting out power supply (mainly, trafo selection) issues.


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## gyrodec

I'm with Covenant and TheRobbStory, but with a twist. I have an Musical Fidelity A370 185W class A monster I don't use much as I do most of my listening at my desk with headphones. I'm thinking - Can we drop the voltages and bias currents a bit and make a balanced B22 killer?

 We are warped people. There is no hope.


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## gyrodec

I forgot to mention. AMB you seriously rock, but everybody here already knows that. Next time I'm at the bar, i'll buy a round in your honour. 
	

	
	
		
		

		
		
	


	




))


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## amb

Details here


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## Lil' Knight

WOW!!
 Look gorgeous


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## infinitesymphony

amb, put this into mass-production and retire! 
	

	
	
		
		

		
		
	


	




 (As long as you keep making designs on the side. 
	

	
	
		
		

		
		
	


	




)

 Super professional-looking. I can't wait to read impressions and see specs of the completed amp.


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## TheRobbStory

I started populating my boards last night. I now know the horror that is desoldering and soldering the JFET quads in their proper configuration. I read the warnings a thousand times, but I still followed the silk screen :slaps forehead:

 I've ordered the rest of the parts for the β24 with the exception of the Panasonic electrolytics and the big MOSFETS. Those add up really fast, so I'm waiting for payday 

 I've got several ideas for casing and power supply options, but nothing definite yet.

 Here's some camera phone eye candy:






 My boards were waiting for me at home when I got home from VA yesterday. AMB really went all out on these. As I get more and more familiar with them, it becomes more and more apparent that they are works of art within themselves. It's apparent from the get-go that a LOT of time and effort went into this design, and for that I am truly thankful to AMB and the DIY community.


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## Ferrari

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Details here_

 

Great news amb. Keep up the good work!


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## TheRobbStory

*06/13/2008 update:*






 Two nearly completed β24 boards (missing MOSFETS and rail caps)

 Two nearly completed σ22 boards (missing MOSFETS and a few caps)

 Two Plitron transformers

 One more Digikey order and these will all be fully populated. Avel transformers for unregulated rails will be ordered at the end of the month.

 Enclosure design nearly finalized.


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## smeggy

Awesome stuff The Rob.....
 How much did the whole shebang cost you so far?


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## TheRobbStory

Estimating roughly off the top of my head, you're looking at about half a G there.

 My estimates have total build cost (including two enclosures, monster heat sinks, two more transformers, ε24 boards/parts, Front Panel Express work, speaker binding posts, XLR and RCA connectors, etc.) at around $1200.


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## smeggy

Thanks, not too bad then.


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## amb

It's alive and ready for this coming weekend's NorCal meet! 
	

	
	
		
		

		
		
	


	




 A lot more pictures and details are at headwize:
HeadWize: View Post [DIY Workshop > β24: A discrete, cascoded, fully-differential power amplifier]


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## krmathis

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_It's alive and ready for this coming weekend's NorCal meet! 
	

	
	
		
		

		
		
	


	


_

 

Awesome looking amplifier! 
	

	
	
		
		

		
		
	


	



 Seems like a lot of amplification for $1200..


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## amb

Quote:


  Originally Posted by *krmathis* /img/forum/go_quote.gif 
_Awesome looking amplifier! 
	

	
	
		
		

		
		
	


	



 Seems like a lot of amplification for $1200.._

 

I actually spent quite a lot more than that on mine, because of the Hifi2000 case (expensive with all the options, and $$$ FedEx shipping from Italy to California), all the Front Panel Express work, and a very pricey Plitron transformer. I honestly don't know exactly how much I spent on this amp, because of the prototype nature of it, I bought many more parts than needed.


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## Beefy

That is _seriously_ impressive AMB. Everything about it is just a cut above anything I've ever seen before!

 I _very much_ look forward to listening impressions


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## Pars

Wow! That really looks great Amb!


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## krmathis

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_I actually spent quite a lot more than that on mine, because of the Hifi2000 case (expensive with all the options, and $$$ FedEx shipping from Italy to California), all the Front Panel Express work, and a very pricey Plitron transformer. I honestly don't know exactly how much I spent on this amp, because of the prototype nature of it, I bought many more parts than needed._

 

I see!
 But it still don't take the glory away...


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## n_maher

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_I honestly don't know exactly how much I spent on this amp, because of the prototype nature of it, I bought many more parts than needed._

 

And I'm sure like many of us you probably didn't track expenses intentionally! 
	

	
	
		
		

		
		
	


	




 Amazing work as always, Ti.


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## Ferrari

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_It's alive and ready for this coming weekend's NorCal meet! 
	

	
	
		
		

		
		
	


	




 A lot more pictures and details are at headwize:
HeadWize: View Post [DIY Workshop > β24: A discrete, cascoded, fully-differential power amplifier]_

 

As I suggested earlier, you should be the first person who completed this amp. Congratulations, Ti. It's simply a _masterpiece!_





 Mine is not so far due to moving from a custom made enclosure to a black 5U HiFi-2000 Pesante Dissipante and my crazy work schedule lately. I'm more or less finished the electronics part but the the mechanical work -the lions share of this build to my opinion- still need to be done. But sooner or later, I will surely complete my β24.


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## infinitesymphony

So clean-looking... I'd almost be afraid to use it. I wonder what others' builds will look like, and if anyone will be selling completed versions. 
	

	
	
		
		

		
		
	


	




 What is the final weight of yours, amb?


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## n_maher

Quote:


  Originally Posted by *infinitesymphony* /img/forum/go_quote.gif 
_What is the final weight of yours, amb?_

 

In the headwize thread Ti reported the amp weighs right around 60lbs, officially a beast and qualifies him for Team Heavyweight.


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## TzeYang

Amb, didnt you remove the BJT pre drivers for the MOSFETS for the later revisions due to signal clipping and difficulty in bias stability?

 I thought i was seeing things, but you still retained them in your build.


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## amb

The BJT pre-driver stage is gone. The TO-220 devices you see on the board are the DN2535 depletion mode MOSFETs used as CCS for the cascoded output stage.


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## holland

AMB, that's an absolutely awesome build. I'll have to pick your brain one of these days about some of the details...like sourcing the brackets and the sub-enclosures, hand drilled and aligned or outsourced.

 Anyhow, I wish I could hear it, but I can't make the meet. grrr. Are you going to have your own room to play it loud?


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## MusicallySilent

Just stunning, even though I could never afford it, it is beautiful to look at and I will follow this thread.

 I would be interested to see if you could make a more affordable speaker amplifier from the CK2III or M^3 or just a new schematic where a base end model costs around 100-150 to assemble with everything included. This isn't much of a request just throwing out an idea for a future product for you since I am one of the Head-Fiers who could never afford something like this.


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## amphead

WOW! State of the art for sure. This is the pinnacle that we should all strive for.


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## MASantos

Quote:


  Originally Posted by *MusicallySilent* /img/forum/go_quote.gif 
_Just stunning, even though I could never afford it, it is beautiful to look at and I will follow this thread.

 I would be interested to see if you could make a more affordable speaker amplifier from the CK2III or M^3 or just a new schematic where a base end model costs around 100-150 to assemble with everything included. This isn't much of a request just throwing out an idea for a future product for you since I am one of the Head-Fiers who could never afford something like this._

 

There is a CKIII power amp thread over at headwize. YOu should check it out. It will probably be more than 150$ but it will be very hard if not impossible at all to build a discrete (or IC based)with complete casing for that value.


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## Daveze

If you're thrifty you could probably pull off a chipamp for $100-150. But that's a conversation for another thread, probably another forum.

 Nice amp AMB, I am envious of just how awesome that is.


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## digger945

I like the perty colors! shweet amp, dude! From a distance it looks like a small futuristic metropolis!, only without any people.
 Thanx,
 Scott


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## amb

qkizz had completed a dual-monoblock β24 build. See his headwize post for impressions. It's worthy of note that he is driving electrostatic panels with the amp, which is a difficult load for many amps.


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## TzeYang

Wow monoblocks. 

 Man, when will be the day that I can finally afford to make professional PCBs and use awesome cases like these for my projects.

 :|


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## Ferrari

Very nice work! 
	

	
	
		
		

		
		
	


	



 Scrolling up and down through the β24 pics of amb and qkizz makes me feel like a inerty slow builder.
 Wishing my β24 build was that far!


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## TheRobbStory

Quote:


  Originally Posted by *Ferrari* /img/forum/go_quote.gif 
_Very nice work! 
	

	
	
		
		

		
		
	


	



 Scrolling up and down through the β24 pics of amb and qkizz makes me feel like a inerty slow builder.
 Wishing my β24 build was that far!_

 

Ditto that! Mine has been sitting on a shelf since June awaiting ideas and funding. It makes me sad to see the boards sitting there.


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## rhys h

To all you gents who are building the b24, how much is it costing you to just populate the boards?


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## krmathis

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_qkizz had completed a dual-monoblock β24 build. See his headwize post for impressions._

 

Really sweet looking amplifiers!


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## n_maher

Quote:


  Originally Posted by *rhys h* /img/forum/go_quote.gif 
_To all you gents who are building the b24, how much is it costing you to just populate the boards?_

 

I don't mean this to sound the way that it's going to and you probably aren't thinking along these lines anyway but I'll say it anyway with the hope of avoiding someone getting in way over their head. Populating the PCB's for this project is a very bad way to try and estimate the total project cost and complexity. There is so much beyond the PCBs I'd be surprised if populating the boards got you 1/3 of the way there in either case.


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## MoodySteve

Quote:


  Originally Posted by *rhys h* /img/forum/go_quote.gif 
_To all you gents who are building the b24, how much is it costing you to just populate the boards?_

 

I've made my BOM already, in case anyone wonders where I pulled these numbers from.

 Populating the two ß24 boards will run over $400. This is not including any transformers, power supply parts or case parts.

 Including the unregulated supply and one σ22 board, the cost is at *least* $600 in parts. This figure can inflate very quickly if you go for expensive transformers or opt for two power supplies. Again, this is not counting any parts for the chassis, including heatsinks.

 I wouldn't be at all surprised if this project broke 4 figures for many builders.


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## TheRobbStory

The biggest expense for me is going to be transformers and casework. 

 My Front Panel Express work alone is going to run close to $400.


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## n_maher

Quote:


  Originally Posted by *MoodySteve* /img/forum/go_quote.gif 
_I wouldn't be at all surprised if this project broke 4 figures for many builders._

 

I'd be surprised if it didn't break that threshold by a good margin. I know when I started running estimates when I was thinking of building one I broke $2k without trying very hard. This is not your run of the mill DIY amp build.


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## rhys h

Do you think this amplifier is completly over the top to power some b&w 686 loudspeakers? $1000 is pushing it just a little bit for me!


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## n_maher

Quote:


  Originally Posted by *rhys h* /img/forum/go_quote.gif 
_$1000 is pushing it just a little bit for me!_

 

No idea about the overkill question but if at the onset the budget feels tight I'd run away from this build. There's just too many ways to spend a lot of $$ building this project. In commercial terms (a comparison I generally loathe) you could easily expect to pay in the high 4 to low 5 figures for an amp of this caliber.


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## MoodySteve

Agreed. This is not the amp to build if you're on a budget.


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## digger945

FWIW, I have not built one of Ti's amps _yet_, but just about half way through a SE Dynahi build with only a few thing left to do, or buy, I would say that it will easily surpass $1100. I have spent more on materials and tools to build a case than all the pcb's and components combined, the power supply not being much cheaper to build than the amp itself.
 I agree with Nate, pcb's and components to populate them would not be 1/3 the way there, for me it was not even 1/5.


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## rhys h

Ok, i think i will pass on this one! Back to the multiple LM3886's for me...


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## digger945

...I must add, and without reservation, it is the most enjoyment I have had in a long long time. I am already planning the next build, even bought some parts here and there.


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## cotdt

This is SUPER impressive work! Though in my opinion a balanced B22 is already as good as it gets for a speaker amp regarding my own tastes, I'll build a B24 just to scare the neighbors.


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## cotdt

what is the lowest impedance speaker that the Beta24 can drive?


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## amb

Quote:


  Originally Posted by *cotdt* /img/forum/go_quote.gif 
_what is the lowest impedance speaker that the Beta24 can drive?_

 

There is no cut-and-dry answer to that. For a certain output voltage level, halving the impedance results in doubling the output current. The output MOSFETs used in the β24 are rated for >30A, but things like how much heatsinking, how efficient the speakers are, how large and the acoustic characteristics of the room, how loud you listen, how complex and reactive the speaker load is, all play into the overall equation. My own home speakers are about 4-6 ohms nominal, but my listening space is small and these speakers present a fairly benign load to the amp.


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## cotdt

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_There is no cut-and-dry answer to that. For a certain output voltage level, halving the impedance results in doubling the output current. The output MOSFETs used in the β24 are rated for >30A, but things like how much heatsinking, how efficient the speakers are, how large and the acoustic characteristics of the room, how loud you listen, how complex and reactive the speaker load is, all play into the overall equation. My own home speakers are about 4-6 ohms nominal, but my listening space is small and these speakers present a fairly benign load to the amp._

 

My speakers are 0.05 ohm (I made it myself from flat strips of aluminum), and I couldn't find any amp that could drive them. 
	

	
	
		
		

		
		
	


	




 But yeah, 30A WOW! Looks like I am going to watercool my Beta24 with a garden hose.


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## amb

0.05 ohms is essentially a dead-short. Very few, if any, amplifiers are going to be happy with such a load. You need a transformer.


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## cotdt

This question may have already been answered but I was wondering, does the Beta24 have short circuit protection? If not, how can they be added?

 If running the Beta24 in pure Class A for 4ohm speakers, how big heatsinks are needed?


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## amb

No, there is no explicit short circuit protection. I am not a fan of such schemes because the threshold at which current limiting is to take place is always an unfortunate compromise. If you want to make it safe for long-term, continuous duty use, then the limit must be set low, but transient peaks (which would have been quite safe at much higher levels) would be clipped.

 Also, the standard V-I (voltage and current) limiting schemes do not take operating temperatures into account. Unlike a commercial/production design, the DIY nature of this amp (where people will be using different casing and heatsinks) makes it impossible to set a single threshold that works in all scenarios.

 So, rather than including a protection scheme that may not work, compromises the performance and adds complexity, I leave it up to the DIYer to use prudent common sense instead.

 And on your question about pure class A into 4 ohms... This amp is a high power class AB amp (170Wrms+ into 8 ohms, 320Wrms+ into 4 ohms prior to clipping, as measured on my bench). At the recommended quiescent current of 200mA, it will remain in class A up to 1.28W peak output into 8 ohms, or 0.64W peak into 4 ohms.

 If you want "pure class A" operation of 320Wrms into 4 ohms, and the fact that class A amps rarely exceed 20% efficiency, you'd need to dissipate at least 1600W of heat, per channel. The output MOSFETs used here will not stand that kind of dissipation no matter how big a heatsink you use.


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## cotdt

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_If you want "pure class A" operation of 320Wrms into 4 ohms, and the fact that class A amps rarely exceed 20% efficiency, you'd need to dissipate at least 1600W of heat, per channel. The output MOSFETs used here will not stand that kind of dissipation no matter how big a heatsink you use._

 

Thanks once again for the delightful information Ti! There is a lot to ponder on. 

 So to dissipate 3200W of heat, as you say heatsinks won't work, but what do you think about watercooling the MOSFETs with a garden hose? Say by mounting the MOSFETs onto a square copper pipe carrying cold water at high speeds. Water can absorb a lot of heat.


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## error401

Quote:


  Originally Posted by *cotdt* /img/forum/go_quote.gif 
_Thanks once again for the delightful information Ti! There is a lot to ponder on. 

 So to dissipate 3200W of heat, as you say heatsinks won't work, but what do you think about watercooling the MOSFETs with a garden hose? Say by mounting the MOSFETs onto a square copper pipe carrying cold water at high speeds. Water can absorb a lot of heat._

 

I haven't run the numbers, but I'm pretty sure the junction to case thermal resistance would prevent that, let alone the case to heatsink resistance.

 You might be interested in this: ESP - Heatsink design and transistor mounting


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## amb

Quote:


  Originally Posted by *error401* /img/forum/go_quote.gif 
_I haven't run the numbers, but I'm pretty sure the junction to case thermal resistance would prevent that, let alone the case to heatsink resistance._

 

Exactly right. This is the reason why you don't see many pure class A high power amps. Even a 40W pure class A amp would need to be about the same size and weight as a 250W class AB. To get to hundreds of watts in pure class A would require many pairs of paralleled output devices mounted on gigantic heatsinks, enough to heat your house in sub-freezing winter days, not to mention give you electricity bill price shock...


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## cotdt

Quote:


  Originally Posted by *error401* /img/forum/go_quote.gif 
_I haven't run the numbers, but I'm pretty sure the junction to case thermal resistance would prevent that, let alone the case to heatsink resistance._

 

The greater the delta T, the easier it is for the heat to transfer onto the pipe carrying the water, and the MOSFETs will operate at a high temperature so I'm thinking that it won't be too hard to cool to below 100 °C, since the water is typically 20 °C. Failing that, I have access to free liquid nitrogen.

 Can anyone calculate what ambient temperature you need the "heatsinks" to be to handle 1600W per channel, assuming that the "heatsinks" have infinite cooling power?


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## amb

cotdt, I suggest that you read Rod Elliott's page that error401 linked to. The problem is not in how big the heatsink is, or how cold the water or coolant you use. A device will fail if its internal junction temperature is too high, and that heat has to go through several interfaces before it even reaches the heatsink. Namely, they are the device junction (or die) to the package, the package to isolating washer (if used, along with thermal compound if appropriate), the isolating washer to heatsink surface, and then from the heatsink to the dissipation media (air, water, whatever). Each of these have a certain thermal resistance, which is usually expressed in degrees C per watt. 

 If you add up the thermal resistances (since they are effectively in series, just like electrical resistance), you get a total temperature rise per watt. You multiply the total thermal resistance by the number of watts you're trying to dissipate, and add the ambient temperature, you get the device junction temperature. And that's for one device.

 If you try the math, you'll see that those thermal resistances quickly become a bottleneck if you're trying to make one device dissipate a lot of heat. No matter how efficient a heatsink you use, you get to a point where the junction temperature will still rise to a level that would cause failure.

 See also the "Board and heatsinks" section of the β22 website which goes into some detail about calculating device junction temperatures.

 The only way to get around this is to use many devices in parallel to divvy up the current, so that each device would dissipate a fraction of the total heat. But that has problems of its own. To ensure equal sharing, all the paralleled devices have to be very well matched. Also, many devices mounted on a large heatsink means running long PCB traces or wires, and they would have inductance that, together with the gate capacitance of the MOSFETs, would cause oscillations.


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## meluko

Hi amb,

 Just one question. From where the input stage come from ?

 Did you engineered it or is it inspired by a well_known topology ?

 Thanks


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## amb

The input stage is taken directly from the β22, which is in turn an adaptation of the classic complementary-differential topology, found in many top amplifiers in the past three decades. In this case, complementary JFETs with direct-connected tails and dynamic cascodes are employed. See the "History" section of the β22 website.


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## Halvor

How much will it cost to build a b24?


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## MoodySteve

Quote:


  Originally Posted by *Halvor* /img/forum/go_quote.gif 
_How much will it cost to build a b24?_

 

My BOM for just the board and power supply parts is over $600. That is not including a case, case finishing supplies or hardware. Reasonably, you can expect to spend $1000 and many many hours of your life.


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## Ferrari

To my opinion, there is no fixed price point for this build. The final cost is much depending on the parts choices, constructions, casing style… 

 I haven’t keep track of the cost of mine, but up to now it’s surely in the north regions of Euro 1000, plus lots of my free time, which is too costly to express it in money (but it’s the fun of this hobby).


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## MoodySteve

This time around, I am doing finishing the mechanical engineering before I solder anything. 

 I'm toying with the idea of idea of attaching polished brass rods between the front plate and the back plate, mainly to provide lifting points but also to help fasten those plates to the chassis.

 I have something like this in mind.


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## Ferrari

How are you going to mount the brass rods to front and back panels? Using screws?
 Btw, what is the effective (internal) dimension of your enclosure?


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## rds

Quote:


 I have something like this in mind. 
 

That's a very nice looking amp.


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## MoodySteve

Quote:


  Originally Posted by *Ferrari* /img/forum/go_quote.gif 
_How are you going to mount the brass rods to front and back panels? Using screws?
 Btw, what is the effective (internal) dimension of your enclosure?_

 

What I'm thinking right now is to tap the front panel from the rear for something like 1/2-13, and then thread a stud into the tapped hole. I may decide to weld the studs in. The brass rods will be tapped on both sides. So the rods thread into the studs, and the rear plate is bolted to the other ends of the rods. Both the front and rear plates will also be bolted to the frame. 

 The inside dimensions are 12.125" x 12.25" x 6.5"H. Front panel dimensions are 7" x 19". It's a pretty tight fit inside - gotta love CAD.


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## amb

That's mighty cool CAD work!


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## Ferrari

Very cool CAD work indeed! Looking forward to see the final results. 
	

	
	
		
		

		
		
	


	



 I’m sticking with the HiFi-2000 Pesante Dissipante 5U (400mm depth), with 10mm aluminum front-, back-, and bottom plates.


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## jazzist

Looking very good, like the CAD work.

 Hope to start thinking about β24 one day, will be a good match for my β22 I'm currently building.

 Probably going with Hi-Fi 2000 as well, very impressed with them.


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## krmathis

Yeah, thats some awesome CAD work.
 The casing looks really nice I must say. Especially with those brass rods.


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## amb

Another β24 is born! housing at headwize posted these pics (see more here and here).


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## jazzist

very nice


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## amphead

Woohoo, that is one beautiful amplifier! Kudos to all the hard work Housing. It's quite an undertaking, and not for the faint of heart, but well worth the effort.


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## Pars

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_That's mighty cool CAD work! 
	

	
	
		
		

		
		
	


	


_

 

That is cool CAD work! What was it done in?
  Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Another β24 is born! housing at headwize posted these pics (see more here and here). _

 

Very nice.


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## MoodySteve

Pars, my rendering was done in Solidworks.

 Housing/AMB - Great to see another finished one! I'm nervous that his unregulated suppy caps look to be about twice the size of mine. Are they 100V rated or something?


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## amb

Quote:


  Originally Posted by *MoodySteve* /img/forum/go_quote.gif 
_Housing/AMB - Great to see another finished one! I'm nervous that his unregulated suppy caps look to be about twice the size of mine. Are they 100V rated or something?_

 

He used _a lot more_ capacitance there than my build.


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## krmathis

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Another β24 is born! housing at headwize posted these pics (see more here and here). 

http://i175.photobucket.com/albums/w.../DSCN3200a.jpg
http://i175.photobucket.com/albums/w.../DSCN3187a.jpg
http://i175.photobucket.com/albums/w.../DSCN3193a.jpg_

 

Nice looking β24 indeed!


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## Ferrari

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Another β24 is born! housing at headwize posted these pics (see more here and here)._

 

Again, another β24 builder is faster than me. Congrat with the successful build, housing!


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## fillemon

well a small question, (it was a while that i looked on the magnificent amb.org site)

 Why build an ß24 if you have a fairly high effency speaker (93db) and can build an ß22 with a 50w balanced out ? (or even 18w unbalanced ?)

 is this ß24 monster developed for speakers who demand high current all the time ? (something like a b&w speaker for example). 

 (im building an passive open baffle, i guess i could do with 50w , even with 18)

 thanx people

 btw: amb you should get a statue


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## amb

fillemon, yes the β22 can be used as a light-duty speaker amp, especially for efficient speakers in a small room, and at moderate listening levels. Note that the catch phrase is "light duty". The β22 was designed primarily as a headphone amp, and as such its output MOSFETs and default heatsink configurations were selected with that in mind. While in balanced config the β22 could easily pump out 50W into 8 ohms, the small-ish output MOSFETs could overheat if you try to "push" it hard for sustained periods, even when large off-board heatsinks are used. There is only so much the TO-220 devices could do. Also, the β22 was designed to run completely from the σ22 power supply, and you will need four of them to get 50W output to keep the power supply from overheating as well. When you factor in the complexity of building a 4x β22 and 4x σ22 amp/PSU combo, all with offboard heatsinks, you're essentially within the realm of a β24.

 On the other hand, the β24 is a "true" power amp with almost 4x the output power of a balanced β22. With its much larger output MOSFETs and appropriately-sized heatsinks the β24 would have no trouble playing at high output levels for long periods of time. You could build the β24 with only one or two σ22 boards. The amp's output stage runs off unregulated power, which takes the lion's share of the load off of the σ22(s).

 Obviously, you don't need a β24 if you have Klipschorns as your speakers, but there are lots of speakers around that are low-to-mid effciency, and could really benefit from a high powered amp to reach realistic listening levels and still have enough headroom for unclipped peaks. To increase the volume by a mere 3dB would require doubling the output power, thus going from a 18W or 50W amp to a 170W+ amp isn't as big a step as you might think.


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## fillemon

thanx amb, your last remark really did it, indeed needing 3db extra is going to require a lot of watts. 

 i was aware that i needed to build 4 times σ22 for a speaker driven ß22. and i would implement very big heatsinks (same dimension as the ß24) it is maybe not the way to go. 

 but maybe the other way around ? could there be a headphone out on a ß24, with the same quality as a ß22. 
 (i'm trying to save money, i can build one of them, but the both might brake the bank a bit). 

 thank you very much
 greetz fillemon


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## amb

lol, the β22 is already quite an over-the-top headphone amp, and β24 would be borderline insane as one. 
	

	
	
		
		

		
			





 It has a gain of 20, which is appropriate for a speaker amp of its class (just a bit under 2Vrms input will drive it to full output), but this is too much gain for most headphones. Also, its 5K ohm input impedance does not lend itself well to having a volume control pot there, so it really needs to be used with a preamp, or a source with a volume control. Currently I use a Benchmark DAC1 (which has a volume pot) feeding the β24 directly in fully balanced mode.


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## fillemon

haha, indeed, let's go to a high end meeting and say the next thing: yes my headphones are 100db/1 mV, and yes my headphone amp is 170Watt/8ohm , theoreticly that would be 150db 
	

	
	
		
		

		
		
	


	





 well i'm looking at this moment at a full range open baffle system with 95-96db, so i might go with the beta22, i suppose that the amp is capable of putting out 8watt continue. that would be enough, if i decide later on to take an inefficient speaker, i will put a beta24 behind it. 

 i think any of your amps will be very good for an open baffle (at least that's what i think): a lot of times an open baffle is very musical but not as detailed as i like, combining it with your amps amb will deliver a stellar sound i suppose. 

 anyway i still need a absurd good usb source : so i'm already looking forward to a high end non portable gamma1. i'll check every once and a while. 
 thanks


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## Chaos4

I was wondering if there is another area to see the measurements for this amplifer as headwize forums are still down. Great looking amplifier! I was considering a build, but would like to see some more info is possible. How about a schematic at least? Thanks amb, for another great design!


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## amb

Schematic (v1.0):


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## digger945

Does the part in red keep the outputs from completely falling out of class A?

 I am seeing the part in blue in other designs and have built it on breadboard to try and understand how it works. Is this used only to balance the positive and negative voltages going to the output mosfet's gates? Can it be used to limit the voltage or does that need to take place at the 74/170's?
 I really like this schematic, thanks Ti.


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## amb

The resistors circled in red are there to set the VAS stage open loop gain. The portion circled in blue is a complementary Vbe multiplier (adjustable voltage source) used to bias the output MOSFETs.


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## digger945

You say a lot with few words.
	

	
	
		
		

		
		
	


	




 Thanks again Ti, I look forward to reading more when HW is back up.


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## qkizz

AMB, I have to try to install output inductors in my Beta24 and I know you posted it already on headwize, which is dead at the moment. Could you please tell me again how to do it? I've just bought new electrostatic speakers, which are much bigger than my old ones and pretty much it doesn't sound right. I've tried my another amp, which have inductors at the outputs and it looks like it would be good solution. 

 Thanks


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## amb

qkizz, make a single-layer cylindrical coil of 18AWG magnet wire, about 10cm in diameter and about 16 turns. Scrape off the enamel off the ends of the coil, insert a 1 ohm to 2.2 ohm 5W metal oxide resistor into the center of the coil and solder its leads to each end of the coil. That's your inductor and you install one in series with each of the four output terminals. You can experiment with the coil diameter and number of turns, if you want.


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## qkizz

Thank you, I'll try this.


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## qkizz

I've read somewhere that inductors are limiting bandwidth. It looks like it's true statement. I did as instructed by amb and it took just one minute of listening to realize that this is no go. Sound became dull, less involving and most of the difference was in highs and some in mids. 
 With the previous post I've jumped in to the conclusion way too fast. I have to give back full credit to Beta24. The problem was positioning the speakers, which is critical with electrostatic panels. The amp handles my new bigger panels perfectly.


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## amb

qkizz, I am glad that no inductor was necessary after all. What electrostatic speakers are you using?


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## qkizz

Currently Martin Logan Vista and previously Clarity.


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## luvdunhill

Ti:

 Looking at your drawings for the angle bracket attachment for the beta22 and sigma22, I notice that the very edge of the casing of the MOSFETs will actually be off the angle bracket a bit. You specify the hole being 0.4" from the edge of the angle bracket, and many TO-220 devices are ~0.5" from the center of the hole to the edge of the casing. Does this pose any thermal issues?


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## luvdunhill

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Ti:

 Looking at your drawings for the angle bracket attachment for the beta22 and sigma22, I notice that the very edge of the casing of the MOSFETs will actually be off the angle bracket a bit. You specify the hole being 0.4" from the edge of the angle bracket, and many TO-220 devices are ~0.5" from the center of the hole to the edge of the casing. Does this pose any thermal issues?_

 

nevermind 
	

	
	
		
		

		
			





 helps to look at the devices themselves sometimes rather than drawings


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## iamwhoiam

That's amazing, can't wait to read the amb.org pages on this!


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## L_and_P21

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_lol, the β22 is already quite an over-the-top headphone amp, and β24 would be borderline insane as one. 
	

	
	
		
		

		
		
	


	




 It has a gain of 20, which is appropriate for a speaker amp of its class (just a bit under 2Vrms input will drive it to full output), but this is too much gain for most headphones. Also, its 5K ohm input impedance does not lend itself well to having a volume control pot there, so it really needs to be used with a preamp, or a source with a volume control. Currently I use a Benchmark DAC1 (which has a volume pot) feeding the β24 directly in fully balanced mode._

 

i have quite a crazy idea for a massive diy build. i have a pair a K701's and was wondering if the β24 would be ok for a headphone amp with them, with a β22 as a pre-amp.

 Edit: by ok, i mean i dont want to harm them in any way.


----------



## aloksatoor

and a sound that can start earthquakes 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *L_and_P21* /img/forum/go_quote.gif 
_i have quite a crazy idea for a massive diy build. i have a pair a K701's and was wondering if the β24 would be ok for a headphone amp with them, with a β22 as a pre-amp._


----------



## compuryan

Quote:


  Originally Posted by *L_and_P21* /img/forum/go_quote.gif 
_i have quite a crazy idea for a massive diy build. i have a pair a K701's and was wondering if the β24 would be ok for a headphone amp with them, with a β22 as a pre-amp.

 Edit: by ok, i mean i dont want to harm them in any way._

 

Why not just drive the headphones straight from the β22 and use the β24 (w/ β22 as preamp) strictly for speakers? I don't think you'd hear much improvement with β22>β24 than with just a β22 because the two amps hold very similar designs, one just has more power. Not to mention the β24 is so powerful you'd really have to be careful that you wouldn't damage the headphones.


----------



## grawk

The B24 with Ti's speakers was the highlight of canjam, for me. Sunday night was a revelation. Thanks for bringing them Ti!


----------



## sachu

Quote:


  Originally Posted by *grawk* /img/forum/go_quote.gif 
_The B24 with Ti's speakers was the highlight of canjam, for me. Sunday night was a revelation. Thanks for bringing them Ti!_

 

hehhe..I egged him on to turn it on..he was afraid folks would make a scene for playing speakers in a headphone econvention...10 minutes later everyone in the room was sitting around listening to magic from Ti's DIy Dynaudio speakers and awesome B24 amp.


----------



## L_and_P21

Quote:


  Originally Posted by *compuryan* /img/forum/go_quote.gif 
_Why not just drive the headphones straight from the β22 and use the β24 (w/ β22 as preamp) strictly for speakers?_

 

if i were to just use the β22 for the headphones i would just use it make it fully balanced. plus i dont have any speakers... yet.

  Quote:


  Originally Posted by *compuryan* /img/forum/go_quote.gif 
_Not to mention the β24 is so powerful you'd really have to be careful that you wouldn't damage the headphones._

 

this is what i would like to avoid and why i asked.

 i know its a crazy idea. but i just like to build and play around with electronics.


----------



## amb

Thanks, even though my β24 sat quietly on the table through most of CanJam '09, it generated a lot of curiosity and excitement. When I finally cranked up the sound at the end of the meet, just seeing people's reactions was worth all the effort (of lugging the heavy beast hundreds of miles).


----------



## grawk

It's the most amazing thing I've ever seen. You wanted something, so you designed and built every part in the chain. Just spectacular. It's what every nerd aspires to


----------



## akcrusier

Someone on another thread asked for details on my uncompleted B24 build so here they are. I have finished one channel so far and tested it with a very poor pair of old speakers. I am not really sure how it sounds beyond the fact that it obviously has tons of power (more than I will ever need) Unfortunately in the process of troubleshooting my other board i ruined enough of the traces that I decided it would be best to simply start over. So I bought another board and am almost done populating it. Hopefully it works ok. For the power supply I have to O22 boards that are both up and running supplied by a 30VA SumR transformer. For the unregulated power supply I have a 500VA SumR transformer and 4 15,000 mfd capacitors. With that much capacitance I think i will have to do an inrush current limiter. I have an extra solid state relay and think i'll make a delay circuit out of a 555 timer to short the caps a few seconds after start up. The entire amp is contained in a 400mm deep 5 rack unit tall HI FI case. The heatsinks are ones I bought off ebay and cut to 8 by 8 so that they will be able to both fit totally in the case unlike versions of the amp done by others. 
Picasa Web Albums - Gregory - audio

 One question for AMB. On my one finished/working board I mounted diodes 7-10 flush to the board. I recall reading on headwize some time ago that those needed to be mounted 1/8 above the board because they get quite warm. When I tested my amp (it was at low volume and for no more than 20 mins) the diodes did not seem to get hot even though the amp seemed to be working just find and heat was pouring off the heat sink. Should I replace them and re-adujust my amp? 

 For the rest of the system I am working on I have the following that are in various states of completeness:
 RelaiXed preamp (i wanted to do a B22 but I ran out of cash...)
 Buffalo 32 DAC
 a pair three ways with Dayton RS270 for bass, a 5.5 SBacoustics for the mids, and a Vifta XT25 for a tweeter. As these are my first pair of speakers I did not want to get to expensive so perhaps later i'll upgrade to something with better drivers (hopefully I can afford some scanspeak drivers by then)

 I also have an 18" Mal-X sub that will be used with the system for movies. 
 I will have the system done by the end of August as I am going to college in early september so I have to finish it by then....

 This all started about last August when my logitech speakers died and I heard a real sound system (McIntosh) for the first time. I decided I wanted something that sounded that good. Its my first real DIY audio project, and first project that deals with AC circuits. Starting with a B24 was probably not a good idea but I have learned quite a bit. I will post more pictures when I am done.


----------



## amb

Quote:


  Originally Posted by *akcrusier* /img/forum/go_quote.gif 
_One question for AMB. On my one finished/working board I mounted diodes 7-10 flush to the board. I recall reading on headwize some time ago that those needed to be mounted 1/8 above the board because they get quite warm. When I tested my amp (it was at low volume and for no more than 20 mins) the diodes did not seem to get hot even though the amp seemed to be working just find and heat was pouring off the heat sink. Should I replace them and re-adujust my amp?_

 

D7 through D10 are 18V zeners, and normally they should have a little more than 30mA flowing through them, regardless of whether the amp is idling or playing music. The power dissipation on each diode is W = V * I = close to 0.6W. On a little DO-41 package without heatsink, that should be pretty hot. The diode can handle it -- it's rated for 3W, but you should mount it elevated off the board, so it doesn't burn a mark on the board over time, and the extra lead length actually acts to help dissipate a little of the heat.

 If your D7-D10 aren't hot, then make sure they're the right diodes (1N5931B) and that they are mounted in the correct orientation. A zener in the reverse direction becomes like a regular diode, the voltage drop is less than a volt.

 Do your DN2535 MOSFETs (Q21-Q24) get warm? They should.


----------



## digger945

Is there another place to find more info on the unregulated PS that feeds the output MOSFETs in this design, besides HW or AMB.com?


----------



## amb

digger945, the unregulated portion is just a big transformer, big rectifier bridge with snubbers, and two big filter/reservoir caps. You can either use one such PS for both channels, or a separate one for each channel. Minimum required voltage is +/-30V under full load.

 Here is the schematic/block diagram of what I did for my "reference" build:


----------



## luvdunhill

Ti:

 I always wondered how you managed to use sigma22 with your power amp. Now I understand. Pretty smart idea with the split power supplies. Is this something that you've seen in other designs, or yet another (yawn) stroke of brilliance on your part


----------



## analogbox

Did anyone get a chance to try it with K1000s?


----------



## amb

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I always wondered how you managed to use sigma22 with your power amp. Now I understand. Pretty smart idea with the split power supplies. Is this something that you've seen in other designs, or yet another (yawn) stroke of brilliance on your part 
	

	
	
		
		

		
			



_

 

Lol. It is fairly common practice in high-end power amps. Typically, though, a far less fancy design than σ22 is used for the regulated sections.


----------



## digger945

Thanks for the images Ti.
 I noticed that cmoy has a post dated 5/25 on HW stating that he is in the process of moving and should be unpacked and set up in a few weeks. Maybe we can browse the forums soon.


----------



## TheRobbStory

For anyone interested, I've decided to pass my partially complete Beta24 on: http://www.head-fi.org/forums/f44/fs...pplies-438031/


----------



## qkizz

I'm so sorry to heat that. Hope you won't regret it in future. My Beta24's never stops to amaze me and makes me feel proud that I managed to complete such a complex project with my mediocre knowledge of electronics wizardry. BTW what's going on with other people projects?


----------



## nattonrice

I got my boards and the s22 supplies last week...
 I gotta polish off a certain b22 and buff32s first then I'll look at getting the toroids and case I want... then finally the actual components :S

 Somewhere in there is a sohaii... after all of this I think I need to diy-sleep for a year lol.
 It's just too much fun~! ^^


----------



## compuryan

I've got all my boards populated, and one channel mounted to it's heatsink. I just need to mount the other channel and put together the unregulated power supply. Back panel is done too. I really hope I finish it before I have to go back to college...


----------



## Iniamyen

Mine's still coming along slowly but surely, as funding permits 
	

	
	
		
		

		
		
	


	




 I got a big 10.125" heat sink extrusion off of ebay awhile ago, and it's been sitting around until I can lap it, drill/tap it, and paint it properly. Most of this stuff I can't do at home so it's more of a time and effort issue.

 I'm also in the process of getting some custom SumR transformers. After that, one quick order to Digikey and I'll at least be able to test out the regulated power section of the amp.

 So the remaining tasks are the unregulated power section and the casing (single enclosure.) I haven't given very much thought to these yet, plus I'm sure they will be the most time consuming.


----------



## akcrusier

Another B24 lives! It took me almost exactly a year (high school interfered during the winter) After many mistakes, and alot of help from AMB my amp finally works! Picasa Web Albums - Gregory - B24
 I have yet to listen to it with a good pair of speakers yet (the veneer is still drying on those) Shame I will have to leave it all for college in about a month, though with as much power as it has I might be able to hear AMB's B24 from my dorm a few miles away.


----------



## nattonrice

Quote:


  Originally Posted by *akcrusier* /img/forum/go_quote.gif 
_Another B24 lives! It took me almost exactly a year (high school interfered during the winter) After many mistakes, and alot of help from AMB my amp finally works! Picasa Web Albums - Gregory - B24
 I have yet to listen to it with a good pair of speakers yet (the veneer is still drying on those) Shame I will have to leave it all for college in about a month, though with as much power as it has I might be able to hear AMB's B24 from my dorm a few miles away._

 

Holy crap! Is that a 5U case? Looks massive 
	

	
	
		
		

		
		
	


	




 Congrats on getting it working!


----------



## qkizz

Congratulations! Hope to hear your impressions soon. Great looking! What are the caps you have for unregulated PSU. I see 4 big blue and 4 smaller ones.


----------



## akcrusier

Quote:


  Originally Posted by *qkizz* /img/forum/go_quote.gif 
_Congratulations! Hope to hear your impressions soon. Great looking! What are the caps you have for unregulated PSU. I see 4 big blue and 4 smaller ones._

 

The big caps are 15,000 mfd ones that I got off of ebay and thge small black ones are 10,00mfd that are listed in the bom. 

 I have been listening to my B24 for two days with the new speakers I made and I am very impressed. It sounds great with the 3 ways. It is a very big upgrade from the Cambridge audio bose wave radio clone that I had before...
 I have identified a couple of issues with it so far. One is that I discovered that my main power transformer buzzes under normal use. I cant hear it unless I get close but its still a bit disappointing after I paid extra to get a SumR transformer. Another is that the main heatsinks get really really hot even if the music is played quietly. When I went to touch them during LOTR (which I had turned up) I was afraid there were getting close to that 170 degree mark where the thermal breakers would go. I am borrowing an IR temp sensor to get an accurate reading. I think for now I will reduce the bias on the main MOSFETs to about 150 mA and perhaps investigate some active cooling. They make computer fans that are virtually noiseless now and combined with a micro controller that I could program to control their speed depending on temperature I dont think I would notice them too much. I know its a bit unusual for hi-fi gear to have active cooling but I would rather break a convention than shorten the life of my amp.


----------



## qkizz

thanks akcrusier. 

 Mine transformers form diycable are also buzzing but rather quietly. As of temp of heatsinks, yours looks adequate enough but temp is propably way too high. Mine is about 100-110F with 200mA quiescent current. I've had a few class A/B amps and they were never getting hot like one of my class A, which would be about 170F.


----------



## amb

akcruisier, your temperature is too hot. Your heatsinks are internal to the case, does the case have good flow-through (bottom to top) ventilation? On my β24, the heatsink fins normally idle at around 46°C (114°F), with 200mA quiescent current through each output stage. It's warm but still comfortable to touch.


----------



## Iniamyen

I notice that most people are using the relay (per AMB's reference build) for the bleeder resistors. My amp is going to have switching done in the rear, and I'm going to be using a rocker switch to keep things simple. Is there any safety-related reason to not use a 4PDT, and just hook two of the poles up to the bleeder resistor switches, and the other ones to the transformer primaries? I haven't yet seen anyone do it this way.


----------



## amb

Quote:


  Originally Posted by *Iniamyen* /img/forum/go_quote.gif 
_...
 bleeder resistors. My amp is going to have switching done in the rear, and I'm going to be using a rocker switch to keep things simple. Is there any safety-related reason to not use a 4PDT, and just hook two of the poles up to the bleeder resistor switches, and the other ones to the transformer primaries?_

 

If you use low-ohm bleeder resistors like I did for quick bleed-down (30 ohms, 25W), when you turn the amp off and the switch cuts in the resistors, the current through the switch will be quite high. Thus you'll need to use a switch with high current rating, which you also need to handle the turn-on surge on the other poles. For switch contact longevity I'd use something rated 30A or more, but such a switch in 4PDT may be hard to find, and clunky to operate.

 Other than that, there is no safety issue as long as you insulate all wiring well, so that the AC and DC portions have no chance of shorting to each other or anything else.


----------



## Iniamyen

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_If you use low-ohm bleeder resistors like I did for quick bleed-down (30 ohms, 25W), when you turn the amp off and the switch cuts in the resistors, the current through the switch will be quite high. Thus you'll need to use a switch with high current rating, which you also need to handle the turn-on surge on the other poles. For switch contact longevity I'd use something rated 30A or more, but such a switch in 4PDT may be hard to find, and clunky to operate.

 Other than that, there is no safety issue as long as you insulate all wiring well, so that the AC and DC portions have no chance of shorting to each other or anything else._

 

Yeah, a 4PDT switch with such a current rating is elusive. I may be forced into using the e24 after all, now it actually seems like a simpler solution given all these considerations. Oh well, I will just have to make it fancier! It's not like I should be trying to save money here anyway


----------



## Iniamyen

I give up. Does the TO-247 package connect to it's drain pin, or just to the metal area on the back? If only the metal area on the back is connected to the drain pin, then I can use whatever mounting bolts & washers I want, right? as long as there's an isolating thermal pad on the back between the metal area and the heatsink.

 This thread needed a bump back to where it belongs anyway.


----------



## amb

Quote:


  Originally Posted by *Iniamyen* /img/forum/go_quote.gif 
_Does the TO-247 package connect to it's drain pin, or just to the metal area on the back?_

 

The MOSFET drain is electrically connected to the middle pin _and_ the metal backing of the package. When mounting the MOSFETs to the heatsink you'll need isolation pads. The front side of the TO-247 package and the mounting hole itself is not connected to drain, so you don't need to use isolation washers on the mounting screw.


----------



## luvdunhill

you may still wish to use a washer to distribute the force across the package. Here's what Papa Pass does:


----------



## Iniamyen

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_you may still wish to use a washer to distribute the force across the package. Here's what Papa Pass does:_

 

Yeah, that was actually my reason for asking the question. If I can safely mount a big, honking metal washer to the front of the package, then that's ideal


----------



## Iniamyen

Finally another update, since I got some time over the holidays to spend on it.

 I got my AC mains wiring and switching hooked up (per amb's reference build) and everything appears to work but I'm not getting what I expect out of the SSR. It looks like AC mains voltage shows up on the other side of the SSR, with respect to neutral right out of the wall. This is regardless of whether the switch is illuminated or not. However, the e24 is supplying the correct voltages to the SSR (~0VDC and ~12VDC) and the switch appears to work in that it comes on and off with the voltages when you push it.

 Could this just be something to do with the way SSRs work? I don't yet have a load attached to the AC mains, other than unloaded transformers. The transformers' secondaries give a reduced output when the switch is selected off (~20VAC), but they give their unloaded voltage when it is selected on (~43VAC for 30VAC secondaries.) I get the feeling like the SSR is playing games with me. Any suggestions?


----------



## amb

SSRs need some load current to work properly, so what you see is normal.


----------



## oneplustwo

Hey folks... I just started the long journey that will be my B24! Couple questions for folks after spending a couple hours reading the headwize and head-fi threads.

 1. I know Amb used shielded trafos but also read that the balanced nature of the amp effectively eliminated any hum. I'm planning on using the monster diycable trafo for the unregulated portion since it's shielded and is priced well (even though it's friggin' huge and I don't need the other secondaries) but do you think I need a shielded trafo for the sigmas too? The amp will be fed from my balanced beta which will be fed from my balanced buffalo so I don't expect to run unbalanced very much at all.

 2. What's the best way of isolating the secondary leads that I won't be using? I was just going to shrink sleeve them (individually) and tuck them away somewhere.

 3. For the unregulated section, i'm having a little trouble understanding how the wiring works from the secondaries to the caps to the rectifier. Would it be much easier to just use a couple of these?

 I'm sure I'll have more questions but at the moment my head is spinning so I'll stop there for now. Thanks.


----------



## amb

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_1. I know Amb used shielded trafos but also read that the balanced nature of the amp effectively eliminated any hum. I'm planning on using the monster diycable trafo for the unregulated portion since it's shielded and is priced well (even though it's friggin' huge and I don't need the other secondaries) but do you think I need a shielded trafo for the sigmas too? The amp will be fed from my balanced beta which will be fed from my balanced buffalo so I don't expect to run unbalanced very much at all._

 

Balanced config helps to eliminate interference by common-mode cancellation -- but it only works well when the hot and cold signals are close together. This would be true in a cable, but when you're talking about a whole amplifier board, the cancellation effect would be reduced except at _very_ low frequencies (where the wavelength is longer than the size of the board). Hence, you should still employ techniques to reduce interference where possible. A shielded transformer helps, as well as mounting location/distance of the transformer from the circuitry.

 Fortunately, speakers are rather inefficient compared to headphones, and you don't normally listen to speakers when they're literally placed on your ears, therefore a small amount of noise (which would be unacceptable in a headphone amp) might be quite inaudible on a speaker amp. But in an amp of this class you should do all you can to minimize any interference.

  Quote:


 2. What's the best way of isolating the secondary leads that I won't be using? I was just going to shrink sleeve them (individually) and tuck them away somewhere. 
 

Yes, that should be fine.

  Quote:


 3. For the unregulated section, i'm having a little trouble understanding how the wiring works from the secondaries to the caps to the rectifier. Would it be much easier to just use a couple of these? 
 

There is no schematic in that listing, looking at the board it appears to be usable. But don't forget you'll also need to add bleeder resistors which that board does not seem to accommodate.


----------



## Beefy

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_2. What's the best way of isolating the secondary leads that I won't be using? I was just going to shrink sleeve them (individually) and tuck them away somewhere._

 

A terminal block works well for this.


----------



## oneplustwo

Ok... I'll get a shielded 36+36V unit from somewhere. Another suggested vendors besides SumR?

  Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_There is no schematic in that listing, looking at the board it appears to be usable. But don't forget you'll also need to add bleeder resistors which that board does not seem to accommodate._

 

Are the bleeder resistors a must have? My understanding is there is a bit of a safety reason in that you would need to wait longer before unplugging anything for fear of a temporary short somewhere. Any others?

 Perhaps I just found a use for my 0-16V seconary on my big trafo? Can't I just wire that across K1? (I'm planning on just a simple 20A rated DPST switch) to connect the primaries.

 As for the ebay PCB, I couldn't find a schematic and frankly, I would like to not take the easy route and figure this out for my own learning anyway... hopefully I don't regret that later. 
	

	
	
		
		

		
		
	


	




 Anyway, are there any pictures out there that might help me understand the mechanics of how things go together? Maybe it's that I've never used a rectifier or such big caps before. Either that or I'm just a bit dense. Thanks!


----------



## amb

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_Ok... I'll get a shielded 36+36V unit from somewhere. Another suggested vendors besides SumR?_

 

Shielded/potted toroids with just the right specs are difficult to find "off the shelf", so a custom-made unit is going to be necessary. SumR just happens to be the most reasonably-priced vendor for custom toroids I've found, not to mention great service/communication and quality.

  Quote:


 Are the bleeder resistors a must have? My understanding is there is a bit of a safety reason in that you would need to wait longer before unplugging anything for fear of a temporary short somewhere. Any others? 
 

Since the β24 uses the unregulated power section only for the output stage, when the power is turned off, the rest of the circuit lose their power fairly quickly, removing the bias from the output stage. The quiescent current through the output stage will stop, and there won't be any more drain on the unregulated rails except for the LEDs. With tens of thousands of uF of capacitance, those rails will remain "live" for a long, long time... Low-ohm bleeder resistors, switched in by a relay, will discharge those caps quickly.

  Quote:


 Perhaps I just found a use for my 0-16V seconary on my big trafo? Can't I just wire that across K1? (I'm planning on just a simple 20A rated DPST switch) to connect the primaries. 
 

Sure, you can use one of the unused secondaries to drive an AC relay for this purpose.

  Quote:


 As for the ebay PCB, I couldn't find a schematic and frankly, I would like to not take the easy route and figure this out for my own learning anyway... hopefully I don't regret that later. 
	

	
	
		
		

		
		
	


	




 Anyway, are there any pictures out there that might help me understand the mechanics of how things go together? Maybe it's that I've never used a rectifier or such big caps before. Either that or I'm just a bit dense. Thanks! 
 

Not sure what you're asking, you could try to "reverse engineer" the ebay board and draw a schematic from it. My power supply reference schematic and various photos at my site should also help.


----------



## oneplustwo

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Shielded/potted toroids with just the right specs are difficult to find "off the shelf", so a custom-made unit is going to be necessary. SumR just happens to be the most reasonably-priced vendor for custom toroids I've found, not to mention great service/communication and quality.


 Since the β24 uses the unregulated power section only for the output stage, when the power is turned off, the rest of the circuit lose their power fairly quickly, removing the bias from the output stage. The quiescent current through the output stage will stop, and there won't be any more drain on the unregulated rails except for the LEDs. With tens of thousands of uF of capacitance, those rails will remain "live" for a long, long time... Low-ohm bleeder resistors, switched in by a relay, will discharge those caps quickly.


 Sure, you can use one of the unused secondaries to drive an AC relay for this purpose.


 Not sure what you're asking, you could try to "reverse engineer" the ebay board and draw a schematic from it. My power supply reference schematic and various photos at my site should also help._

 

I've had good experience with SumR in the past as well... guess that's where I'm headed next.

 As for my confusing question, perhaps I just need to wait until the parts come and touch and feel them so I can figure out how things go together. Are you bringing the B24 to the meet in Feb? Maybe I can take a look at yours (and take some pictures) and pick your brain a bit if that's ok.

 A more basic question though... since my trafo is only dual secondaries and not quad secondaries, would I still wire it up like your schematic with 2 rectifiers and so on? I would just have to "y" my wires... so it would mostly be dual mono, right? 
	

	
	
		
		

		
		
	


	




 (I think I read I could do it with just one set, but it seems like maintaining the dual mono setup for this section would be beneficial.)


----------



## amb

Yes, I will bring my β24 to the February meet.

 You can "Y" the trafo secondaries to two bridge rectifiers and separate capacitors per channel, or you could use just one rectifier and one capacitor bank to feed both channels. You decide how much less "dual mono" you want to go.


----------



## oneplustwo

Ok... in my infinite wisdom 
	

	
	
		
		

		
			





, I'll go dual mono up to the trafo.

 Can you describe how you mounted your big caps (C9-C12)? It looks like you have a machined piece of Al with some sort of brass looking brackets on the bottom? Are those brackets custom or something you can buy?


----------



## amb

They are chassis-mount capacitor clamps. Mouser sells them (look at the bottom of this Mouser catalog page):
http://www.mouser.com/catalog/catalogUSD/640/737.pdf


----------



## oneplustwo

Ahh... gotcha. For reference, these are the ones that should fit the caps in your BOM (1" diam).


----------



## amb

I don't actually spell out a specific model of 10000uF cap in the BOM, so you should choose the mounting clamp based on what cap you chose.


----------



## nattonrice

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_Hey folks... I just started the long journey that will be my B24!_

 

Aha! So your the wanker who took the last of the pana caps form digikey 
	

	
	
		
		

		
		
	


	




 I can't believe the wait time they quoted me.
 I'll be overseas and working for a decent amount of it but still... bah~


----------



## oneplustwo

Sorry, should have been more precise. The digikey nichicon cap that is listed in the BOM as one of the 10000uF options and happens to be 1" in diameter. 

 Natto - the only pana caps I got were the P10356-ND ones. looks like there are still lots available? Everything else I got from mouser (or Amb) except for the mosfets and Kemet caps (399-4451-1-ND).


----------



## nattonrice

Haha sorry AU humor~ I was only kidding =)
 I was referring to the P6994-ND... I put the order in with out paying attention to the stocked to order status lol.


----------



## oneplustwo

Ah, gotcha. I had the same problem... going back and forth between mouser and digikey to figure out where I could get stuff. Pain in the butt. Talk about wankers.

 I should use "wanker" more often in my everyday interactions. What a great word. BTW, (warning, OT) do you really like natto? I lived in Japan for a while and that was one of the few things I didn't really get a taste for. And I'm Chinese and there isn't too much I won't eat. 
	

	
	
		
		

		
		
	


	




 So are you in the middle of a B24 build? Would be great to compare notes.


----------



## oneplustwo

Amb - can you provide a little detail about the process you used for drilling the threaded holes to attach the MOSFETS to the heat sink? My thought was to go ahead and transfer punch the holes for mounting the PCB's first. Then once the PCB is mounted, bend the MOSFET leads and position them by hand before transfer punching to locate those holes. Then drill and tap, position and screw in place, and finally solder in place. Is that about right or do you have any tips based on your experience. (FWIW, I bought the same hifi case you did. Pricey, but after considering getting a case and separate heat sinks and having to deal with fabricating brackets and such, this seemed like a good way to go.)


----------



## amb

Drilling and tapping the heatsinks will be very tricky if you want blind holes like I have (i.e., the hole doesn't go all the way through). I ended up sending my heatsinks to FPE to have them do this for me on their CNC. Maybe you could ask around your local machine shops and see if any of them would do this for you at a reasonable cost.

 As for the big MOSFETs, yes, you should mount them to the heatsink first, then mount the board, and solder the pins last. This way they will be perfectly aligned and not stressed. Same for the Caddock resistors. I needed to add aluminum shims for the resistors because the pins are not long enough.


----------



## oneplustwo

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Drilling and tapping the heatsinks will be very tricky if you want blind holes like I have (i.e., the hole doesn't go all the way through). I ended up sending my heatsinks to FPE to have them do this for me on their CNC. Maybe you could ask around your local machine shops and see if any of them would do this for you at a reasonable cost.

 As for the big MOSFETs, yes, you should mount them to the heatsink first, then mount the board, and solder the pins last. This way they will be perfectly aligned and not stressed. Same for the Caddock resistors. I needed to add aluminum shims for the resistors because the pins are not long enough._

 

I actually have a mini mill at home... it's travel isn't huge but I should be able to make it work. Do you happen to have the locations of the holes for the MOSFET and Caddock holes? (The PCB hole dimensions are somewhere... I just need to remember where I saw them.) Or if you have the drawing you gave to FPE for the holes, that would be super helpful! I assume the sigma 22 holes are specified there as well?


----------



## nattonrice

It is indeed a great word! 
 Yup amongst all Japanese food I do love natto; awesome breakfasts are made of it 
	

	
	
		
		

		
		
	


	



 Don't ask what possessed me all those years ago to use it for an avatar everywhere lol.

 Hehe well if you count having placed orders for all the parts as progress then yes! I am in the middle of building it.
 I take it you are using the same modushop case Ti did?
 I have a 4u, 300mm one in black somewhere between Italy and here.

 I pretty much am plagiarizing everything that Ti did with the exception of the traffo, zobel components, ect.
 I have something fancy in mind for the case panels if I can get access to the uni's machine/cnc shop~


----------



## oneplustwo

Quote:


  Originally Posted by *nattonrice* /img/forum/go_quote.gif 
_It is indeed a great word! 
 Yup amongst all Japanese food I do love natto; awesome breakfasts are made of it 
	

	
	
		
		

		
		
	


	



 Don't ask what possessed me all those years ago to use it for an avatar everywhere lol.

 Hehe well if you count having placed orders for all the parts as progress then yes! I am in the middle of building it.
 I take it you are using the same modushop case Ti did?
 I have a 4u, 300mm one in black somewhere between Italy and here.

 I pretty much am plagiarizing everything that Ti did with the exception of the traffo, zobel components, ect.
 I have something fancy in mind for the case panels if I can get access to the uni's machine/cnc shop~_

 

I did get the same case Ti did. I got silver and the handles too... but I might do a wood front panel. Or maybe embellish the 10mm plate with a wood panel or something. Don't know yet. Otherwise, I'm using the diycables trafo but the same sumR trafo. So yah... very similar to Ti's build as well. Looking forward to seeing your progress!


----------



## oneplustwo

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_
 As for the big MOSFETs, yes, you should mount them to the heatsink first, then mount the board, and solder the pins last. This way they will be perfectly aligned and not stressed. Same for the Caddock resistors. I needed to add aluminum shims for the resistors because the pins are not long enough._

 

Amb - did you use thermal compound on both sides of the Al shim? (No insulator required for the Caddocks, right?)

 Also, do you have a reco for what to use for internal wiring? I was thinking about stranded 16 gauge throughout but wasn't sure if that was beefy enough given some of the sections may carry significant current.


----------



## TimmyMac

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Drilling and tapping the heatsinks will be very tricky if you want blind holes like I have (i.e., the hole doesn't go all the way through). I ended up sending my heatsinks to FPE to have them do this for me on their CNC. Maybe you could ask around your local machine shops and see if any of them would do this for you at a reasonable cost._

 

When I did this for my B22 I just measured the thickness of my sinks, subtracted 2mm or so, and sharpie'd that depth on my drill bit so I'd know when to stop. For tapping I stopped when it was at the bottom of the hole. Worked great.


----------



## amb

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_Amb - did you use thermal compound on both sides of the Al shim? (No insulator required for the Caddocks, right?)_

 

The Caddock resistors are already isolated, so no need any more isolation pads. They should normally never get hot, so no thermal compound is necessary on them. For the MOSFETs I used Berquist Silpads -- no messy thermal compound either.

  Quote:


 Also, do you have a reco for what to use for internal wiring? I was thinking about stranded 16 gauge throughout but wasn't sure if that was beefy enough given some of the sections may carry significant current. 
 

I used 18AWG for power and ground in the regulated sections, and 16AWG for the unregulated sections. All are "normal" stranded copper hookup wires.


----------



## oneplustwo

Amb - Any opinions about the signal wires to the boards and the output wires from the boards? I'm personally not interested in spending tons of money on fancy wire, but I would like to know what gauge (stranded) you'd recommend.

 Also, any issue with routing the power wires from the rear panel IEC and fuse and then all the way to the front panel where the switch will be before heading back to the rear where I'm planning on putting a terminal strip? I figure I'd keep the routing in the center on the bottom under the subchassis to keep them as far away from the sigma and beta boards as possible.

 Actually, any problems with using speaker cable wire for the regulated power? I have some 18 AWG stuff lying around that's nice and flexible... it's "oxygen free" copper. 
	

	
	
		
		

		
			





 Might be able to find some 16 AWG stuff somewhere around the house too.


----------



## amb

I used Belden 8451 (foil shield with 2 internal conductors) cable to go from the rear panel input jacks and selector switch to the amp board. At the output I used 16AWG stranded hookup wires to the binding posts. The unregulated V+/V-/G and output wiring all have Molex .093 quick-disconnect inline connectors so the whole assembly can be removed for servicing without desoldering anything.

 Yes, you can run the power wires to the front panel switch and back, as long as you keep them away from low level signal wiring and the amp boards.

 As for using speaker cables, you could do that, but most "good" speaker cables have unnecessarily thick jackets for use inside the chassis.


----------



## fishski13

Ti,
 what Bergquist Silpads are you using? i like to support my local guys whenever possible 
	

	
	
		
		

		
		
	


	




.


----------



## amb

Quote:


  Originally Posted by *fishski13* /img/forum/go_quote.gif 
_Ti,
 what Bergquist Silpads are you using? i like to support my local guys whenever possible 
	

	
	
		
		

		
		
	


	




._

 

Digi-key BER120-ND


----------



## fishski13

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Digi-key BER120-ND_

 

perfect! Digikey is in my back-yard too. i have some mica i can cut down for TO-247, but i was also looking at the K series.


----------



## oneplustwo

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_I used Belden 8451 (foil shield with 2 internal conductors) cable to go from the rear panel input jacks and selector switch to the amp board._

 

What do you do with the shield wire? Just trim it flush or connect it to the chassis somewhere?

 Do those molex connectors work just like the smaller ones? Looks like you have to buy the male and female housings but do you also have to buy male and female pins? Or do they housings come with them?

 Here are the interfaces I was thinking I would want a quick disconnect (represented by red.)






 Looks like four molex connectors with 4 pins each... I think. Might have to split disconnect #2 of them into two 2-pin connectors. Need to think through it some more.


----------



## amb

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_What do you do with the shield wire? Just trim it flush or connect it to the chassis somewhere?_

 

The shield wire carries the ground from the jacks to the board. See this diagram:






  Quote:


 Do those molex connectors work just like the smaller ones? Looks like you have to buy the male and female housings but do you also have to buy male and female pins? Or do they housings come with them? 
 

Yes, they are larger, heavier-duty versions of the Molex .062 series. You have to get the housings and pins for both sides. I picked up some from my local Fry's Electronics, sold as blister packs containing the housings and pins.


----------



## oneplustwo

Ah... duh. That makes sense. I'll have to make a trip down to Fry's one of these days.


----------



## oneplustwo

Got the big trafo today! Here it is with my Senns to give you a sense of the size.






 As I was looking at it, I started thinking about the wiring and had a couple things I wanted to verify.

 1. I'm trying decide if I should use the 0-16V 0.5A or one leg of the 13-0-13V 1A secondary to feed the omron relay that will switch in the bleeder resistors. The nominal coil power is 1.7VA which either should handle fine. And the data sheet says it can take between 6 and 240 VAC so my thinking is that I should use the 13V... less is more. Does that make sense?

 2. I believe the yellow wire (0 of the 30-0-30 secondaries) goes to the star ground. But does the YEL/GRN "SCN" wire also go to the star ground? Or should it be attached to some other part of the chassis? Does it matter? Here's the trafo wiring for reference:





 3. For the primary, I think I just hook up the BRN and BLU wire to the IEC - and + respectively and just leave the WHI wire unattached. (I'm in the US.) Is that right?


----------



## amb

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_1. I'm trying decide if I should use the 0-16V 0.5A or one leg of the 13-0-13V 1A secondary to feed the omron relay that will switch in the bleeder resistors. The nominal coil power is 1.7VA which either should handle fine. And the data sheet says it can take between 6 and 240 VAC so my thinking is that I should use the 13V... less is more. Does that make sense?_

 

That's a DC relay and needs 12V DC across its coil to operate. The transformer puts out AC, so you'll need to rectify/filter/regulate that to 12V DC. Something like a σ25 would be good here. I'd take one half of the 13-0-13 to do this. 

 Alternatively, you could look for an AC relay and skip the σ25. But it's may be hard to find an appropriate relay for this. I did a quick search of Mouser and Digikey and did not find any usable DPDT relay with 16V, 13V or 26V AC coils.

  Quote:


 2. I believe the yellow wire (0 of the 30-0-30 secondaries) goes to the star ground. But does the YEL/GRN "SCN" wire also go to the star ground? 
 

Yes. The SCN lead is for the internal shield "screen".

  Quote:


 3. For the primary, I think I just hook up the BRN and BLU wire to the IEC - and + respectively and just leave the WHI wire unattached. (I'm in the US.) Is that right? 
 

Leave the white wire unconnected (but insulated and tucked away). If you ever move to a country with 230V mains, then you need to change to use the white wire instead of the blue.


----------



## linuxworks

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_Got the big trafo today! Here it is with my Senns to give you a sense of the size._

 

wow 
	

	
	
		
		

		
		
	


	




 good idea having something in there to show sense of scale.

 what's the weight on that thing?


----------



## oneplustwo

Doh! For some reason I thought it was an AC relay. There seem to be lots of 12VAC relays out there. Would running 13VAC through it kill the relay? If yes, sigma25 may be in my future after all. Oh well... that's one of the few things in the Amb audio shop I haven't built yet. =)

 I haven't weighed the trafo, but it's gotta be 12-15 lbs or so. I'll weigh it tonight...
 EDIT: UPS says the entire box was 16.2 lbs. So it's probably right around 15 lbs.


----------



## oneplustwo

Does anyone have a good picture of the unregulated power supply from the leads of the trafo to the caps, to the rectifier, to the big caps? I'm trying to figure out in my head the best way to do this cleanly and safely.


----------



## amb

Just follow the schematic diagram as closely as possible, using thick, short wires, and you'll be fine:

 Basically:
 trafo -> rectifier -> bulk caps -> amp board


----------



## oneplustwo

Got the boards mostly populated. Enclosure came yesterday. Got some aluminum scraps from the local metal works shop for the sub chassis assemblies. Will try to drill and tap the heat sinks this weekend. And finish populating the boards.


----------



## mattcalf

Awesome work! Moaaarrr pics please.


----------



## oneplustwo

Few questions... mostly for Amb.

 1. Looking at your build pictures, I can't figure out where C1-C8 go. I'm guessing they're tucked under the subchassis where the big electrolytics are? Or are they next to the rectifiers?

 2. Where did you phyiscally put your star ground? Is it under the bottom plate?

 3. Are the LED's supposed to be oriented so the long lead (+) goes to the side with the straight line?

 I got my aluminum cutting table saw blade today (thinking about using aluminum diamond plate for either the sub chassis or the top of the enclosure) and have the heat sinks punched for drilling and tapping. Should have some more pictures this weekend for you mattcalf.


----------



## amb

1. These are axial-leaded multi-layer ceramic caps, soldered directly across the big bridge rectifier terminals. You can see them in a couple of the pics.
 2. I used a barrier strip, mounted to the bottom chassis plate. In the pics you see a bunch of black shrink-wrapped wires going to it.
 3. An LED is a diode, so I use the convention of _marked band = cathode_ ("-" pin). The LED's longer pin is usually the anode.


----------



## spookygonk

Quote:


  Originally Posted by *oneplustwo* /img/forum/go_quote.gif 
_Got the big trafo today! Here it is with my Senns to give you a sense of the size._

 

Blimey, that's as big as your head!
 What size & weight is the finished amp going to be then?


----------



## oneplustwo

Quote:


  Originally Posted by *spookygonk* /img/forum/go_quote.gif 
_Blimey, that's as big as your head!
 What size & weight is the finished amp going to be then?_

 

I think Amb said his was about 70 lbs IIRC? Mine will be pretty close. Same enclosure, almost identical build. His will be fancier though... no FPE for me. Just some DIY with my mini mill. I may add some wood accents though just for fun. And maybe use some diamond plate aluminum on the inside for a bit of an industrial accent. It will have little contasts here and there. Not sure if they'll really gel together but whatever. It'll be fun for me regardless.


----------



## amb

About 60 lbs.


----------



## oneplustwo

Is there a prize for heaviest B24? Or surely, there must be a technical benefit for having more mass... shielding, right? 
	

	
	
		
		

		
		
	


	




 There was some stainless in the scrap bin that I picked through for my pieces. And that stuff was HEAVY! Harder to machine though, and I don't really want to hurt myself lugging this thing around.

 Drilled the holes in the heat sinks today and cut the pieces to size for the rear panel and the bottom sub chassis. (Aluminum cutting blade on the table saw rocks!) Did a little wet sanding too. Gonna try to tap the heat sink holes and figure out what I'm going to do for the top as well. Is diamond plate with slots in it too industrial looking?


----------



## amb

lol. While sheer mass might earn you bragging rights, you'll curse while working on the beast. I nearly smashed my fingers a few times when assembling mine.


----------



## oneplustwo

Amb - I got the exact same SumR toroid you got. Can you please verify the wiring from the IEC and to the sigmas for me?


----------



## amb

oneplustwo, did SumR not provide any documentation with your transformer?
 Anyway, mine is a 50/60Hz dual primary, dual secondary unit.

 Primaries:
 a) 115V 17VA Blk*/Wht
 b) 115V 17VA Brn*/Org

 Secondaries:
 a) 35V 15VA Red*/Yel
 b) 35V 15VA Blu*/Gry

 * denotes beginning of winding (polarity)

 So, for 115V AC mains:
 IEC live -> power switch -> Blk+Brn
 IEC neutral -> Wht+Org
 IEC ground -> chassis

 On the secondary side to the σ22s:
 ~ G G ~ = Red, Yel, Blu, Gry (either left to right or right to left)

 Now, I don't know if this is indeed the _very same_ transformer you have, or whether SumR always use the same wire color coding for custom-wound units, so don't just take my example at face value. Check the docs that came with your transformer to be sure. If no doc was supplied, you should contact SumR for clarification.


----------



## oneplustwo

I found the documentation... same exact color coding. Also, how did you take power from the IEC to both trafos? Did you use a terminal strip? And was the terminal strip after the power switch in your flow above?


----------



## amb

I didn't use a terminal strip. I simply spliced/soldered/heatshrinked the wires and ran them below the support plate inside the chassis.


----------



## oneplustwo

Amb - I'm considering orienting the big unregulated trafo vertically with it's axis going down the middle from to back. Any issues with that? I've seen it done on other B24's but wanted to see if there's any potential issue with trafo hum or anything like that. The smaller trafo for the sigmas would still be oriented as it is in your build.


----------



## amb

I don't know whether changing the orientation of the toroid would make a tangible difference in this case.

 My main concern would be mechanical -- the toroid is secured by a single bolt, if it's sitting vertically then that bolt will be stressed by gravity. Also, the vertical "wall" to which you mount the transformer will also become load-bearing, so unless you use a very thick and stiff plate it would probably warp, and how that wall is attached to the rest of the case must also be very strong.


----------



## oneplustwo

My main motivation is mechanical actually. I was thinking about orienting the trafo vertically and bolting to a 1/4" thick piece of aluminum plate. (The mounting bolt is super beefy so I'm not worried about it... i think it's probably 1/2 or 5/8" diameter.) That plate would have 8 holes in it and would be bolted to the front panel with spacers to allow room for the on/off switch. This way, it can be supported directly by the handles/thick front panel without having to reinforce the bottom panel with a sub chassis or beefing up the brackets that hold the bottom to the heat sinks. This takes the stress off the bolts that hold front panel to the heat sinks as well. Also, I think it would make the front panel a little more interesting to have some large (maybe slightly recessed) socket head caps surrounding the on off switch. There is also a benefit in terms of layout since this reduces the footprint of the trafo. And finally, although there probably isn't much if any impact here, the two trafos would be working on orthogonal axis.


----------



## linuxworks

one thing to think of is: will the thing be 'heavy as predicted'. ie, people expect the weight to be somewhat even inside a chassis. if you have a real heavy part on one side (a vertical wall) then that unbalances things. when lifting this, it may catch people off guard.

 something to think about, perhaps. another facet to product design


----------



## m1abrams

Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_one thing to think of is: will the thing be 'heavy as predicted'. ie, people expect the weight to be somewhat even inside a chassis. if you have a real heavy part on one side (a vertical wall) then that unbalances things. when lifting this, it may catch people off guard.

 something to think about, perhaps. another facet to product design 
	

	
	
		
		

		
		
	


	


_

 

I actually have a commercial AVR that is not "heavy as predicted" the tranny sits far to one edge and every time I go to move it I forget about that and always bump the edge of the furniture with it.


----------



## oneplustwo

This will move the CG slightly forward and up. But the CG will still be close to the center of the chassis so I'm not too worried about it. Actually, being closer to the handles themselves might help in this regard and being higher will definitely help.


----------



## oneplustwo

Amb - do the caddock resistors not need any heat sinking at all? I thought I remembered reading that somewhere but that you had used an aluminum spacer to get them to the large heat sink. The standoffs I got will require a pretty thick spacer so I thought I'd just screw the pairs to a piece of aluminum as a little heat sink of their own if that would be sufficient. I could even mill out some grooves to make it more efficient.


----------



## amb

No, the Caddock resistors do not get hot enough to require heatsinking during normal use. However under bench test conditions they may get warm. Screwing them down on the heatsink takes care of all situations and make them mechanically more secure as well. But no isolation pads or thermal compound is required.


----------



## oneplustwo

Do the Mosfets need both thermal compound and isolation pads? I thought it was just the pads but thought I'd check.


----------



## amb

Depends on the type of isolation pad you use. If you use the Bergquist Silpads like I did, then you don't need thermal compound. If you use mica pads, then you do.


----------



## nattonrice

I just sat my traffo in the modushop case and yeah... it already is off the deep-end in terms of ridiculousness size wize.

 I have an metric crap-load (SI unit) of PRP here for this as well.
 If anything the boards will look pretty.

 The scarier part of all of this is that the t2 pcb is essentially the same foot print as the b24 case... What


----------



## Iniamyen

I finally got my frontpanelexpress hardware and mounted everything up, it's beginning to look like an amp!

 My only problem is, I only have the regulated power supplies going at the moment. I tried hooking up my 500VA SumR unit I got for the unregulated power supplies, but with no load on the secondaries, and blew a fuse and tripped my circuit breaker the second time I powered it up (not the first time - very odd 
	

	
	
		
		

		
		
	


	




)

 After thinking and researching my hypothesis is that the inrush current to the big 500VA transformer might be an issue. My house circuit is 20A and I have a 10A slow-blow in the amp. The whole build is pretty much per AMB's reference build. Does this mean I have to go for broke and set it up per the instructions without even verifying the 500VA unit is outputting the correct secondary voltages? It seems like I must be missing something else here.

 Anyway here is a pic, although it probably won't show any detail you might be interested in.


----------



## amb

I don't see why you'd trip the 20A breaker with nothing connected to the trafo. Are you sure you have the primary wired up properly and nothing is shorted on the secondary side?


----------



## oneplustwo

Looks awesome! Can't wait to see the finished product. Gotta get mine started up again.


----------



## Iniamyen

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_I don't see why you'd trip the 20A breaker with nothing connected to the trafo. Are you sure you have the primary wired up properly and nothing is shorted on the secondary side?_

 

Yeah I had the 115VAC windings in parallel (not connected to ground) and the 30VAC windings in series with the common node connected to my star ground.

 The only thing that I did notice is that I had my 0.5A fuse for the e24 circuit on the neutral line, instead of the hot line, which I have corrected. However I can't see how this would have an effect.

 edit: I had my computer running at the time, but as this is well under 10A, I would still have an issue with my 10A fuse.


----------



## Iniamyen

According to my measurements with my crappy DMM, the combined (parallel) DC resistance of the transformer primaries is about 0.5 ohm (0.6 ohm from the big one and about 5 ohm from the smaller one.) When the relay is closed would the AC mains going across this ever "see" this resistance? If so, this is like 192 amps if even for a short period of time. I would think not, since at 60Hz the impedance is probably way different. But I can't think of anything else. I'm convinced that the big trafo is blowing the fuse, and I'm also convinced I have everything wired correctly.


----------



## amphead

If your circuit is unloaded <scratches head>, as Amb stated you must have something wired wrong or maybe there is a winding shorted in the trafo(not likely on new ones however). There shouldn't be any reason not to just get the PS working first. Build quality looks impeccable. Good Luck and I'm hoping you find the solution soon.


----------



## amb

Yup, measuring the transformer windings' DC resistance doesn't tell the full story. Who is the vendor of your transformer and are the wiring color codes provided? Why not post them and how you had wired them up?


----------



## Iniamyen

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Yup, measuring the transformer windings' DC resistance doesn't tell the full story. Who is the vendor of your transformer and are the wiring color codes provided? Why not post them and how you had wired them up?_

 

Definitely. They are both from SumR. From memory right now - beginning of winding marked with a * on spec sheet:

 Primaries: *Black/white & *brown/orange (both 110Vac). These are wired in parallel with white & orange connected to one side of the SSR, and black & orange connected to AC mains neutral.

 Secondaries: *Blue/gray & *red/yellow (both 30Vac). These are wired in series with blue and yellow unconnected to anything at the moment, and gray & red both tied to star ground.

 FWIW, I have it wired exactly the same as the 30VA unit with the same color coding, and that one seems to be working without issue.


----------



## Iniamyen

Quote:


  Originally Posted by *amphead* /img/forum/go_quote.gif 
_If your circuit is unloaded <scratches head>, as Amb stated you must have something wired wrong or maybe there is a winding shorted in the trafo(not likely on new ones however). There shouldn't be any reason not to just get the PS working first. Build quality looks impeccable. Good Luck and I'm hoping you find the solution soon._

 

Yes, that's what I thought, too 
	

	
	
		
		

		
			





 From my measurements both primaries have a small but non-zero DC resistance across them (less than 1ohm.) And they have infinite resistance between each other. Same story with the secondaries. So right now it looks like the trafo should behave ok, but if all other possibilities are eliminated....


----------



## Iniamyen

Some more information, the circuit I am testing on is a bedroom circuit and it is 15A, not 20A. And it is on a AFCI breaker, which after researching, could be the issue. I still do not understand, however, why it would blow my 10A slow-blo fuse. The current would have to be very high for a very long time to accomplish this, and it was almost instantaneous.


----------



## Beefy

I don't know if this is your problem, because you haven't specified what sort of fuses you are using. But I have found that ceramic slow blow fuses are MUCH more prone to blow than equivalently rated bog-standard glass fuses......


----------



## Iniamyen

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_I don't know if this is your problem, because you haven't specified what sort of fuses you are using. But I have found that ceramic slow blow fuses are MUCH more prone to blow than equivalently rated bog-standard glass fuses......_

 

If I can verify that my trafo is working properly (and I am fairly confident it is, I did have it running the very first power-up) I will buy glass fuses instead of the ceramic ones when I make my next order. Thanks for the info. Until then I'm leaving the fuse out to try to eliminate possible sources of error.

 edit: Sorry Beefy, to actually answer your question, the fuse that I blew is a Littelfuse ceramic-type. Here is the Mouser part #: 576-0326010.HXP


----------



## Beefy

You could probably get appropriate fuses locally at Radioshack or a hardware store....?


----------



## Iniamyen

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_You could probably get appropriate fuses locally at Radioshack or a hardware store....?_

 

Yes I'm sure I can, I will check on my way home today.

 However I will still trip my breaker with my current setup, assuming the fuse conducts for a little while


----------



## Beefy

Yes, I see your point there


----------



## digger945

Having one primary wired out of phase would cause fuse-blowing and breaker-tripping with nothing on the secondaries.

 I've got a diagram that came with a 320va Sumr around here somewhere. Gimme a minute to dig it up.


----------



## Beefy

Quote:


  Originally Posted by *Iniamyen* /img/forum/go_quote.gif 
_Primaries: *Black/white & *brown/orange (both 110Vac). These are wired in parallel with *white & orange* connected to one side of the SSR, and *black & orange* connected to AC mains neutral._

 

Wait, what? I missed this first time round......

  Quote:


  Originally Posted by *digger945* /img/forum/go_quote.gif 
_I've got a diagram that came with a 320va Sumr around here somewhere. Gimme a minute to dig it up._

 

On my four SumR units, for 115V I have to connect black and brown together, and orange and white together.


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## digger945

Quote:


  Originally Posted by *Iniamyen* /img/forum/go_quote.gif 
_Definitely. They are both from SumR. From memory right now - beginning of winding marked with a * on spec sheet:

*Primaries: *Black/white & *brown/orange (both 110Vac). These are wired in parallel with white & orange connected to one side of the SSR, and black & orange connected to AC mains neutral.*

 Secondaries: *Blue/gray & *red/yellow (both 30Vac). These are wired in series with blue and yellow unconnected to anything at the moment, and gray & red both tied to star ground.

 FWIW, I have it wired exactly the same as the 30VA unit with the same color coding, and that one seems to be working without issue._

 

^^^ white and orange, then black and orange. Maybe you just posted that wrong and meant black and brown?

  Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_Wait, what? I missed this first time round......



 On my four SumR units, for 115V I have to connect* black and brown together, and orange and white together*._

 

The bolded parts do not match to me(between the two of you, I'm sure you have it right Beefy as you've done this many times already). It's been a long day so.....
 One way to find out if it's a primary phase problem( without a diagram ) is to just switch the wires on one set of primaries.
 It would seem to me that the two primary wires with the "*" would need to be connected together in order to have them in phase parallel.

 I found the diagram in the car the other day but I don't know where it is now???


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## MASantos

AMB, I tried to find the information, but didn't succeed...

 With standard biasing, how many whats are biased into class A at idle?

 Is there any problem with making this a "full" class A amplifier by increasing the biasing, apart from the need of much larger heat sinking?

 The new hifi2000 5U dissipante 500mm long would probably suffice, rated 0.11W/C


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## Iniamyen

Quote:


  Originally Posted by *digger945* /img/forum/go_quote.gif 
_^^^ white and orange, then black and orange. Maybe you just posted that wrong and meant black and brown?



 The bolded parts do not match to me(between the two of you, I'm sure you have it right Beefy as you've done this many times already). It's been a long day so.....
 One way to find out if it's a primary phase problem( without a diagram ) is to just switch the wires on one set of primaries.
 It would seem to me that the two primary wires with the "*" would need to be connected together in order to have them in phase parallel.

 I found the diagram in the car the other day but I don't know where it is now???_

 


 I probably didn't explain very well, I have the white and orange wires physically connected together, I didn't mean that they constituted one of the primaries. Similarly I have the black and brown wires physically connected together, as they constitute the other side of both primaries, which are in parallel.

 Small victory, though - I got home and lugged the beast downstairs onto a circuit breaker without the damn AFCI functionality (same amperage rating), and... IT WORKS! I am keeping an eye on it until I get another fuse, but I think this was the primary source of the tripping.

 As for the fuse, is it possible the tripping action itself could have blown it (twice in a row too??) Is this a really bad choice of fuse for this application?


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## digger945

Quote:


  Originally Posted by *Iniamyen* /img/forum/go_quote.gif 
_Definitely. They are both from SumR. From memory right now - beginning of winding marked with a * on spec sheet:

 Primaries: *Black/white & *brown/orange (both 110Vac). These are wired in parallel with white & orange connected to one side of the SSR, and black & orange connected to AC mains neutral.

 Secondaries: *Blue/gray & *red/yellow (both 30Vac). These are wired in series with blue and yellow unconnected to anything at the moment, *and gray & red both tied to star ground.*

 FWIW, I have it wired exactly the same as the 30VA unit with the same color coding, and that one seems to be working without issue._

 

On the PS schematic the center taps are connected to ground. Does your transformer have center tapped secondaries?

 If not, then don't connect any part of your dual secondaries to ground, anywhere(See below)

 EDIT: My bad if you're talking about 4 wires(in series) for only one secondary of one transformer, and using the two wires as center tap. Maybe I need to shower and hit the sack now.


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## Iniamyen

Quote:


  Originally Posted by *digger945* /img/forum/go_quote.gif 
_On the PS schematic the center taps are connected to ground. Does your transformer have center tapped secondaries?

 If not, then don't connect any part of your dual secondaries to ground, anywhere.

 EDIT: My bad if you're talking about 4 wires(in series) for only one secondary of one transformer, and using the two wires as center tap. Maybe I need to shower and hit the sack now._

 

They are separate secondaries but since they are in series, it's basically a center-tap. At least that's my current (har har) understanding.


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## digger945

Quote:


  Originally Posted by *Iniamyen* /img/forum/go_quote.gif 
_They are separate secondaries but since they are in series, it's basically a center-tap. At least that's my current (har har) understanding._

 

I see now. My bad. 

 May I say that I think you have a great looking build going there. I am anxious to know what you think of it when it's finished and you're listening to it.


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## Nebby

I must say after having brought my beta24 into my apt from the car, I have a much greater appreciation of the efforts of Amb to bring his amp to the last CanJam I went to.


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## amb

Quote:


  Originally Posted by *MASantos* /img/forum/go_quote.gif 
_AMB, I tried to find the information, but didn't succeed...

 With standard biasing, how many whats are biased into class A at idle?_

 

Sorry for the late reply, I missed this post somehow.
 Anyway, "standard" biasing is 200mA quiescent on each bank of output MOSFETs. A push-pull output topology will remain in class A as long as the peak output current is less than twice the quiescent. Into 8 ohms, this means about 1/3W peak. You could turn up the bias to make the transition to class AB higher, but the MOSFETs will run very hot.

  Quote:


 Is there any problem with making this a "full" class A amplifier by increasing the biasing, apart from the need of much larger heat sinking? 
 

Not without drastically reducing the supply voltage and power output.
 A pure class A speaker amp of an equivalent size and heatsinking to my β24 should realistically be a 40W/channel amp, not 180W/ch.

 The TO-247 MOSFETs in this amp cannot take a huge amount of increased heat dissipation, even if the heatsink size is increased. A traditional method of increasing heat dissipation capability is to parallel multiple sets of output devices, but the PCB design doesn't lend to such a modification, and the gate capacitances of the output MOSFETs will be multiplied by the number of added sets, which is not desirable.


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## oneplustwo

Made some progress today after not touching this for weeks.

 Front panel:










 Boards mounted on heat sinks:


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## oneplustwo

Posted some new pics over at Amb's forum site. I'll probably be using that thread for updates ongoing:

 Here's the link.


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## rsaavedra

Nice!


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## amb

I just posted about a 30W/ch pure class A variant of β24.  Some of you might be interested in building such a beast.


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## rarebear

Nice looking job on the case...


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