# Balanced TPA6120 amp - photos & thoughts...



## doobooloo

(Note: This is a continuation of a project started two and a half years ago, on this thread.)

 First, some photos:










































 And the board layouts and pending front and rear panels:

 All:





 Top:





 Bottom:















 To recap, my three primary objectives of designing and building this amp were:

 1. Create a transportable amp that will take an unbalanced source but drive both balanced and unbalanced headphones;
 2. Design the amp section around the TPA6120 chip; and
 3. Utilize the DS1802 digital pot.

 To achieve this, I have one TPA6120 in noninverting configuration and the other in inverting configuration, both buffered by dual opamps for matched input impedance on the TPA6120 side. So, both headphone jacks are independently amped outputs, with opposite polarities. Hence, both jacks will function properly as single-ended headphone amps, but the real kicker is when you build a cable to connect both for a balanced output.

 Since this was the first batch, I ran into a few issues. After everything was put together and powered on, I tested the amp for any DC offset before plugging my headphones in and found out that there was +/- 3V (!!) on all channels! I was a bit bummed, but remembered that n_maher had a similar issue with his build two years ago so I thought it's probably not the issue with my soldering or some other silly error. So, I went through the board with my multimeter checking where this could be coming from... and eventually I found out that the pads for the voltage reference for the DS1802 power supply were mixed up and hence was supplying all the wrong voltages to the chip! Fortunately all I had to do to get it in the right configuration was rotate the TO92 package a little (i.e. so that pins 2 and 3 go where 1 and 2 were supposed to go - see the photos above) and once this was fixed, everything was working fine without any issues.

 So, how does it sound? I initially did all my listening tests in single-ended mode (primary reason being me not having made the adapter cable yet). First, it has that immense impact and sense of power that is characteristic of the TPA6120 chip. Compared to my Headamp GS-1, everything sounds much more forward and impactful. Bass is not the only thing that contributes to this sense of impact - all throughout the frequency spectrum, there's a sense of power and the effortless nature of how the amp drives headphones.

 I tried it out with three opamps in the pre-TPA stage - AD8066, AD8620, and the LM6172, all three of which I have had fond experiences with and have stellar reputation among DIYers. Listening comparisons were pretty easy because I could install one chip in one channel and another on the other - I couldn't detect any sonic difference from polarity shift so for me that was good. My source was the Gigalab moon Non-OS DAC.

 Previously, my favorite was the AD8066, which had the most forward and impactful presentation of all, so my first choice was to try the amp out with this chip. Oh boy, what a combination! So much bass impact, treble detail, and forwardness, it was real fun to listen to. However, it was too much and I felt that combination lacked fluidity, texture and a natural presentation needed for a more enjoyable, extended listening session. In other words, often the combo sounded artificial and a bit fatiguing. Now on to LM6172. After 30 seconds on this chip I promptly de-soldered it. It sounded thin, harsh, and just wrong to my ears. So my extended comparison at the end of the day comprised of AD8620 in one and AD8066 in the other. AD8620 sounded somewhat veiled compared to AD8066 at first after having been accustomed to the AD8066 sound. Also, there was less of that immediate sense of impact and deep bass response that came out of AD8066. Sondstage-wise, the AD8066 had the upper hand as well due to its highly resolving nature and the AD8620 sounded more "room-like" in comparison. However, I found that the sound was more balanced and easier to listen to with the 8620, and tracks just sounded more real. What really got me after an extended comparison was the really crunchy midrange texture that came out of AD8620 - how shall I put it, it was both lush and very textured, kind of "tasty" to the ears. (I'm running out of audiophile speak here!) This really got me, and at the end of the day, I decided to go with a pair of 8620s in the amp.

 So, how do things change in balanced mode? To be honest, given that TPA6120 is such a marvelous and powerful chip, I expected very little. But the difference wasn't subtle, for the better. The relative "veil" of the AD8620 was lifted, and the amount of impact and sense of power had increased. The picture that came into my mind was the amp holding the headphone drivers by the collar and shaking it around! I tried the amp with two headphones - Grado HP-2 and Sennheiser HD580 - and it was a little funny how the two cans' differences had narrowed on this balanced amp. I thought the HD580 sounded smooth and laid back, all of a sudden it sounded smooth but quite forwardly articulated. I thought the HP-2 sounded forward but a bit airy, all of a sudden its sound gained mass and substance. It was quite a revelation, it seemed as if the amp really had full control over the cans' drivers and could dictate the diaphragm's motion to a degree I've never experienced before (and hence my imagery of amp holding cans by collar. 
	

	
	
		
		

		
		
	


	




)

 In other words, it sounds real good, and it makes me want to try all over again the HD650s and a bunch of other headphones that I had given up on in the past.

 Ah, a few final comments - the DS1802 paired with the Alpha rotary switch works like a charm. I think with a proper knob in place the switch would feel very nice but for now it the clicks feel a little hard/sharp. That said, I feel having a stepped attenuator with 60 or so steps is a huge advantage over any conventional pot and even the expensive Elma stepped attenuators in my GS-1. Also, even with a humble WM080 the amp is pretty quiet, probably thanks to a beefy PSU rail caps. Even with the Etymotic ER-4S/hf2, the noise is almost nonexistent. This was a real surprise to me and now I am completely de-motivated to build a nice dedicated power supply. 
	

	
	
		
		

		
		
	


	




 Anyway. I think that sums it up nicely. Of course I'm emotionally biased about this amp, so take all my comments above with a grain of salt, but I really am enjoying this amp a lot. I still haven't ordered the front panels yet, need to wrap that piece up soon. I've also got some new ideas cooking for the next batch (including a PPA-style bass boost) and hopefully I can move to that phase soon and have a second build with a lead time of less that 2.5 years. 
	

	
	
		
		

		
		
	


	




 Any comments, thoughts, or feedback would be greatly appreciated!


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## Gross

I love how clean that board looks. I am also jealous of your Grados.

 I look forward to when this design goes a bit more public, as I think I will build one.


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## olblueyez

Im in too,I want one of those.


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## error401

Very nice doobooloo. Might be interested myself to use up these TPA6120 I've had sitting around for months 
	

	
	
		
		

		
		
	


	




.


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## Nisbeth

Yep, count me in! Who couldn't use another PCB in the drawer 
	

	
	
		
		

		
		
	


	




 /U.


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## gyrodec

This amp looks just perfect for me, and many people, great work. I have a build question. As the TPA is a PowerPad part and the pad is underneith, how do you get it soldered so it can do its heat-dissipation work?


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## paradoe

very nice design


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## jogor

doobooloo, congratulations! very well made. is that the alpha potentiometer? where do you source this pot?


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## H22

I want one too, i sent you a pm with some info. great looking amp and clean build! 
 I know you haven't made a schematic for it, is this something you might do in the near future? if not i try to build one based on the photos of the board. 
 The reason I want to do that is two fold, I would like to design my own board, only a smaller li-po powered version for better portability, and also would like to add a few audio controlls as well.
 again, nice work and thanks for sharing!
 Joe.


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## doobooloo

I do have a few more boards, and accompanying parts too.

 Not sure why I am holding onto them still. I need to get rid of them! 
	

	
	
		
		

		
		
	


	




 Not sure when that will be though. Always so tied up with work, I just need to find some time some weekend to sit down and prepare packages for people interested in building this amp...


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## Ynis Avalach

Very nice work there!
 I'm Very interested too.


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## mugdecoffee

This is my first post but I've been watching the forum for a while. If you still have boards/kits I'd be very interested in one. How much do you imagine them costing?


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## decayed.cell

Quote:


  Originally Posted by *mugdecoffee* /img/forum/go_quote.gif 
_This is my first post but I've been watching the forum for a while. If you still have boards/kits I'd be very interested in one. How much do you imagine them costing?_

 

I'd also like to know the answer to this question


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## momerath

I too would be interested in either a kit or a prebuilt one.


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## Kitarist

Looks clean


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## rhester

I mtoo would love to build this and compare to the Mini3. Hold me a pcb and parts.


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## linuxworks

I have the ds1802 chip(s) and some alpha encoders.

 I'd buy some boards if they were for sale...


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## matthewcarlrose

This looks interesting, I've always wanted to try my hd650's balanced. Could be interested in building one if PCB's go on sale.


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## nsx_23

Ooh, very interesting project.

 Shame I don't have any balanced headphones 
	

	
	
		
		

		
		
	


	




 Maybe my prolines are now in line for some modding


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## Hifihedgehog

I hate Cmoys (muffled garbage!). This looks like my ticket audio paradise! Can I get one! I'll buy parts for $150, or $200 assembled! This thing looks like the world's best amplifier!


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## dhw4488

Awesome, I was very interested in building one when I first saw this thread with the finished product. Since you have some extra boards, I am interested in purchasing one or a kit.

 Thanks.


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## decayed.cell

Quote:


  Originally Posted by *nsx_23* /img/forum/go_quote.gif 
_Ooh, very interesting project.

 Shame I don't have any balanced headphones 
	

	
	
		
		

		
		
	


	




 Maybe my prolines are now in line for some modding 
	

	
	
		
		

		
		
	


	


_

 

From the description it seems like you can use non balanced because each output can work single endedly


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## nsx_23

If thats the case, then awesome!


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## decayed.cell

Quote:


  Originally Posted by *nsx_23* /img/forum/go_quote.gif 
_If thats the case, then awesome!_

 

Only problem is that OP has gone quiet as of late. I want ma boards and parts lol!


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## matthewcarlrose

Quote:


  Originally Posted by *decayed.cell* /img/forum/go_quote.gif 
_Only problem is that OP has gone quiet as of late. I want ma boards and parts lol!_

 

I guess he's busy at the moment! Shame really, I have both amps and the digipot already in my parts stash, The TI amps caught my eye when ordering other samples and the digipot looks interesting as it can be controlled by pushbutton (no memory thou!)...

 Matt


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## fierce_freak

doobooloo, great looking work. Do you happen to have a BOM for this you could send my way?


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## matthewcarlrose

If you get an answer I wouldnt mind knowing myself.


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## doobooloo

All,

 Sorry I've been so busy with work and not getting any sleep, I haven't been able to reply to all the PMs and interests here on this thread.

 I do have a BOM for this and a bunch of spare parts and extra boards as well.

 I'll try to post the BOM at least on this thread over the weekend, and officially post all the boards and parts for sale as well.

 Sorry for the delay and just not being there. Hope you all understand!


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## fierce_freak

Thanks doobooloo. I understand the work thing...I end up disappearing from here for months sometimes due to it. Anything you can do is appreciated


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## v3nom

WOW!! This thing looks SUPER clean!! excellent board layout. This thing could get huge!


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## matthewcarlrose

Quote:


  Originally Posted by *doobooloo* /img/forum/go_quote.gif 
_All,

 Sorry I've been so busy with work and not getting any sleep, I haven't been able to reply to all the PMs and interests here on this thread.

 I do have a BOM for this and a bunch of spare parts and extra boards as well.

 I'll try to post the BOM at least on this thread over the weekend, and officially post all the boards and parts for sale as well.

 Sorry for the delay and just not being there. Hope you all understand!_

 

100% understand, I know about not getting any sleep! (9 month old!!) I will have a pcb off you when they are for sale!!


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## fierce_freak

I'm thinking of different ways to power this, and I'm currently leaning towards a battery pack with built-in charger. 2x9v would work, but who doesn't want more power? Anyone with any ideas?


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## NelsonVandal

Quote:


  Originally Posted by *fierce_freak* /img/forum/go_quote.gif 
_I'm thinking of different ways to power this, and I'm currently leaning towards a battery pack with built-in charger. 2x9v would work, but who doesn't want more power? Anyone with any ideas?_

 

With a 50 mA quiescent current draw, you wont get much playing time. I think you should go for AAA's. 10 of them doesn't take much more space than two 9V's. To have some margins I guess you should be looking at 12. You could build a nice power pack in a mint tin with 12 AAA's, an LM317T as trickle charger and a DC-jack.


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## fierce_freak

Yeah, I was thinking the 9v batteries would be drained very quickly. I've seen some people use a couple 3.6v cells in series in addition to a voltage booster for some things. AAA's is a good idea, but I'm trying to decide how big a pack I can live with. 12 AAA's shouldn't be a big deal, but with most rechargeables coming in around 1.2v I think I'd want more than 12.

 -edit- I've also considered using a small transformer I've seen people use for things like guitar pedals with tubes. They'll take 12V in from a DC adapter and use a transformer to jump it up to 120V or 210V.

 -edit2- maybe use some of these guys or lipo's.


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## fierce_freak

doobooloo, have you had a chance to find the BOM yet? I appreciate your time.


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## matthewcarlrose

Boing! I am still interested in one.


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## fierce_freak

I am too, obviously 
	

	
	
		
		

		
		
	


	




 I think I've managed to figure out most of the resistor and capacitor values, but I still need to find out what D1, D2, L1, and the opamp after D2.


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## ziplock

I want a PCB please


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## decayed.cell

Me too. If we keep bumping the thread, maybe we'll all get PCBs ahaha


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## Gross

I would love to put one of these together. 

 Thanks for your time.


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## matthewcarlrose

Quote:


  Originally Posted by *Gross* /img/forum/go_quote.gif 
_I would love to put one of these together. 

 Thanks for your time._

 

Your not the only one, unfortunately the creator seems to have gone silent! best just waiting and see if something happens..

 Matt


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## decayed.cell

Bit of a bump. Any updates OP? ^^


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## ting.mike

this is such a killer little amp...


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## bearmann

It'd be really awesome if we could get a group-buy for the PCBs!


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## matthewcarlrose

I would be up for a group buy!


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## matthewcarlrose

Maybe if the OP is unable to supply pcbs he would be good enough to supply layouts and schematics and let us do with as we please, there seems to be a small but interested few that wouldnt mind building this amp. Otherwise this has to be the longest tease ever! 
	

	
	
		
		

		
			





 Heres hoping..


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## bearmann




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## dw1narso

I for one would be interrested if there is a groupbuy developed for the pcb and parts...

 Regards,
 ---
 David


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## lordearl

the headphone amp circuit looks quite similar to this;
Mini DACPre


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## decayed.cell

Quote:


  Originally Posted by *lordearl* /img/forum/go_quote.gif 
_the headphone amp circuit looks quite similar to this;
Mini DACPre_

 

Hm true that. Perhaps he sold the design to this company? *shrugs*


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## guzzler

Quote:


  Originally Posted by *lordearl* /img/forum/go_quote.gif 
_the headphone amp circuit looks quite similar to this;
Mini DACPre_

 

It's nothing like that, aside from using the same chip. That is single ended output, not balanced. The whole design is just application of datasheet circuits anyway. Nicely done, but nothing new in it.


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## H22

+1 I wold love to build this thing. Group buy PLEASE!


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## bearmann

Don't know if it's worth the effort... doobooloo doesn't answer PMs. Don't know what's wrong with him. If he doesn't want to make his schematics and other info public he could write it here, at least.

 regards,
 bearmann


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## steven2992

I'd love one to. I've just built a mini^3 and a am very interested in comparing it.


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## ziplock

Quote:


  Originally Posted by *bearmann* /img/forum/go_quote.gif 
_Don't know if it's worth the effort... doobooloo doesn't answer PMs. Don't know what's wrong with him. If he doesn't want to make his schematics and other info public he could write it here, at least.

 regards,
 bearmann_

 

Yeah, what's up with that? Perhaps his inbox got flooded with too many requests and now he's hiding from the mob


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## decayed.cell

Quote:


  Originally Posted by *ziplock* /img/forum/go_quote.gif 
_Yeah, what's up with that? Perhaps his inbox got flooded with too many requests and now he's hiding from the mob 
	

	
	
		
		

		
		
	


	


_

 

You'd think if he had time to post the pictures he'd be able to post up the schematics too


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## Zigis

doobooloo or anyone,
 where can I get these nice 6.3mm sockets? Are they gold plated?


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## doobooloo

Before I go on, I'd like to say that I'm really sorry for dropping the ball with this project. My work has been very busy and honestly I have not had much time to enjoy headphones as much as I used to... but I'm slowly coming back.

 Anyway, now that I've done my apologies, here's why I'm back on this thread.

 I've got a number of spare boards and related parts, and the Pad2Pad file that I used to order the boards (no schematic, however; I worked directly on Pad2Pad without one), a BOM Excel file, and FrontPanel Express files that would work as a template for the front and rear panels. I believe I've got a few spare unused Lansing cases that this amp board was designed for as well that I'll throw into the mix.

 If there's a qualified volunteer who would like to pick up this project, I'll hand all of this over for FREE (heck I'll pay the shipping too). If you want to take over, ideally you need to be a trusted, well-established member of Head-Fi with decent eletronics/DIY experience and experience in some sort of a Head-Fi organized event (helped put together a group-buy or a meet, etc.). Once you have the stuff in hand, you can either elect to distribute them for free as I did, or sell the boards under the condition that the proceeds go to a Head-Fi donation.

 Any takers? Let me know by PM or email, preference goes to those who have already contacted me in the past. Please cite any references if needed. I'll try to make the decision by the end of the weekend and post the "winner" here.

 Thanks - I hope this gets this project going again (and perhaps I'll be on the other side of it soon).


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## digger945

Fantastic opportunity for someone to take all that she's done so far and run with it. Sounds like a lot of fun.


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## j4cbo

Snazzy!

 There's no way I can pick up another build project now, but I think someone should build one of these with a Switchcraft TY4F four-pin mini-XLR connector. Much more elegant than two 1/4" jacks.


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## qusp

wow, I dont have the time or honestly the amp building experience to take the management of this project on, but OMG I want one of the sets for sure!!~! whos gonna do it so we can get this happening?? I have a laptop battery supply with multiple outputs that I can use to power this and the rest of my rig simultaneously, so this is really great. I have a balanced silver JH13 cable with 4 pin XLR just screaming for this little amp.


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## jcx

at ~ 130 dB/V the JH13 don't need an amp, certainly not one with V gain

 they would be better served by a quality step down transformer, possibly driven by a unity gain buffer


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## qusp

lol, mate, really!! is that so??? seriously, you really gotta stop trying to tell people what to do with their gear. perhaps if you had actually owned JH13 you might know that although they sound fine out of my iphone 3G HP out, they sound quite noticeably better out of my Buffalo32 feeding Lisa III and also a couple of tube amps I tried down at the sydney meet. it is pretty much consensus in the JH13 appreciation thread that they sound good without, but quite noticeably better with an amp, i'm looking at a tube buffer or output transformers for my buffalo32 (dual mono) JH13 are not the only balanced headphones I have, and who say I would stick to the stock build anyway. this project just interests me to no end and I thank you for what i'm sure are good intentions, but also, please do NOT make assumptions about what improves with an amp or not based on spec, especially if you are going to go around giving advice based solely on that information.

 for instance, there is a mod to the cowonX5L that drops in a PCM1798 on a daughter board that i'm likely going to follow through with, (optional balanced output), a dual BB WM8740 D10 (not so difficult to mod to balanced, and I also have an envelope full of samples from Ti including PCM1794A, some DIR9001 and a few different opamps with differential output that i'm interested in putting together a transportable balanced dac with..... 

 so a balanced transportable amp project is just what the doctor ordered


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## lybbert

such a intresting project... sadly dont have time or the experiance needed to take the lead on such a project.

 -Lybbert


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## dw1narso

I'm really glad that there's a hint about the life of Doobooloo's excellent design.


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## doobooloo

(drum roll)

 A respected member of Head-Fi has volunteered to pick up this project. Hopefully it will pick up a bit more momentum in that member's hands! I will not announce who it is right now, rather once the member has received the boards and parts hopefully the member will make an announcement here and take over.

 Thanks all who waited with so much patience!


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## decayed.cell

*uncorks wine bottle*


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## qusp

yippee!!!


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## matthewcarlrose

Woo!


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## lordearl

YOU BETCHA!


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## fierce_freak

Great news. I have some of the original boards, and I'll send them to the person taking over if they'd like. Please let me know.


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## DoYouRight

that is fantastic! minixlrs would rock


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## matthewcarlrose

Just a thought guys? Is the TPA6120 still on the TI sample program was a few months back when i got a few...


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## MisterX

Ordering parts from Maxim is a major pain so I did that for the people that are interested in the remaining boards.
 I have even installed them. 
	

	
	
		
		

		
		
	


	




 Here is an example photo: 







 There are 0 partial kits and 0 circuit boards remaining.

 The circuit boards include a preinstalled DS1802 and 2.5mm DC jack that has been modified to fit the board. 
 The price is $16 plus shipping. 

 The partial kits include a preinstalled DS1802, natural aluminum extrusion, RCA jacks, Mini jack, 2.5mm DC jack that has been modified to fit the board, 1/4" stereo output jacks, pulse switch and a red LED. 
 The price is $38 plus shipping. 

 PM me if you are interested in purchasing ......
 A full BOM, schematic, Mouser project link and Front Panel Express files will be provided via email.


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## matthewcarlrose

PM Sent.


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## matthewcarlrose

As all boards seem to be sold does anyone have any spares they wish to sell?


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## lybbert

wow they went fast


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## Nisbeth

Have anybody else received their kit/board? 
	

	
	
		
		

		
			





 I am just waiting for the last parts for mine but I have one question: How should the headphones actually be connected to the amp since the outputs are labelled +/- and not L/R?

 /U.


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## doobooloo

Gah! You just reminded me. HiGHFLYiN9 also asked me the same question via PM and I totally forgot to reply! My public apologies, HiGHFLYiN9!

 Anyway, the TRS outputs are configured so that both outputs can be used as standalone single-ended outputs, in other words, regular headphones can be plugged directly to both outputs. The + will provide non-inverted outputs and - will provide inverted outputs. So...

 The TRS on the + output are L+/R+/G in that order, and TRS on the - output are L-/R-/G in that order.

 So if you have a 4-pin XLR headphone you need to wire pins 1~4 in this order: L+/L-/R+/R- (so alternating wires from + and - outputs). And similarly for a dual 3-pin XLR configuration.

 Hope this helps!


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## Nisbeth

Thanks. Just so I am sure, for balanced use I'd have to build an adapter from 2x TRS -> 1x XLR4 and leave the TRS grounds floating, right?

 /U.


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## doobooloo

Right. The TRS ground is floating if you are building an adapter to use the amp as a balanced amp.


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## pistolsnipe

damn, wish i had saw this...


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## matthewcarlrose

Even if you where sub'd to the thread, which i was you still didnt have a chance - they sold whilst the rest of the world slept!


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## pistolsnipe

yeah, hopefully there will be more....


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## cegras

I am also quite interested in a prebuilt or a kit, if it will pop up once again.


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## Ferrari

The BUF634U seems to be hard to source and is out of stock at both Mouser and Digikey… the only missing part on my amp.

 Btw, anyone finished the build yet (other than Doo)? What is your impression of this little balanced amp?


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## MisterX

Try Newark Part Number: 27C6567 

 The original BOM also listed LMH6321MR as an alternate but there is a via located under the part that could be problem if it comes in contact with the exposed thermal pad.


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## Ferrari

Thanks for the tip, MisterX.


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## pistolsnipe

any chance of this project continuing?


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## matthewcarlrose

By the looks of it, very few pcb's where produced and any questions to weather or not any more boards would be produced after the inital run was as resounding NO. So unless you got in there in the first instance - no, personnally I have given up the ghost on this.


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## doobooloo

I have one completed amp with converter cable (2x 1/4" to 5-pin XLR) that I'll let go of below cost, since there seem to be so many people wanting to try this amp out. It's the very amp featured on the first page of this thread. 
	

	
	
		
		

		
			





 PM me if interested!

 The case is half complete - the aluminum Lansing shell is there, but I have never gotten to producing the faceplates. The amp uses BUF634 for ground and AD8620s buffering into TPA6120s.


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## qusp

and what would that cost be? PM me, dont need the cable, I would make my own


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## bearmann

Any news regarding PCB group buy or anything like that?!

 regards.
 bearmann


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## francisdemarte

Necro bump. Color me interested in bringing back this amp.


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## lampee

I would like to buy one of these if someone has one for sale. Of course the bare pcb would be enough too. PM me if you have one!


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