# The DIY transformer box thread (for electrostatic phones) (coming up: review on JRM M99B trans)



## AudioCats

Lets start a thread on building DIY electrostatic transformer box.

 I have one in work since who-knows-when. Never got to finish it up (yet), come to think of it, it is probably because of the ESP950 recable situation (still not fully done, waiting for stax extention cords). But anyway, I am using a pair of JRM M99B 1:50 transformers, originally intended for full size electrostatic speakers, the price was about $120 after shipping.

 The M99B's are relatively large, the external dimensions are 76mm x 72mm x 64mm (h), weights exactly 2 LB each. Just so you have an idea how much bigger they are comparing to the stax ones, here is a picture of the M99B's next to a SRD-6 box (the transformers in a SRD-7 box are said to be the same as the ones in the SRD-6)....











 Will post a review after I (eventually) finished the JRM box.
   
   
  ----- UPDATE: after about 2 years of use, the JRM box developed major channel inbalance (happened over night, about 2 weeks ago). upon trouble shooting, the "quiet channel" transformer's secondary DCR is a lot less than the good one: quiet= 200 ohms vs. good =330 ohms. The quiet channel transformer also gets warm during use (while the good one is cool), also the protector resistor for the quiet channel is hot (while the good channel resistor is cool). Looks like some kind of partial short has developed in the secondary winding.
  I will not recommand JRM transformers due to this reliability problem.


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## AudioCats

and has anybody done a Stax type box using transformers from a Koss E/9?


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## krmathis

This is going to be a great thread! 
	

	
	
		
		

		
		
	


	



 I am seriously looking into building a higher quality transformer box myself, and its nice to discuss possible transformers (vendor, model, dimensions, ...).


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## n_maher

If you're going to really go nuts with this I think an adjustable bias supply and built in power amp (something like a gainclone maybe) would be fun. At least that's what I was mulling over in my head.


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## spritzer

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_and has anybody done a Stax type box using transformers from a Koss E/9?_

 

Nope but they should work since they have a CT. The ESP10 units do not (not that I've seen at least) which is a shame since they are huge!! Other transformer candidates would be push-pull tube output trafos. Just wire them backwards and an instant transformer that can handle a lot of power.


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## AudioCats

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_If you're going to really go nuts with this I think an adjustable bias supply and built in power amp (something like a gainclone maybe) would be fun. At least that's what I was mulling over in my head. 
	

	
	
		
		

		
		
	


	


_

 

another reason why my transformer box hasn't gotten done, is because of the mutiple bias (it has something to do with the recabling situation). I am using a Neutrik 7 pin outlet allowing up to 3 different bias in one socket. Needless to say there will be a bit of recablings for my phones. The planned voltages are 230, 580, and a selectable, up to 620V.


 Birgir, for ESP10 trans without the center tap, can't you just use two 10M resistors aross the output and use the center point as ground? The transformers in my E/9B box have no center taps either (actually, the wire was there but cut flush).


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## ericj

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_and has anybody done a Stax type box using transformers from a Koss E/9?_

 


 I'm working on it. 

 E./9's vary widely, so your energizer may have a different configuration, but the ones i pulled out of the sad old 220v unit i had here have 1-ohm primaries, and there were 6.8ohm resistors on the board bringing the impedance up to 8 ohms. 

 Which is weird, but i suppose it's one way of minimizing the reactive nature of of the transformer as a load. 

 I bought some big sandstone resistors because the original koss resistors were in pretty sad shape. 

 At the moment my plan is to build an SRD-7 MkII circuit around them on perfboard. This is in addition to my plan of converting one of my SRD-7's to MkII functionality. 

 The pipe dream with the koss transformers is to max out my M3 headphone amp so that it can drive them directly, and mount it all in a 19" steel chassis that used to be a 24-port ethernet switch. The M3 should be able to push 6 watts RMS into them, which is probably enough. 

 If not, I'll stick the kossstax hybrid circuit another enclosure and stick something else in the box with the M3. 


  Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_another reason why my transformer box hasn't gotten done, is because of the mutiple bias (it has something to do with the recabling situation). I am using a Neutrik 7 pin outlet allowing up to 3 different bias in one socket. Needless to say there will be a bit of recablings for my phones. The planned voltages are 230, 580, and a selectable, up to 620V._

 


 I've been wondering about ways to get 620v for a potential future ESP950 as well. Adding another rung to the ladder in the MkII circuit would add too much. I could have a whole separate ladder with a different zener at it's start, or something. Or maybe have three different zeners selectable with a rotary switch, giving me a final voltage of 580, 600, or 620. 

 I'm interested in any cheap & cheezy theories on this. 


  Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_ The transformers in my E/9B box have no center taps either (actually, the wire was there but cut flush)._

 


 How flush? I bet you can expose enough to tack a wire onto the stub.


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## AudioCats

I am going the Koss style, using zeners. 
 The 110~ voltage goes through a 100k resistor to a 8x multiplier to get about 800-900v. The high voltage then goes throught a 200K resistor to a string of zeners. Different voltage can be taken from different location of this zener string. You can basically get whatever voltage you need by doing it this way. of course, there will then be the mega ohm load resistors and high voltage caps. 

 A zener string has a lot of zeners. My string:
 GND+ 91 + 91 + 51 (233v at this point, for low bias) + 51+51 (335v at this point, for ESP7) + 51 + 51 +51 +51 (539v, for a softer pro-bias) + 33 (572v, pro-bias) + 33 (605v, for ESP950, HE1.2) + 15 (620v).


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## spritzer

Ouch that is a lot of diodes!! 
	

	
	
		
		

		
		
	


	




 The Gilmore variable bias would also work well if you either feed it from a transformer (300v) or add a stage to it. In stock configuration it only gets up to 500v. A DC-DC converter is a good way but doesn't fit the cheap bastards motive. 

  Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_Birgir, for ESP10 trans without the center tap, can't you just use two 10M resistors aross the output and use the center point as ground? The transformers in my E/9B box have no center taps either (actually, the wire was there but cut flush)._

 

That would do it but I've yet to test it. Hmm I should have plenty of 10M resistors... 

 If you can see the stub then you can use it. 
	

	
	
		
		

		
		
	


	




 I got away with a few mm's on a Stax power trafo and the amp works just fine.


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## AudioCats

Is anybody doing, or plan to do, a higher end box using Lundalh transformers? I am curious about the difference between the "normal" core and amorphous core.


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## spritzer

I would rather go with the Sowter ESL transformers since they were designed for this.


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## ericj

By the way, if one or two people need just one WPI 6 pin socket and can't make the $20 minimum order at allied, I ordered half a dozen and might be willing to part with a couple of them. Plugs too.


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## spritzer

This one should work just fine for a DIY trafo box if wired backwards. It even has a 1:25 ratio on the 8 ohm tap. With some quality speaker terminals, box and a bias supply it should come in at about 200$ for a complete unit.


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## krmathis

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_This one should work just fine for a DIY trafo box if wired backwards. It even has a 1:25 ratio on the 8 ohm tap. With some quality speaker terminals, box and a bias supply it should come in at about 200$ for a complete unit._

 

Thanks for the link!
 This one and the Sowter 4342 seems like strong candidates for transformers for a DIY energizer unit.


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## ericj

I'd like to advise anyone following along with my hair-brained schemes that koss E/9 transformers are somewhat fragile. 

 The secondary windings are connected with the sort of gauge of wire you find on dynamic headphone voice coils, and these are folded over the bottom lip of the plastic bobbin to where they're soldered to the wires that are looped through the top of the bobbin. 

 And they can, it turns out, easily be severed by letting your extracted transformers knock around the desk for a few weeks.


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## AudioCats

...... were you able to re-connect the thin wire?


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## spritzer

Similar thing happened to be while searching for a CT on my ESP10 trafo and it was a pain to repair but I did manage it in the end. No CT though...


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## ericj

Quote:


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





...... were you able to re-connect the thin wire?_

 

Can't even find it. 

 Did more damage while looking for it. 

 So I'm gonna need different transformers for my project. Assuming the other transformer is ok, i can figure out if it was going to work at all for this project by hooking it up to the M3 and my spare SR-30 driver, i guess. 

 E/9's aren't expensive or rare. I have another, in fact. The question is how much value i perceive in perhaps passing my ESP9 kit to someone or buying another E/9, or instead gutting some other transformer box - like the magnavox transformer box i have, or the superex transformer box, or the marantz transformer box, or . . . you get the idea.


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## RDK845

This thread is exactly what I was looking for. I'm thinking about about developing electrostat headphone transformer adaptor in a several steps over the time. I would like to compare O2 and HE audio jade on this in future. I have several high quality tube and SS SET that works fantastically with K1000 and plan to use them for electrostatics.

 1. First I could add bias circuit of SRD-7 MkII that spritzer posted on my SRD-6, if the output transformer is the same between SRD-6 and pro bias of SRD-7 mkII. Could any one comment on this? I’m having a hard timefinding out what specific parts are to be used in the circuit and finding source of the parts, so if any one has list of parts number and source, please post here or pm me? 
 I wonder ericj could help….

 2. If that set-up works, I could upgrade the transformer with Sowter or any other boutique transformer sthat spritzer or other stax experts recommend.

 3. Finally once I narrow down to the optimal amp / headphone combination, may be I can integrate the transformer and bias supply to the amp, bypassing the output transformer of the SETs for speakers? This probably require some custome transfprmer , but sonically this should be good, next to electrostatic amps like BHSE? I’d appreciate any comment on this.

 Thanks!


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## spritzer

The only thing you need to know about a transformer is its step up ratio and for Stax that is 1:25. All the transformers Stax has ever used can be fitted with Pro bias supplies since the 580v bias was chosen so that the two bias systems would have the same efficiency. 

 For parts you can use normal 1000v/1a diodes, any caps that exceed the ratings and two 100v zeners on the input, the rest isn't really needed. 

 There is a lot more to the BHSE than meets the eye, grounded grid config, high slew rate, low output impedance, ample current reserve etc. so you need a very , very good speaker amp to come close to that. You can how ever connect the phones through caps directly to the tubes of some push-pull amps so no transformer is needed. How good this will be is tough to say though...


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## RDK845

Thanks spritzer!

  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_……. For parts you can use normal 1000v/1a diodes, any caps that exceed the ratings and two 100v zeners on the input, the rest isn't really needed._

 

 If I’m right, the two 100V zeners will be in place of z101 and Z1100 at the AC input? What current rating should the zeners have? I’m guessing that the schematic is for 100V Japanese AC, so should there be some changes for 115V US AC?

 I’m guessing that the ZL01 and ZL02 across the transformers are already there in SRD-6? What W ranges would you recommend for the resistors if I choose to include all of them anyway?

  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_……so you need a very, very good speaker amp to come close to that. You can how ever connect the phones through caps directly to the tubes of some push-pull amps so no transformer is needed. …_

 

 Yea, BHSE is of course under consideration, but my K1000 out of one of my 845 SET sounds so much better in most ways than SR 404 driven by SRM-1, that it makes me to want pursue this route before I drop a lot of money and time on BHSE. Also, I don’t know BHSE would provide optimal sound signature for electrostatics other than Omega or O2. Putting caps directly to the output tubes can be considered, but I’m not sure I’d be comfortable with idea of having just only a cap between my headphone and 850V 845 bias voltage…
 Since the stax transformer being 1:25 step up from 8 ohm output of speaker amps, am I right in thinking that ideal output transformer connecting tube SET tube output to stax headphone would be that wound for hypothetical 8*25 = 200 ohm speakers?
 Finally what would be transformer that you would use if you’d go for the bar-non performance transformer box?

 Sorry for many questions. , particularly if some of them are a little dumb...


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## spritzer

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_Thanks spritzer!

 If I’m right, the two 100V zeners will be in place of z101 and Z1100 at the AC input? What current rating should the zeners have? I’m guessing that the schematic is for 100V Japanese AC, so should there be some changes for 115V US AC?_

 

The two zeners are wired in opposite direction and replace the Z1100. 1.3w unit will be more then enough since the bias supply needs very little juice. 

 The zeners limit the input voltage to 100v so it doesn't matter where you use the bias supply in the world, they will only let 100v past them. 

  Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_I’m guessing that the ZL01 and ZL02 across the transformers are already there in SRD-6? What W ranges would you recommend for the resistors if I choose to include all of them anyway?_

 

They are a few watts but it's been far too long since I last checked. They are only there to make sure a novice will not overdrive the unit and burn up the transformers. One thing missing from the schematic is the protective zeners on the pro output socket, 461v units, back to back on the + and - poles. 

  Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_ Yea, BHSE is of course under consideration, but my K1000 out of one of my 845 SET sounds so much better in most ways than SR 404 driven by SRM-1, that it makes me to want pursue this route before I drop a lot of money and time on BHSE. Also, I don’t know BHSE would provide optimal sound signature for electrostatics other than Omega or O2. Putting caps directly to the output tubes can be considered, but I’m not sure I’d be comfortable with idea of having just only a cap between my headphone and 850V 845 bias voltage…_

 

The BHSE has very low output impedance and is fully DC coupled so it has very little sound of its own. Some headphone designs need help to sound presentable and then there is always the line between the purists and the audiophools and what each camp deems to be musical. 

 850v is nothing to worry about since we are already thinking about +/-900v supplies to feed the Blue Hawaii design. A EL34 will not do naturally but there are a few NOS tubes that will work just fine. 

  Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_Since the stax transformer being 1:25 step up from 8 ohm output of speaker amps, am I right in thinking that ideal output transformer connecting tube SET tube output to stax headphone would be that wound for hypothetical 8*25 = 200 ohm speakers?
 Finally what would be transformer that you would use if you’d go for the bar-non performance transformer box?

 Sorry for many questions. , particularly if some of them are a little dumb..._

 

No, since the step up ratio is the square root of the impedance which means 40k and not 200ohm. The 1:25 ratio isn't locked in stone though so you can go higher then that. 

 For a no holds barred approach I'd ask somebody like Electraprint to make something for me or just get Sowter units.


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## RDK845

Thanks again for such a quick and complete reply!

 It seems there is one, so called "Transient voltage suppression diode" = 2 zeners back to back at the input. If 2 zener diodes replace Z1100, what part should I use for Z101? 
 Also, are the directions of protective zeners on the pro output socket in a way that current is allowed flow into the + and - poles?


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## luvdunhill

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_For a no holds barred approach I'd ask somebody like Electraprint to make something for me or just get Sowter units._

 

Plitron makes some wide-bandwidth step-ups made for electrostatic use that might be worth considering. I bet they are pretty pricey though. I have a feeling the frequency response from this type of setup will always leave something to be desired, no matter how nice the amplifier is.


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## spritzer

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_Thanks again for such a quick and complete reply!

 It seems there is one, so called "Transient voltage suppression diode" = 2 zeners back to back at the input. If 2 zener diodes replace Z1100, what part should I use for Z101? 
 Also, are the directions of protective zeners on the pro output socket in a way that current is allowed flow into the + and - poles?_

 

The Z101 is the just the name on the PCB. 

 Anybody with a Mk2 unit would have to open up their units to check the zeners since I can't remember the polarity. The idea is to "clamp" the output if it ever goes above 460v. 

  Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Plitron makes some wide-bandwidth step-ups made for electrostatic use that might be worth considering. I bet they are pretty pricey though. I have a feeling the frequency response from this type of setup will always leave something to be desired, no matter how nice the amplifier is._

 

The Plitron's are 300$ each so not cheap. Transformers will always loose some info no matter how good they are and the mating amp is very important if you want to get close to the BHSE level of performance. Slew rate is an often overlooked spec and with the BH having such amazing specs (300v+u/s if I remember correctly) there aren't many amps that can close to that.


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## RDK845

Actually both sowter 4342 is ~ US250$ and philtron PAT 4133-ES is ~US252$ using today's exchange rates. But the shipping for 2 to US from sowter website is ~U$ 156! (I hope shipping from phitron is not that much.)
 Does any one have previous experiences in comparing these transformers, let say in an electrostatic speaker?
 Here is the spec for philtron. PLITRON - audio transformers - toroidal transformers - toroids - output transformers - current transformers - power transformers - medical isolation transformers - power toroids
 How does it look like compared to sowter? Can't find detailed info in Sowter's site. 

 Another possibility I can think of is custom wound transformer. Sowter 4342 is rated 50W and philtron 4133-ES is rated 80W, both seem to be overkills to me. I wonder whether anyone looked into custom wound transformer using silver wire at power rating of say 10W or less. How much would be (subjective) optimal W rating for Omega II in your opinion guys?

 I know electraprint makes output transformer with silver wired secondary for speaker amps, but with reduced W ratings, may be one could possibly have silver wired primary within sane amount of money? I know tranny design in much, much more than just wire materials, but all other things the same, it would have advantages in details in extreme frequencies compared to coppers ones?


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## krmathis

RDK845. Thanks for the link to the PLITRON PAT 4133-ES.
 I am trying my best to collect information, and eventually parts, to build my own higher-grade transformer unit for my Stax'en.

 Sowter 4342 I were aware of, but had so far found no real alternative.


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## RDK845

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_ The Z101 is the just the name on the PCB._

 

 thanks!

  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_ Slew rate is an often overlooked spec and with the BH having such amazing specs (300v+u/s if I remember correctly)_

 

 That certainly is amazing number. I guess amp designed to drive purely capacitive load has advantages.

 But I think high end transformer box does make sense, when you already have a very good speaker amp with sound signature of your liking... 
 Although it is hard for me to measure up where to draw line in terms of cost of such box and move on to say BH. That is until I can actually compare BH with very good transformer /amp in first hand... 
 I'm also considering to build a BH. According to Pabbi's post, it would cost about 1800$ with very good parts. But I need a help from guys with previous build experience... $4500$+ and long wait for BHSE would be 3rd option for me.


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## RDK845

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Anybody with a Mk2 unit would have to open up their units to check the zeners since I can't remember the polarity. The idea is to "clamp" the output if it ever goes above 460v._

 

Now anyone?....


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## spritzer

Transformers are a good idea but the need mostly went away with the rise of line level sources. 

  Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_Now anyone?...._

 

I don't have one so I'm out.


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## RDK845

Could you elaborate on your experience a bit? I'm not sure why transformer box vs. amp has to do with type of sources...


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## RDK845

sorry double posts.


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## spritzer

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_Could you elaborate on your experience a bit? I'm not sure why transformer box vs. amp has to do with type of sources..._

 

In the old days we had phono as the primary source along with tape so you needed a preamp in front of the headphone bit. Stax has always made amps though but they had built in MM phone stages. This all changed with the domination of CD and turntables with built in preamps with a set line voltage of around 2v. This is why Stax stopped making the boxes and also the annoying tendancy of the transformers to over volt the drivers and making the arc.


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## RDK845

thanks for explaining. 

 By the way, in SRD-7 mk II schematics, what does the Z01 ~ Z04 do? They bypass the + and - poles, I think. Are they the protective Zeners ?


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## spritzer

They are there for protection. The transformers had been a constant headache for Stax since they arced so many phones on a regular basis so all those protection measures were implemented.


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## RDK845

I didn't know this, but ZL01 - ZL04 is surge arrestor. Didn't know such thing exhisted. There are two for each channels in the schematic. If Pro socket of SRD-7 is protected against > 461V, can I just use 1 470V arrestor per channel?

Digi-Key - 495-1478-ND (EPCOS Inc - L71-A470X)


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## RDK845

By the way, could any one let me know how I should be measuring the bias voltage? I think at some point Spritzer mentioned something about measuring at the socket is not right? Should I measure them with phone connected to the energizer?
 Thanks.


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## philodox

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_This one should work just fine for a DIY trafo box if wired backwards. It even has a 1:25 ratio on the 8 ohm tap. With some quality speaker terminals, box and a bias supply it should come in at about 200$ for a complete unit._

 

Cool, Digikey carries this one as well. Would it be possible to build a balanced transformer box and would that require 4 transformers?


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## spritzer

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_I didn't know this, but ZL01 - ZL04 is surge arrestor. Didn't know such thing exhisted. There are two for each channels in the schematic. If Pro socket of SRD-7 is protected against > 461V, can I just use 1 470V arrestor per channel?

Digi-Key - 495-1478-ND (EPCOS Inc - L71-A470X)_

 

The surge arrestor is there to protect the transformers and not just the headphones so you could just leave it out if you are careful. Overloading of transformers has always been a problem due to the different sensitivity of the adapters and the speakers often connected through them. Users set the volume too high and then switched resulting in fried transformers and headphones. 

  Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_By the way, could any one let me know how I should be measuring the bias voltage? I think at some point Spritzer mentioned something about measuring at the socket is not right? Should I measure them with phone connected to the energizer?
 Thanks._

 

If you measure at the socket then you are completing a circuit that is meant to be open and the bleed resistor that controls the constant charge of the diaphragm drops the voltage. Measure before the resistor to get the correct reading. 

  Quote:


  Originally Posted by *philodox* /img/forum/go_quote.gif 
_Cool, Digikey carries this one as well. Would it be possible to build a balanced transformer box and would that require 4 transformers?_

 

All electrostatics are balanced by nature and driving a single transformer with a dual differential amplifier is no different then driving a normal dynamic headphone that way. Both are just a coil of wire which the amp pushes and pulls.


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## RDK845

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Measure before the resistor to get the correct reading._

 

Is R104 then a bleeder resistor? If so, do I measure between before the resistor and either one end of the double zener diodes?


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## spritzer

R104 and R103 are the bleed resistors and you can also use the CT on the transformers as ground.


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## RDK845

O.K. 

 So I built the SRD-7MkII bias supply on perforated board. I have included all the parts that are within the perimeter of dash line in the schematics, except the thermistors and NL, which seems to be some light device. It seems to be working but the DC bias I'm measuring seems low.Only deviation I have is that voltage rating of caps are all 630V instead of 250V. I have not yet connected the circuit to transformer or a phone. 

 Pro bias tap 

 measured before bleed resistor 400V 
 after the bleed resistor 355V

 Normal Bias

 Before the resistor 180V
 after the resistor 155V.

 Any idea why the lower voltage? i guess I can add a diode and cap to get higher voltages but I don't want to deviate from schematic without making sure i'm doing right...


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## RDK845

I measured the voltage at the end of each diodes.
 1: 90V, 2: 180V, 3 260V 4 328V 5 377V 6 410V.

 I understand there should be some drop in voltage as it multiplies, but they seem to drop too fast. Is this normal or was my part selection wrong? I used 100V zeners, metal poly caps and IN 4007...

 Thanks...


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## spritzer

Something is clearly amiss since you should see a lot bigger drop over the bleed resistor. Where are you getting the ground connection from, the CT of a transformer or somewhere else?


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## RDK845

The ground is measured from the side of R105 = 910K which is connected to CT of transformers. The voltage are the same whether R105 is connected to transformer or not. I tried to desolder the bleeder resistor from the circuit, but it only increased the voltages by 2 volts. I can't find any possible shorts on the perforated board itself. Maybe it is leaking through the board itself? Or may be I'm measuring wrong?

 When they are connected to Lamda in normal bias, it does play fine, but It would be not be ideal if the bias is low like 150V. It also slight hums...

 Thanks.


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## spritzer

At the end of D106 you should have 600v (six steps in the multiplier) so I would check to see if the zener bridge is outputting the right voltage and then just try to use higher value zeners to get the right voltage.


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## RDK845

Some more zeners ordered. 

  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_ You can how ever connect the phones through caps directly to the tubes of some push-pull amps so no transformer is needed. How good this will be is tough to say though..._

 

 Would this idea work with things like 300B or 845 SET? If so, I guess something like interstage tranny would also work since its hard to find high voltage caps with large enough capacity. In such case, would interstage with impedance like 5Kohm work with something like omega II?


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## spritzer

It won't work on a SET design since all electrostatics are push-pull and thus need an output stage capable of that or a phase splitting transformer. 

 You only need small value caps for the output but the voltage rating should be 1kV at least. A 1:1 transformer would always be better then any capacitor on the output but you can use filmcaps on Stax amps and not the terrible electrolytics used on dynamic phones. 

 The SR-007 is 120k or something like that so 5k is far too small.


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## randytsuch

So, has anybody built a working box?

 I am trying to decide if I want to buy a Jade, and then build a transformer box to drive it with, for now. Eventually, I want to build a blue hawaii.

 Is there any reason not to just build this design,
the STAX Transformer
 but with the hammond output transformer, and another non lundahl (cheaper) tranny to generate the 580 bias voltage?

 Randy


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## RDK845

I found that when bias is measured from transformer center tap to end of each diodes, 

 1: 90V, 2: 180V 3: 260V 4: 328V 5: 377V 6: 410V

 Clearly multiplied voltage is reducing. But when I measureed voltage across individual diodes themselves, they are all ~ 100V, so at the end of diode No 6 it should be ~600V not 410V!

 So is my digital volt meter measuring wrong values as it goes above 200V? And if so how could I properly measure the bais voltage?

  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_The SR-007 is 120k or something like that so 5k is far too small._

 

So then how much would be most appropriate?


 Thanks again!


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## AudioCats

what is the input impedance of your multi-meter? I think you need at least a 10M input.


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## luvdunhill

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_Clearly multiplied voltage is reducing. But when I measureed voltage across individual diodes themselves, they are all ~ 100V, so at the end of diode No 6 it should be ~600V not 410V!_

 

in addition to what Audiocats suggested, depending on how your meter trys to approximate RMS voltage, you could have problems. If you have a "true RMS" meter you should be good, otherwise all bets (may) be off. Also, voltage multipliers collapse after repeated stages and will not double each stage. They just get progressively less than double. Just something to note.


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## spritzer

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_So then how much would be most appropriate?_

 

I'm quite frankly not sure. Lower output impedance is normally better though


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## RDK845

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_... You can how ever connect the phones through caps directly to the tubes of some push-pull amps so no transformer is needed......_

 

I hear from experts that electrostatic is inherently push-pull and using single-ended is not as desirable for these headphones, even when using step up transformer. I don't really get this. I understand electrostatic is push pull in the sense that + and - bias is alternating between two stators, but I don't know exactly why it has to do with amp output stage. Push-pull give + and - current with complementally output devices, while single ended give same + and - current, albeit with single output device? Could any one explain?
 Thanks!!


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## spritzer

If electrostatics weren't push-pull then their distortion would be closer to 30% rather then 0.30% or what ever crazy number they are down to now. Since the diaphragm has no suspension then there is nothing to "return it" to the starting position. This makes them behave in a non-linear fashion unless there is something to push and pull against. Normally this is a +/- output (AC so it's really different phase) of equal voltages but there is nothing that says that is the only way. You could ground one stator (or a diminished signal) or even apply the bias to the stators and the signal to the diaphragm. The former was used by Koss in the ESP6 and 9 to combat their closed nature but I've never seen the latter used in full blown electrostatics (the element with the bias has to be resistive which metal is not) but is has been used in electrets. 

 Single ended is really + and then the - is ground while the - is active on push-pull amps. Not a perfect way of explaining it but it will do for now. All you need is a phase splitting transformer to get a push-pull output from a single ended amp which is exactly what the Stax transformers are doing.


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## luvdunhill

Quote:


  Originally Posted by *RDK845* /img/forum/go_quote.gif 
_I hear from experts that electrostatic is inherently push-pull and using single-ended is not as desirable for these headphones, even when using step up transformer. I don't really get this. I understand electrostatic is push pull in the sense that + and - bias is alternating between two stators, but I don't know exactly why it has to do with amp output stage. Push-pull give + and - current with complementally output devices, while single ended give same + and - current, albeit with single output device? Could any one explain?
 Thanks!!_

 

given the responses here, and the other fora you've asked the same question, why not build a direct-drive amp? Messing with this transformer box is just going to be one big compromise, IMHO.


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## AudioCats

judging from the performence of my (finally finished) JRM box, I am not too sure if a direct drive amp is by default better. 
 The performence edge of the JRM is quite obvious comparing to a stock SRD-6 ( supposedly the SRD-7 also has the same transformers as in the SRD-6). Boxes were driven by a Kenwood KA89, pushing SR-Lambda's.


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## spritzer

With direct drive you have access to a whole lot more power (when talking about TOTL like the BH) that is matched to the needs of the drivers, lower output impedance and truly spectacular slew rate. That doesn't mean that a transformer solution would be bad though but the amp driving it is crucial.

 Btw. Why do you use the 7-pin XLR instead of the 5-pin version?


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## krmathis

I think transformers have a potential.
 Perhaps not quite up to the most powerful direct-drive amplifiers, but hopefully a step above the SRD-7 series...


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## AudioCats

7 pin so I can have three bias line options in one jack.

 why do people keep bringing up the BH? Yes it is probably more powerful and better than most everything, but the purpose of a high end transbox is not to out perform the best, it is to provide good enough headphone driving capability for people who already have a good speaker amp. 

 My guess is a Lundahl box driven by $600~$1000 SS speaker amp should be at least as good as, most likely better, than a T1s/W.


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## spritzer

Well the BH only costs about 1500$ or so to build if you have the chops to pull it off so it is a valid point for comparisons. 
	

	
	
		
		

		
			





 The KGSS and 717 are more realistic contenders against a TOTL transformer box as both have much more power compared to the T1's and even more detail.


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## AudioCats

True, but the BH is a lot more complex than a transformer box 
	

	
	
		
		

		
		
	


	




 basically anybody with entry level skill can do a transbox (7x multiplier, then stepping down with a zener string), in a day or two, while a BH will take a few weeks just for the planning if doing point-point style.


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## luvdunhill

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_I am not too sure if a direct drive amp is by default better_

 

 Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_why do people keep bringing up the BH? Yes it is probably more powerful and better than most everything, but the purpose of a high end transbox is not to out perform the best, it is to provide good enough headphone driving capability for people who already have a good speaker amp. 

 My guess is a Lundahl box driven by $600~$1000 SS speaker amp should be at least as good as, most likely better, than a T1s/W._

 

I think the Blue Hawaii was brought up because your first post seemed to imply that a transformer box can sound as good as a TOTL direct drive amp. This just isn't possible. A T1S, okay, that's a more reasonable goal.


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## spritzer

A DIY transformer box will be even easier to pull off once the new bias supply PCB has been beta tested. 

 I also wouldn't recommend the BH for a P-P wiring job as it simply is too complicated.


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## AudioCats

hehehe, looks like the BH is safe, for now... 

 From what I am hearing right now (Kenwood -->JRM -->ESP950), I can assume (only assuming) a high-end SS amp driving JRM transformers can be on par with a T1s. For speaker people looking for easy entry to electrostatic headphones, it is a rather low cost option as long as they have some DIY skills. 

 The JRM shines more when driving more difficult phones (such as ESP950), which brings up the main advantage of using higher-end transformer: there is no "power" issue, provided the speaker amp is up to the task.


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## AudioCats

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_your first post seemed to imply that a transformer box can sound as good as a TOTL direct drive amp. This just isn't possible. A T1S, okay, that's a more reasonable goal._

 

I re-read the 1st post and....where did I mention "top of the line"?

 anyway, so far there has not been any _ comparison review _on using Lundahl transformers for electrostatic, let alone the amorphous core version. Anybody brave enough to be the first to build one? (amorphous core, of course!) Come on, even if they don't work as well as hoped, you can always use them for building that push-pull 2A3 amp, right? 
	

	
	
		
		

		
		
	


	




 (Don't look at me, even if I do want to build one such box I still don't have a good enough SS amp to drive it 
	

	
	
		
		

		
		
	


	




)

 Have fun


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## luvdunhill

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_I re-read the 1st post and....where did I mention "top of the line"?

 anyway, so far there has not been any  comparison review on using Lundahl transformers for electrostatic, let alone the amorphous core version. Anybody brave enough to be the first to build one? (amorphous core, of course!) Come on, even if they don't work as well as hoped, you can always use them for building that push-pull 2A3 amp, right? 
	

	
	
		
		

		
		
	


	




 (Don't look at me, even if I do want to build one such box I still don't have a good enough SS amp to drive it 
	

	
	
		
		

		
		
	


	




)

 Have fun_

 

you didn't mention it, hence the word "implied" 
	

	
	
		
		

		
		
	


	




 anyways, if I was to do this I'd go with iron from Electra-print. I know they have worked with electrostatic speakers before and the brief conversation I had with Jack was promising.


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## AudioCats

but if the electra-print doesn't accomplish the "kill-all" goal, you can't use it for anything else (unless electrostatic pannel speakers), no?


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## krmathis

Keep the JRM impressions, and details, coming.


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## AudioCats

acutally not much to say, other than it is a LOT better than the SRD-6. Sound stage is about the same, more dynamic range, bass is much stronger( the clean kind), and goes much deeper (more bass than the T1, and goes at least as deep). Feels like it has unrestricted power. The sound is not rolled off at the top end at all; blacker background (not sure why I felt that). 

 Like the T1 it seems to provide the "there" feel. The down side is some of the micro sonic details are missing so it doesn't reproduce the ambient/atmosphere nearly as well as the T1s, so not as "there" as the T1s. It is the kind of situation that "if you listen for it it is all there", but if I have ot listen for things then I am not as involved into the music.

 I seriously think the bottle neck is the amp, the Kenwood is just not that detailed to start with, plus it might have been stressed too hard: I don't think it is meant to drive directly wired transformers.( I did not use any 1 Ohm transformer, connection posts are directly connected to the transformer.) If I play Rock music hard enough the Kenwood will actually kick itself out, somehow the extra current demand can trigger the amp's protection circuit.

 Lots of potentials. That is all I can say. I think a high end amp can solve the detail problem so the amp+JRM box will outperform the T1s, but again, I don't have one such amp to connect it to so that is still uncertain.


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## AudioCats

Lundahl's are on the way. 

 Lets hope they are better than the JRM's.


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## burgunder

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_Lundahl's are on the way. 

 Lets hope they are better than the JRM's._

 

It will be interesting to see if you can get better performance from the Lundahls or if the limiting factor migth be the amp?

 Keep us posted!


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## krmathis

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_Lundahl's are on the way. 

 Lets hope they are better than the JRM's._

 

Aahh, sweet!


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## AudioCats

burning in (test configuration, of course)






 Not sure if I want them to sound better than my other boxes or not. Deep down I kind of hope they don't out perform the JRM and the SRD-mod, because.... if these LL do sound better, the next logical step will be their AM (amorphous core) version..... the AM's are $400 a pop! 
	

	
	
		
		

		
		
	


	





 --- 7/2/09: bad news..... the Lundahl seems to be worth the major price differences. Debating when to try some AM ones.


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## pidesd

what lundahl trafos are you using? i d like to put these in my srd-6 (well not actually inside...
	

	
	
		
		

		
		
	


	




)

 also can you describe how connect them?


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## smeggy

I have a 7Mk2, can I just strip it out and rebuild in a bigger case with new transfos as a direct replacement without changing anything else?


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## krmathis

Quote:


  Originally Posted by *pidesd* /img/forum/go_quote.gif 
_what lundahl trafos are you using? i d like to put these in my srd-6 (well not actually inside...
	

	
	
		
		

		
			





)

 also can you describe how connect them?_

 

Would not be surprised if he use the same transformers as in this project.
the STAX Transformer


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## spritzer

Quote:


  Originally Posted by *smeggy* /img/forum/go_quote.gif 
_I have a 7Mk2, can I just strip it out and rebuild in a bigger case with new transfos as a direct replacement without changing anything else?_

 

Yup but you might as well sell it and start off fresh. I got the upgraded SRD-7 Pro bias PCB's yesterday but have to test them to see if all is a-ok. If all is well then I can build one for you. I even added some extra mounting holes to make them easier to use in a non SRD7 configuration.


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## pidesd

thanks for the link krmathis! but even though they likely are ll1630 that audiocat is using, i d like to have some kind of approval before i order them. furthermore, i have still no idea if these would be the best bang for my buck, especially with the not THAT high-end lamdas normal bias i plan to buy.


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## pidesd

spritzer,

 i d really be interested in buying one of your pcb's if you have some spare and if you want to. of course they have to pass the test first. i m not sure about the circuit, but if it is similar to the mk2 one shown earlier in this thread, then i guess i just have to tap the the supply line a bit earlier when it s 230v if i want to feed normal bias phones?


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## spritzer

One thing about choosing the correct transformers is to keep the capacity of the windings vanishingly low or you will run into trouble. Almost any OPT will function as a Stax transformer but few are optimized with regards to capacitance. 

  Quote:


  Originally Posted by *pidesd* /img/forum/go_quote.gif 
_spritzer,

 i d really be interested in buying one of your pcb's if you have some spare and if you want to. of course they have to pass the test first. i m not sure about the circuit, but if it is similar to the mk2 one shown earlier in this thread, then i guess i just have to tap the the supply line a bit earlier when it s 230v if i want to feed normal bias phones?_

 

It started out life as the SRD-7 Pro supply but has been modified to meet the standard to which Stax designs bias supplies for the Omega lineup. It also has a built in voltage divider (i.e. spots for 3 extra resistors) which allows you to set a second output to what ever voltage you like. The values for 230v and 500v (HE90 bias) configuration are printed on the board. 

 Once I'm sure that it functions perfectly then I will be selling them at cost.


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## pidesd

awesome!


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## les_garten

Spritzer,
 Do you think that a TOP quality amp like a Krell or Threshold and this Transfo Box would be "better" than a GES, KGSS, BH, etc?

 .


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## pidesd

if i can permit myself to try an answer...

 i dont think it can surpass a dedicated amp as the trafo is an adapter. but my little finger tells me it could come pretty close. but keeping in mind that the goal is to make a stat amp for those who already have a dynamic amp or for those who dont only listen to electrostatics, i think the approach as its merits and the value might be outstanding. i guess only testing will tell...


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## spritzer

A transformer will never match a properly designed direct drive amp. There are a number of factors that contribute to this but it's largely due to optimizing the amp for the given task. A speaker amp, driving an odd load through a transformer will always be at a disadvantage.


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## les_garten

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_A transformer will never match a properly designed direct drive amp. There are a number of factors that contribute to this but it's largely due to optimizing the amp for the given task. A speaker amp, driving an odd load through a transformer will always be at a disadvantage._

 


 Kewl, thanx for the answer, this helps direct my attentions.

 .


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## smeggy

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Yup but you might as well sell it and start off fresh. I got the upgraded SRD-7 Pro bias PCB's yesterday but have to test them to see if all is a-ok. If all is well then I can build one for you. I even added some extra mounting holes to make them easier to use in a non SRD7 configuration. 
	

	
	
		
		

		
		
	


	


_

 

can it run pro and normal bias as I use both?

 Great work btw, very cool indeed!


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## spritzer

Quote:


  Originally Posted by *smeggy* /img/forum/go_quote.gif 
_can it run pro and normal bias as I use both?

 Great work btw, very cool indeed!_

 

Yup, the pro bias is taken directly off the multiplier and the same goes for the NB, except it is taken through a voltage divider first. Stax just tapped into the multiplier after two stages on the Mk2 bias supplies to get NB but this works better IMO since it is adjustable. 

 That said a bias supply like this is a compromise since it doesn't have a transformer on the input. That's why I will be designing another one which will be fully isolated for the better transformers.


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## AudioCats

Quote:


  Originally Posted by *krmathis* /img/forum/go_quote.gif 
_Would not be surprised if he use the same transformers as in this project.
the STAX Transformer_

 

Mine are LL1627, similar turn ratio, larger and heavier.


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## Victor Chew

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_Mine are LL1627, similar turn ratio, larger and heavier._

 

How is the performance with the Lunahl?


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## AudioCats

more realistic mids, wider stage. Bass is about the same as the SRD7. Less harshness.

 the only problem is, the big LL's are $400~$500 a pair, while a SRD7 is less than $100. But if you already have a good SS speaker amp, the LL is the way to go.


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## pidesd

would nt the ll1630 be a better bargain at about half the price, especially with not top of the line headphones like the lambdas, as it might present the same characteritics as the 1627 but with perhaps a smaller soundstage? what you guys think? if the prognostics are good, i m tempted to give it a try


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## Victor Chew

Trouble is that there are not as many pro biased transformer/energizer boxes out there for easy comparison. Apart from stax and illusion, I am no aware of any others.


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## AudioCats

the main advantage of using pre-amp output xformer (smaller than the speaker output xformers) is that they are a bit easier to drive. The DC resistance of 1630 is already 14 ohms, the overall impedance will be even higher, any amp should drive it ok. The same thing can not be said about the big LL1627 I am using, my modded Kenwood KA89 (100w x2) can drive it quite well, but with a low power amp the sound gets messy really fast at complex passages. I will guess it needs 50w per channel of good power to run well. 

 My little class-T experiment setup can drive the modded SRD7 box quite well (this is with direct wiring from the amp to the transformer), but the "lack of juice" is apparent when pusing the big LL's.

 Spritzer got a bunch of smaller LL's laying around, maybe he can give us some helpful info in that area.


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## spritzer

I haven't had much time to work on the Lundahls but I hope that changes soon.


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## BoilermakerFan

I have 1:20 CT'd E-P iron that I'm using with Spritzer's boards for two transformers. Also have a SRD-6 on the way that will be upgraded to a Spritzer board.

 I need to order a second set of E-P iron for another application with either1:25 or 1:50 since the power available will only be 25W/ch.


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## AudioCats

updated the first post in the thread (JRM transformer reliability issue).


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## spritzer

It's a shame the transformers have failed but it appears to be a common problem with anything JRM related.


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## Jon L

Quote: 





audiocats said:


> Bass is about the same as the SRD7.


 

 Too bad your transformer failed.  Still, it's disappointing that the bass was not improved over SRD7, since that's one area I would like to see improvement from my SRD7 MkII setup, esp with OII 
	

	
	
		
		

		
		
	


	



   
  BTW.  Anyone try contacting Jack at Electraprint to get a quote on custom transformers?  Last time I tried that for another project, the quoted price was way less than I was expecting...
   
  Anyhow, once the transformer and bias supply from Spritzer are finalized, I would personally love to see a group-buy/group-build type of thing happening


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## AudioCats

Jon,
  that review was done with a Kenwood KA96, which somehow is too overpowering (that is my TV amp.... ).
  With my battery powered Gainclone, the bass of LL was quite a bit better than the SRD7. LL goes deeper and cleaner; (the SRD7 gives mostly mid bass). But that Gainclone, being battery powered and low voltage, doesn't have the juice to drive the 1627 to it's full potential.
   
  I don't think we need some kind of custom electrostatic transformers. The large LL has highly sectionalized windings, and can be wired so the primary and seconday interweave. (well, kind of). 
   
  Anyway, I will put the existing "good" JRM transformer aside, maybe use it to make a parafeed guitar amp later on.


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