[headphonejunkie]

I was wondering if anyone has the schematic and bd layout for the original SOHA amp. Headwize no longer works and there is no other place to find anything on this amp.
 
Thanks in advance

 

[tomb]

I was wondering if anyone has the schematic and bd layout for the original SOHA amp. Headwize no longer works and there is no other place to find anything on this amp.

Thanks in advance

I probably have a lot of the documentation. I'll try to post it later today.

 

[headphonejunkie]

Thanks.
I would hate for this amp to disappear into nothingness. I am still using mine and like it. If you have anything on the JISBOS that would help too.
 
Thanks.

 

[headphonejunkie]

 

[headphonejunkie]

I just picked up these k240 studios yesterday and they are nice thru the SOHA

 

[headphonejunkie]

only 10 hrs or so burn in on the k240's

 

[tomb]

  Thanks.
I would hate for this amp to disappear into nothingness. I am still using mine and like it. If you have anything on the JISBOS that would help too.
 
Thanks.

You already tapped me out on the JISBOS.  Although, I had this from Steinchen:
 
Quote from Steinchen:

The regulators on the SOHA board are a bottleneck to the buffers. Note that they have to supply the current for both channels and depending on the bias setting dissipate quite some heat. Regulators in TO-220 package (781x / 791x) are mandatory for each buffer option, 78Lxx / 79Lxx in TO-92 package won't cut it.
 
Furthermore, when using a 2x15VAC transformer you should get at least 2x19VDC after rectification. Hence +-15V regulators are highly recommended, giving more voltage swing and output power to the buffer while reducing heat dissipation at the regulators (in comparison to +-12V regs).
 
Depending on the targeted bias setting of the buffer heatsinking the regulators probably becomes mandatory. The heatsinks may interfere with large electrolytic capacitors installed on the SOHA psu section. Large electrolytic capacitors after the regulators are not useful and rather harm the work of the regs than support it. To improve the regulation (with 781x/791x that means reduce the impedance at higher frequencies) 1uF - 4.7uF metallized polyester box caps or 1uF - 10uF tantalum caps are recommended after the regulators. Additionally they leave enough space for using small bolt-on heatsinks on TO-220 regulators.
 
 

 

[tomb]

There seems to be some sort of bug in posting these.  Let's see if this works:
 
 

 
 
 

 
 

 

[tomb]

 
 
SOHA bass:
 

 You also might try increasing the capacitance across the end of the B+ supply from 100uF to 200uF or so. Mains_hum reported that this tightened up the bass a bit. - Batman, 3/20/2006
 
I've added an additional 100uF capacitor in parallel to the final B+ capacitor because it lets the SOHA work fine with really low bass frequencies .. not that it was bad in the first place. - Mains_Hum, 2/26/2006
 
One change that might be necessary if anyone really tries to pull 200mA would be to increase the size of the input caps in the bipolar PS to more like 2200u. Even bigger possible to get full bass. - Runeight, 10/26/2005.

 
Batman is Bill Pascule.  Of course, "Runeight" is Alex Cavalli.
 
DigiBoard Corrections:

you're probably right. Hopefully, everyone who uses the LND150 reads that R7/R17 and R8/R18 are silkscreended in reverse because that was one of the other problems I had, resulting in only 0.6mA of CCS current.
 
To summarize for the skimmers:
I used an LND150 is plate drive configuration with ST L7812ACV/L7912ACV voltage regulators. What I found was:
1) with no op amp in, the -12v supply will be more like -16v. put in the op amp and it drops to -12v (thanks neurotica)
2) R7/R8 and R17/R18 are silkscreened in reverse to what they should be when using an LND150 on the v3.0 digi boards. R7/R17 should be 360 Ohms and R8/R18 should be 1KOhms. You can verify this by looking at the tracings and checking to make sure the G pin of the LND150 connects to a 1KOhm resistor and the S pin connects to a 360 Ohm resistor.
3) You can't set the plate voltage correctly without the volume pot installed. With it out, I could only bias across a range of roughly 2.5V (~38-~40.5). Putting in volume pot allowed me to sweep a broader range.

[Edited by rreynol on 08-19-2006 at 10:53 AM.]
 

 
Adjusting bias/trimmers:

  About the trimmers - it may be that you haven't turned them enough, but you will notice a definite change if its working.  Put your meter where you're measuring tenths of a volt and you will see the difference.  If the heater is not on, or the plates are not conducting (bad tube socket/pins), then it won't change - period.
 
As for turning the trimmers, some say you will feel a detent or a small click - I've never had that happen for me.  Instead, the ones I've had you can turn forever - once they hit max in one direction, you can still turn them.  However, they reset if you start turning them the other way.
 
The 72 Volts is another sign of this.  It should be lower if the tube is under load.  The 11.75 on your 12V regs is fine.  I don't know why, but those 78**/79** are always a tad low than advertised.  (probably another reason to go with 15V reg's)
 
One might want to see your transformer connections, but I think the 72V is exactly what you get if the tube is not in (or conducting).  What about your heater votage - 12.6V?  Does that check out?

 

[tomb]

More:
 
 
THIS IS THE ENTIRE HEADWIZE ARTICLE:
 

 

[tomb]

Head-Fi User MB3K's build diary:
 
 
 
NOTE: NSFW - you should check out what MB3K's been doing lately - modelmayhem.com .  He posted a couple of years ago and stated that he was "back" on Head-Fi, then he disappeared again.  I guess it's easy to see why he's not interested in headphone amps anymore!!!

 
 
EDIT: Mods, just to be clear, this is the Head-Fi user: http://www.head-fi.org/u/5505/mb3k
Same guy -
 
EDIT2: Cleaned up - use link above with caution.

 

[tomb]

I think I'm done posting what I have on the SOHA.
 
I gotta take a break.

 

[headphonejunkie]

Thanks greatly. You have given me a ton of info I would not find anywhere else.

 

[headphonejunkie]

I want his job.

 

 

[tomb]

 
I want his job.

 

Yeah ... really.