[Sathimas]

I twisted the torriod - wires now - and it worked.
The hum now starts to be noticable at a level that I'll never use to listen to music.

That Amp has so much power ... wow.

Thank you again for your advice, I would have gone crazy without the good documentation here.
______________________________________

Since it completely works now, it's about time to think about some modifications

Everybody here seems to be crazy about diamond buffers.
I already found at that those transform the SOHA into a Class Amplifier (Is that correct?)
and that this takes the sound quality to a new level - But how does it do that?
What enhancements can I expect?

First I'll try to get a new tube, but I haven't found any good supplier here in Germany.

 

[headphonejunkie]

Good to hear you got somewhere with your problem. For a tube I like a German RFT I have been using. It cost me $30 at tubedepot.com. Maybe you can find one right at the source.GE 5963's are supposed to be good too. I have a GE5814A that sound very good.

 

[PJotr]

Hi
When I look on default config with LND150 http://www.mb3k.com/pics/SOHA/LND150.gif and PCB SOHA http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.pdf
I think when we change only jumper from PC to CS we haven't change config for the source follower, because we switch C2 to pin G LND150 not to pin S.
It's correct or I'm wrong?

 

[tomb]

Quote:

Originally Posted by PJotr /img/forum/go_quote.gif Hi When I look on default config with LND150 http://www.mb3k.com/pics/SOHA/LND150.gif and PCB SOHA http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.pdf I think when we change only jumper from PC to CS we haven't change config for the source follower, because we switch C2 to pin G LND150 not to pin S. It's correct or I'm wrong?

The note on that pic is mis-leading. For the source follower using the LND150's, you also have to move the LND150's to the other two positions - Q1 and Q3

, and jumper from D to S in the Q2 and Q4 positions:

Don't forget that R8 is reversed with R7, and R18 is reversed with R17. Not very confusing is it?

 

[PJotr]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif For the source follower using the LND150's, you also have to move the LND150's to the other two positions - Q1 and Q3 , and jumper from D to S in the Q2 and Q4 positions:

Thanks for your answer, but I know about it.

I want to change config between "LND150 MOSFET CCS" and "LND150 Source Follower" only with switch jumper PCS (config as writed in http://www.mb3k.com/pics/SOHA/LND150.gif)

I think it is possible in config http://www.mb3k.com/pics/SOHA/LND150.gif.
Only we must change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360. And now we can change config by jumper PCS.

Look in http://headwize.com/ubb/showpost.php...52060&fpage=12

 

[Blooze]

Quote:

Originally Posted by konder8u /img/forum/go_quote.gif According to the designers/first proto builders, T1 should be a toroid if it's in the case. If you mount it remotely in a different box or walwart, then whatever you want. Unfortunately, I've found the 30VCT uncommon enough that the toroid is the simplest choice anyway.

I never had any problem sourcing the flat-pack trafos. Never had an issue with any hum being loud enough to cause any problems with the music either, and I built one of the first several SOHA's, long before there were any PCB's, with the trafo right in the case.

http://www.pedalforroses.homestead.c...phoneamps.html


Tomb is right, use a flatpack in a wall wart case if you want the least amount of PS noise.

 

[tomb]

Quote:

Originally Posted by PJotr /img/forum/go_quote.gif Thanks for your answer, but I know about it. I want to change config between "LND150 MOSFET CCS" and "LND150 Source Follower" only with switch jumper PCS (config as writed in http://www.mb3k.com/pics/SOHA/LND150.gif) I think it is possible in config http://www.mb3k.com/pics/SOHA/LND150.gif. Only we must change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360. And now we can change config by jumper PCS. Look in http://headwize.com/ubb/showpost.php...52060&fpage=12

That last link has no bearing on the LND150's or the final board that Digi produced. The production boards were different from the ones supplied to several people during prototyping, anyway. If you can find a way to do it, fine, but it's not possible with the production board as implied in that note.

EDIT: It's not even implied in the note - see the sentence about "FETs" below.

Only the J113's are switchable only by changing the P-C-S jumpers. This is explained on Digi's own website, which is where I referenced the image I posted:
http://taihu.bjtzh.gov.cn/~digi01/soha-v3.0.htm
Scroll down to about the bottom third of the page, and you will find the different CCS configurations referenced.

Besides, the "FETs" are only the J113's. The 1N5297's are constant current diodes and the LND150's are MOSFETs.

As stated earlier in my previous post, the LND150 Source Follower has a different configuration entirely from the "regular" LND150 CCS. Good luck.

 

[headphonejunkie]

I am wondering if there is any difference between the sound using these two configs. I would go with source follower (which is what i am using) if there is no difference. Although, I think this config was for if you were going to use the diamond buffer bds. I think. I am planning on using the jisbos when they become available.

 

[tomb]

Yep. Runeight said they debated source follower vs. the "regular" config during design, but the LND150's are only available at Mouser, and the J113's have limited availability, too, I believe. So, they added the 1N5297's, but I don't think source follower is even possible with those.

He said if you have the parts, there's no reason why you shouldn't use "source follower", period. It will work just as well with BJT or FET opamps - and it is needed for Steinchen's buffers.


EDIT - P.S. Another reason for having so many configs - the J113's have to be handled carefully. Quoting Runeight:
"Care should be exercised when building the SOHA with the J113 JFETs. Their maximum Vdss is 35V. Under normal operating conditions they will see only about 15-20V, but if the plate voltage on the tube is too low it is possible to exceed this maximum and destroy them. To protect the JFETS, the minimum plate voltage should never be set below 20V (see below the warning about adjusting the trimpots). "

What that means is that unlike the convenience we have with the Millett MAX - not caring what the tube is biased at until the output stage is adjusted - if you have the tube biased incorrectly on startup in the SOHA with the J113's, you could burn them out.

 

[ericj]

15-0-15-0 transformers are relatively easy to find.

I obviate the hum issue by mounting the transformer in a wallwart case and placing it a few feet away from the amp. Use a 5-pin DIN connector for power.

 

[PJotr]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif As stated earlier in my previous post, the LND150 Source Follower has a different configuration entirely from the "regular" LND150 CCS. Good luck.

Yes, I know.
But

look in http://www.mb3k.com/pics/SOHA/LND150.gif on bottom writed:
"... For the source follower configuration for the fets, just change the PCS jumper to go from C to S instead of C to P."

But I think it is mistake because jumper PCS in position CS: switch C2 to pin G LND150 not to pin S.
But will be work it, when we change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360..

 

[tomb]

Quote:

Originally Posted by PJotr /img/forum/go_quote.gif Yes, I know. But look in http://www.mb3k.com/pics/SOHA/LND150.gif on bottom writed: "... For the source follower configuration for the fets, just change the PCS jumper to go from C to S instead of C to P." But I think it is mistake because jumper PCS in position CS: switch C2 to pin G LND150 not to pin S. But will be work it, when we change in Q2/Q4 pin S with pin G and resistors. R7 must be 1k, R8 must be 360..

I'll repeat this for the last time - just to be helpful - "FETs" does not mean the LND150's.

 

[PJotr]

OK, but when I want add eg. jisbos bufer whitch CCS option I must chose:
1.LND150 MOSFET CCS
2.LND150 Source Follower
3.J113 JFET CCS
4.1N5297 Diode CCS

I read many info and I think I must chose 2. or 3.
When I want eg. OPA2134 I chose 1.

It's correct?

 

[tomb]

#2.

Or #3. - by switching the P-C-S jumpers. "FETs" in the bottom note of the CCS diagrams refers to the J113's.

 

[ericj]

Wow. What a lot of confusion. Especially since the LND150 is most assuredly a FET. Depletion mode, which is weird, but still a FET.

FWIW my perfboard soha (w/ lnd150) switches between regular and mu-follower by just moving one jumper per side.