PeeCeeBee - Page 95 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th July 2013, 06:26 AM   #941
diyAudio Member
 
DAMANHURI's Avatar
 
Join Date: Jul 2007
Default My Design VSSA

please if you like it Size 100mm x 58mm
Attached Images
File Type: jpg DipTrace PCB - Vssa Edit.dip.jpg (490.7 KB, 711 views)
Attached Files
File Type: pdf Buttom Layer.pdf (44.2 KB, 140 views)
File Type: pdf Top Layer.pdf (21.5 KB, 110 views)
__________________
Best regards - Damanhuri

Last edited by DAMANHURI; 17th July 2013 at 06:29 AM.
  Reply With Quote
Old 17th July 2013, 09:13 AM   #942
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
Quote:
Originally Posted by PMI View Post

I DO think the parts LC sent out are worth measuring to see how close a complementary pair they make. I can try to do that, because I have not installed them yet, but someone else would have to provide a little direction.
I believe that for this kind of circuit (symmetrical CFB) one needs transistors with high hfe and as closely matched as is realistic. For me, ultra low Cob is not absolute priority, unless one really wants to play a lot with the scope. All you need is DMM that can measure hfe. I think that the best option is to buy a lot of KSA1220/KSC2960, like Jason did, and try to match hfe.

Why don't you measure hfe for transistors that LC delivered with pcbs? I guess that there is greater mismatch than with Jason's 1220/2960 matched pair. I doubt if LC matched them. He simply provided transisitors with the same hfe rank, that's all.
  Reply With Quote
Old 17th July 2013, 12:19 PM   #943
diyAudio Member
 
jkuetemann's Avatar
 
Join Date: Dec 2010
Location: Paris, Ontario
I think I've found my new favourite TO-126 device, these are fast enough for VAS, robust enough for pre driver or even driver in lower power applications, isolated tab for easy mounting, easy to match, relatively high gain. Oh, and reasonably priced at ~$0.20 each in 100 quantity.

I'm able to get a 10% hfe match on about 50 pairs of the KSA1220AY / KSC2960AY, so pretty good. I can get about 20 pairs to less than 3% hfe difference. I do agree that a low-ish Cob is nice, but more like 'icing on the cake' for me too.
__________________
---Jason Kuetemann---
When the student is ready, the master appears.
  Reply With Quote
Old 17th July 2013, 03:30 PM   #944
PMI is offline PMI  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Milwaukee, Wisconsin
Quote:
Originally Posted by jkuetemann View Post
I think I've found my new favourite TO-126 device, these are fast enough for VAS, robust enough for pre driver or even driver in lower power applications, isolated tab for easy mounting, easy to match, relatively high gain. Oh, and reasonably priced at ~$0.20 each in 100 quantity.

I'm able to get a 10% hfe match on about 50 pairs of the KSA1220AY / KSC2960AY, so pretty good. I can get about 20 pairs to less than 3% hfe difference. I do agree that a low-ish Cob is nice, but more like 'icing on the cake' for me too.
KSA1220AY / KSC2690AY seem to be intended to perform well at much higher currents/higher power. Using them as a replacement may be a good idea, but I doubt that they will be good drop-in substitutes, without making some other adjustments.

If I remember correctly the SA1381/SC3503 were both quite linear in the same range of collector current, which is about were LC had his VAS circuit biased (showing that he is a Careful Cat, and not just a Lazy one... )

KSA1220/KSC2960, were not, at least not in the 10-20mA range of bias current. The published "typical" NPN device curve looks fairly steep in our area of interest (certainly when you take into account that the graphs are logarithmic). So, as the base current of the pair changes, the PNP device will be more-or-less linear, but the NPN device, not so much.

The end result may be that the amplifier will sound fine at one volume setting, but when you turn the volume up, or simply when the material played changes, the sound signature you like will change. Personally, I have found this annoying in the past. (Not horribly objectionable, but still...)

One of the things I like about the VSSA circuit, is that it seems to yield an amp that sounds uniformly good no matter what speakers, volume level, or material I try.

Having said all that, I am willing to measure and compare different pairs of transistors, but someone with a bit more knowledge will have to suggest a meaningful test - translation, I do not have the experience to do that on my own.
Attached Images
File Type: jpg Current Gain ksc3503.jpg (127.3 KB, 626 views)
File Type: jpg Current Gain ksc2690.jpg (155.1 KB, 521 views)

Last edited by PMI; 17th July 2013 at 03:36 PM.
  Reply With Quote
Old 17th July 2013, 03:43 PM   #945
PMI is offline PMI  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Milwaukee, Wisconsin
Another issue is when the bias current of the VAS is intentionally changed, or allowed to change with changes in supply voltage. When someone intentionally changes the bias point of the VAS transistors to be lower or higher, or changes the supply voltage without adjusting the VAS bias to stay in the desired range, some additional distortion will result...

This does not mean that we should not use different VAS transistors or different supply voltages... for all I know, it may even sound better...
  Reply With Quote
Old 17th July 2013, 04:58 PM   #946
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
Quote:
Originally Posted by PMI View Post

One of the things I like about the VSSA circuit, is that it seems to yield an amp that sounds uniformly good no matter what speakers, volume level, or material I try.
You shall have it with many replacement VAS transistors, including Jasons choice. I think that uniformly good sound quality at different volumes is more cosequence of topology itself than of transistor choice. Many people in this thread built PeeCeeBee with suboptimal transistors (Shaan himself does not have access to first class components) and they still have great sound.

LC used particular transistors because he did not want some competent engineer to criticize his skills, not because VSSA can not sound good with different components.

(I always liked sound of quasi complementary output stages although the mismatch between n and p side is huge. In fact I like it more than the sound of complementary EF.)

But if one can find LCs VAS tranies in the same hfe rank, which is probably impossible now, it's OK. He will have great sound and great specs.
  Reply With Quote
Old 19th July 2013, 10:52 AM   #947
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Near the Ganges
Today I did some tweaking with the emitter degenerators and VAS base to PS resistors, just out of curiosity, to see what happens when...

Replaced the 10R and 470R with 22R and 220R and decreased current injectors to 5K. Supply is +/-28V. Still no Cdom and zobel.

The modded amp is now singing, with noticeable change in the mid-range. The vocals are different. Bass/highs seems the same as before.

more later...
  Reply With Quote
Old 19th July 2013, 10:54 AM   #948
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Near the Ganges
Quote:
Originally Posted by gives you wing View Post
hey, Shaan
which is the best for the sound result as your experiment before, the diode in V+/- rail, 1N4148 / Schotky / MUR?

thanks, g.y.w.
1N4148, so far.

Couldn't source MUR. Local stockist out of stock.

Will update once the experiments are done.
  Reply With Quote
Old 19th July 2013, 11:02 AM   #949
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Near the Ganges
Quote:
Originally Posted by ivanlukic View Post
(Shaan himself does not have access to first class components)


Quote:
still have great sound.
  Reply With Quote
Old 19th July 2013, 12:15 PM   #950
diyAudio Member
 
Join Date: Jul 2010
Location: Cacak
Shaan,

As the late Curtis Mayfield would say:

Keep on pushing!
Move on up!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 10:20 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2