PeeCeeBee - Page 14 - 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 29th March 2013, 11:33 PM   #131
diyAudio Member
 
jkuetemann's Avatar
 
Join Date: Dec 2010
Location: Paris, Ontario
Default Peer Review Requested

Please see attached images and review for errors. The schematic shows BC547C/BC557C input devices that use a different pin-out than the 2SA965/2SC2235 I'm actually going to use (only because I have them), so don't let that misguide you, the pin-out I'm using is ECB.
Attached Images
File Type: gif TeeOhThreePeeCeeBee.GIF (42.9 KB, 698 views)
File Type: gif VSSA.gif (31.8 KB, 701 views)
__________________
---Jason Kuetemann---
When the student is ready, the master appears.
  Reply With Quote
Old 29th March 2013, 11:55 PM   #132
PMI is offline PMI  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Milwaukee, Wisconsin
I assume you simulated the circuit? Main reason I ask is b/c I am wondering if there is anything in your model to account for a difference between gate capacitance of the two mosfets.
Quote:
from http://www.sound.westhost.com/project101.htm:

...additional capacitors ... shown are to balance the gate capacitance. The P-Channel MOSFETs have significantly higher gate capacitance than their N-Channel counterparts, and the caps ensure that the two sides of the amp are roughly equal.
  Reply With Quote
Old 30th March 2013, 12:13 AM   #133
diyAudio Member
 
jkuetemann's Avatar
 
Join Date: Dec 2010
Location: Paris, Ontario
The VSSA is a very different animal from Rod Elliot's Project 101, so I'm not sure what Rod felt was required for his design directly translates to the VSSA. I used Bob Cordell's models for my simulations and did not find any issues with stability. The models used do account for the differences in the capacitances between the device polarities.

Other designs exist where there has been no specific need to match the capacitances of the N-channel and P-channel devices that seem to work just fine; just look at designs using vertical MOSFETs, the devices can be very different.
__________________
---Jason Kuetemann---
When the student is ready, the master appears.
  Reply With Quote
Old 30th March 2013, 12:33 AM   #134
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Near the Ganges
Hi Jason.

Peeceebee seems okay.

Just some points:

1) Use R1 in parallel with C2.
2) Try to draw a lone trace from GND to input "-ve", i.e. no other parts between input ground pin and main ground supply.
3) R18 is not necessary.
4) Decrease R12 and R16 to 10ohms and increase the two 15K resistors slightly to keep VAS bias same.
  Reply With Quote
Old 30th March 2013, 01:07 AM   #135
PMI is offline PMI  United States
diyAudio Member
 
Join Date: Feb 2013
Location: Milwaukee, Wisconsin
Quote:
Originally Posted by jkuetemann View Post
...The models used do account for the differences in the capacitances between the device polarities...
That was basically what I was wondering, thanks! Looks like a nice layout...

And, I did not mean to say that Rod's circuit is similar, but it just struck me that he found it necessary to compensate for that difference.
  Reply With Quote
Old 30th March 2013, 01:55 AM   #136
spind is offline spind  Canada
diyAudio Member
 
Join Date: Feb 2003
Location: Winnipeg
Quote:
Originally Posted by jkuetemann View Post
Please see attached images and review for errors. The schematic shows BC547C/BC557C input devices that use a different pin-out than the 2SA965/2SC2235 I'm actually going to use (only because I have them), so don't let that misguide you, the pin-out I'm using is ECB.

I'm not an expert (by far) and I haven't gone all the way through it, but I'm interested in this design as I do have a bunch of TO3 Hitachi's

Looks like nice work so far (to my uneducated eye). Just wondering if the low level grounds around the input should be on the same routes as the 1000 and 2200 uF capacitors? Could the lower level grounds be connected to the ground via 10 ohm resistors and parallel diodes in both orientations as seen on some other designs on this forum? May not be needed, but just a thought.

Thanks for doing this layout!
Steve.


ps. The values for R's 5-10 are not the same on the schematic and the pcb.

Last edited by spind; 30th March 2013 at 02:02 AM.
  Reply With Quote
Old 30th March 2013, 03:07 AM   #137
diyAudio Member
 
jkuetemann's Avatar
 
Join Date: Dec 2010
Location: Paris, Ontario
Quote:
Originally Posted by shaan View Post
Hi Jason.

Peeceebee seems okay.

Just some points:

1) Use R1 in parallel with C2.
2) Try to draw a lone trace from GND to input "-ve", i.e. no other parts between input ground pin and main ground supply.
3) R18 is not necessary.
4) Decrease R12 and R16 to 10ohms and increase the two 15K resistors slightly to keep VAS bias same.
Shaan,

My input filters are arranged to avoid the voltage divider (attenuator) that the usual arrangement ends up being. I'd think it is still effective with two minor caveats - The base bias goes through both the 1k and 10k resistors and the input 'sees' the 10k in parallel with the sum of the 1k and the native input impedance of the amp, so a slightly lower input impedance. Still IMHO effective without sacrificing 10% of the input signal. If there is some other issue I'm not aware of my ears and mind are open.

The input grounding was something of a compromise due to limited space for traces. That said, my traces are fairly thick for the expected currents and I could likely go thinner to make one of the 1000uF cap terminals my audio ground or perhaps go all the way back to the ground spades. I was hesitant to go all the way to the ground spades because the input power is decoupled there, so the ground of one of the 1000uF caps seemed to be a better choice. Maybe I'm wrong...

The 100K at the input is simply to prevent the input from floating at a very high impedance. I agree it is not strictly necessary, but it is my preference to not allow the input to float.

R5, R10, R12, and R16 set the bias conditions and are interactive. I was experimenting with the values in simulation. Your advise is sound, it sims better with R12 and R16 at 10 ohm and R5 and R10 at 18k ohm.

Jason
__________________
---Jason Kuetemann---
When the student is ready, the master appears.
  Reply With Quote
Old 30th March 2013, 03:16 AM   #138
diyAudio Member
 
jkuetemann's Avatar
 
Join Date: Dec 2010
Location: Paris, Ontario
Quote:
Originally Posted by spind View Post
I'm not an expert (by far) and I haven't gone all the way through it, but I'm interested in this design as I do have a bunch of TO3 Hitachi's

Looks like nice work so far (to my uneducated eye). Just wondering if the low level grounds around the input should be on the same routes as the 1000 and 2200 uF capacitors? Could the lower level grounds be connected to the ground via 10 ohm resistors and parallel diodes in both orientations as seen on some other designs on this forum? May not be needed, but just a thought.

Thanks for doing this layout!
Steve.


ps. The values for R's 5-10 are not the same on the schematic and the pcb.
Grounding is a sore spot on this layout due to the limited space. I could go thinner on the traces as they carry little current.

The 10 ohm with reverse polarity parallel diodes is a common ground loop breaker. I am not sure it is needed but if the room is available it could perhaps be included as a PCB option.

The R5-R10 values differ as the schematic was simply the values of my last sim and I labeled the PCB based on a hard copy I had from a prior sim. Sorry for the confusion. R5 and R10 set the bias current for Q1 and Q2 and the ratios of R7/R6 and R8/R9 set the gain. There seems to be some advantage to the lower values given the nature of the low impedance present at the summing nodes (the CFA variety this amp is billed as).
__________________
---Jason Kuetemann---
When the student is ready, the master appears.
  Reply With Quote
Old 30th March 2013, 07:16 AM   #139
shaan is offline shaan  India
diyAudio Member
 
shaan's Avatar
 
Join Date: Mar 2009
Location: Near the Ganges
Hi Jason.

All's well.

I think you are okay to go.
  Reply With Quote
Old 30th March 2013, 10:34 AM   #140
Tyimo is offline Tyimo  Hungary
diyAudio Member
 
Join Date: Nov 2002
Location: Hungary
Quote:
I re-arranged the original placement of the input stage so that all the transistors that processes the +ve part of the signal remains above the ones processing the -ve part. To me this makes it look better and easier to digest.
O.K. Thanks!
  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 11:11 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