my gilmore class A amp - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

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 20th May 2012, 08:03 PM   #11
diyAudio Member
 
Avro Arrow's Avatar
 
Join Date: Sep 2010
Location: Toronto, eh
Quote:
Originally Posted by dirkwright View Post
All those paralleled small signal output transistors could have been replaced with just a pair of BD139/140.
They could...but somehow I don't think it would sound quite as good...
  Reply With Quote
Old 20th May 2012, 10:10 PM   #12
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Quote:
Originally Posted by Telstar View Post
And they would sound better IYO?
I'm surprised this sounds good, or even measures good.

The VAS is wimpy as hell, for example.

This is the schematic I'm looking at:
http://www.djgardner.com/headphone/g...nalo_rev_c.pdf

Maybe it's the wrong one, I don't know, but it appears that you've merely substituted discrete jfet's for the monolithic original ones.

You can delete R17 and R21, and then replace the load resistors on the two long tail pairs with a current mirror each, no problem.

The collectors of Q3 and Q4 are extremely sensitive to load, so trying to make them drive the bases of 4 transistors is just dumb in my opinion.

The constant current sources for the jfet input differentials is far too complicated. A simple jfet + resistor would have been plenty fine there.

So no, I think this designs sucks.
  Reply With Quote
Old 21st May 2012, 12:34 AM   #13
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Of course, this is my opinion only. It's free and worth every penny you paid for it.
  Reply With Quote
Old 21st May 2012, 04:38 PM   #14
diyAudio Member
 
Join Date: Nov 2004
Location: Germany
Quote:
Originally Posted by dirkwright View Post
I'm surprised this sounds good, or even measures good.
The basic topology seems to make a lot of sense if you ask me. Some companies have built very fine speaker amps with more "grown-up" versions.
Quote:
Originally Posted by dirkwright View Post
The VAS is wimpy as hell, for example.
You think so? About 4.4 mA of Ic isn't too bad for a small-signal transistor. That's close to the levels you'd find in a simple speaker amp.
Quote:
Originally Posted by dirkwright View Post
You can delete R17 and R21, and then replace the load resistors on the two long tail pairs with a current mirror each, no problem.
And end up with an "undefined VAS current" topology. I've simulated ones like that and they seemed to behave reasonably well, but I dunno... an uneasy feeling does remain. One approach I've seen that seemed to make sense was using current mirrors plus (smaller) load resistors. The current mirrors go under the VAS tap then, making VAS Ic well-defined again.
Quote:
Originally Posted by dirkwright View Post
The collectors of Q3 and Q4 are extremely sensitive to load, so trying to make them drive the bases of 4 transistors is just dumb in my opinion.
The output Qs are high-beta transistors running at considerable Ic (about as much as a TO-92 case will allow, actually). They'd do a fine job at load isolation well down into the double-digit ohms range. With R18/20 there already is considerable loading present in the first place.

I guess capacitive loading at this point forms the dominant pole.
Quote:
Originally Posted by dirkwright View Post
The constant current sources for the jfet input differentials is far too complicated. A simple jfet + resistor would have been plenty fine there.
I think the point of the pots was nulling (input stage) distortion. Plus, he gets to attach a DC servo there (for noise reasons?). That one does seem overly fancy when an Evil Electrolytic(R) in the feedback would pretty much have done the same job (it's not like a 100 F 25V part would be huge or cost a fortune).

Last edited by sgrossklass; 21st May 2012 at 04:45 PM.
  Reply With Quote
Old 21st May 2012, 05:23 PM   #15
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
I modeled it in Tina, a spice simulator. THD is about 0.01% @ 1khz and 970mV output driving 150ohms. Bandwidth is good. I don't have the exact models for the jfets, so I used general purpose ones. I have good models for the other transistors. I measure about 3.6mA for the VAS transistors, and about 10mA each for the outputs. DC offset is over 100mV, so a servo is needed. I didn't use the servo because they don't reduce distortion. I'm sorry but I am not impressed.
Attached Images
File Type: jpg Gilmore amp.JPG (84.2 KB, 506 views)
  Reply With Quote
Old 22nd May 2012, 04:38 PM   #16
Telstar is offline Telstar  Italy
diyAudio Member
 
Join Date: Dec 2007
Location: Italy
The jfet models matters quite much, and btw a few thousands happy customers matters more than a spice sim.
__________________
"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
  Reply With Quote
Old 27th May 2012, 06:29 AM   #17
awpagan is offline awpagan  Australia
diyAudio Member
 
Join Date: Nov 2004
Location: sydney
Quote:
Originally Posted by RNMarsh View Post
K. Gilmore's electrostatic headphone amp looks great. Are pcb available - bare or stuffed?
I believe the KGSS has stopped a while ago but been replaced by a newer version. The kgsshv
KG seems to hang out here-- i'm on a roll... the kgsshv - Do It Yourself - www.Head-Case.org

I got the last of the KGSS pcb's from headamp.
I will make it, sooner or later.
__________________
Indecision makes the world gone round.
Maybe

Last edited by awpagan; 27th May 2012 at 06:35 AM.
  Reply With Quote
Old 18th June 2012, 03:16 PM   #18
Remolon is offline Remolon  Spain
diyAudio Member
 
Join Date: Dec 2010
I have finished a Dynalo amplifier with some minor differences, BJT in place of the differential amplifier jFET, and 1N4148 diodes for the current source.

Click the image to open in full size.

I started with a Spice simulation for two set of available BJT, BC550/BC560 and ksa1015/ksc1815. Both behave well on the computer, so I mounted them with point to point wiring.
Click the image to open in full size.

Both BJT performed well connected to a sigma22 PSU, and I ordered PCBs. I also ordered a PCB for a more simple PSU with +/-15 VDC output.
Click the image to open in full size.

This is the final assembly with E-96 Series resistor (1/4W, 1% and 50ppm), BJT ksa1015 and ksc1815, Gain of 6dB, servo with TL051, current source with 1N4148 diodes and PSU of +/-15.00 VDC
Click the image to open in full size.


Click the image to open in full size.

The amplifier measures very well:

Difference between channels of 0.04 dB and flat response, identical in the two channels: -0.03 dB at 20 Hz and 0.00 dB from 80Hz to 20kHz, bandwidth of 2 Hz to 500KHz with + /-3dB.

Less than 1 mV DC offset, after stabilized by the servo

Input impedance greater than 23 kOhm

Output impedance less than 0.75 Ohm

And sounds good too.

Last edited by wintermute; 19th June 2012 at 10:21 AM. Reason: Images fixed at Remolon's request
  Reply With Quote
Old 19th June 2012, 06:27 PM   #19
diyAudio Member
 
Join Date: Feb 2012
Location: Chicago
Remolon - did you have those PCB's made for you? or did you source them somewhere?

Looks great!

L
  Reply With Quote
Old 19th June 2012, 06:50 PM   #20
diyAudio Member
 
Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
Quote:
Originally Posted by dirkwright View Post
All those paralleled small signal output transistors could have been replaced with just a pair of BD139/140.
I don't know whether it was a consideration here, but some designers prefer to parallel small-signal transistors just to obtain a better statistically averaged match between the push and pull sides. Evens out any individual anomalies. But often that's an attempt to get product consistency within loose production and supplier specs.
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
LME49811 front-end for Gilmore amp? Artie Solid State 7 29th April 2009 08:36 PM
Some questions on the Gilmore headphone amp. Artie Headphone Systems 2 22nd April 2009 12:21 AM
Kevin Gilmore stottie Solid State 1 30th November 2006 07:37 AM
Any design info on the Gilmore Raptor Digital Amp? LineSource Class D 21 8th September 2006 07:55 PM
Gilmore amp troubleshooting name773 Solid State 10 31st August 2003 04:44 AM


New To Site? Need Help?

All times are GMT. The time now is 06:32 PM.


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