Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Pass Labs This forum is dedicated to Pass Labs discussion.

Aleph-X builder's thread.
Aleph-X builder's thread.
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 19th May 2017, 11:19 PM   #2591
muhy3 is offline muhy3  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Sydney, Australia
Quote:
Originally Posted by Dennis Hui View Post
Hi Vlad,

Do you recall how the matching for the diff pair Q5/Q7 was done?

Another thing I noticed is that the total current through R23/R25 seem a bit low,
even with V2 at its lowest value. Can you confirm your part values for D1 and R17?

Cheers,
Dennis
I purchased matched Q5/Q7 from Jim's Audio. I have a few spares, so I'll set up tonight and match them myself and replace once matched.

D1 = 1N5239B and R17 = 1.5k ohm

Thanks!
__________________
There used to be a time, when penguins filled the sky!
  Reply With Quote
Old 20th May 2017, 12:08 PM   #2592
Dennis Hui is offline Dennis Hui  Canada
diyAudio Member
 
Join Date: Aug 2002
Location: Toronto, Canada
OK. Try measuring and matching the Vgs of the IRF9610 at around 12mA.
Also can you please check for voltages across D1 and R24.

Cheers,
Dennis
__________________
We are fearless amplifier builders. A little heat doesn't scare us at all.
- NP 2002
  Reply With Quote
Old 21st May 2017, 12:08 AM   #2593
muhy3 is offline muhy3  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Sydney, Australia
Quote:
Originally Posted by Dennis Hui View Post
OK. Try measuring and matching the Vgs of the IRF9610 at around 12mA.
Also can you please check for voltages across D1 and R24.

Cheers,
Dennis
D1 = 8.5v
R24 = 4.6v

Vgs of IRF9610 was 10mA from Jims Audio.
The parts bin I have, I was able to match to 15mA.

D1 should be 9.1v shouldn't it?
__________________
There used to be a time, when penguins filled the sky!
  Reply With Quote
Old 21st May 2017, 04:28 AM   #2594
muhy3 is offline muhy3  Australia
diyAudio Member
 
Join Date: Jul 2004
Location: Sydney, Australia
So I bought a bench top PSU and went through to try and match Vgs for the 9610 from Jim's Audio... turns out none of them matched! I had a stack of others, and matched a couple exactly, to like within 0.001v. It didn't seem to make a difference to the circuit. To me it seems like the overcurrent protection on Q9 is being triggered with the volts reading 0.65 across R39... but 0.15 across R13


Sent from my iPhone using Tapatalk
__________________
There used to be a time, when penguins filled the sky!
  Reply With Quote
Old 21st May 2017, 01:20 PM   #2595
Eric is offline Eric  United States
diyAudio Member
 
Eric's Avatar
 
Join Date: Nov 2000
Location: Central PA, USA
Aleph-X builder's thread.
Yes, D1 should provide forward voltage of about 9v (give or take a few tenths). It is critical that Q5 and Q7 be as closely matched as possible. 0.001v is about as good as it gets. If you were using poorly matched transistors the first time around, this could be part of the problem of large offset that won't move with V2 and overheading output resistors.

I'm still suspect of Q4 and Q9 given the short you found.
__________________
My DIY Basement Theater, Aleph-X Amplifers and Avro Open Baffle Speaker construction pages.

Last edited by Eric; 21st May 2017 at 01:23 PM.
  Reply With Quote
Old 22nd May 2017, 05:08 AM   #2596
Rodeodave is offline Rodeodave  Austria
hates ground loops
diyAudio Member
 
Rodeodave's Avatar
 
Join Date: Dec 2004
Location: in the alps
Aleph-X builder's thread.
I have a question regarding the output loading resistors (R1/R4 and R44/R45 on the Aleph-X rev 1.0 pcb). As I'm building my Aleph X specifically for driving planar headphones (HE6), the load impedance seen by the amp will be a flat 50 Ohm. How should I size the loading resistors? From what I've gathered, the typical value used is usually about four times the impedance of the speaker's impedance, so about 32 Ohm for an 8 Ohm speaker. In the case of a 50 Ohm impedance that would amount to 200 Ohms, which would practically barely load the output... So, what do? 100 Ohm maybe?

Also, about the McMillan resistors (R46/R47), is there any sense in trying to omit them? Or are they most definitely needed to insure low and steady DC offset at the outputs?
__________________
Gravity - Making the G since 13.7 billion B.C.
  Reply With Quote
Old 22nd May 2017, 06:19 PM   #2597
Eric is offline Eric  United States
diyAudio Member
 
Eric's Avatar
 
Join Date: Nov 2000
Location: Central PA, USA
Aleph-X builder's thread.
I don't have definitive answers for your questions. My R1/R4 and R44/R45 are set to about 78R with five 390R resistors in parallel. Guess this puts me somewhere above 8x my speaker impedance. As for the McMillan resistors, there was a great deal of discussion earlier in this thread or the other huge Aleph-X thread. The discussion that I remember is that they solve a problem related to offset stability (though I don't remember the details at this point). You can try building without them, but my guess is that you'll end up putting them in anyhow.
__________________
My DIY Basement Theater, Aleph-X Amplifers and Avro Open Baffle Speaker construction pages.
  Reply With Quote
Old 13th July 2017, 08:32 PM   #2598
Rodeodave is offline Rodeodave  Austria
hates ground loops
diyAudio Member
 
Rodeodave's Avatar
 
Join Date: Dec 2004
Location: in the alps
Aleph-X builder's thread.
Another question: With FQP3N30 as output devices (headphone amp...), what Vgs figure should I be aiming at? How do I best determine ideal Vgs for the output stage? Symmetrical clipping? Lowest distortion?
__________________
Gravity - Making the G since 13.7 billion B.C.
  Reply With Quote
Old 13th July 2017, 11:41 PM   #2599
needtubes is offline needtubes  United States
diyAudio Member
 
Join Date: May 2003
Quote:
Originally Posted by Rodeodave View Post
Another question: With FQP3N30 as output devices (headphone amp...), what Vgs figure should I be aiming at? How do I best determine ideal Vgs for the output stage? Symmetrical clipping? Lowest distortion?
You should vary Vgs in order to set the bias current you desire, no?
  Reply With Quote
Old 14th July 2017, 04:58 AM   #2600
Rodeodave is offline Rodeodave  Austria
hates ground loops
diyAudio Member
 
Rodeodave's Avatar
 
Join Date: Dec 2004
Location: in the alps
Aleph-X builder's thread.
For the bias current (upper FET, current source) that's correct. But I'm asking about the output stage FET's Vgs (lower FET). It looks like the FQP3N30 needs a few more volts then a IRF610 or IRFP240 to turn on. Question is, how much is ideal?
__________________
Gravity - Making the G since 13.7 billion B.C.
  Reply With Quote

Reply


Aleph-X builder's thread.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

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 07:46 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki