Aleph Mini riddle makes no sense to me... - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 5th August 2003, 04:57 PM   #21
diyAudio Member
 
Join Date: Dec 2002
Location: Houston
Default Component Swapping

I am waiting on a set of boards from Kristijan to arrive. Looking over the circuit, I want to try IRF044 Mosfets and something else in the front end.
Can the ZVP3310 be used instead of the 9610's here? The lower input capacitance looks like a small improvement. I also see the BC250 has a very low input capacitance.
Does the circuit as shown on Kristijan's diagram have active current gain? Excuse the DA questions, the inner details of how the Aleph circuits work still eludes me.
Looking it appears that a higher than normal output impedance is unavoidable due to the single output devse used. The 044 should help compared to a 240.

George
  Reply With Quote
Old 5th August 2003, 05:33 PM   #22
MBK is offline MBK  Singapore
diyAudio Member
 
Join Date: Apr 2002
Location: Singapore
Default Re: Component Swapping

Quote:
Originally posted by Panelhead
I am waiting on a set of boards from Kristijan to arrive. Looking over the circuit, I want to try IRF044 Mosfets and something else in the front end.
Can the ZVP3310 be used instead of the 9610's here? The lower input capacitance looks like a small improvement. I also see the BC250 has a very low input capacitance.
Does the circuit as shown on Kristijan's diagram have active current gain? Excuse the DA questions, the inner details of how the Aleph circuits work still eludes me.
Looking it appears that a higher than normal output impedance is unavoidable due to the single output devse used. The 044 should help compared to a 240.

George

Don't know about the ZVP3310 but the 9610's are exceptionnally linear devices.

I took IRFP140 also in part of better transconductance (and as by Nelson Pass himself, the lower voltage transistors should sound better).

The circuit does have active current gain, yes, through the 1.3k / 220uF feedback network. Since I changed resistor values and IRF's, I had to readjust it.

BTW - My output Z is a riddle because I measured it into a resistor and got Z=0.16 Ohms. Then after some changes including raising the gain to 26 dB, I measured again, this time using real speaker driver, and got (now) Z=0.75 Ohms. So it's not that the devices can't go lower, but that either a resistive R gives a different result from a real speaker, or that (more likely) my daring gain change made the circuit suboptimal in that respect...
  Reply With Quote
Old 5th August 2003, 06:23 PM   #23
MikeW is offline MikeW  United States
diyAudio Member
 
MikeW's Avatar
 
Join Date: Sep 2002
Location: North of Boston
When you use output devices with higher capacitance do you need to change the 221 ohm gate resistors?
__________________
MikeW
  Reply With Quote
Old 5th August 2003, 07:46 PM   #24
diyAudio Member
 
Join Date: Dec 2002
Location: Houston
Quote:
Originally posted by MikeW
When you use output devices with higher capacitance do you need to change the 221 ohm gate resistors?
Hot Damn, a question I can answer!
The 221 value of the gate resistors is not critical. They are there to damp any ocillations in the circuit.
The 221 value is used a lot here, but anything from 100 - 300 ohms should work as well. These are used the same as grid resistors in tubed circuits. In tubed circuits the resistor of choice is a carbon comp to minimize high frequency occilations. The grid resistors are normally around 1K ohms or higher. The high impedances used in most tube circuits is what creates these problems.

George
  Reply With Quote
Old 5th August 2003, 07:47 PM   #25
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
You don't have to, but feel free to experiment with lower
values, as low as say 22 ohms. I would bet that 47
ohms is about as low as you would want to go.
  Reply With Quote
Old 14th August 2003, 05:31 PM   #26
MBK is offline MBK  Singapore
diyAudio Member
 
Join Date: Apr 2002
Location: Singapore
Default Listening, and component choices

Well... after sorting out my self inflicted weird problems, I built the second channel, using the Aleph30 front end this time. Now that I have both channels operating, I should say something about my impressions about the sound. Works like a charm.

I had my mid driver on chip amps before, now Mini-A. It surprised me that there seemed little gross differences. But there seems to be a lot of small differences which make all the difference... if that makes sense. The largest difference seems much better PRAT - everything is more "normal", in an unspectacular way. Cool, really. You don't even know it's there.

I don't have any bass problems (bi amped, the Mini-A's operate >310 Hz), in fact the bass improved in definition and clarity as well - because now I can use one chip amp per driver. Before, it was one chip amp for 2 drivers. No hum problems in spite of one single 375 VA transformer for 2 Mini-A's plus 4 chip amps, and of course I will fix that configuration too once the transformers arrive for the Mini-A.

Mid neutrality and clarity are exemplary, so are the highs. Again, I don't know how to verbalize it - it's like saying, "no difference, except that now there is nothing wrong anymore".... Before, I was quite happy with the chip amps - except, except... that here and there, there was some hitches, mostly, on certain passages, some low level distortion, something like "jittery highs". The highs on the Mini-A are just straight. Hmm, eventually I should make a proper AB test.

Now for the final part: rebuilding both channels to same topology, values and components, proper PSU and connectors, and final tests.

Here I have a resistor question:

I will so far stick with non-exotic parts. In stores here I found 2 types of power resistors: snow-white-coffin types, presumably inductive, but tested non magnetic, and long, thin ones, presumably carbon, but with end caps, and tested magnetic at those end caps.

What trade off do I choose: non inductive but magnetic - and slightly capacitive (virtue of end caps), or non magnetic but inductive?

My gut feeling is that a little inductivity shouldn't hurt because we want to get rid of that HF hash anway... BUT since these resistors are in the feedback loop, that could actually work the other way around (increasing feedback for HF hash) ... opinions?


Add-on question: I used BC549 instead of BC546. The Vceo is dangerously low (30V) and I have +-24V rails - wonder how come they haven't blown yet... then again, don't touch a running system... I get a Vbe drop of 0.64 V, fine with my choice of source R=0.39. Is it worth changing to BC546 for safety, and have to recalibrate everything from bias to AC current gain feedback?
  Reply With Quote
Old 15th August 2003, 01:23 AM   #27
diyAudio Member
 
Join Date: Dec 2002
Location: Houston
Default Re: Listening, and component choices

Here I have a resistor question:

I will so far stick with non-exotic parts. In stores here I found 2 types of power resistors: snow-white-coffin types, presumably inductive, but tested non magnetic, and long, thin ones, presumably carbon, but with end caps, and tested magnetic at those end caps.

What trade off do I choose: non inductive but magnetic - and slightly capacitive (virtue of end caps), or non magnetic but inductive?

My gut feeling is that a little inductivity shouldn't hurt because we want to get rid of that HF hash anway... BUT since these resistors are in the feedback loop, that could actually work the other way around (increasing feedback for HF hash) ... opinions?

My opinions on this subject are very biased, but I never use magnetic components if avoidable. To my ears, a big fat Allen Bradley 2 watter is the way to go.
For higher power applications I check with my trusty pocket magnet. I sometimes find some plastic cased 5W 1% Dales. And some ceramic cased WW are non-magnetic too.
The long ones you saw may be a version of wirewound. If banded, and the bands are wide these are wirewound in a conventional shape. These are almost always magnetic.
Having the power resistor in the feedback loop should help correct for the non-linearities. Just like having a large value coupling cap. JMHO

George

Add-on question: I used BC549 instead of BC546. The Vceo is dangerously low (30V) and I have +-24V rails - wonder how come they haven't blown yet... then again, don't touch a running system... I get a Vbe drop of 0.64 V, fine with my choice of source R=0.39. Is it worth changing to BC546 for safety, and have to recalibrate everything from bias to AC current gain feedback? [/B][/QUOTE]
  Reply With Quote
Old 2nd September 2003, 05:42 PM   #28
MBK is offline MBK  Singapore
diyAudio Member
 
Join Date: Apr 2002
Location: Singapore
Well, looks like I have a "final version", all (most?) troubles ironed out, so to celebrate I created a new thread:

Ta-daaa! New Mini Aleph

Hope I got the schematic right this time around...
  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
Boulder's Jeff Nelson makes sense! mikeks Solid State 9 27th November 2011 06:16 PM
whats makes sense to have class A amp? space2000 Solid State 64 7th July 2008 03:46 PM
So, you still not sure if building a GC makes sense? Peter Daniel Chip Amps 65 28th January 2004 11:23 AM
Balanced DAC stage makes no sense to me jwb Digital Source 16 26th March 2002 03:20 AM


New To Site? Need Help?

All times are GMT. The time now is 12:01 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