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.

ACA amp with premium parts
ACA amp with premium parts
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 30th June 2020, 04:54 AM   #331
Variac is offline Variac  Costa Rica
diyAudio Editor
 
Variac's Avatar
 
Join Date: Dec 2001
Location: San Francisco, USA & San Josť, Costa Rica
ACA amp with premium parts
The stock kits are back in the store!

Amp Camp Amp – diyAudio Store

Cool new labeled rear panel and wiring to make it easy to select 2ch stereo or
Monoblock balanced, bridged or balanced.
__________________
"The geek shall inherit the earth"
2019 Burning Amp is Nov. 9 & 10 in S.F. Thread here on diyAudio:
Burning Amp 2019!!!
  Reply With Quote
Old 30th June 2020, 02:35 PM   #332
TungstenAudio is offline TungstenAudio  United States
diyAudio Member
 
Join Date: Jan 2014
Location: Kenmore, WA
These kits are great to work with. Buy two
One of the best ways to 'upgrade' the ACA is still to bridge the two channels inside one chassis, then use a pair as monoblocks. The type of bridging that works best will depend on your speakers, and it is easy to try the different types.
  Reply With Quote
Old 2nd July 2020, 10:44 AM   #333
wrath is offline wrath  Poland
diyAudio Member
 
Join Date: Jun 2004
Location: Poland Poniatowa qwidolek
What do you think about using IXFB82N60P

(V-MOS, N 600V/ 82A/ 1250W/ 0,75R) to ACA?
Overkill?
  Reply With Quote
Old 2nd July 2020, 01:28 PM   #334
dfoulk is offline dfoulk
diyAudio Member
 
Join Date: Jun 2013
Default IXFB82N60P

Hi there Mr. Wrath,


I don't know that much about it, but those are kinda pricey, around $20 a piece.
I had asked Tungsten what he thought about the IRFP440, a beefier selection than the IRFP044 that I am currently using for Q1, with 29 volt rail voltage, and he suggested the FQP44N10, as he was using them and was pleased. I like the IRFP044, but I think I will try the IRFP440 just to see. They are around $3 a piece, and are 500 volt rating. If your pockets are deep, there is the Semisouth SJEP120R100,
at $100 a piece, supposed to be very nice, used by Mr. Pass in some of his highly regarded amps. I have also heard from Jordi that they really sound good in his ACA for use as Q1. Of course they are not made anymore, so the high prices, and beware of fakes. When I try the IRFP440 for Q1 and the current used IRFP140 for Q2, I will post what I hear.
Den
  Reply With Quote
Old 2nd July 2020, 03:42 PM   #335
TungstenAudio is offline TungstenAudio  United States
diyAudio Member
 
Join Date: Jan 2014
Location: Kenmore, WA
The IXFB82N60P is one of a new series of parts that have been designed for switching applications, rather than linear. It has a different set of design tradeoffs from the IRFP440, which is also a newer part. Where the IRFP440 has a moderate input capacitance, low gate charge and low transconductance, the IXFB part has very high input capacitance (23 nF) and high gate charge in order to obtain its high transconductance. Both parts would be rated at about 140V for continuous Vds, rather than 500V or 600V for pulsed operation.

The IRFP440 might be Ok for linear operation, but its low transconductance doesn't offer any advantage, at least on paper, over the IRFP240 or IRFP140. The IXFB82N60P, with its extremely high input capacitance, is probably not suitable for the ACA. Certainly not for the Q1 position, though it might work for Q2, but with different sonic character. Remember that Q2 in the ACA functions as part of an interactive current source, so its dynamic behavior is important.

These are examples of some of the different tradeoffs that are inherent in the fabrication of Mosfet transistors. High Vds capability and high current both tend to result in high gate capacitance and high gate charge. High transconductance and low Rds-On are similar. Optimizing for those parameters extracts a toll in other areas of performance that we find desirable for audio.

There are other amplifier designs that make good use of the newer physically large Mosfets. Probably the best example is the Pass Labs XA25, which has enjoyed great critical and commercial success. Though its exact design remains a topic of much speculation, we can safely say it uses IXFN140N30P and IXTN40P50P transistors. Another design is the BA2015 50Watt Shade amp which uses a pair of IXFN140N20P Mosfets. These are examples of big "hockey puck" transistors that require very different designs to drive them properly. The front end of the XA25 is a power amplifier in its own right. The BA2015 hockey puck amp uses a transformer to drive the lower IXFN140N20P, and in turn requires an input stage (or preamp) of very low output impedance. The simple design of the ACA cannot support such large transistors.
  Reply With Quote
Old 2nd July 2020, 04:34 PM   #336
dfoulk is offline dfoulk
diyAudio Member
 
Join Date: Jun 2013
Default mosfets

I must say that I am just curious about the sonic character of the IRFP440, and it
is an inexpensive part. I know from the past that every transistor does have it's own sonic character, and mixing them can sometimes give you something different that you would not be able to obtain otherwise. Kind of like the taste of the right amount of lemon in your sweet iced tea Also, I am experimenting with the specific sound of my own home brew open baffle speakers, so what I hear may not be applicable to everyone. There are parts that just won't work in the ACA circuit, but I sure enjoy the exchange of ideas and information from knowledgeable experimenters!
  Reply With Quote
Old 2nd July 2020, 05:01 PM   #337
twocents is online now twocents  South Africa
diyAudio Member
 
twocents's Avatar
 
Join Date: Jan 2016
Location: Johannesburg
ACA amp with premium parts
Default R12 - feedback?

If I understand correctly R12 is the feedback resistor here. I find another member, xrk971ís use of carbon film resistors for the feedback very interesting and wonder if someone here has considered or tried it for the ACA yet? See the comment from another thread:
Quote:
Originally Posted by AKSA View Post
I was always fascinated with X's measurements using carbon resistors v. metal film resistors in the feedback networks of the Alpha. He demonstrated conclusively that metal films bring up the third harmonic over the second; the carbons do the opposite.
Best sounding amps have a monotonic decrease of successive harmonics, and the more linear, the better. This is from Jean Hiraga in the 60s - nothing is new and demonstrates how the marketing speak drives the equation rather than the truth.

Cheers,

Hugh
  Reply With Quote
Old 2nd July 2020, 06:35 PM   #338
dfoulk is offline dfoulk
diyAudio Member
 
Join Date: Jun 2013
Default carbon resistor

Maybe this phenomenon is why Tungsten has found that a small capacitor added in parallel to R12 improved the sound of his ACA when driven hard. Perhaps the capacitor has reduced the odd harmonics in a similar way to the carbon resistor?

Just a guess, I do not have the equipment to test the idea
  Reply With Quote
Old 3rd July 2020, 01:57 AM   #339
kking85743 is offline kking85743  United States
diyAudio Member
 
Join Date: Jan 2017
Location: Desert SouthWest, USA
Quote:
Originally Posted by dfoulk View Post
Maybe this phenomenon is why Tungsten has found that a small capacitor added in parallel to R12 improved the sound of his ACA when driven hard. Perhaps the capacitor has reduced the odd harmonics in a similar way to the carbon resistor?

Just a guess, I do not have the equipment to test the idea
Wow! I had completely forgotten about that. Adding it to the list of things to try...

What I have seen so far is that (as you and others have mentioned) the 140 is a much nicer part, especially at higher voltages. I'm seeing 20-30% reduction in THD with no other changes, which is always welcome. I am also seeing between 2/3 to 3/4 dB of gain, just by switching Q1/Q2 from 240s to 140s.

I'm seeing a sweet spot in the 32-36v range for the power into the circuit. Jumping to 40v doesn't seem to add anything, and bumps the THD by a tiny bit, at least with stock values for R1-R4. Time to change them up and see what happnes...

To do:
  • try a variety of bias points for Q1 Drain voltage (adjusted by P1) and see how H2 and H3 change - is there a sweet spot there?
  • look at changes to R14 and see if it impacts the PHASE of the harmonics, post 315 implies it does (negative phase for H2 is presumed)
  • verify my R16 isn't cutting too much voltage (3k, others are using much smaller values), as baseline current thru Q4 is about 4mA
  • check capacitor on R12, see if that impacts harmonics and their phase (prior post implies it might decrease H3 or impact phase)
  • do research on IRFP044 and 440 as possible candidates for Q1 or Q2 positions
  • increase bias current (start with R4a of 2 ohms - from TA's mods) and see what changes

Yeah, that should keep me busy for a while...

Unfortunately, I'm limited to testing only with equipment, as the variable power supply has a small turbine keeping it cool (actually it only sounds that way). Once I get a better feel for what the power supply will be, I'll make a linear supply and be able to listen to the sound and use that to fine tune the circuit. I should have plenty of data by then...
  Reply With Quote
Old 3rd July 2020, 06:54 PM   #340
triode_al is offline triode_al  Netherlands
diyAudio Member
 
triode_al's Avatar
 
Join Date: May 2004
Location: Westland
Quote:
Originally Posted by twocents View Post
If I understand correctly R12 is the feedback resistor here. I find another member, xrk971ís use of carbon film resistors for the feedback very interesting and wonder if someone here has considered or tried it for the ACA yet? See the comment from another thread:
I made a line stage a month ago, (based on EAR, so FB across one stage) and using a metal resistor 3 w for feedback had an overshoot; when I moved to carbon 3 watt the overshoot disappeared. Now guess . .

I have carbon but just .5 watt for the feedback in the ACA for the same reason; my bandwidth open is > 1.2 MHz. No later resonances I can see.
  • Note that most metal film components have iron-clad wires, so with a built-in long inductor. And like Heavyside said: the signal will allways try to run 'through' that iron (that is, behave like as-if).
__________________
ņ la recherche d'un son perdu
  Reply With Quote

Reply


ACA amp with premium partsHide 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
FS: F5T V3 Premium Parts Kits Horio Swap Meet 4 15th August 2016 10:17 PM
Parts Connexion's New Premium Tube Sale ** 2 DAYS LEFT ** PCXstaff Parts Connexion 0 30th October 2013 10:15 PM
Parts Connexion's New Premium Tube Sale ** 2 DAYS LEFT ** PCXstaff Vendor's Bazaar 0 30th October 2013 10:14 PM
RH84 Rev2 Build w/Premium parts craigtone Tubes / Valves 3 23rd April 2013 11:33 PM
Premium parts for your Son of Zen project. CCOZGO40 Swap Meet 1 10th August 2002 04:05 PM


New To Site? Need Help?

All times are GMT. The time now is 01:25 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki