My MOSFET amplifier designed for music. - Page 2 - 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 11th March 2008, 08:01 AM   #11
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hi, I don't think to be honest it's quite that easy, (oh by the way whose Molly ) the operating point of Q1 would be shifted away from it's linear region. With higher values of R7 what you suggest would work, but as R7 is reduced, decreasing the global feedback, the servo would not compensate. Think of an "old" A.C. coupled design on a single rail with a pot to set the "mid point" voltage of the output transistors. If you shorted the equivalent cap in an amp like this you could never readjust the midpoint to compensate. This design more closely resembles this configuration. Thanks for you're interest, I think even some of the "Tube" fans out there would be suprised how musically engaging this amp is.
Thanks again Karl
  Reply With Quote
Old 11th March 2008, 08:39 AM   #12
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hi Mike, The original P.C.B.'s were all hand-drawn one offs unfortunately. Now P.C.B. layout is another subject on it's own, and layout and correct grounding is vital to get the best performance. I will say this though, designs like this are far more "docile" to work with than many of the more complex (I am thinking of what are really discrete power opamps here). I can't help but feel this stability is one reason why it does sound so good. When making a stereo amp with a single P.S.U. I could never quite "get my head around" the best or ideal grounding configuration. The problem is that while it is easy for one amp(channel) with one P.S.U. I could never reconcile what happens when the two signal grounds (Left and right) are connected together at the input which at some point they must. I know there are various techniques used e.g. a "ground lift resistor" to overcome these problems but I was not happy with any. In the end I actually built a model consisting of two OpAmps on two P.C.B.'s which represent the two channels. I used 10 ohm resistors in the ground leads to highlight and get a feel for what really happens when each channel is supplying a different signal to there respective load. Doing this I came up with a scheme that eliminates as much as possible any interaction.
Regards Karl
  Reply With Quote
Old 12th March 2008, 01:48 AM   #13
diyAudio Member
 
Join Date: Apr 2001
Greetings,

I'm interested with your amplifier.

if you don't mind can you send me the photo of your current amplifier layout?

many thanks and best rgds,
  Reply With Quote
Old 12th March 2008, 01:56 AM   #14
eyoung is offline eyoung  United States
diyAudio Member
 
eyoung's Avatar
 
Join Date: Aug 2007
Location: Sunny SC,USA 15 min south of Charlotte NC
OK ya got me...


Elwood
__________________
"Lead me not into temptation...I can find it myself."
  Reply With Quote
Old 12th March 2008, 08:06 AM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hi Dexter & Eyoung, Thanks for you're interest in this amp, as mentioned at the start, this was built and designed pre p.c. (for me anyway) and all the layouts really were one off's. Have a close look at the pictures I mention, the power amp modules were designed to fit those metal "cans". on quite small boards. The cans were actually P.S.U.s from the Sony C9 Betamax and were ideal for my use as they also include that heatsink at the rear of each one. I designed the board to be an exact fit replacement and even the MOSFET.s fit into the original places that the P.S.U. chopper transistors fitted. Everything is extremely tightly screwed together, and integrated into the case. But I am playing around with a P.C.B. software package at the moment so there is yet hope. To be continued !
Regard Karl.
  Reply With Quote
Old 5th June 2008, 12:06 PM   #16
KLe is offline KLe  Australia
Banned
 
Join Date: Jul 2005
Location: Brisbane
Hi Mooly

I had a friend of mine have a look at your schematic and he made some nice comments which I thought you might like to read. They are as follows ...

Quote:
nice design!

Yes this is indeed a sort of Linsley Hood breed.
I built one of his famous amps designed back in 1969, a 10 W class A amp with very transparent sound sonics.

This Mooly Amp draws from the tight grip on the non-linearities of the output stage, keeping them under control by heavy local NFB. The non-linearities usually account for the spectral spray of THD and IM signals. So, keeping them well under control makes the amp sound rather nice.

The input stage is quite a bit outdated and a true copy of Hood's design, added a servo loop to get rid of the Vbe offset.
  Reply With Quote
Old 5th June 2008, 05:10 PM   #17
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hello KLe,
Thank you for posting your friends thought's on my design-- you must thank them from me. " The Mooly Amp " wonder what that would look like silk screened on the front --- that could be the next big seller
The amp though in all seriousness, it's not just good sonically, it's absolutely marvellous, better than anyone would expect from a quick look at the circuit. THE MUSIC LIVES. No other words to describe it. Someone PLEASE PLEASE build it and shout to the world how good it sounds.
Karl
  Reply With Quote
Old 5th June 2008, 09:02 PM   #18
KLe is offline KLe  Australia
Banned
 
Join Date: Jul 2005
Location: Brisbane
Quote:
Originally posted by Mooly
... The amp though in all seriousness, it's not just good sonically, it's absolutely marvellous, better than anyone would expect from a quick look at the circuit. THE MUSIC LIVES. No other words to describe it. Someone PLEASE PLEASE build it and shout to the world how good it sounds.
Karl
Hi Mooly

Did you do/have a PCB for your amp?
If so, do you have any spare ...
I would be happy to buy 2 from you and build it ...

  Reply With Quote
Old 6th June 2008, 07:04 AM   #19
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Hi,
Erm-- A few have asked this . As I have said earlier the originals were one off's in the truest sense-- have a look at the pics I mentioned at the start.
The best I can offer I am afraid is an untested layout-- which was really an exercise in using DipTrace for me. Having said that the whole design is extremely stable and not prone to any "nasties" and even on prototyping board it performs well, and I can not see any major problems with using this layout.
Attached Images
File Type: jpg notes.jpg (96.8 KB, 5818 views)
  Reply With Quote
Old 6th June 2008, 06:43 PM   #20
Banned
 
Join Date: Apr 2005
Location: Stockholm
Mooly,
it`s easy, isn`t it...just to follow the successful path of great sounding English topologies.
Did you experience oscillations in the output? How did you determine R13/18?
  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 02:47 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