Cambridge Audio A3i repairs and mods - 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 7th May 2008, 08:05 AM   #11
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
This circuit is a very interesting one. Very unique VAS

x-pro, I presume this amp was designed to a budget. If you could make more exotic device substitutes and tweaks, what would you have done? My guess is you would have used a triple stage as you have already mentioned, and better driver transistors.
  Reply With Quote
Old 7th May 2008, 12:30 PM   #12
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Quote:
Originally posted by jaycee
This circuit is a very interesting one. Very unique VAS
Thank you, the VAS is indeed quite interesting - it combines a very high open loop gain and a good linearity for such a simple circuit. I've used a somewhat modified version of it (with fully balanced cascoded JFET inputs) in Creek Audio A52 series of power amplifiers.

Quote:
Originally posted by jaycee
x-pro, I presume this amp was designed to a budget. If you could make more exotic device substitutes and tweaks, what would you have done? My guess is you would have used a triple stage as you have already mentioned, and better driver transistors.
These are obvious ways of potential improvement. A3i was made to a very tight budget. In general, this VAS could be easily coupled to another good quality output stage with good results.

Alex
  Reply With Quote
Old 7th May 2008, 01:35 PM   #13
ppa is offline ppa  Italy
diyAudio Member
 
Join Date: Mar 2005
Location: Italy
Hi All,

Alex, what do you think about the change of bd139 and bd140 with the MJE243/53 ? their pin sockets are the same but power and curret are both bigger in the seconds, moreover MJE243/53 are made by ONsemi and this is a guarantee.

Pier Paolo
__________________
PP
  Reply With Quote
Old 7th May 2008, 01:40 PM   #14
ppa is offline ppa  Italy
diyAudio Member
 
Join Date: Mar 2005
Location: Italy
Hi All,


I forgotten that in the a3i schematic C216/7 are inverted.

Pier Paolo.
__________________
PP
  Reply With Quote
Old 7th May 2008, 01:44 PM   #15
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Quote:
Originally posted by ppa
Hi All,

Alex, what do you think about the change of bd139 and bd140 with the MJE243/53 ? their pin sockets are the same but power and curret are both bigger in the seconds, moreover MJE243/53 are made by ONsemi and this is a guarantee.

Pier Paolo
Hi Pier,

yes, these look like a suitable replacement, thought according to the datasheet there is a noticable difference in a current gain between n-p-n and p-n-p devices. I may order some from Farnell to try and measure.

Cheers

Alex
  Reply With Quote
Old 7th May 2008, 01:47 PM   #16
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Quote:
Originally posted by ppa
Hi All,


I forgotten that in the a3i schematic C216/7 are inverted.

Pier Paolo.

True! My mistake - did not check the schematics properly . Sorry!

Unfortunately I can not edit the post now. Let's hope that this is such an obvious mistake nobody would fall for it...

Alex
  Reply With Quote
Old 7th May 2008, 04:35 PM   #17
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally posted by x-pro


Email me through the forum - I'll send you the schematics.

Cheers

Alex

sorry, tried. New user, my account is under moderation. Can you send it to me? Thanks a million.
  Reply With Quote
Old 7th May 2008, 04:59 PM   #18
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Quote:
Originally posted by blue_dog1
sorry, tried. New user, my account is under moderation. Can you send it to me? Thanks a million.
No, I can not email to you through the forum either. Please go to my web page and use email address from "Contacts" page (note anti-spam bits)

Alex
  Reply With Quote
Old 12th May 2008, 01:02 AM   #19
x-pro is offline x-pro  United Kingdom
diyAudio Member
 
x-pro's Avatar
 
Join Date: Apr 2003
Location: London
Quote:
Originally posted by ppa
Hi All,

Alex, what do you think about the change of bd139 and bd140 with the MJE243/53 ? their pin sockets are the same but power and curret are both bigger in the seconds, moreover MJE243/53 are made by ONsemi and this is a guarantee.

Pier Paolo
Hi Pier!

here is an update. I've received some MJE243/253 and tried these in A3i circuit. They work very well - certainly better than modern versions of BD139/BD140. I also have measured the gain of these devices and from 50 of each all PNP have gain between 140 and 150, and NPN are mostly at 130, with a range from 100 to 150. I plan to make a redesign of A3i circuit for DIY and will probably use ON Semi drivers and output devices.

Alex
  Reply With Quote
Old 12th May 2008, 01:50 AM   #20
G33/33 is offline G33/33  Indonesia
diyAudio Member
 
G33/33's Avatar
 
Join Date: Dec 2004
Location: Djakarta
Quote:
Originally posted by x-pro



I plan to make a redesign of A3i circuit for DIY and will probably use ON Semi drivers and output devices.

Alex

Hi Alex,

is there any alternatives for ZVP3306A ? I can't find it in Indonesia

can I use IRF 9610 / 9510 ?



rgds,
G33/33
  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
Cambridge Audio 640C v1 Mods Thomo Digital Source 423 4th October 2013 07:42 AM
Cambridge Audio 340A SE preout conversion and other mods mikesnowdon Solid State 0 31st May 2008 08:00 PM
Cambridge Audio DacMagic 2i repairs query Fizzy Parts 3 11th January 2006 07:54 PM
Cambridge Audio CD5 Mods? edpgc Digital Source 7 9th May 2004 11:58 PM


New To Site? Need Help?

All times are GMT. The time now is 01:08 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