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 22nd April 2001, 05:54 PM   #1
khayman is offline khayman  Portugal
diyAudio Member
 
Join Date: Apr 2001
Location: Portugal
Hello everyone,

I have recently came across a nice little amplifier from Goldmund - model SRA. It's a stereo 2x50W audio amplifier with a very nice sound. One thing that struck me was it's physical size - about 30cm x 30cm x 6cm ! The manufacturer uses a design approach in which the bandwidth/slew rate of the amplifier is very high (for an audio amp) and he calls it a JOB circuit.

It's small, it looks cute, but it's no little cosmetic piece whatsoever. It's a very musical and pleasant amplifier that costs about $1500 (surprisingly higher end price for such a size ).

I did a search and found out that the JOB was first made by http://www.jobsys.com and Goldmund used it under license apparently.

Also, on the http://www.goldmund.com site you can see internal pictures of this little amplifier. 2 output power transistors (mosfets ?) per channel and little more. The heatsink is very small, and when I tested it myself, I could touch it no problem, it wouldn't hurt my fingers.

I'm not an electronics wizard but I do understand a little of it. Each designer has it's own approach to solve a problem but this thing, coupled with the sound quality I heard and the reviews I've seen seems to go against what I've seen designed - big class A amplifiers dissipating generous amounts of heat, or fast amps like the Stochino and others which have more complex circuitry than this one seems to have at first sight, etc.

Anyone ever investigated these kind of amplifiers and came out with some ideas of what is being used ? I was kind of amazed that I searched and couldn't find any discussion on the topic on this forum

Relevant links :

http://www.jobsys.com/
http://www.jobsys.com/jobstereodoc.htm

http://www.goldmund.com/old/phlib.html#secr
(inside pictures of the SRA amplifier, scroll down)


Best regards to all,

K.
  Reply With Quote
Old 23rd April 2001, 03:39 AM   #2
mlloyd1 is online now mlloyd1  United States
diyAudio Member
 
mlloyd1's Avatar
 
Join Date: Feb 2001
Location: illinois
Unhappy re: yeah, it does arouse the curiousity ......

Sorry, I can't post anything more than what you've found about the JOB circuit. I agree with you that it certainly sounds intriguing. The more I think about it, the more I think it's just a very well optimized version of a fairly conventional circuit. I am reminded of material I've read by David Rich in "The Audio Critic". Dr. Rich thinks very highly of of Bryston's design and performance. They appear to take a good basic topology and engineer the heck out of it to squeeze out the best performance and highest reliability the design is capable of. For example, very low gain stage distortion across the entire audio band (and beyond) without using cascoded gain stages.

Maybe someone who has one (or access to one) will open and give us some reverse engineering notes :-)

Please ...
  Reply With Quote
Old 30th August 2002, 01:57 AM   #3
diyAudio Member
 
dhengkoel's Avatar
 
Join Date: Nov 2001
Location: CIA
Quote:
Maybe someone who has one (or access to one) will open and give us some reverse engineering notes :-)

Please ...
Yes ... I'm waiting too ... where's the experts??????
__________________
:: The last but not least ::
  Reply With Quote
Old 30th August 2002, 05:49 AM   #4
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Default Re: re: yeah, it does arouse the curiousity ......

Quote:
Originally posted by mlloyd1
Dr. Rich thinks very highly of of Bryston's design and performance. They appear to take a good basic topology and engineer the heck out of it to squeeze out the best performance and highest reliability the design is capable of.
Same with NAIM (at least the early ones). I have heard it said that the circuit is essentially right out of the RCA ap notes.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 30th August 2002, 07:34 AM   #5
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Hi all

The following might probably apply:

http://www.goldmund.com/old/tecampst.html

There is not much info though, but at least a little hint. When you look at these job amps you see that there is a module covered with a small heatsink which might in fact be a power op-amp plus some additional control circuitry. There seems to be no means for adjustments in this amps so there must be some functionality in these modules to overcome this (they write about using a DC servo, so there is just the bias current control that remains a mystery).

Regards

Charles
  Reply With Quote
Old 30th August 2002, 06:29 PM   #6
Account Disabled
 
Join Date: May 2002
I would urge caution with Bryston's amps., its been reported that these are prone to cross-conduction, as the output topology does not facilitate efficacious base-charge extraction from the output devices....
  Reply With Quote
Old 30th August 2002, 06:42 PM   #7
frugal-phile(tm)
diyAudio Moderator
 
planet10's Avatar
 
Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Blog Entries: 5
Quote:
Originally posted by mikek
I would urge caution with Bryston's amps., its been reported that these are prone to cross-conduction, as the output topology does not facilitate efficacious base-charge extraction from the output devices....
cross-conduction? Could you explain (when it comes to SS i'm still pretty much lost)?

I used Brystons extensively when i was doing proPA. Good sounding and VERY reliable. The newest generations are even better. Somewhere here i have a 3B/4B schematic if anyone is interested in seeing it.

dave
__________________
community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
  Reply With Quote
Old 31st August 2002, 12:13 AM   #8
Account Disabled
 
Join Date: May 2002
Smile Howdy folks...

Cross-conduction......In otherwords, driving the amp. with a suitably high-freq. stimulus, (eg a 20KHz cosinusoid), will cause high, and uncontrolled shoot-through currents as one supply rail is intermittently shorted to the opposite rail.

This is a recipe for the rapid overheating, and eventual destruction of the output stage.

This is caused by a driver stage that is inadequate with respect to the rapid extraction of base-charge.

Such a facility is necessary for controlling the turn-off of one output BJT, while the device connected to the opposite supply rail is turning on.

Michael in Chigwell, Essex, UK.



P.S: Bryston schematics are available from their website...
  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
UcD like topology amp. Bender.ru Class D 245 12th December 2013 02:48 PM
Anyone seen this amp topology before? BlackUnikorn Tubes / Valves 14 6th August 2008 08:51 PM


New To Site? Need Help?

All times are GMT. The time now is 03:28 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