Problem with st151.. - 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 28th August 2008, 03:52 PM   #1
kibet85 is offline kibet85  Kenya
diyAudio Member
 
Join Date: Aug 2008
Unhappy Problem with st151..

Hi all..sorry to bother u guys but i have a problem with my st151..its smoking the 680 ohm resistor..wat could be the problem..was testing without first connecting the outputs which are mj15024 and mj15025...my transformer is a 38-0-38 with 15000 uf 63v caps...i have checked and double checked my design..please help..sorry for my bad english..
  Reply With Quote
Old 28th August 2008, 09:16 PM   #2
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
You were already told in the ST151 thread... 38VAC from your transformer produces 53V DC power supplies - this is too high for the transistors in the circuit. The transistors T1/T2 and T5 are probably fried and shorted C-E hence all the voltage is being dropped over R11 and making it smoke.

You could probably build the same circuit using MPSA42/92 instead of BC546/556, and MJE340/350 instead of BD139/140. Bear in mind the MPSA's have reverse pinout from the BC's. You might also have to adjust the compensation capacitors.
  Reply With Quote
Old 28th August 2008, 10:39 PM   #3
kibet85 is offline kibet85  Kenya
diyAudio Member
 
Join Date: Aug 2008
Default Thank you very much..

Thanks mate..wil do tht..
  Reply With Quote
Old 29th August 2008, 10:34 AM   #4
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
buy the correct transformer for the st151.
__________________
regards Andrew T.
  Reply With Quote
Old 29th August 2008, 12:17 PM   #5
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Well yes, there is that too.

ST151 is not really a circuit that is designed for sub use. Sub amps are supposed to be very rugged and have a larger output stage than normal. The ST151 is a hifi amp, and not suited to this task. It is certainly not suitable for higher voltage rails than shown!

Personally I would consider looking at Elliot's P68 amp, or maybe one of Quasi's amps - the N-BIP300 amp would probably work fine with mj15024 transistors in there. You could even change it for a complementary output stage too, if you designed your own PCB.
  Reply With Quote
Old 30th August 2008, 10:35 AM   #6
kibet85 is offline kibet85  Kenya
diyAudio Member
 
Join Date: Aug 2008
'Elliot's P68 amp or the N-BIP300 amp'

i checked out the above amps and they seem ok..the thing is that they are to expensive for me to make and an error would be costly...i also checked out the nmos 200...this seems ok..
  Reply With Quote
Old 30th August 2008, 03:41 PM   #7
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
If you can get the mosfets then NMOS200 is your best bet

The reason these designs are expensive is because those extra parts and high spec parts are whats needed to get the stated output power *reliably*.

The NMOS200 is probably best because you can get some good mosfets quite cheap. For example, you could use IRF540 quite easily, and they are pretty cheap.
  Reply With Quote
Old 31st August 2008, 09:19 AM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the irf540 are 100V devices and should be used on PSU that never exceeds +-50Vdc when supply voltage is at highest worst condition.
Effectively that means +-45Vdc for normal operational use (about 30 to 32Vac depending on transformer regulation).
You can risk a higher voltage but you must accept the unreliability that comes with a decision to use +-53Vdc.
__________________
regards Andrew T.
  Reply With Quote
Old 31st August 2008, 12:47 PM   #9
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Well spotted. Oops

There are quite a range of IRF devices that would work though - I think ideal for this would be IRF640. IRF740 also would work, and you quite often find these two used inside CRT monitors.

The recommended IRF840 works of course, but doesn't carry quite as much current.
  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
"ST151" 100W amplifier sixtek Solid State 140 9th June 2012 01:39 PM
Big Amp Problem mikelawrey Car Audio 0 4th July 2005 07:31 AM
psu problem metebalci Tubes / Valves 11 25th April 2004 10:15 AM


New To Site? Need Help?

All times are GMT. The time now is 10:44 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