Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 20th February 2013, 01:44 AM   #251
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Well I will change the caps as soon as they come in.

When you say it sounds like the bias is at fault. I assume you mean because I had to double the resistance of R95 and 96? That cuts the current doesn't it? Or do I have that backwards?

As for the fans, mine are marked 12v I don't have any experience with venting amps. Will these run off the +16v rail or so I have to mock up a circuit to cut the voltage? Or better yes, is it better to create such a circuit? And will wiring two in series cause enough of a V drop to accomplish this?
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 20th February 2013, 01:51 AM   #252
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Yes increasing the resistance decreases the bias current.

16 volts is a bit much for a 12 volt fan, put a resistor in series. Something like 22r 7 watt.
You would need 24 volts if you put two fans in series.
__________________
http://www.murtonpikesystems.co.uk PCBCAD50 pcb design software.
  Reply With Quote
Old 20th February 2013, 09:19 AM   #253
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by badraven View Post

Anyway I ohmed the old cap and its shorted. So I guess its no wonder the outputs were running hot.
I should check C39 as well - C40 on it's own shouldn't cause any ill effects, as it's referenced to ground on both sides.
__________________
Nigel Goodwin
  Reply With Quote
Old 21st February 2013, 12:45 AM   #254
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Smile Nigel Goodwin

Nigel

I'm ordering caps for the amp. C40 may not be the whole problem but things sure changed dramatically when I changed it.


Quote:
Originally Posted by Nigel Goodwin View Post
I should check C39 as well - C40 on it's own shouldn't cause any ill effects, as it's referenced to ground on both sides.
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 21st February 2013, 12:54 AM   #255
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Default Nigel

It is great playing my amp again!!!

Quote:
Originally Posted by nigelwright7557 View Post
Unless the amp case has lots of large vents then for a power amp you definitely need a fan or two.
I use pc cases for my amps and have 2 fans at opposite corners, one sucks air in while the other blows it out the opposite corner.
When you say PC Cases are you talking about a PC power supply to power the fans?

Quote:
It sounds like your bias is at fault for the overheating problem. You need to find the setup procedure for the amp.
A simple approach would be to play a sine wave through the amp and look for crossover distortion on a scope. I was surprised just how little bias you can get away with.
However quite a few people prefer the sound if the bias is run a bit hot.
How do I get the Setup Procedure for my amp? From Fender? If so, they will give this info to non-dealers?

Do you have a suggestion for creating the sine wave you are talking about? Of course I don't have access to a scope for maybe it doesn't matter at this point.
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...
  Reply With Quote
Old 21st February 2013, 06:01 AM   #256
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
There is no "setup procedure", after all there are no adjustments. Fender publishes the schematic, and that is all there is. it is expected any service tech can do what is necessary to check for bias being appropriate and take whatever measures might be required. Ther is no procedural manual. Sorry.

It will be very hard to look for a crossover notch in the waveform without a scope.


Is the overheating happening while the heat sink is bolted to the chassis? Or is the board off the chassis at the time? The board must be mounted to chassis to provide proper cooling.

Q14,15 are thye bias transistors, I forget, are they stock types? And have any of the diodes been substituted? D30,D31 are schottky types, having a low forward voltage drop. Putting a "regular" diode in their place would warm the amp up.
  Reply With Quote
Old 21st February 2013, 08:16 AM   #257
diyAudio Member
 
badraven's Avatar
 
Join Date: Dec 2012
Location: The heart of the South, in other words -Redneck Territory lol
Default Enzo

Quote:
Originally Posted by Enzo View Post
There is no "setup procedure", after all there are no adjustments. Fender publishes the schematic, and that is all there is. it is expected any service tech can do what is necessary to check for bias being appropriate and take whatever measures might be required. Ther is no procedural manual. Sorry.
That's what I was thinking but I didn't want to contradict.

Quote:
Is the overheating happening while the heat sink is bolted to the chassis? Or is the board off the chassis at the time? The board must be mounted to chassis to provide proper cooling.
The "primary" heatsink where the outputs are mounted and the thick aluminum block/spacer that goes between the chassis and the mounting for the transistors is what I had for a heat ballast until I mounted everything back in the case the other night. I had clamped a pair of locking pliers on the heatsink to add to the ballast capacity of the sink. The heating problem pretty much went away when I replaced C40.
Last night and the night before I sat here and played the amp for several hours with no problems that I know of.
Quote:
Q14,15 are thye bias transistors, I forget, are they stock types? And have any of the diodes been substituted? D30,D31 are schottky types, having a low forward voltage drop. Putting a "regular" diode in their place would warm the amp up.
Q15 was replaced with a KSA1013 I installed a TIP31C at Q14 because that's the only NPN I had with the correct pinout. When my order arrives I will swap in the correct transistor.

I have not changed D30 or 31. Not sure how to test them yet.
Attached Files
File Type: pdf KSA1013 PNP TO-92L Transistor.pdf (55.5 KB, 0 views)
__________________
If at first you dont succeed, perhaps it isn't your bag. Lol...

Last edited by badraven; 21st February 2013 at 08:19 AM.
  Reply With Quote
Old 21st February 2013, 08:35 AM   #258
diyAudio Member
 
chris661's Avatar
 
Join Date: Feb 2008
Location: Sheffield
Blog Entries: 8
Quote:
Originally Posted by Enzo View Post
It will be very hard to look for a crossover notch in the waveform without a scope.
Its easy enough to hear if pure tones are being played.

I actually rather liked the sound of my amp (when it was working) with a little crossover distortion going on.
  Reply With Quote
Old 21st February 2013, 11:05 PM   #259
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
That may be, and I agree, a little crossover does no harm, but our original poster here has no signal generator and asked earlier how to come up with test tones.
  Reply With Quote
Old 21st February 2013, 11:11 PM   #260
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
Quote:
That's what I was thinking but I didn't want to contradict.
Badraven, if I counter someone else's stratement, it is not done out of disrespect, it is a point of information, hopefully useful information. We all have things we are used to having, but not all situations comply with those expectations. I sure as heck have made faulty assumptions in trying to post things in forums like this, and unless someone points out my error, it won't be corrected. SO if something seems wrong or you don't understand, say so.
  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
Fender help Docc25 Instruments and Amps 3 2nd January 2013 10:18 PM
1970s fender champ givin me problems beauxweiss Instruments and Amps 4 21st February 2012 04:53 PM
MiniWatt N3 problems, oscillation thumping and RF/motor problems. Destroyer OS. Tubes / Valves 18 6th July 2010 12:14 AM
Fender Adjustments JDeV Tubes / Valves 6 7th April 2006 08:17 PM
Another Fender on the bench. Netlist Tubes / Valves 3 6th March 2004 08:03 AM


New To Site? Need Help?

All times are GMT. The time now is 03:33 AM.


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