Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Music fidelity A5 intergrated amp SAP15 transistor modification
Music fidelity A5 intergrated amp SAP15 transistor modification
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 15th June 2019, 07:27 PM   #1
Pure sound is offline Pure sound  United Kingdom
diyAudio Member
 
Join Date: Mar 2012
Location: Bolton
Default Music fidelity A5 intergrated amp SAP15 transistor modification

Hi all, got myself a MF A5 intergrated amplifier thats using the sap15 transistors.
These transisitors have the emitter resistor built in and are prone to failing. Ive read that you can lift a leg on these transistors and put your own cement 0.22ohm resistor in its place.
Question is can anyone advice what leg to lift and where to solder new resistor please, or any pictures of this done or drawings would be fantastic!

Thanks inadvance
Richard
  Reply With Quote
Old 15th June 2019, 07:39 PM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Here is the data sheet on it. If the resistors have failed, the odd are so has the Darlington pair.
datasheet SAP15
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 15th June 2019, 07:40 PM   #3
ubergeeknz is offline ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
Lift the "E" leg, and put your own emitter resistor from "S" to "E".

But why, if it works, leave it IMO \_(ツ)_/Screenshot_20190616_073908.jpg
  Reply With Quote
Old 15th June 2019, 07:43 PM   #4
Pure sound is offline Pure sound  United Kingdom
diyAudio Member
 
Join Date: Mar 2012
Location: Bolton
Quote:
Originally Posted by JonSnell Electronic View Post
Here is the data sheet on it. If the resistors have failed, the odd are so has the Darlington pair.
datasheet SAP15
They have not failed, i just dont want them to.
  Reply With Quote
Old 15th June 2019, 07:45 PM   #5
Pure sound is offline Pure sound  United Kingdom
diyAudio Member
 
Join Date: Mar 2012
Location: Bolton
Quote:
Originally Posted by ubergeeknz View Post
Lift the "E" leg, and put your own emitter resistor from "S" to "E".

But why, if it works, leave it IMO \_(ツ)_/Attachment 763232
I get that, but doing this mod will make the transistor a lot more reliable is my thought
  Reply With Quote
Old 15th June 2019, 07:51 PM   #6
ubergeeknz is offline ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
Quote:
Originally Posted by Pure sound View Post
I get that, but doing this mod will make the transistor a lot more reliable is my thought
Your call. My approach is usually to not fix things unless they are, well, broken.
  Reply With Quote
Old 15th June 2019, 08:00 PM   #7
Pure sound is offline Pure sound  United Kingdom
diyAudio Member
 
Join Date: Mar 2012
Location: Bolton
Quote:
Originally Posted by ubergeeknz View Post
Your call. My approach is usually to not fix things unless they are, well, broken.
What watt resistor would you use? The amplifier has 2 pairs for each channel and is rated at 250w per channel. I see how they are unreliable if you compare the size of the eg 5w cement compared to the transisitor one built in!
  Reply With Quote
Old 16th June 2019, 08:55 AM   #8
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to Leolabs
They will failed if your are running them continuously at high temperature.Did read some on the internet that they will fail but never mentioned what cause the failing, yet I doubted those who claiming failure, were really using them or not.

Am a big fan of those SAPs, make my layout neat and lesser components, but sourcing them might be a pain.They already replaced by a smaller (but standard package) STDs, which the internal resistor already remove and one pin gone.
  Reply With Quote
Old 16th June 2019, 09:36 AM   #9
ubergeeknz is offline ubergeeknz  New Zealand
diyAudio Member
 
Join Date: Aug 2018
Someone needs to check my math but this is what I came up with...

At full power:

* 250w/4ohm output.

* 2 pairs (so, 125W per pair).

* That's about 24v RMS into 4 ohms

* Each transistor does about half the waveform, assuming class AB. That's 12v RMS.

* 12V RMS into 4 ohms is 3A

* 3A / 0.22 ohms is a drop of 0.66v

* Dissipation across 0.22 ohm at 0.66v is 2W

5W seems like a good choice.

Keep in mind cement resistors are designed to dissipate 5W directly into air. The IC is mated to a heatsink so it can easily dissipate more heat than the package size would suggest. For example TO220 devices are able to dissipate over 50W into a suitable heatsink.
  Reply With Quote
Old 16th June 2019, 09:54 AM   #10
jan.didden is offline jan.didden  Europe
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
Originally Posted by JonSnell Electronic View Post
Here is the data sheet on it. If the resistors have failed, the odd are so has the Darlington pair.
datasheet SAP15
The resistor inside this transistor is known to fail early with the darlington being fine. Replacing the build-in R with an external one is a known cure.
The follow-up devices to the SAP series, STD03N and 03P, look exactly the same but miss the internal R, for just this reason.

Jan
Attached Images
File Type: png std.PNG (13.4 KB, 148 views)
__________________
Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.

Last edited by jan.didden; 16th June 2019 at 09:57 AM.
  Reply With Quote

Reply


Music fidelity A5 intergrated amp SAP15 transistor modificationHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Helping a Friend:- Musical Fidelity A3.2 Integrated Dual Mono Schematics and SAP15 Ronj Solid State 33 2nd March 2015 12:46 PM
FS: Musical Fidelity X-A1 Intergrated Amp ChrisR1983 Swap Meet 2 20th June 2010 06:14 PM
Blown power transistor SAP15 on a Cambridge A500 jmillerdoc Solid State 8 3rd April 2009 12:13 AM
Musical Fidelity A1 modification ilimzn Solid State 5 19th January 2007 12:34 AM
Musical Fidelity X-A1 Modification adfairless Solid State 7 31st December 2006 01:12 PM


New To Site? Need Help?

All times are GMT. The time now is 09:33 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki