Hafler 9270 Toroidal Xfo Mod - A Different Hafler Mod - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 11th April 2011, 12:23 AM   #1
diyAudio Member
Taterworks's Avatar
Join Date: May 2007
Default Hafler 9270 Toroidal Xfo Mod - A Different Hafler Mod

Hello amp-tweakers,

Here's a different sort of Hafler modding thread. I've found a few threads that deal with the older pre-Fosgate Haflers (DH series), but none that deal with the Series 9000 amps. I have a mid-90's Hafler Series 9270 power amp, which is 135W/ch into 4 ohms., and sounds quite good. I have no idea about the amp's topology, except that the front panel of the amp states "High Gm JFET Topology Lateral MOSFET Power Amplifier". I scored the amp used, and it sounds good and seems to be in good working order except that one side of the amp idles slightly (barely noticeably) warmer than the other (and both sides run hot). This amp uses two special-design transformers, but they aren't toroids. See below for a photo of the internals of this amp (I can disassemble mine and provide better photos if needed):

Click the image to open in full size.

I've been considering upgrading to a toroidal power transformer. This amp is listed at up to 1200W of AC power draw from the wall socket, which confirms the rumors of bridgeability at 2 ohms, but also means that I'll need a big toroid to avoid degrading performance. I bought the 9270 used, and I don't think I'll be able to make a significant amp upgrade in the near future, so I'm looking for ways to improve the performance of this classic amp, and I thought an upgrade to the power transformer seemed as simple a mod as any (since 60 hz is 60 hz, so there'd be the least likelihood of screwing anything up). This amp does produce a very faintly audible hum at about 12 inches from the housing when powered on and not passing a signal, but I haven't heard the hum through the speakers.

Would you agree that upgrading from the dual power transformers to a single toroid with dual secondaries would probably improve the performance of this amp? Would it be a fool's errand?

Manual (with circuit diagram) http://www.hafler.com/techsupport/pd...70_amp_man.pdf

If it works, but you don't know why it works, then you haven't done any engineering.
Taterworks Audio (nothing for sale)

Last edited by Taterworks; 11th April 2011 at 12:25 AM.
  Reply With Quote
Old 26th May 2011, 04:33 AM   #2
diyAudio Member
Join Date: May 2011
Default how did it turn out?

Hello! I need to replace the T301 transformer and was wondering if you completed your mod. My amp is non functional right now, and I am trying to troubleshoot it with a multimeter with little skill under my belt. If the mod did work, which transformer did you use and where did you get it? Did you mod anything else? Thanks for the help.
  Reply With Quote
Old 14th December 2012, 05:42 PM   #3
diyAudio Member
Join Date: Dec 2011
Bump for an OLD thread. Did you ever end up upgrading your Hafler to a Toroid transformer? I have a Hafler 9303 TransNova amp that also has an audible hum from the transformer. I tested several other 9303s and they all had this transformer hum. The hum is not audible through the audio stream but it's pretty noticeable to me from the case, unless I damp it by stacking things on top of it. I was surprised to see an amp in this price class had an EI transformer in it (the 9303 was around $1300 new I think?)


  Reply With Quote


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
Waht is difference between hafler 9270 and 9290? kang Solid State 2 16th September 2010 08:16 PM
Hafler DH 200 musical concepts mod db5owat Solid State 2 27th April 2009 11:27 PM
FS: Hafler 1000VA Toroidal Power Transformers seanc Swap Meet 5 20th March 2009 10:13 PM
Hafler 9130 feedback loop MOD question reiver Solid State 3 5th June 2008 02:34 AM
Looking for someone in Toronto interested to mod my Hafler 9290 rmihai Swap Meet 0 29th May 2005 11:17 AM

New To Site? Need Help?

All times are GMT. The time now is 06:52 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.
Copyright 1999-2016 diyAudio

Content Relevant URLs by vBSEO 3.3.2