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.

Im testing my leach amp and its acting funny
Im testing my leach amp and its acting funny
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 19th February 2006, 09:07 AM   #1
frckid is offline frckid  United States
diyAudio Member
Join Date: Dec 2005
Location: Terre Haute, IN
Default Im testing my leach amp and its acting funny

Hi everyone,

I have constructed two channels, both with the same problemss.

Testing conditions: short C12, connect signal and non-signal grounds, and wire the two resistors between either side of R36 and the output

Rails: +/- 8V

Input voltage: 1Vpp sine wave at 1kHz

I end up getting a huge current draw (nearly 1A) from the negative voltage supply and about 40mA from the positive supply with rails of +/- 8V.

If I remove the short across C12, i get balanced current draw from each supply (about 48mA at +/- 8V rails), I get a sine wave centered at 3.5V on the output that is not amplified at all, actually slightly attenuated.

If I ground the feedback path and remove the short across c12, I can get a small sine wave on the output with a +3.0V offset.

What could be going on? Has anyone else had any trouble getting their leach amp to work?

  Reply With Quote
Old 19th February 2006, 10:42 AM   #2
MikeB is offline MikeB  Germany
diyAudio Member
MikeB's Avatar
Join Date: Apr 2004
Location: GŁtersloh
If i remember the leach schematic correct, it uses zeners to set the reference for the cascodes in input-ltp having a voltage bigger than 8v.
This means, the Leach can't work yet at +/- 8v. About shorting caps, this could result in big dc-offset, showing such behaviour. Maybe your Leach is fully functional, just the test setup not ?

  Reply With Quote
Old 19th February 2006, 10:56 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Power up your bare PSU and check supply voltages. Switch off.
Connect to the amplifier.
Fit 100r resistors to the two main fuses.
Set bias pot to maximum resistance (minimum bias current).
Fit a mains light bulb in line with the primary windings of the mains transformer.

Stand back and switch on.

Now go measure.
regards Andrew T.
  Reply With Quote
Old 19th February 2006, 11:04 AM   #4
Eva is offline Eva  Spain
diyAudio Member
Eva's Avatar
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
Follow AndrewT advice (I don't want to sound redundant ).
  Reply With Quote


Im testing my leach amp and its acting funnyHide 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
testing super leach without a scope bigpanda Solid State 86 10th April 2008 12:53 PM
My amp is acting like a transducer!? audio_moksha Tubes / Valves 9 15th March 2008 07:04 PM
Testing Leach Low TIM ptah Solid State 27 21st December 2006 05:39 PM
Relay acting funny Vivek Everything Else 14 10th August 2004 08:55 PM
Testing Leach Amp, questions about output wigginjs Solid State 2 11th July 2004 12:07 AM

New To Site? Need Help?

All times are GMT. The time now is 12:17 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio