need help with leach amplifier - Page 3 - 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 4th September 2010, 11:06 AM   #21
sng001 is offline sng001  Australia
diyAudio Member
 
Join Date: Sep 2009
Location: Sydney
Quote:
Originally Posted by elektrogeek View Post
Its at 25v because I was afraid that something might go wrong, since the output would go out, but i shall raise the supply voltage. Also, on r21 and r22 when you power it up the dc voltage on r21 is slowly decreasing and the dc voltage on r22 is slowly rising. Then when the "phenomenon" occurs, there is quick drop of voltage on r21 and a quick increase on r22. I noticed that if the two voltages were added together it would equal the supply voltage.

Thanks

Andy
Hi Andy,

I used Dr Leach's method to test the Amp at full supply voltage (52V). It did not blow up anything expensive as the output transistors were not connected.

I have attached an FAQ here from Dr Leach's site:
The Leach Amp FAQ

"I do not need the 120 W power and I am going to remove transistors Q20 and Q21. Should I change any other elements, e.g. R36, R37/R38, or R41/R42? What about connecting C19 and C20 to R37 and R38?
Removing 1/2 the output transistors will not reduce the output power. It reduces the maximum output current by a factor of 1/2. For an 8 ohm load, the power output would not change. For lower load impedances, the protection circuits would kick in at a lower output current than with all 4 output transistors. If you want to operate the amplifier with 1/2 the output transistors, Q18 and Q19 are the ones to omit. You can also omit R37, R38, R41, R42, R45, and R46. These changes will reduce the maximum output current by a factor of 1/2. If you wish to decrease the output power, you must reduce the rail voltages. I do not recommend reducing them to less than +50 V and -50 V."

Good luck with your amp.
  Reply With Quote
Old 4th September 2010, 11:46 AM   #22
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
this reminds me of when I suggested that we should stop specifying amplifiers by Power.
Instead I said we should specify by output voltage and output current with a recommended load impedance.

eg, is a 22Vac 5Aac amplifier significantly different from a 24Vac 4.5Aac amplifier?
In Power rating it looks like there is an extra 11.5W available from the 24Vac amp.
I can and I'm pretty sure everyone else can see that there is actually very little difference between the amps. This avoids all the confusion and bragging rights of using exaggerated, or even truthful Power ratings.

Now if one were to compare amp outputs of:
22Vac 10Aac
to
24Vac 4.5Aac

I think we can all see there is a significant difference.

The 22Vac is designed to drive lower impedance loads than the 24Vac amplifier.
__________________
regards Andrew T.

Last edited by AndrewT; 4th September 2010 at 11:49 AM.
  Reply With Quote
Old 7th September 2010, 05:44 PM   #23
nattawa is offline nattawa  Canada
diyAudio Member
 
Join Date: Apr 2010
Location: Mississauga, Ontario
Quote:
Originally Posted by elektrogeek View Post
......when you power it up the dc voltage on r21 is slowly decreasing and the dc voltage on r22 is slowly rising. Then when the "phenomenon" occurs, there is quick drop of voltage on r21 and a quick increase on r22. I noticed that if the two voltages were added together it would equal the supply voltage.
Andy, the input stage of a Leach amp should work just fine in terms of DC setup at your supply voltage. The strong degeneration of the diff-pairs insures a stable and symetric DC status of the input stage even before the zener diodes begin to kick in. At +/-25V supply you should get about 0.79mA per transister (Q1 - Q4) by my quick calculation.

Therefore, with +/-25V supply, at no signal input, you should be expecting the following stable DC voltages (in the neighbourhood of):

voltage across C2/C3 = 19.8V
voltage across R11/R12 = 0.94V
voltage across R21/R22 = 0.026V

You should never see voltages greater than 0.6V across R21/R22 as it's supposed to be clamped by the emitter P/N junction of the Q8/Q9.

You probably need to double-check your board thoroughly for any mistakes/bad-parts/wrong-parts.
  Reply With Quote
Old 7th September 2010, 08:37 PM   #24
diyAudio Member
 
Join Date: Aug 2010
Location: Kalamazoo, MI
Hi, I think what my problem is, is my pcb. I made it myself with the provided foil pattern. As I look at it, I can see some spots that didnt show up when I removed the press 'n' peel sheet. Kinda embarassing. But, I want to order a set from Dr. leach. But I have emailed him like 4 times and he hasn't responded.
  Reply With Quote
Old 8th September 2010, 06:14 AM   #25
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by elektrogeek View Post
Hi, I think what my problem is, is my pcb. I made it myself with the provided foil pattern. As I look at it, I can see some spots that didnt show up when I removed the press 'n' peel sheet. Kinda embarassing. But, I want to order a set from Dr. leach. But I have emailed him like 4 times and he hasn't responded.
Is it not fixable ?... at least for you to prove it all works. Any shorts can be cut with a craft knife, any opens can be linked.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  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
High Current Leach/leach super amp bowdown Solid State 41 2nd March 2011 02:15 PM
Modified version of Leach amplifier gretzteam Solid State 44 19th December 2008 06:16 PM
leach amplifier pcbs camt1 Parts 1 16th October 2006 04:04 PM
PCB's for Leach Amplifier 6 Transistor Svetlana Solid State 3 19th September 2006 08:37 PM
Super Leach power amplifier for sale supernet Swap Meet 0 4th February 2006 12:51 PM


New To Site? Need Help?

All times are GMT. The time now is 11:44 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