Leach Amp strange things

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shadow

Member
Joined 2002
Just finnished my Leach Amp,and find out some strange things.
Amp dont work with two speaker ground wires connected to the central ground point.With connection amp produce static and silent distortion on high volume levels.If i just short circuit these two wires amp works fine.
And some other thing:two ground wires from the filter caps connected to the central ground point hums (silent) when connected.
I solved problem same as above.

Anyone have same problems?
 
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paulb

Member
Joined 2001
I think there's something seriously wrong here, if I understand you correctly. You "solved" the problem by wiring the two speaker grounds together, but not anywhere else? This is not what you want.
Check if you have a high DC offset at each output; this may be the problem.
I'm not sure what you mean by "static and silent distortion on high volume levels".
 
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shadow

Member
Joined 2002
I think there's something seriously wrong here, if I understand you correctly. You "solved" the problem by wiring the two speaker grounds together, but not anywhere else? This is not what you want.
Check if you have a high DC offset at each output; this may be the problem.
I'm not sure what you mean by "static and silent distortion on high volume levels".
Click to expand...

Yes speaker ground wires are conected together and nothing else.It seems power is lower than aspected too.
When i connect ground wires to central ground point on low volume levels cant hear nothing on high sound is distort and very quiet.
How can i measure DC offset?
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
Your central ground should have these things connected to it:

4 - 2 grounds from each circuit board
1 - Input ground from AC Line
1 - Centertap transformer ground
2 - Grounds from your filter caps
2 - Grounds from output terminals
---
10 - Total grounds

I would reference the central ground point and probe all of the lines from the board going to the output devices, and the wires going to the thermal diodes (8 total). Also make sure that you have continuity from the central ground to the board grounds. Make sure that your heatsinks are grounded to the chassis.

Also, have you tried running each channel seperately (remove fuses for one channel and test the other one). Basically to determine whether it is an isolated problem with one channel.

That would be my process of attempting to fix this problem.

--
Brian
gte619j@prism.gatech.edu
 
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shadow

Member
Joined 2002
Thanks

I have all that wires connected,accept transformer ground.Transformer have only 2 wires in output.These wires i cant connect:Grounds from output terminals,and i have heat sinks with chassis connected to central ground pint is this wrong?
OK i will do some testing
 
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paulb

Member
Joined 2001
Re: Thanks

shadow said:
Transformer have only 2 wires in output.
Click to expand...
This would be a problem. The attached is the schematic from the Leach site. The ground at the centre tap of the transformer is very important.
 

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shadow

Member
Joined 2002
I just buy this one! hm :(
I done some experimen and:
If i connect while power is on caps ground wires(both channels connected) and speaker ground (both channels connected) left channel shuts down and only right is working.Both play when i restore and disconnect.
And if i disconnect right input amps cuts competely off.If disconnect left input there is no difference! Dhis suggests for wrong channel wiring but i done right(i think).
 
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shadow

Member
Joined 2002
All O.K.

Thanks for all your help and support.
I find out problem:I tested amp with Discman,two output chinch and ona 3.5mm bannana.Now i connected amp to real CD player and all works fine.
Problem was in the interconnect,some strange ground-signal wires,it was changed so only one signal was connected.Not my fault.
Thanks again.
P.S. pictures of finnished amp soon :D
 
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PassFan

Member
Joined 2001
I've noticed some old tube amp designs share a common signal ground between the left and right channel also. I tried to use a tube preamp like that with my A75 and man, it did not like that at all. It made it perfectly clear as well. I suspect it must be an impedance problem for the amp. Glad you got it figured out.
 
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shadow

Member
Joined 2002
Maybe later i will change transformer.
Hm my problem kinda still exist but all now works fine.Now speaker ground works connected,but input signal ground and output ground i cant connect.Amp works for 5s and shuts down.Maybe some problems with caps ground(smal spark when ground are connected)
Anyway this configuration works fine and that is final :)
 
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