Leach Amp strange things

[shadow]

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?

 

[paulb]

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".

 

[BrianGT]

Do you measure any voltage on your chassis? It sounds like you have a grounding loop in there somewhere. I had a friend with a similar problem, and one of his output devices was grounded on the chassis. Check the thermal diodes also.

--
Brian
gte619j@prism.gatech.edu

 

[shadow]

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".

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?

 

[shadow]

Brian all devices are isolated from chassis.Chassis is connected to central ground point with heat sinks.
When i connect these ground wires with powered amp,sound become distort and cuts off with complete silence.

 

[BrianGT]

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

 

[shadow]

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

 

[BrianGT]

I believe that you want the heatsinks grounded to the chassis, and make sure that they are isolated from all of the devices.

--
Brian
gte619j@prism.gatech.edu

 

[paulb]

Re: Thanks

Transformer have only 2 wires in output.

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.

 

[shadow]

i know

I know that transformer ground is important,but my dont have one.Why i dont know.
If i powerup only one channel that channel dont even work.Hm strange things.

 

[swede]

How about getting another transformer?

//magnus

 

[shadow]

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).

 

[shadow]

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 😀

 

[BrianGT]

Great! I am glad that you got it working.

--
Brian
gte619j@prism.gatech.edu

 

[PassFan]

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.

 

[Elso Kwak]

Centertapped Transformer

Hi Shadow,
I am still convinced you need a centertapped transformer for the powersupply!🙂

 

[AudioFreak]

Without a proper power supply ground, you will not be getting a proper stereo output from your speakers as the ground point will appear to shift with the signal and each speaker will share about 1/2 the averaged output. You CANNOT operate the amp correctly without a proper ground @ the power supply.

 

[shadow]

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 🙂

 

[shadow]

Problems

Problem gor even stranger.Now Amp works fine for about 30 min then shuts down! I dont know if this cause transformer.Output and input grounds from circuit boards i still cant connect.Damn

 

[supernet]

Lep pozdrav shadow. Tudi jaz imam že leto dni Leach amp in sem z njim zelo zadovoljen, prav zdaj gradim Super Leach kateri bo postal moja referenca. Povej mi kje si dobil mica kondenzatorje in katere kondenzatorje imaš v napajanju?

Lep pozdrav!

Supernet