Commercial Gainclone kit- building instructions

[tbrooke]

My amp still overheats and isn't right but I think I figured out the problem. I looked back at the instructions and I believe I have input and output wires wrong.

I have a picture and the black and white wires are input output; you can see the connection to the terminals for the output. I think I should move them to the Cz Rz locations

(I hope the picture link works it's my first try)

It l

[Peter Daniel]

Don't move anything to Cz, Rz, those pads are not being used.

It should be obvious that IN means input and OUT stands for output

One other thing; the nuts on mounting screws are two big, while power plains are protected by solder mask, it is not enough isolation and you are risking shorting the rails to the chassis: use either plastic isolation washers or screws with small heads.

[tbrooke]

The RCAs need to be isolated from a chassis. You are using what looks like Cardas RCAs, they should come with plastic isolation washers.

I saw this earlier and noticed that my RCA input jacks clearly aren't isolated from the chassis. Actually I have them screwing fairly tightly into the chassis and there is no isolation washer. Could this be my

Are there isolated and unisolated RCA Jacks?

Tom

[VictoriaGuy]

Originally posted by tbrooke

Are there isolated and unisolated RCA Jacks?

Tom-
The isolated type come with plastic washers and require a larger hole.
Alternatively you can mount the non-isolated style on a plastic/phenolic plate, so they are electrically isolated from the rest of the chassis.

Cheers
John

[cyxg]

Hi,Peter

I finished my 3875 chip amp, sound very good!

[cyxg]

Peter

i measured DC offset at speaker terminals - 8om speaker load

Right - 8 mV
Left - oscillates between 10mV -14 mV

I can hear the transformer humming a little.

[cyxg]

it's really good.

[cyxg]

the amp is 14.5kg.

[tbrooke]

I can't figure out what to do next

So far I have

1. measured voltages at V+ PG+ V- PG- etc its about 35 volts

2. Checked DC Offset on output terminals - it varies between
.005 V .050V I have tried it with a 8 ohm load and I used a preamp to vary the input and I have even played music which does come out but unamplified and distorted.

3. Removed the bolts that held amp boards down and may have caused a short

see picture:
http://picasaweb.google.com/tom.broo...79046144343858

4. Insulated RCA input jacks.

Amp still get very hot, no sound except for static

I ran continuity checks with my multimeter and it seems almost everything may be shorted to ground but then again maybe this is the way it is supposed to be - it is ground - maybe continuity isn't the way to check for shorts

So
1. Anything else to check and how?
Visually soldering looks ok

2. Could I have damaged the LM3875? How do I check?

3. Anyone in NC that can check it?

4. Should I order a new kit and start from scratch?

Tom

[Peter Daniel]

One other thing to check is if you place resistors in right places. I recall someone had sililar problems and it was because of mixed up resistors. You can find some pics here: http://www.diyaudio.com/forums/showt...48#post1508848

R1 which is 220R looks slightly different now, but the other two 22K should be the same.

If the chip shows offset, that may indicate it's not damaged.

If you won't be able to make it work, you can ship it back to me and I will fix it

Originally posted by cyxg
I finished my 3875 chip amp, sound very good!

Congratulations, it looks really good