How to first test a gainclone?

[ransom peek]

On a briangt lm3875 amp (one rectifier board, two amp boards), the rectifier board output voltages tested ok, and now the rest of the circuit is in place but untested.

Is it recommended to attach a cd player input and two speakers and fire it up, or is their a more systematic approach?

Should I alert the local fire department and have them on standby?

[cpemma]

Originally posted by ransom peek
Is it recommended to attach a cd player input and two speakers and fire it up, or is their a more systematic approach?

Check at minimum volume for no appreciable DC at the speaker terminals before plugging them in, and/or use a cheap pair.

[ransom peek]

What would a dc signal at the signal terminals indicate?

[pinkmouse]

Anything over about 50mV suggests a construction fault.

[Leolabs]

Lower is better.

[davidlzimmer]

Make sure your heatsinks are attached, even if just temporary. I test mine one side at a time at first. Put a very low level signal in then turn on power. Like before stated, check for DC on output. Then you can power down and switch to better speakers.

Be prepaired for a thrill! I've made three now and was amazed each time.

Let us know!

[davidlzimmer]

Peek.

You still with us???

[Dick West]

I have found a Variac to be irreplacable. How much current do most chip amps pull? A Variac, used, off an eBay auction, often does not cost a lot and can help keep the magic smoke in the parts.

Is there some reason a Variac will not work with these chip amps?

[ransom peek]

Originally posted by davidlzimmer
Peek.

You still with us???

First time powered up today with junker speakers.

Works like a champ first time. Good job to all that so generously answered my questions and studied my pictures. The help from these forum members has been superb.

No hum. Amazing sound and haven't tried with good speakers yet.

Now have to button everything up, tighen all the hardware.

I am building the cherry enclosure this fine instrument warrants. I am very proud of this amp, but, in truth, the credit goes to you folks - my mentors!

I will post a pic of the finished unit in the polished cherry cabinet.

Now I am looking for bookshelf size speakers for the amp. From posts on this forum I understand that 90+ db efficiency is desirable for gain for the LM3875.

Am considering building a kit (speakers) for the fun of it. Also need to research what kind of cd player to buy to drive the amp.

THIS IS TERRIBLE! THE AMP IS SO NICE NOW I HAVE TO UPGRADE EVERYTHING ELSE. You guys didnt tell me about this. Really let me down.

Also trying to find a schematic for the particular braingt amp I built - rev 3 boards dated 07-05.

This hobby is fun!

[davidlzimmer]

Way to go!!!

Same thing happened to me. Got to build new speakers! This is an addictive hobby!

Word of advice. Build yes, but do not design speakers. Plenty have guys have already done the hard work for you. What ever speakers you decide on, follow the design exactly especially in the crossover.

Waiting for those pics.