My first GC is in testing

[DC Dave]

It has taken awhile but I finally got my NIGC up and running. I don't like the name gainclone so I call it the DC1. It is based on the LM3875. I went with dual monoblocks each with its own external power supply. There are no fancy components inside, metal film resistors, Panasonic FC caps and a BG input cap. I'll post the schematic I used shortly (if I can locate it).

The cases started as surplus budd-like 4x4x2 inch aluminum boxes with removeable top and bottoms. From there I added a surplus 4x4x3/4 inch aluminum heatsink to the top of the boxes and a piece of 3/16" aluminum for the bottoms. The sides are maple and the front is 1/4" aluminum. The overall size of each monoblock is 5.5" wide by 4.25" deep and 2.5" tall. The heatsink extends an extra 1/2" up. I figure it cost about $30 for both cases with connectors.


The power supply's are temporary until more funds can be found. They utilize the Parts Express $5 clearance tranny mounted inside a pair of scavenged Dell PS cases. I want to build a pair of power supplies that will complement the amp enclosures eventually with the same aluminum/maple look and a pair of toroidals.

As for the sound, I must say that I am impressed so far. I can only test with a portable CD player now until I get my preamp up and running. So I am using the headphone jack There is no noise or hum. They put out good bass. And the overall sound is clean. I'll have a much better idea of their sound once the breakin for awhile and I connect a real source and preamp to them.

I'll post some pictures if they are not too big.

[DC Dave]

Here are the monoblocks sitting flat. They were designed to sit either flat or on their sides for more airflow through the heatsinks.

[DC Dave]

Here is a shot of them standing upright. They were assembled as mirror images of each other.

[DC Dave]

Here is a picture of the PCbs I made. I have never made anything like this before and never worked with PCBs in general. It is single sided with 2 oz copper that I eched with a dremel

[DC Dave]

Here is a picture of the cases from the back. The connectors are from Parts Express. I laid them out so as they would mirror eachother. I kept the power wire as far away from the signal wire as possible to help prevent interference.

I have been listening for about 2 hours now and the heatsinks are not warming up at all. I wonder if I could but both channels in one case and share the heatsink? I have extra parts so maybe I will try that for my next amp.

[ble0t]

Great job...my next project is definitely going to be some monoblocks based on the LM3875. Which toroids are you refering to btw? Those in the 'Web Specials' section?

[DC Dave]

Here is a picture of one of the power supplys. I trimmed the original top of the budd boxes to mount to the Dell power supply case.

I noticed that when the power supplies are plugged in they hum and vibrate a little bit. The sound is amplified when they sit on my desk. I think rubber feet will help quite them down a bit, but is this normal? The trannys are those $5 ones from Parts Express awhile back about 100 to 150 VA. With no load they are pushing about +/- 29 volts

[DC Dave]

Originally posted by ble0t
Great job...my next project is definitely going to be some monoblocks based on the LM3875. Which toroids are you refering to btw? Those in the 'Web Specials' section?

I checked and the tranny is no longer available. It was located here:
http://www.partsexpress.com/pe/pshow...number=129-030

They had them on deal-of-the-day awhile back for 5 bucks and I quess they got wipped out.

Thanks for the compliment.

Dave

[ble0t]

Darn, that would have been a nice deal to get in on

I agree that it'll be nice to sync everything up, but even the Dell cases don't look too shabby at all.

[DC Dave]

I found a copy of the schematic that I used.

Is there a rule that states what the output impedence of the preamp should be relative to the input impedence of the amplifier?

Also since the amps have the 4.7uf input cap to block DC voltage, do I need to keep the cap at the output of the preamp which was in it's design for the same purpose? I'm guessing that the BG caps I used in these amps are of better quality than the ones in my preamp. I might try to remove it and see if I measure any DC voltage and go from there.