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Old 15th June 2007, 05:13 PM   #1
wboyd is offline wboyd  United States
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Default Gainclone PCB suggestions

Hey everyone,

I have decided to build my fourth gainclone and would really like to fashion my own pcb. Nothing fancy, single sided etc. I would like to etch and drill it myself.

I have been looking around for some simple designs...LM3875 or 3886. Anyone have any suggestions or links. I am not looking to design the PCB myself (not yet atleast). I am just looking for some easy to work with designs.

Thanks for the help,

Wayne
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Old 15th June 2007, 05:34 PM   #2
BWRX is offline BWRX  United States
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There are a few floating around. Try searching for them. At the end of this thread sek posted a design for a single sided PCB that looked pretty good. Not sure if he or anyone else has made one yet.

However, I would suggest you have a go at designing it yourself. It's more fun that way
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Old 15th June 2007, 06:57 PM   #3
wboyd is offline wboyd  United States
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I am considering it....but seeing as I have never designed one before, I would like to have a few to help me prototype and build before jumping into my own.

I have searched the forums and Googled the subject a bit....but keep coming up with the same results...I am sure that their are more out there than what I am finding.

Thanks for the reposnse,

Wayne
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Old 15th June 2007, 10:09 PM   #4
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I am at a similar stage.

My GF is getting the hifi bug and I was thinking about making a compact Gainclone for her.

Was thinking about combining a few ideas.... Jfet Buffer, lm3875(or 3876) digital volume control and a flat profile. My plan is to make an amp that will fit in a standard 100mm wide circuit board. Simple reason, I like the Hammond 1455 range of alu cases, and I reckon I can fit 4(at least) lm3875's in there to make a very compact biamp setup. The case measures 100mm*160mm*55mm and has slots to hold boards

I was thinking about making a series of modules that fit the hammond case so that I can experiment with various designs, ie making the buffer, volume control etc on seperate modules that are designed to be stacked.

What plans do you have?

So far I have built the decibel dungeon inverting design (point to point), But the pedjas jfet is very well reckoned. I am interested in what all the fuss is about, so this may be my next project.
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Old 16th June 2007, 10:46 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by justblair
My plan is to make an amp that will fit in a standard 100mm wide circuit board. Simple reason, I like the Hammond 1455 range of alu cases, and I reckon I can fit 4(at least) lm3875's in there to make a very compact biamp setup. The case measures 100mm*160mm*55mm and has slots to hold boards
......................So far I have built the decibel dungeon inverting design (point to point)..........
what heat did the DD version give out?
What size sink kept it cool?
How do you plan to make four chipamps and four sinks fit inside that case?
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Old 17th June 2007, 09:24 AM   #6
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[QUOTE]Originally posted by AndrewT

what heat did the DD version give out?
What size sink kept it cool?
How do you plan to make four chipamps and four sinks fit inside that case?
[/QUOTE

Hi

The DD version doesn't seem too hot to me. I am using it with 12v supplied by four skynet smps 8080's. Heatsink wise they are bolted onto the top plate of the amp (420mm*55mm*3mm), in alu pods. This gets barely luke warm, even with the heat of the smps coming through it

Click the image to open in full size.

I took this piccy when I was laying out the four amp pods, it gives you an idea, in each pod, a lms387 is face down. Each of those alu boxes ends up about half full, though I removed the input caps which did take up a fair bit of space (mfp x2 4.7uf)

I had two ideas for the chips. One couple them thermally to the case via an alu or copper bar, I prefer this as it would leave the hammond case untouched. In this I would produce two stereo boards, with the chips mounted horizontally on the board rather than vertically.

Click the image to open in full size.
This diagram hopefully makes it clear

The second I came up with is to attach heatsinks to the top or back of the hammond case

There are loads more ways that it can be done of course.

I dont see a problem fitting four in there, well it will require a fair bit. The power supply would be in a seperate case.

WBoyd... Hope this isn't too far OT for you?
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Old 17th June 2007, 09:55 AM   #7
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hi wboyd,

Here's a simple single-sided PCB for a LM3875 NIGC based on Peter Daniel's (BrianGT) schematic from a few years ago. The component values may have changed over the years.

You need to remove one pin on the LM3875 and the output may need a bigger hole. The physical size of the zobel components may be questionable, if you decide to use them.

WARNING: This is an untested PCB.

regards
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File Type: gif lm3875 pcb.gif (16.3 KB, 801 views)
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Old 17th June 2007, 10:56 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi Greg,
are the two extra holes up beside the C1 & C2 labels for film caps on the back of the PCB?
The r1 to r4 and input pins looks particularly neat and compact.
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Old 17th June 2007, 11:04 AM   #9
Nordic is offline Nordic  South Africa
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JB, very elegant implementation.
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Old 17th June 2007, 02:30 PM   #10
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Quote:
Originally posted by Nordic
JB, very elegant implementation.

Thanks Nordic.

Do you mean the horizantally moutnted chip/heatsink combo?
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