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Old 29th June 2005, 02:47 PM   #1
OFI is offline OFI  United Kingdom
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Default Gainclone project for apprenticeship..

I have had a look around and can't find many gainclone amps constructed using veroboard. After reading alot about these gainclones I decided this could be the amp I want to build. I'm currently doing an apprenticeship with QinetiQ MoD in avionic electronics and we have just been given the task of creating a 'self design' project of some sort. However there are some rules...

* The project must use 240v mains somewhere
* The budget is £100
* Must have at least 5 semiconductor devices
* Must utilise veroboard. NO PCB
* Project must be housed in a safe box capable of being PAT tested.

and the latest rule is..

* All 240v areas must be housed in a seperate box to the rest of the design, but that seems fine...

I was just wondering how many people have made a GC on veroboard, if it is possible on this budget (I have looked at the components and it seems so) and also what kind of spec should I be making? mono, dual-mono, stereo, pre-amp or not, toner control or not? Which IC should I use? LM3886, LM4870 etc
You get the idea

For case design I was thinking of something along the lines of what this guy has done..

Thanks for any help
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Old 29th June 2005, 03:22 PM   #2
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BCE not FRN?

You have never seen a GC constructed on stripboard because stripboard spacing is 0.1 inch and LM3886 and their ilk are some stupid other spacing. I think the TDA chips might use 0.1 inch pitch so you could use one of those perhaps, but that might not qualify for the official GC dudes

If your project requires 5 semiconductors you might be struggling with a chip amp unless you can count the power supply diodes

Although I do have a bunch of LM3886T and nice power supply capacitors going cheap if you're interested. And I can give you a receipt

I would build a stereo amp sharing one power supply.
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Old 29th June 2005, 03:41 PM   #3
Nuuk is offline Nuuk  United Kingdom
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Perhaps adding a (discrete) buffer would up the semi-conductor count!
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Old 29th June 2005, 03:44 PM   #4
Moose is offline Moose  Canada
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I have built two seperate ones on veroboard no problem. If you trim off the NC pins on the 3875/3886, you can "adjust the other pins to fit the spacing of the veroboard. Its not that hard at all, just make sure you don't cross any of the pins.
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Old 29th June 2005, 03:51 PM   #5
waltona is offline waltona  United Kingdom
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Have a look at this thread.
Chinese GC

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Old 29th June 2005, 04:06 PM   #6
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Perhaps adding a (discrete) buffer would up the semi-conductor count!

And/Or adding a simple regulator on the rails (atleast 2 more semi's!)
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Old 29th June 2005, 05:01 PM   #7
macboy is offline macboy  Canada
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You have never seen a GC constructed on stripboard because stripboard spacing is 0.1 inch and LM3886 and their ilk are some stupid other spacing
If you use the veroboard at a 45 degree angle, then the holes line up pretty closely to the 3886/3875 spacing. You'd use the holes marked green as below, and chop off the corner of the board...
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Old 29th June 2005, 05:52 PM   #8
mateo88 is offline mateo88  United States
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A very simple and inexpensive project that will fit your requirements and is easy to fit on veroboard (I did anyway) is to use two lm338 regulators, a preamp using something inexpensive like a TL072, and two lm1875's. The trasformer for this setup could be sourced rather inexpensively, since it wouldn't have to be powerful at all.

Also, If you use an lm3875 rather than an lm1875 (much easier than a lm3886 for use on veroboard, in my opinion), make sure you cut off all the NC pins.
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Old 29th June 2005, 09:44 PM   #9
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You could use digital pots (Dallas Semi) for volume and/or the LM3915 (National Semi) driver chip for an output reading. Those chips would theoretically add 4 more ICs to your design...
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Old 29th June 2005, 10:26 PM   #10
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As far as the pin spacing goes, just bend the pins a little (be careful that you don't rip them out of the chip). If the actual diameter of the pin is too large (I had this problem when building a prototype once) either sand them down for two seconds or drill a slightly large hole in the veroboard (or whatever you're using).

If I were you I'd do an input buffer on each chanel and get a push button digital pot for volume control (maxim makes a few though I can't remember the part numbers off the top of my head)

If you want the project to be more involved than 2 hours worth of work, you could build a really simple pre-amp to do bass/treble control.

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