Gainclone project for apprenticeship..

OFI

Member
2005-06-27 2:15 pm
UK
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..

http://www.plastichead.net/audioworks/redir.php?m=amps/ampmenu.htm&p=amps/clone4/clone4.htm

Thanks for any help
 
BCE not FRN? :D

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 :rolleyes:

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

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.
 
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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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.
 
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.

Doovieman
 
Sure you can

I know you could build a GC on veroboard within that budget-- I've done it myself. Can't find it? click here and look at the "1st" or "old" version.

OK, I'm probably over that budget but my transformer was really expensive.
I built one with:
2 LM3886
2 voltage regulators
2 INA134 differenential receivers.

Hmm....I have a pcb for the INA's, but this can be easily done on veroboard; I just made the pcb for the fun of designing it.

If you don't want balanced inputs put in a buffer instead of the INA134s. A JFET buffer is around here somewhere.
 

OFI

Member
2005-06-27 2:15 pm
UK
Cheers for the help :) how did you know BCE... stalker... :D
I'll have a look at the links posted it would be nice to include the preamp and toner control really but obviously if the budget is stretching then i'll just make it simple. Might take you up on that offer for the chips and caps have to have some words because they're suggesting we only order from rswww.com because QinetiQ has an account with them but I know others are sourcing components from elsewhere. I'm pretty sure the diodes in the power supply would be enough to cover almost all of the semiconductor requirement as that has been a big part of our recent classes. I think I need to read up on these buffers and some decent transformers (as I can see the transformer will be the most expensive part!)
To e honest I think i'd get away with veroboard for the power supply and then hard wiring some of the rest but obviously I have to make this as neat and as safe as possible.
Just wish they'd let us use the pcb facilities :D
 
Check out using the Dallas DS1802 digital volume control (previously mentioned) along with the Quantum QTouch chips (http://www.qprox.com/products/qtouch.php). I am implimenting this setup for my pre (one chip each for volume up/down, one for mute, and one in toggle mode driving a relay for power).

They are $1 US each from DigiKey. I got a few and played with them over the weekend. Having one drive an LED right now: 1 chip, 1 10nF cap, one LED. Works great in both toggle and pulse modes.

You can mount the sensor pads (anything really) behind wood, glass, etc.
 

OFI

Member
2005-06-27 2:15 pm
UK
bleh :p

On a side note where can I order materials for the case? My mind has just gone blank on suppliers in the UK just looking for alu sheet really and obviously not large amounts and possibly some drilled if im going to make a similar design to above, might just be easier to find somewhere local...
 
For an amp I'm working on, there are a few little additions to the gainclone that will up the chip count.

I'm using a few Maxim iButton touch buttons PN#DS9092L for a few different purposes on my amp face. They are basically a center conductor with a LED in the middle surrounded by some blue nylon insulation and an outer conductor. I'm using these with the notion that if you put your finger across the conductor a small voltage can pass through the skin of the finger to act like a switch.

3 buttons that you touch to change inputs. This will require both a few transistors to run a touch switch and a digital 3 way (or more) audio switch.

1 button for on/off of the amp. I haven't decided if this should fully shut off the amp, or just put it on mute and have a physical switch in the back. Again, this will take a few more transistors and some more logic chips and maybe something like an SCR to control high current.

I personally don't like push button up and down volume. If you decide to do a digital audio pot then I recommend letting it have memory to save your volume when you turn off your amp.

If you want digital volume you should build it off an optical encoder so you can have a knob.
 

OFI

Member
2005-06-27 2:15 pm
UK
Ok 1am.. just had an idea for the case... mount it in an old console case :D there are no shortage of broken PS2's on ebay for instance:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=11328&item=8202451862&rd=1

They are pretty cheap really just rip everything out then and get mounting :)

Thoughts? problems?

For it to work well I think you would need to mount everything discretely at th eack and maybe only a small black knob at the front I dunno...