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Old 17th August 2003, 10:34 AM   #1
antomas is offline antomas  Europe
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Default Yet another GC pcb...

This is my first post on this forum, so I firstly would like to say thanks to out landlords and to the people willing to share their wisdom here.

I designed a pcb for the original Thorsten Loesch's Gainclone circuit with ExpressPCB and I'd like to share it with everybody interested. I'm not an electronics engineer so I don't know how bad my design is . Any advice or suggestion is very very welcome.

The inspiration for my pcb comes from another post on diyaudio showing a mono power amplifier without volume control, built around a cheap Hammond (?) aluminium enclosure. The pcb doesn't need to be bolted to the enclosure, since the LM 3875, the input and the output connectors should keep it in place.

A few details:
- the .1" traces should be thick enough to allow 4 Amps;
- the placement of the input and output pads is provisional and it should be updated, depending on the choice of connectors available;
- I privileged the placement of the feedback resistor (R3) and of the 1uF decoupling cap (C5) over the placement of the reservoir capacitors (C3/C4), that are a bit far from the chip;
- I assume the resistors are BC 0.6W (like the ones sold by Digikey) except for R5, that should be a 3W (bigger) resistor; Eventually, on the pcb there's place to lay 4-5 BC resistors
in parallel;
- R3 is soldered between the "legs" of the LM3875;
- the 1uF capacitor (C5) could not fit the little space available on the pcb; in this case a smaller (.1uF ?) cap should be used;
- the reservoir caps are Panasonic FA/FC 2200uF, 50V;
- the "-G+" yellow box is a Weidmuller 3 poles connector (code 176050);
- R1 is a Bourns cermet trimmer;
- There is a naive attempt to star ground the circuit .

The Panasonic caps, the Weidmuller comnnector and the Bourns trimmer are sold by Digikey in Usa and by RS-components in Europe.

Thanks very much for your comments. I'll post the ExpressPCB and postscript files as soon as I'll have a decent version of this pcb. If anyone is interested in the current version of these files, please let me know.

Ciao,
Massimo
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Old 17th August 2003, 12:53 PM   #2
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The layout looks pretty good...would beat the original GainCard PCB anytime...assuming the pictures where real...how can they sell such a thing at such a crazy price...marketing??
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Old 17th August 2003, 01:20 PM   #3
Nuuk is offline Nuuk  United Kingdom
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Quote:
The layout looks pretty good...would beat the original GainCard PCB anytime
Amazing! That's some simulation software you must have there.
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Old 18th August 2003, 12:26 PM   #4
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I´m still hoping that someone will make a PCB layout for Joe Rasmussen´s Gainclone with the tube buffer.

Maybe one should start with the "standard" version first...

/Erik
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Old 18th August 2003, 12:31 PM   #5
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Default Re: Yet another GC pcb...

Quote:
Originally posted by antomas
I'm not an electronics engineer so I don't know how bad my design is . Any advice or suggestion is very very welcome.
I say the pcb layout is pretty good at first sight.
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Old 18th August 2003, 12:37 PM   #6
antomas is offline antomas  Europe
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Li,
Thanks for your kind words. Unfortunately, since the pcb is fully untested, in spite of the (at least apparently) clean design I cannot say anything about it sound...

Nuuk,
may I ask what do you think about the pcb?

Thanks very much for your help,
Massimo
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Old 18th August 2003, 12:56 PM   #7
antomas is offline antomas  Europe
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PerAnders,
Thanks very much for your positive comments. I'm very happy to hear than I can start my project with some confidence...
Thanks a lot!

Erik (and the others who requested the pcb files),
I'm sorry I cannot help very much with the Tube-GC pcb. Nevertheless, you may find the pcb source files as an attachment; you (or someone else) could maybe spend some time on them to add the tube buffer...

You may freely download the program for modifying the pcb here:
www.expresspcb.com
The program is a pleasure to use and very easy to learn.

For the press-and-peelers, you may find enclosed a Postscript and Pdf version of the pcb as well.

Any comment and feedback is very welcome.

Ciao and happy gaincloning,
Massimo
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Old 18th August 2003, 01:04 PM   #8
Electrons are yellow and more is better!
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I was too slow.....

Maybe I would have a 4-pole connector instead and let the speaker ground be even shorter.

100 mil traces can cope with more than 4 ampere!

BTW: I think the moderators should increase the edit time (just test it to have 24 hours or more). See what happens.
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Old 18th August 2003, 02:55 PM   #9
antomas is offline antomas  Europe
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Since I'm a new user, my messages get quarantined and appear only after a few hours. Please note I'm not complaining about the diyaudio policy... Moreover, my attachment got lost in the hyperspace. It was certainly my fault. Hope you may find this one.

PerAnders
Quote:
Maybe I would have a 4-pole connector instead and let the speaker ground be even shorter.
Stupid question: would you like to use the fourth pole to improve the contact of the two ground lines from the rectifiers or to connect the speaker ground?

Speaker: my initial idea for the pcb was to solder or to bolt some kind of speaker connector (e.g. Neutrik Speakon) more or less directly to the pcb. Using binding posts and accepting some asymmetry on the rear panel, the speaker gound could be made very short.

Ciao and thanks once again,
Massimo
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Old 18th August 2003, 05:56 PM   #10
Nuuk is offline Nuuk  United Kingdom
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Quote:
Nuuk,
may I ask what do you think about the pcb?
Hi Massimo,

I haven't had a chance to go over it and check every detail as I have a visitor at present. However, it is very neat and compact, you have kept connections as short as possible and I can't see any reason why it should not work well.

And it's a good idea to leave space for any of the 'extra' components that may be needed later.
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