My MOSFET amplifier designed for music. - Page 34 - diyAudio
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Old 4th October 2012, 01:14 PM   #331
Mooly is offline Mooly  United Kingdom
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It was a 10K Alps that I got from Farnell a long time ago. They seem really hard to obtain now from normal sources.
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Old 5th October 2012, 06:37 AM   #332
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OK - It seems I'm underway now, at least with the hard-to-find bits. This is going to be a long haul as I have build commitments with another member who is still down for the count as far as DIYAudio is concerned. (Good to see you are with us again and a speedy recovery, Hugh!)

Still, for those interested, there a couple of stereo motorized types of ALPS log. pots still available with plain shafts. i.e. the standard small black body RK168 and familiar, blue velvet RK27 types. A German source, Familygate, seems to specialise in these and other high-end bits, having a decent range of 10k,50k,100k etc. The prices are around 20 and 33 Euros respectively but the post+handling is not cheap either.

Chinese Ebayers offer mainly RK168 type in 100k, like those supplied by many sellers of DIY remote control kits. Suspect these as clones, not genuine ALPS as they are offered at prices beginning at US$12 and are available everywhere. They may be OK but don't expect great tracking. There are unmotorized genuine RK27 pots available but mainly in strange values suiting tube amplifiers or with spline shafts. The economical choices for these now seem very small. Buy while you can!

Yes, I could use any cheaper stereo pot or just plug in a remote control preamp but this is the M1 - Mooly Amp, so I think builds shouldn't stint on the quality but follow a little closer to the designer's integrated amp. concept, something I much prefer to a mass of metal boxes, cables and Hi-fi furniture anyway.
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Old 5th October 2012, 08:14 AM   #333
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Thats great that you are building it Ian... for some reason I hadn't realised
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Old 6th October 2012, 06:06 AM   #334
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Quote:
Originally Posted by Mooly View Post
...for some reason I hadn't realised
You too, eh? I find many things I do now just seem to happen without any decision by me - like this one!

I hope it will work out as comparable to the original. I thought of using a low cost assembly for the remote controller, a small, finished 2U case to give it some bling, and I have a few 300VA 30-0-30v toroids to spare. Perhaps a pair of 160VA 30-0 + 30-0V windings for floating supplies would be better, if harder to fit. Any thoughts?

Input selection is something to still think about as a narrow internal space of 220W x 300D is already tight for a transformer, PSU, an amplifier mounted to each side heatsink, remote controller & preamp/volume control. The rear panel is already set out as a bare amplifier so I'm undecided (again) until I can get some idea of how much effect the transformer and PSU radiation will have.

EMR is one great hassle of planning DIY amplifiers. We usually just position assemblies for max. separation and hope that shielded leads will do the rest for low level signals but my experience has often led to a laborious shifting and re-cutting of leads and fitting shields to get amps dead quiet. If not, why bother with DIY as I think we do it to improve on commercial products as much as express our taste in audio electronics.
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Old 6th October 2012, 07:29 AM   #335
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I went with a single toroid for the whole amp but really thought all the wiring through to achieve as near silent result as possible... and its good. The input selection has the absolute minimum lead lengths (couple of cm) which ensured good crosstalk and was all mounted vertically.

Mine was a real one off though (as you can see looking at the pictures) with each power amp built into a shielded can that serves as 80% of the heatsink too.
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Old 24th November 2012, 05:57 PM   #336
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Hi Mooly, I am a beginner and have built f5 and chipamps on pcb before. Has anyone made a pcb run for your amp? I did not see it in the thread. What size of heatsinks would this need, I thought of looking at the diyaudio AB honey badger amp but it looks quite complicated for a beginner. Besides a the preamp, power supply at 45 v, and chassis what else would be needed? What would a small run of pcb cost for this amp, any ideas? Has anyone else expressed interest in a pcb run?
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Old 24th November 2012, 06:51 PM   #337
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Hi John,
I've no idea how much PCB's cost to produce tbh... I've always done mine the hard way by hand and only in recent years started using PCB software to make it easier to lay out and draw.

Heatsinks depend on what kind of use the amp is for, and I say that because there is a world of difference between heatsinks for continuous power testing and heatsinks suitable for normal domestic use (music at home). For home use something in the 0.5C/W region should be suitable. The heatsinks I used were a one off as you can see in the pictures and in fact the whole "can" they are built in also acts as a heatsink.
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Old 25th November 2012, 08:49 AM   #338
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Thanks the note Mooly, re Alex design on post 300.

I got an online quote for about ten dollars each minimum 20 pcb and am happy to pick up cost for 20 boards using Alex design on post 300. I thought I would give it a go, and keep six, and with your authorization, offer the others to the forum which can be sold and proceeds donated to diyaudio.

my intention is to build an amp for myself, but will probably need a little handholding from the forum. The quote is from the pcb company GoldPhoenixpcb.com website.

Specification :
2layers, 0.062", FR4-TG130, 1oz, HAL, GREEN SOLDER MASK, WHITE SILK SCREEN, 2.8" x 5.7"
Special Notes: Shipped As Individual Boards
QTY: 18pcs USD9.222/pcs; Subtotal: USD166
Lead time: 5 days Business Days + 3 Business Days Shipping

They need Gerber files, so I assume that the files you posted on post 300 are gerber files, is that correct Alex. (In the past I always purchased pcb from forum members or diystore before so not sure what Gerber files are).

I thought I would keep six, and donate 14 to the DIY audio store, or to you and you can sell them here with proceeds to DIYaudio. Then I could build two amps, one for myself and one for a friend and keep two pcb in case I melt something or who knows what.

This would make this project easier for a relative beginner like myself.

Please let me know what you think and if you want to proceed.

best, John
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Old 25th November 2012, 09:46 AM   #339
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Hi John,
thanks for the interest


I've absolutely no problems with the design being offered but the PCB's are Alexs' "property" so must check that Alex doesn't mind.

I've printed the board from Alexs' file and see that these are for using two pairs of FET's, a configuration that is untested by me although I would not forsee any electrical issues. A practical issue might be mounting the four FETs on a standard heatsink if you wanted to use four and keep the FET's PCB mounted. The original single pair is much easier to mount. If the FET's are mounted away from the PCB then the usual advice of keeping the wiring short and putting the gate stopper resistors directly on the FET's applies. It's a super stable design though and has been built on veroboard by some with yards of wiring and no problems.

Looking at the PCB there is no problem using just one pair of FET's and keeping one pair of spaces unused.

I've printed the image and I'll give it a close look later today although it all looks good to me.

Any problems or questions can be addressed via the forum and thanks for the interest
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Old 25th November 2012, 10:07 AM   #340
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Default Index

I've added an index to post #1 to help find the important parts of the thread.

My MOSFET amplifier designed for music.
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