My first LM3875 gainclone

maurycy · 7th February 2008, 02:15 AM

Actually few months ago I have completed my first gainclone based on BrianGTs LM3875 stereo kit. Besides test light bulb turning on after assembly, I have not encountered any major problems. Removing all parts out of the case and putting them back on fix the bulb problem. Kit was pretty easy to assemble but I wish the manual was updated to the latest revision with better description of the pot and CT trafo instalation (for noobs like me). I had to buy the kit, case, trafo and all the small accessories so the total cost was way more than I have anticipated. Still worth it though.

My current setup is Denon DRA-295 stereo receiver, Yamaha DVD/CD player model DV-S5750 and Mission m30i speakers with Infinnity BU-1 subwoofer. Nothing fancy but it suits me well. When I have replaced the Denon receiver with gainclone I was running only the Mission speakers without the subwoofer. After the test run, I was pretty surprised at the bass response of the speakers without the subwoofer. I must say that I like the sound. The highs and lows are incredible (comparing to the Denon receiver). In my opinion, the only thing the gainclone lacks are the mids. Gainclone sounds more dynamic but the lack of midrange is noticeable. Still blows away Denon.

So that's what I wanted to share. Pictures are attached. You have to excuse the mess of wires as it was my first project. Space in enclosure is very tight because I think I went overboard with heatsinks. After 4-5 hours of playing the heatsinks are not even warm (did not try touching chips).

I just wanted to thank everyone who replied to my posts asking for help. Special thanks to AndrewT for his patience. Without you guys I wouldn't be able to finish the gainclone (remember, I am total noob when it comes to electronics).

maurycy · 7th February 2008, 02:18 AM

For some reason, I can only upload one file at the time

maurycy · 7th February 2008, 02:19 AM

Another view

dark_avenger · 7th February 2008, 02:33 AM

very nice, i like the case nice and simple. bit over kill on the heat sinks but oh well :P

good job

sukyone · 7th February 2008, 02:36 AM

Wow . very nice power Amp.

danielwritesbac · 7th February 2008, 03:35 AM

I'm so jealous! I have the newer model kits with LM3886, and there is certainly no shortage of midrange on mine. It remains unplugged because there's too much.
So, yeah! I like yours much better.

marcus7601 · 7th February 2008, 08:07 AM

Nice work. I also did this kit as a first time ever amp build. Not encountering any problems is good, myself i forgot to plug in the transformer and sent 230V right into the amp. Puff!

johnmax · 8th February 2008, 01:03 AM

No photos from me, but I just finished my first pair of gainclones. One is an integrated amp driven by a 160VA 2x25V transformer, regulated down to 28V DC using LM338T regulators, using a passive pre-amp (rotary selector and alps blue 10k pot). The other is a dual mono power amp, with twin 120VA 2x25V transformers, regulated to 25V (for my 6R speakers). Both are non-inverting.

The dual mono uses Panasonic FC caps - 1000uF on each rail before the regulators, then Pana FC 1000uFs on each chip, with an ELNA Starget 4.7uF as the input dc blocking cap. All resistors are maplin metal film types.

The integrated is the same, but uses EVOX-Rifa PEG124 series 1000uF caps on the chips, which were harder to implement as they are axial, but I think sound better than the Pana FCs.

Both amps use the optional Ci from the NatSemi datasheet - one runs at 0.1mV of offset, the other has 0.0mV according to my (admittedly cheap) multimeter.

Anyway - basically wanted to thank everyone here as I have found the solutions to all my build issues in the forum here - its been an invaluable resource, and thanks to you all both amplifiers sound amazing - much better than the NAD C320 that I was using before (driving B&W 601 S2s and a set of Quad Lite satellites - which I highly recommend!)

So, thanks, and now I am buying in Black Gates and Allen Bradley resistors for a higher spec 3rd time lucky one

danielwritesbac · 8th February 2008, 05:33 AM

Quote:

Originally posted by johnmax
No photos from me, but I just finished my first pair of gainclones. One is an integrated amp driven by a 160VA 2x25V transformer, regulated down to 28V DC using LM338T regulators, using a passive pre-amp (rotary selector and alps blue 10k pot). The other is a dual mono power amp, with twin 120VA 2x25V transformers, regulated to 25V (for my 6R speakers). Both are non-inverting.

The dual mono uses Panasonic FC caps - 1000uF on each rail before the regulators, then Pana FC 1000uFs on each chip, with an ELNA Starget 4.7uF as the input dc blocking cap. All resistors are maplin metal film types.

The integrated is the same, but uses EVOX-Rifa PEG124 series 1000uF caps on the chips, which were harder to implement as they are axial, but I think sound better than the Pana FCs.

Both amps use the optional Ci from the NatSemi datasheet - one runs at 0.1mV of offset, the other has 0.0mV according to my (admittedly cheap) multimeter.

Anyway - basically wanted to thank everyone here as I have found the solutions to all my build issues in the forum here - its been an invaluable resource, and thanks to you all both amplifiers sound amazing - much better than the NAD C320 that I was using before (driving B&W 601 S2s and a set of Quad Lite satellites - which I highly recommend!)

So, thanks, and now I am buying in Black Gates and Allen Bradley resistors for a higher spec 3rd time lucky one

Hi John! What cap did you use for Ci? I mean, what's the brand, value, and voltage rating? That Ci has so much effect on sound, I'd love to know of a good cap to use there.
Thank you!

johnmax · 9th February 2008, 02:44 AM

The C1 caps on both amps are ELNA Starget 4.7uF 50V electrolytic caps (£0.33 each + the tax in the UK from RS min of 5 i think) - I use them in my headphone amps as well, really think they sound great for the money, my next amp is going to use the NX Black Gates though, I might try getting an extra set so I can compare with the Stargets in my existing amp.

My dual mono is up to 20 hours playing now and I don't know if its just that I am getting used to it, but it does seem to be getting more musical. I have added active cooling to the chips now as well - running CPU fans from an old pc under each heatsink - blowing a ready stream of cool air over them - they are rated at 5VDC, but got them running from 3V at the moment (2xAA - haven't worked out the best way to run them from the transformer yet!) and I can't hear a thing - they keep the chip temperature down to roughly room temp, so hopefully no risk of meeting SPIKE

Next project is some active pre-amps/buffers for them.... (the amps, rather than the fans!)

7th February 2008, 02:36 AM	#5
sukyone diyAudio Member Join Date: Jul 2006 Location: Bangkok	Wow . very nice power Amp. __________________ All DIY by me.http://sukyone.blogspot.com

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7th February 2008, 02:33 AM	#4
dark_avenger diyAudio Member Join Date: Sep 2007	very nice, i like the case nice and simple. bit over kill on the heat sinks but oh well :P good job

7th February 2008, 03:35 AM	#6
danielwritesbac diyAudio Member Join Date: Nov 2007	I'm so jealous! I have the newer model kits with LM3886, and there is certainly no shortage of midrange on mine. It remains unplugged because there's too much. So, yeah! I like yours much better.

7th February 2008, 08:07 AM	#7
marcus7601 diyAudio Member Join Date: Jun 2006	Nice work. I also did this kit as a first time ever amp build. Not encountering any problems is good, myself i forgot to plug in the transformer and sent 230V right into the amp. Puff!

8th February 2008, 01:03 AM	#8
johnmax diyAudio Member Join Date: Jan 2008	No photos from me, but I just finished my first pair of gainclones. One is an integrated amp driven by a 160VA 2x25V transformer, regulated down to 28V DC using LM338T regulators, using a passive pre-amp (rotary selector and alps blue 10k pot). The other is a dual mono power amp, with twin 120VA 2x25V transformers, regulated to 25V (for my 6R speakers). Both are non-inverting. The dual mono uses Panasonic FC caps - 1000uF on each rail before the regulators, then Pana FC 1000uFs on each chip, with an ELNA Starget 4.7uF as the input dc blocking cap. All resistors are maplin metal film types. The integrated is the same, but uses EVOX-Rifa PEG124 series 1000uF caps on the chips, which were harder to implement as they are axial, but I think sound better than the Pana FCs. Both amps use the optional Ci from the NatSemi datasheet - one runs at 0.1mV of offset, the other has 0.0mV according to my (admittedly cheap) multimeter. Anyway - basically wanted to thank everyone here as I have found the solutions to all my build issues in the forum here - its been an invaluable resource, and thanks to you all both amplifiers sound amazing - much better than the NAD C320 that I was using before (driving B&W 601 S2s and a set of Quad Lite satellites - which I highly recommend!) So, thanks, and now I am buying in Black Gates and Allen Bradley resistors for a higher spec 3rd time lucky one

9th February 2008, 02:44 AM	#10
johnmax diyAudio Member Join Date: Jan 2008	The C1 caps on both amps are ELNA Starget 4.7uF 50V electrolytic caps (£0.33 each + the tax in the UK from RS min of 5 i think) - I use them in my headphone amps as well, really think they sound great for the money, my next amp is going to use the NX Black Gates though, I might try getting an extra set so I can compare with the Stargets in my existing amp. My dual mono is up to 20 hours playing now and I don't know if its just that I am getting used to it, but it does seem to be getting more musical. I have added active cooling to the chips now as well - running CPU fans from an old pc under each heatsink - blowing a ready stream of cool air over them - they are rated at 5VDC, but got them running from 3V at the moment (2xAA - haven't worked out the best way to run them from the transformer yet!) and I can't hear a thing - they keep the chip temperature down to roughly room temp, so hopefully no risk of meeting SPIKE Next project is some active pre-amps/buffers for them.... (the amps, rather than the fans!)