LM3875 Gainclone completed

anilva

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Folks,

Just completed my long pending Gainclone project.

I have used Peter Daniel's LM3875 premium gainclone kit, 300VA Toroid from Miracle, Quad 405 chassis with some of the old connectors changed to better ones.

Took nearly a day to complete including soldering, drilling, wiring and testing.

Playing extremely well. High, Mids and Lows are all there. No problem. Again no hum, no distortion and no switch on/off transients.

I am ofcourse using a ground to earth connection through a thermistor a-la Pass F5.

Never paid attention to others, when they were singing praises of a gainclone. Now I know. For it's simplicity, price and sound quality, I don't think there anything else to compare. Absolutely wonderful project for a DIYer.

The powersupply seems to have a lot of muscle to supply sudden requirements of current for bass and the amp is extremely fast with awesome attack and decay.

Will upload the pictures shortly.

Cheers.
Anil
 
Congrats! So will 200VA be enough for both L+R or do you recommend 300?

Thanks

My experience with 300VA is very good. Absolutely no issue of hum, buzzing, heat etc. Loads of reserve for both channels driving full. Solid bass.

I don't know about 200VA. May fall tad short.

Cheers.
 
Thanks everyone for appreciating this.

Here are the pictures that I shot today. The amp is working extremely well. Only modification I am going to do is to add a decoupling capacitor at the input in order to prevent any inadvertent DC getting to the amp from my preamp or any other source that I may connect in the future. Just a preventive measure.

So far I am yet to feel any heat in the heatsinks of the Quad while playing music at fairly high levels. I tend to believe that they are too big for the Gainclone design.

Cheers.








 
Nice! Where did you get this chassis? Is it available locally?

My preamp gives a loud pop 20 secs after start. Can I use the decoupling caps on the output of the pre to block this?

Cheers
 
Nice! Where did you get this chassis? Is it available locally?

My preamp gives a loud pop 20 secs after start. Can I use the decoupling caps on the output of the pre to block this?

Cheers

Something does not sound right to me here. 20 secs for a turn-on pop appears to be too long a time that too for a preamp. Normally the turn-on pop is around 1-2 secs after start.

Disconnect the preamp from the amp, and measure the DC voltage at the output of the preamp, without playing anything. If possible, short the input of the preamp to ensure no other signal is being amplified by the preamp. See if there is any big DC voltage at the output. If there is voltage, use output caps (normally preamp would have it as a part of the design) to ensure no DC is passed to the power amp.

Cheers.
 
Nice! Where did you get this chassis? Is it available locally?

My preamp gives a loud pop 20 secs after start. Can I use the decoupling caps on the output of the pre to block this?

Cheers

The chassis is an old Quad 405 amp, which I emptied and now using for the GC.

Getting a chassis is the toughest thing for a DIYer. My Pass F5 is still lying on a piece of wood.
 
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