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10 channel HT amp based on Inverted Gainclone design

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10 channel HT amp based on Inverted Gainclone design

Post by jat on Wed Mar 16, 2011 12:29 pm

hopefully someone would find this helpful.

my cheap avr don't really have a good power amp section. and i can't afford multi thousand ringgit to splurge on a good multichannel amp. so no choice but to build myself an amp.

gainclone are quite well known to be a good sounding stereo amp. but there's not much information on how to apply the good circuit for multichannel purpose. if you're going pass the standard 2 channel configuration, the information are scarce at best.

i've tested the standard configuration (non-inverted gainclone) and inverted gainclone. also tried the simplest 3 resistor amp (non-inverted). the thing is, non-inverted designs are easy to get unstable after going pass a few channel.
and i'm targeting to bi-amp all my speakers (5 speakers) thus requiring 10 channels of amplification. usually the amp goes unstable after hitting 5 channels.

the only thing that kept its stability beyond 5 channel is the inverting circuit with DC offset adjustment.

here's a picture of the amp (old picture)


have to wait till my wife gets home as she happen to misplace the digicam inside her handbag. no wonder that thing weighs a ton.
i'll try to post more detailed pictures plus the circuit in my next post.
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Re: 10 channel HT amp based on Inverted Gainclone design

Post by pmc on Wed Mar 16, 2011 6:43 pm

What do you mean by 'unstable'? Do the amps shut down half way through a movie? Do the clipped?

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Re: 10 channel HT amp based on Inverted Gainclone design

Post by jat on Wed Mar 16, 2011 9:16 pm

some of the channels decide to go haywire and put off high DC offset. anything more than 20mV is too high for me.

and maybe there's something wrong with my grounding scheme (using the non-inverted topology), but after hitting 5 channel there's lots of buzzing. doesn't happen when there's only 2 or 3 channel running.

the inverted design kept running stably after 5 channels so i decided that it's easier to just leave the non-inverted design rather than troubleshooting.
and not to mention with the inverted topology i could fine-tune the DC offset using a simple trimmer. non-inverted topology needs a rather complex compensation circuit or opamp integrated into the feedback loop to control the dc offset.

would be nice to have 5 channels running inverted and another 5 channels running non-inverted. that way easier to listen which one sounds better.

but oh well.. there's a multi-loop gainclone in the work. that one will sound better than both inverted and non-inverted anyways
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Re: 10 channel HT amp based on Inverted Gainclone design

Post by pmc on Fri Mar 18, 2011 10:01 am

20mV is considered good. The original gaincard's DC offset is at 80mV....can't remember where I got this info, it was stuck in my head all the time. Buzzing is difficult to troubleshoot, most probably ground loop? What is a multi loop gainclone?

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Re: 10 channel HT amp based on Inverted Gainclone design

Post by jat on Sat Mar 19, 2011 8:58 am

80mV is way too high for my brains to comprehend. maybe i'm just paranoid hehe. since i'm a builder i tend to try and make all my amps have as low offset as possible.

from 5 channels of the non-inverted gainclone, a few have unstable offset. it goes up and down. and in my years of experience building amps this translates to an oscillating amp.

with the manual offset adjustment of the inverting gainclone, all 10 channels have an offset of less than 5mV before and after warming up (with some channel adjusted to less than 1mV offset).

and a multi-loop gainclone is a gainclone (class AB) that's supposed to beat a lot of class A amp. i'll explain later. gonna go out with the family.
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Re: 10 channel HT amp based on Inverted Gainclone design

Post by pmc on Sat Mar 19, 2011 9:47 am

Getting DC offset at 1mV?...man, you're good. Interesting...i like to hear more about this multi-loop and how to do this.

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Re: 10 channel HT amp based on Inverted Gainclone design

Post by chchyong89 on Wed Mar 30, 2011 10:53 am

Ground point.
For the signal ground(green), in your case, you are crossing the rca ground together and end up "single ended" ground, don't ground in that way, twist together with the signal and end up to one point(let say Point-A).

Your ground from your PSU is to deliver to all amplifer sections with wires and wires( If my eyes don't failed me). Don't ground in that way too. Take only one wire from PSU ground, and that wire directly bring to Point-A.

There is only one ground from each of your gainclone, take the ground from each gaincard and directly points to point-A as well. ( Don't route here and there.)

Don't attach the point-A to casing or the case will act as antenna, if you intend to do so, make a Ground Loop breaker.

For the speaker output, i have no idea in your design yet, so i suspect it's bridge connected so no ground. If it's ground as well, twist the output and connect to point-A too.

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