Trafo question...

[Dxvideo]

A quick question;

If I make a DUAL MONO gainclone with;
1 x LM3875 amplifier,
Onboard rectifiers (8x MUR860 or equivalent)
Onboard reservoirs (10,000u)
Per board.
Should I use one 150VA 2x24v (center seperated) per board or,
a 300VA 2x24v (center seperated) for whole system?

Which gives the best result? And if I use one 300VA for all, then gorunds will be seperated for each amplifier, in this case using the same trafo will cause any problem like gorund loop or potential difference between gorunds or like that?

This is my PCB layout;

 

[BWRX]

Either should work fine. I would personally choose the 2 x 150VA approach so you can go full dual mono. However, this will be more expensive, take up more space, and require twice the number of components.

 

[Dxvideo]

In any case, I would put dedicated rectifiers and reservoirs on board. So the only extra charge will be only on trafos.
Thx...

 

[AndrewT]

Hi,
I see seven alternatives.
1. Full dual mono with separate transformers, in separate chassis.
2. Full dual mono with separate transformers, in a single chassis.
3. Dual mono using a four secondary transformer, completely separating the two channels.
4. Dual mono using twin secondaries but with separate dual rectifiers on each channel, allowing separate audio ground per channel.
5. Stereo using twin secondaries and separate single rectifiers per channel, on a common audio ground.
6. Stereo using twin secondaries and a dual rectifier but shared between the two channels, on a common audio ground.
7. Stereo using twin secondaries and a single rectifier shared between the two channels, on a common audio ground.

I have listed them in order of best chance of minimising Hum on the resulting two channel amplifier. Have I missed any?
I know which gives me best performance.

 

[Dxvideo]

I had bad experiences with,
One trafo, one PSU (with one rectifier and one reservoir per rail), two amp boards. Because in this case, each amp take GND from both PSU and signal source.
However I havent tried totally seperated option. May be I can use;
Two combined boards (like my attachment) and one trafo with four seperated 75VA secondary. This is more simple and economical alternative I guess.
What do you think about snubberising on rails? (Like Carlos done)

 

[AndrewT]

I had bad experiences with,
One trafo, one PSU (with one rectifier and one reservoir per rail), two amp boards. Because in this case, each amp take GND from both PSU and signal source.
However I havent tried totally seperated option. May be I can use;
Two combined boards (like my attachment) and one trafo with four seperated 75VA secondary. This is more simple and economical alternative I guess.
What do you think about snubberising on rails? (Like Carlos done)

Hi,
that sounds like you are rejecting alternative 7 and proposing to adopt alternative 3. I managed to get reasonable performance from 3, but do remember to keep the input RCA grounds separate as well.
I have not compared all the others, but alternative 6 is usually recommended (not by me) for a two channel chipamp. Option 7 also gets many recommendations for chipamps.
I have tried alternative 4 in the past, but could never get it hum free and eventually realised than I could never make a success of it.

 

[Dxvideo]

In fact I am open to all seven alternatives. And I have more alternatives;
- Dual mono regulated design (seperated trafos, rectifiers, reservoirs, regulators and amplifier boards)
- Semi dual mono regulated design (one trafo, one rectifiers per rail, one reservoirs per rail and one regulators per rail per amp [total four regulators])
- Snubberized regulated design (also for dual mono and semi dual mono)

To be honest,
My real need is;
I have a lot of amplifier in my house. Three gainclones, one LM4702+MOSFET, two MOSFET amps etc...
And they have two main problems;
If theyre little gainclones (like LM4780), they made in the dark ages (one or more years before) and with low quality components. I dont like their sounds.
If theyre big (and good sounding), theyre really huge (and ugly) ones, and WAF doesnt accept to put it to the living room!
So,
I want to make a;
Really good sounding, (comparable with my MOSFET amp)
Tiny as possible,
Simple as possible,
And handsome as possible
Amplifier which can standable on TV desk and my wife can never reject it and I can never throw it to my amplifier cemetary!

First I thought that an Amp4 (41Hz) or an Amp1 will be a very strong canditate for that position. However,
I have never made a Class D amp and I dont trust their sounds in fact. Because a lot of Chinese sh itty equipment uses that kind of amplifiers and I cannot identify non of them as HIFI..
And I made a lot of gainclone like amplifiers and know a lot of things about the gainclones.

So I decided to make an ULTIMATE gainclone this time. I will purchase all audio grade parts and make a really good enclosure for it.

As a conclusion, I am open to all ideas... Please give more advices about that;
- Should I add a buffer stage to it?
- Should I add a preamp to it?
- What kind of power supply to use?
- And any other advices on gainclone title..

Thanks a lot.

 

[BWRX]

First I thought that an Amp4 (41Hz) or an Amp1 will be a very strong canditate for that position. However,
I have never made a Class D amp and I dont trust their sounds in fact. Because a lot of Chinese sh itty equipment uses that kind of amplifiers and I cannot identify non of them as HIFI.

There is absolutely nothing wrong with the Tripath based amps from 41hz. Browse the 41hz forums or the class d forum and look for reviews about those amps. You will find that they are in fact quite good.

As a conclusion, I am open to all ideas... Please give more advices about that;
- Should I add a buffer stage to it?
- Should I add a preamp to it?
- What kind of power supply to use?
- And any other advices on gainclone title.

There is no definitive answer to your questions. You can go as crazy as you want, but I would suggest to start with a basic design and make it full dual mono. Leave room for expansion and work your way up from there until you are satisfied.