Dual Mono vs Stereo Power Supply Question

[bluegti]

I bought the LM3886 Dual Mono Kit from Brian at chipamp.com. I probably should have asked more questions before I bought...

The kit comes with 2 Power Supply Boards. I don't really want to build 2 monoblock amplifiers. I want to have stereo amp in a single chassis.

Is there any reason to use a separate power supply board for each channel in a single chassis?

If I do use a separate power supply board, do I need two transformers or can I still use one with dual secondaries?

Still learning. Thanks.

[pwillard]

You may or may not notice any difference.

By using two isolated transformers, there is almost no way the load from one channel will impact the other. With a single unit, there is always a possibility of interaction and therefore a negative sound experience.

If the dual secondary unit is well above minimum specifications for the two amp blocks then you may not have any issues. Let's face it... your average SONY AMP has a single supply dual secondary transformer.

Be very aware of how you connect your common grounds.

[phn]

http://www.stereophile.com/solidpowe...47/index4.html

I have posted this link here before.

I second pwillard. But would like to add that the Gaincard seems to have a poor PSU. 170W, or 85Wpc, should be enough for a 2x25W amp.

[ianpengelly]

Hi Bluegti,

I have built the same amp kit into a single chassis using 1 transformer (300VA) and it works like a charm. I used a couple of connectors to share the pair of secondary windings between the rectifier board. You can see it here:

Yet another 3886 gain clone!

There are pleanty of people that have done the same if you look at the pictures posted on the chipamp.com site.

Hope this helps!

Ian

[AndrewT]

Hi,
a single transformer with dual secondaries will work a charm driving two amplifying channels, but, you must use two separate PSUs (rectifier + dual smoothing caps) each dedicated to it's own amp channel.

There is a problem with the chipamp PCB. Most chipamps combine the signal ground and power ground. When combining these into a two channel amp you end up with a ground loop through the two inputs.

I have not researched a solution (I don't use chipamps) but some have found that mounting the chip amps VERY close together and linking the audio grounds with a very short and thick wire, then running the midpoint of this common ground wire to the PSU 0volt common and speaker return and Zobel return and to disconnecting network will provide a partial solution that results in almost inaudible hum. A bit of experimentation here will require all the extra off board grounds to be bolted earth tags until you find the quietest arrangement.

An alternative is to build two truly isolated channels inside the stereo case and use a four secondary transformer, but these are expensive or difficult to source.

The transformer VA~=1.5times the total power from the two channels.