Jens Rasmussen Leach clone group buy

[tryonziess]

Any suggestions to what VA rating would be best suited for a separate frontend supply for the Leach TIM amp. I Will be using a separate transformer for each channel on the frontend. Also, if not utilizing the power from the main supply does the rail voltage have to be 5 to 10 volts higher. Thanks Tad

[BobEllis]

The front end pulls less than 5W at anything under 100V rails. Virtually any transformer of the appropriate voltage will do. You may have trouble finding a >50V transfomer at 15VA, though.

You'll want at least 5V unregulated above the regulated rails to give the regulator room to work.

Two schools of thought on the regulated front end voltage.
One says that it ought to be no higher than the rails so that the front end clips first.

The other is go higher so that the output stage gets full swing. Some amps do this using a bootstrapped VAS (usually these are mosfet amps). Vertical mosfets need ~5V here so compensate for the Vgs. The Vbe of bipolar devices is on the order of .6V, so you don't lose much if your front end voltage matches the output voltage.

I don't think you'll go wrong either way, but you might want to stick a scope on your amp and watch the clipping behavior if you go with higher than output front end rails.

[BobEllis]

The front end pulls less than 5W at anything under 100V rails. Virtually any transformer of the appropriate voltage will do. You may have trouble finding a >50V transfomer at 15VA, though.

You'll want at least 5V unregulated above the regulated rails to give the regulator room to work.

Two schools of thought on the regulated front end voltage.
One says that it ought to be no higher than the rails so that the front end clips first.

The other is go higher so that the output stage gets full swing. Some amps do this using a bootstrapped VAS (usually these are mosfet amps). Vertical mosfets need ~5V here so compensate for the Vgs. The Vbe of bipolar devices is on the order of .6V, so you don't lose much if your front end voltage matches the output voltage.

I don't think you'll go wrong either way, but you might want to stick a scope on your amp and watch the clipping behavior if you go with higher than output front end rails.

[tryonziess]

Bob, Are there anymore of the psu reg boards available at this time.
If I can not get a reliable reg board i think just separating the frontend supply with it's own transformer and isolating the channels will provide some margin of improvement Small 50 va transformers are only 13.00 apiece. Tad

[BobEllis]

Sorry Tad, I have plans for all of the regulator boards that I have. There is a group buy brewing, but I have no idea when it wll go.

[JensRasmussen]

Hi All,

Do you want 3 seperate panels so we can order each type on its own, or should I make a panel for:

1) Input + extended output (10 transistor) + Thermal diodes
2) Input + super Leach output + Thermal diodes
3) Everything in one panel

3 Will be the cost optimal for the builder that want to try different stuff out, but if you only want the extended or the super amp you will have boards to spare.

Please let me know - I have limited time at the moment, so when the layouts are done, I'd like to let someone have the .brd eagle files and generate gerbers and so on.

Bob are you up for this?

\\\Jens

[BobEllis]

Jens, I don't have the time to run a GB either. Tad said he might do it.

Maybe you could send me or Tad gerbers of the options so that we can get a ROM quote to see how the pricing would work out. At the moment it looks like an even split between the versions. At the quantities we are discussing it may even make sense to split it Front end/thermal diodes as one board and then have the two output boards together on another panel.

I'm somewhat interested in experimenting but I'd probably end up just building some of both.

[tryonziess]

I will be able to handle the group buy for this project. All I am going to need are the gerber files to submit to the pcb jobbers. I believe if we had three separate board quotes, one for each design application we would have more choice in the number of each item we wish to purchase.
If the diode board could be implemented in the frontend section somewhat similar to Jens earlier designs we could proceed from there.
As soon as we are able to submit for quotes I will publish a cost estimate to the forum.
One small suggestion --- since Jens is unwilling to take anything in trade for his expertise and hard work I propose we include a small fee on the price of each board to be donated to the DIY Audio Forum. Any comments please reply. I do not believe running this website is free. Tad

[lesherons]

I enthusiastically second Bob's suggestion that we have a front end buy on one board and the output stages on a second one. --HK

[lesherons]

Tad's suggestions are good also. It does seem that offering the front end board separately, with the compensation diodes would be the most universal option for those planning to use metal case output transistors and/or other heatsinks which do not accommodate the current output section design. The one common denominator that everyone needs is the front end---HK