500 series tube preamplifier

I  am very happy to announce that we just released the MP566 kit:

Sound Skulptor MP566 - 500 series Tube pre

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• Dual triode design,
• Input and output transformers,
• 0 to 68dB of gain,
• Variable input and output levels for total control over tube saturation,
• Input pad (Low Gain) for hot mics or line levels,
• Full 225 Volts tube supply and full 150mA tube heater,
• 1/4" DI jack, high impedance input for instruments or line,
• Total current draw less than 160 mA,
• Easy build build but care is required because of the high voltage,

Full details are available here: http://www.soundskulptor.com/uk/mp566.html

Is this a hybrid design or is the signal path 100% tube?


Cheers

Ian

Great news! looks promising and very affordable, will give it a try soon

It is a tube pre followed  by a solid state buffer.

JPK said:

It is a tube pre followed  by a solid state buffer.

Click to expand...

So it's a hybrid then.

Cheers

Ian

Nice looking design, will you be posting a schematic like with most of your other designs?

JPK said:

It is a tube pre followed  by a solid state buffer.

Click to expand...

If one wished to build this as a tube-only signal path, would it be possible to omit the buffer and use a stepdown output transformer?  I'm sure you've gone through variations of this circuit during design, maybe you tested something like this?  If so how were the results? 

Thanks!

One of our design goals was to keep the power consumption compatible with a single 500 module.  That is around 150mA. That resulted in the necessity of using only one tube. And one single tube cannot achieve both enough gain and driving an output transformer with a low enough output impedance.
This is why we chose to have one tube gain stage followed by one solid state buffer stage. The buffer stage uses the same current feedback design as our headphones amp in the MC624 which proved to be very pleasing and transparent. The output transformer is placed after this buffer.

@mitsos: it is simply not possible to do this with only one tube, it needs a minimum of 2 if we want enough gain.
I will post the schematic after a little time.

I already kinda knew you had done the research, that's why I asked.  Thanks for getting back about it.  Looking forward to seeing the schematic, always learn something from your designs!

cheers!

I made a boneheaded move and didn't bend the 63 volt 1uf electro flat to the board, so I had to pull it. (the one under the output transformer.) I've got a bunch of 1uf 50 volt caps lying around.  Would that be cutting it to close? Should I just order a handful from Mouser?

Other than that, the project has been pain free.

Thanks.

No problem, 1uF-50V will work perfect.
Make sure you did not break any via when removing the cap: check continuity between top and bottom pads.

JPK said:

No problem, 1uF-50V will work perfect.
Make sure you did not break any via when removing the cap: check continuity between top and bottom pads.

Click to expand...

Thanks, It works like a charm. Sounds lovely on guitar di -- and I'm sure everything else. Nice and round and sweet.

Since this is a single opamp, is there space one could possibly use a DOA-Pdip adapter to go discrete for the buffer? How much headroom of current is there at the buffer stage?

Also, I'd love to get a take on the type of sound this is achieving, maybe a comparison.

Thanks!

No spare room for a DOA, I am afraid.
In this design the two transformers and the tube dominate the sound so largely that I doubt you can hear a difference when modifying the output stage.

Input transformer is OEP A262A3C
but there's also a footprint for a Carnhill alternative.
Which one?

Do you consider the Carnhill an upgrade,
or just a different tone?

Edit, from email: The footprint is for  Cinemag like CMMI-8-PCA

The output-transformer is a Edcor PCW 150-150-150
configured 1:2.

How does this compare to more high-end transformers like Lundahl and the like?