#26 pre amp

[vgeorge]

Thanks for the reply Magz.

[Magz]

Originally Posted by albertli

.

Long to see your CCS schematic.

The CCS are available right here:

K & K Audio - Lundahl Transformers, audio DIY kits and more

I used the Large Cascode CCS with heat sink for the VR tubes and the Compact Cascode CCS for the 26 tubes. The schematic is just the usual one for a CCS made from depletion mode MOSFETs (see picture below) except K&K uses 910R resistors instead of 1K, and there isn't a resistor on the input.

[albertli]

Originally Posted by Magz

The CCS are available right here:

K & K Audio - Lundahl Transformers, audio DIY kits and more

I used the Large Cascode CCS with heat sink for the VR tubes and the Compact Cascode CCS for the 26 tubes. The schematic is just the usual one for a CCS made from depletion mode MOSFETs (see picture below) except K&K uses 910R resistors instead of 1K, and there isn't a resistor on the input.

Thanks Magz. So you use Mu out/or normal out.

[Magz]

Originally Posted by albertli

Thanks Magz. So you use Mu out/or normal out.

Normal out. It gives better power supply rejection than the mu out, and I achieve low output impedance by using an output transformer.

[albertli]

Originally Posted by Magz

Normal out. It gives better power supply rejection than the mu out, and I achieve low output impedance by using an output transformer.

Thanks

[sjs]

If you are looking for an active load solution, it may be worth checking out the thread on the DiyHifiSupply DHT OTL Linestage

It is a 2A3 or 45 linestage pre, with a "Super MU" active load, made up of an IXCP10M45S based CSS with a 6AS7 above it.

Best of luck.

[albertli]

Originally Posted by sjs

If you are looking for an active load solution, it may be worth checking out the thread on the DiyHifiSupply DHT OTL Linestage

It is a 2A3 or 45 linestage pre, with a "Super MU" active load, made up of an IXCP10M45S based CSS with a 6AS7 above it.

Best of luck.

You have the schematic to share.........

[sjs]

Originally Posted by albertli

You have the schematic to share.........

The schematic is not mine to share, but if you check out the DiyHifiSupply site and get hold of the Tram 2 manual, and the CCS Manual, I am sure it would be possible to piece it together.

btw it appears to use the MU out for low impedance drive

[Magz]

Originally Posted by Magz

Here is a frequency response plot of both channels of my 26 preamp. You can clearly see the difference in low-end response between the 200H and 176H transformers. Overall the plot is nice and flat out past the measurement capabilities of my laptop soundcard, which verifies the good results I saw on the 2kHz square wave response with my scope.

Just a caveat to the FR measurements - these were made with my laptop sound card, which has a 5K input impedance. In the real world with most amps the LF extension should be better due to higher input impedance, so the differences between the two transformers might not be as important.

[albertli]

Originally Posted by sjs

The schematic is not mine to share, but if you check out the DiyHifiSupply site and get hold of the Tram 2 manual, and the CCS Manual, I am sure it would be possible to piece it together.

btw it appears to use the MU out for low impedance drive

Thanks