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Toccato MK II Phono Pre-amp

bigpandahk

Member
2009-07-22 3:28 pm
I want to build this pre-amp design by Dr. Arthur Loesch and modified by Thorsten Loesch and have the following questions:

1. I already have a 300B-SE, can I omit the 5687 stage and directly connect the output of 6GK5 to my 300B?

2. Is the MOSFET for the B+ for soft start? Will there any advantage to add Salas Shunt HV regulator ?

3. The pre-amp and PSU will be installed in separate chassis, can I use a 4 pins connector for both HV and LV? Will there be any interference?

Please advise.
 

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Yes the mosfet is slow start.
A salas has advantages - in the first stage there is about zero PSRR - all the noise in the supply can be heard.
So having a salas for that stage is a good idea; the RC can then be omitted I think.

the last stage is plus 18 db I thnik, like a preamp could have, so yes try to omit, but be aware: a cable will give a high ogg with the output. So then use the 5687 as a cathode follower.
 
4m7 is OK but just attach it to the top of the bias (which sort of is the new ground).

Wait a second. You cant omit the output tube! It will kill the phono stage.
This 50k--> 5k --> 62n is part of the RIAA.

At best you can take the output as a buffer, making it into a cathode follower.
For instance, turn the battery around the other way, insert a Rk = 2k cathode res (there will be about 6 volts Vk), omit the Ra 10k, attach the output coupling to the Rk and maybe it will give enough level for your listening environment.
If so with line 3, the other att resistances 33k/22k could be omitted. Just some thoughts.