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.
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.
Attachments
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.
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.
Hi Triode_al
Thanks for your prompt advice. For the RC, do you mean the 39R and 47uF? will the output voltage too high for SSHV2 without the RC stage?
Thanks for your prompt advice. For the RC, do you mean the 39R and 47uF? will the output voltage too high for SSHV2 without the RC stage?
the iput to the 5842 first stage will be about 200-210v I guess, salas HV is fine with that. the 8k2/33uf could be omited.
you are going to get a thump going to phono as the 4.7m drops the bias on the grid by 10% or .3 volts and then 5687 amplifies this.
Thanks, triode_al & stocktrader200.
@Stocktrader200
Should I change the 0.1u and 4.7M if I omit the 5687?
@Stocktrader200
Should I change the 0.1u and 4.7M if I omit the 5687?
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.
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.