610B preamp build with EQ

[Spencerleehorton]

Hi All,

Wanting now to see if I could build either a channel or a pair of 610B tube preamps with EQ.
I have a 610A schematic with the low and Hi cut and boost but not the 610B EQ section which I’m assuming would add into the circuit in a similar fashion?
Could anyone shed any light on the fabled 610B EQ section?

 

[Spencerleehorton]

Should be able to knock up both input and output transformers.
What’s the best way to do the -15db pad?
Phase switch is no problem and could have that after the output transformers.
EQ selection of 70hz, 100hz and 200hz with +/- 9db on 3 way switch
Along with 4.5k, 7k, 10k with +/- 9db
Don’t know if the original unit had the +/- 12db output ? But I can put a output pot as master.

Is there any similar schematics with the same style EQ section?

 

[Spencerleehorton]

Is the EQ section inductor based?

 

[C.B. - Boudio]

I'm probably wrong, but the 610-B seems to exist only as a plugin?

 

[Spencerleehorton]

Here it is as the preamp part in the modern version.
Not sure if the original had all these bits?

 

[Spencerleehorton]

Here you see inside the 610 solo unit.

 

[C.B. - Boudio]

Maybe you could try a normal shelving feedback EQ, but the different frequencies will require (too?) much switching it seems.

15dB pad is, of course, the easiest after the OT, or in-between stages, but overloading of the first stages could be a logical issue then.