API output attenuator

Hi all,

Moving on from putting an output pot on my Neve 1290 I wanted to do the same to my API-312 preamps.
I’ve found a post that seems to suggest putting a T pad 600 ohm pot on the output of the OP transformer, also I think it was Ian who suggested a 1k pot config but the post is so old I can’t see the images?
Could someone explain or put an image/schematic up of how to implement this correctly please?

You can use a 1K log pot. Transformer hot to top of pot. Transformer cold to bottom of pot. Pot wiper is hot out and pit bottom in cold out. With most log pots this will give you around 20dB attenuation at the mid point. For some applications this may be too coarse. At Neve, a 10dB drop at the centre was preferred. This was achieved using a 2K LIN pot slugged with a 1K resistor from wiper to cold.

Cheers

Ian

I found this....

btw, is there a good source for 1k log pots???

I tried the Sta Level output idea from the Preservation Sound site and I'm not sure it works  the way I like for my application .....but I haven't spent too much time with it....

think I found these from Ian on GS.....Not sure though...

that is a pretty low gain preamp to put a pot on,

plus what about the output transistor, can it handle the extra load?

you can put a pot in place of the feedback resistor to dial in optimum gain to noise to sweet spot setting,

I use this on My API312 and it's great.....

Ian suggest me and works fine.

A 1k variable pot it is then for API-312, didn't think it was that easy!!

Spencerleehorton said:

A 1k variable pot it is then for API-312, didn't think it was that easy!!

Click to expand...

Yes it is that easy. The dual 1K log circuit I think I nicked from New York Dave. The other single pot design is my own.

If you want nice chunky pots of any value or law, then Blore Edwards here in the UK is the pace to go.

https://www.blore-ed.com/

Cheers

Ian

Good shout Ian!! Nice one.

A H-pad can be better solution for balanced output attenuation ?
Back in the day they use a lot of complicated attenuator ( H-pad step  with 5 stages Rotary switch ) Daven , Langevin etc ....
I read somewhere that the impedance is more respected with those design ?
for a fixed attenuation it s just 5 resistors in fact

> impedance is more respected with those design ?

If none of the parts, or the source, are grounded, the difference is just the few-pF of stray capacitance.