Adding an output level to API 312 preamp

[saint gillis]

Hello guys,
I'd like to add an output level pot to my API preamps, I ve read the whole 312 thread but didn t find any infos concerning this..

  Is it possible to add a pot before the output transformer, is it problematic to connect one of the pot's pin to the ground?

 

[saint gillis]

Ok, sorry sorry I ve just seen that :
http://www.groupdiy.com/index.php?topic=31472.0

 

[gemini86]

It would be more beneficial to put a u pad after the transformer, so you get some of that legendary iron saturation.

 

[okgb]

Jeff at classicapi and Mike at Hairball offer attenuators with pcbs
easy & quick

 

[baadc0de]

I used a 600:600 T-pad that hairball uses but it's been a bit of an overkill price/performance wise. The way mitsos's PCBs offered an output pad worked superb for almost all situations. My 5c.

 

[mitsos]

The way mitsos's PCBs offered an output pad worked superb for almost all situations. My 5c.

It would be more beneficial to put a u pad after the transformer, so you get some of that legendary iron saturation.

That's exactly what those boards used, a U pad just like the input pads, 383R for the series resistors, and 360 for the shunt. Gives you about a 10dB pad. Works really well. For a couple bucks though, the 3 pole lorlin idea Peter Purpose posted is pretty cool. 

 

[chrispsound]

New York Dave has a balanced 600 ohm attenuator schematic, it uses 2 alpha 4 pole switches (only 3 poles on each switch being used).  If you use the first alpha switch and the 600 ohm shunt resistor(with spdt if you want)you get a sweet 10db attenuator for transformer saturation goodness. Soldering it is a bit of fun though.  ChrisP

 

[shabtek]

for those on a budget:a 2 pole switch can be used to insert different t-pad values
switch the ins and outs series R's and connect together all the cold/shunt