BOSOZ Volume Control - any suggestion

[jh6you]

Originally posted by ruangrit
I'll try to avoid input attenuator to minimize wiring complexity

You could make it with fixed resistors--it is very simple.

JH

[ralf]

hi,

my problem is othe way round.
my gain is too less.

i use a elna 5k attenuator in output of bosoz and my gain is too less.

what kind of options do i have . i dont want to lower R15 because of higher distortions.

whats with using a 100k pot instaed of a 5 k pot? or soldering the pot to the input of bosoz?

greets,
Ralf

[Pan]

Ignatz,

one of the good thing I mentioned was the fixed paralelled resistor, no matter if dual to GND or single between phases.
Only drawback of this is the fact you can not get "full" volume, but if you have enough system gain it´s no problem.

Of course one can question if this would be audible, but it sure is a more simple "circuit" in that a part of the signal (or all of it) always go thru a soldered path instead via the rotary switch (or what have you).

The fixed resistor is chosen via listening test for the max volume you need in the system. I for instance could never use the full balanced source signal level from my SACD, then the volume would be far to loud for my room/setup.

So you see, you can use three (your way) or four (my way) quality resistors which make out most of the attenuator, and then use lower quality for the switch or pot.

If one uses "your way" with one paralell resistor, the common mode thing could be better while "my way" still has some of that in the single variable resistor in the switch, but the benifit of paralell resistor to GND is that the input capacitance could be less of a problem since it sees a lower resistance to GND.

Otherwise (depending on the topology I guess) if the input has no
resistor to GND between input terminals and first stage, then the only path to GND is via the series resistor in the attenuator... do you understand now?

The capacitance in cables and inputstages (of particurlary FET´s)
is troublesome and a source to distortion especially when passive volumecontrols are used. By using a high current outputstage in the source you can use a low value for the attenuator and in that way the circuit damping factor is much better, especially if a low value resistor to GND is used after the series element.

Some people have problems with passive solutions, I say, made right it´s the very best.

My recipie for a passive set up;

A source with 50-100 ohm output capable of driving 100 ohm or at least 600 ohm without problem.

Use a low series resistor (500 ohm - 2k) and use fixed resistors to GND after the series element to give the att, a LOW output impedance and to set the max volume of the system.

Then use resistors or pot´s of choice between the phases for volume control.

/Peter

[ruangrit]

Gotcha! I think I found what has been missing...also the fact that the circuit gain will be reduced as output potentiometer value is lower.

I'll try to find a lower 4-deck potentiometer.

To Ralf,
I would suggest that we follow the recommendation in the document "<=25K"...

Thanks,
RR.

[jh6you]

Originally posted by ruangrit
the circuit gain will be reduced as output potentiometer value is lower.

...?!?!

JH

[ruangrit]

I know...I know...It was my mistake...

By the way, I tried last night fixed parallel resistors seemed to help...If I could not find a lower value 4-deck POT I may end up with the circuit revision (with proper fixed paralleled R(s)) or 2 x 2-deck stepped attenuators that may be easier to find locally (of course lower value than the current 100K).

Thanks,