Hi All

Quick note on the digipot saga, well the EL84 project is over and up and
running, sounding extremely good. So I now have push button controlled
volume and mute, originally my idea was to have 2 stereo channels feeding
into a mixer and then into the first ECC83 (power amp based on a dynaco
ST-35). However all was not as easy as it sounds (let's face it, it never
is!), the digipots used were DS1802 and as suspected by myself and others
from RAT the output from the DVD/CD player was way to much for the chips to
handle. It suggests in the documentation that a +-0.5v could be handled
easily, however this is not the case, it couldn't even handle 100mv rms. A
massive 120K resistor had to be put in series to bring down the input
voltage to the chips, it was trial and error to find the right value. This
meant that the digipots could work quite happily without distorting the
audio, although this left the output drastically low for the power amp and a
single transistor per channel had to added to bring the signal back up to
line level. To be honest it was a pain in the bipolar! but it did mean there
was no ugly knob to twiddle. The extra transistors and related components
took up valuable room and I had to leave out the second stereo channel, so
no mixer input and I have a spare DS1802 (must try fitting to wife....it has
mute!). Also power for the chip (5v) and the trannies (12v) could be taken
from the HT as current consumption was low.
All in all the digipot worked fine, as long as you know the limitations
on the signal level then I must admit its worth doing if you are using a
chassis which already has push buttons.

Cheers
Fox

Fox wrote:
Hi All

Quick note on the digipot saga, well the EL84 project is over and up and
running, sounding extremely good. So I now have push button controlled
volume and mute, originally my idea was to have 2 stereo channels feeding
into a mixer and then into the first ECC83 (power amp based on a dynaco
ST-35). However all was not as easy as it sounds (let's face it, it never
is!), the digipots used were DS1802 and as suspected by myself and others
from RAT the output from the DVD/CD player was way to much for the chips to
handle. It suggests in the documentation that a +-0.5v could be handled
easily, however this is not the case, it couldn't even handle 100mv rms. A
massive 120K resistor had to be put in series to bring down the input
voltage to the chips, it was trial and error to find the right value. This
meant that the digipots could work quite happily without distorting the
audio, although this left the output drastically low for the power amp and a
single transistor per channel had to added to bring the signal back up to
line level. To be honest it was a pain in the bipolar! but it did mean there
was no ugly knob to twiddle. The extra transistors and related components
took up valuable room and I had to leave out the second stereo channel, so
no mixer input and I have a spare DS1802 (must try fitting to wife....it has
mute!). Also power for the chip (5v) and the trannies (12v) could be taken
from the HT as current consumption was low.
All in all the digipot worked fine, as long as you know the limitations
on the signal level then I must admit its worth doing if you are using a
chassis which already has push buttons.

Cheers
Fox



IIRC there was a big thread or two on www.diyaudio.com about digipots
and how they all seem to want a *very* low signal level,or they distort.
It might be worth a search,if you havn't been there already.

Hi

I missed it, pity cuz it would have saved a lot of trial and error but
that's how you learn I suppose.
Thnk god for prototype boards!! :-)

cheers
Fox


"Ptaylor" wrote in message
...
Fox wrote:
Hi All

Quick note on the digipot saga, well the EL84 project is over and up and
running, sounding extremely good. So I now have push button controlled
(cut)
All in all the digipot worked fine, as long as you know the
limitations
on the signal level then I must admit its worth doing if you are using
a
chassis which already has push buttons.

Cheers
Fox



IIRC there was a big thread or two on www.diyaudio.com about digipots
and how they all seem to want a *very* low signal level,or they distort.
It might be worth a search,if you havn't been there already.