Tuning... distortion :(

hi,
now that i have the trimpots in the right place and have borrowed a midi controller keyboard, i’m trying to sort out the tuning.
the thing is, it all sounds really distorted or overdriven.
i think i’m following the tuning instruction right.
but when i turn the Reso the sound doesn’t go from silence to distorted, it just changes in pitch.

do you think i have a short somewhere?
i guess i will have to take a close look over the board to see if i got something wrong somewhere…

(edited to put in correct section)

When turning the reso trimpot it goes from silent, not distorted, distorted with a change in pitch accompanying the transition from not distorted to distorted. So the raise in pitch is normal, but can you at least reach the “silent” zone?

Out of curiosity: put the oscillator 2 to none, and the oscillator 1 to fm, with prm = 0, and set mix to 0. The synth should now play a sine wave. Does it sound distorted or not? If this is the case, it might simply be the input level on your mixer/soundcard which is too high.

hi,
thanks for the quick reply!
i cannot reach the “silent” zome, all i seem to get is a change in pitch as i turn the trimpot…

i tried as you said, osc2 to none, osc1 to fm, prm = 0, mix=0
it sounds the same as the setting both oscs to none, with res@63 and cutoff@50.
i also tried plugging in to my mac, the sound was a little less distorted, but the other info above leads me to think something isn’t right somewhere…

thanks!

Can you at least silence the resonance by decreasing its amount from 63 to 60? On this forum Muldee had a similar problem and could solve it.

It would also help if you could post a recording of the first presets.

hi,
i’ve done a little recording and here’s the results:
http://soundcloud.com/droneface/sets/shruthi-1-tuning-issues
though i don’t think i’ll be online over the next few days, please let me know what you think :slight_smile:

oh, and i’ve now played the unit through a computer and two different mixers (one being my analog synth mixer) and do think that the output volume is really high!
so maybe i have put something in the wrong place and that’s causing distortion…

So even when resonance is set to 01 you have a sound when all the oscillators are set to none? If the output is too high, you can try swapping the 68k resistor above IC3 (which sets the output gain) to a 33k or 10k.

great! thank you :slight_smile:
i’ll try that and report back my results

hello again :slight_smile:

ok, i have followed your suggestion and swapped the 63k resistor to a 10k.
along with the advice above, i have also worked through Muldee’s post here: http://tinyurl.com/tunar
all to no avail :frowning:

all the various settings just change the pitch, like before.
no turning of the Reso trimmer puts it into the silent zone.
i have had a close look to see if i have a short and can’t see one.

what can i do now?

Nothing that comes to me that wouldn’t require a scope to inspect what’s really going on… Maybe it’s not a problem with the feedback path itself, but the resonance control signal generation (all parts above IC4). Are the two diodes and the two transistors between IC4 and IC5 correctly oriented?

thanks :slight_smile:

i’ve had a close look at the parts you mention and think they are correctly placed.
i took some pictures and posted them here:
http://picasaweb.google.com/allthesixes666/Shruthi1?feat=directlink

otherwise, i have no idea what i’m looking for… is it possible to send you the board for inspection?

I haven’t checked the rest but you have swapped those two guys:

ah, ok, so i have a 220k where i should have a 2.2k, and the 2.2k where the 220k should be…!
i’ll swap them tomorrow and see what happens!
thank you :slight_smile:

Also if there’s a petition to sign to make 1% resistors white instead of blue, please let me know, I want to sign it several hundreds of times.

You may laugh at me but i always use my Multimeter (aka Mr. Voltcraft) to check for the resistor values before soldering.

grrr!
i swapped the resistors over (220k and 2.2k) and there’s still no silent zone…
i guess i’ll have to spend some time checking all the other resistors next.

i was having trouble seeing the colours on some of the resistors, a blue or black band on blue, next to a blue or black band… one colour influences another too much, so yeah, white resistors would be much more helpful!

thanks again!

ps. any more suggestions are more than welcome :wink:

Should be a 220, looks like a 2.2k.

I know it’s not easy to read those values, but all the resistors of similar values are bundled together, and the instructions show the board at each step.

ha ha @ me… :frowning:
thank you, i’ll have to get the multimeter out wont i?
feeling quite embarrassed now

8>< edit
testing things with the multimeter and am finding a few 10ks measuring as 5kk.
strange

Multimeters work by sending a current between the two probes, measuring the voltage, and doing the division. This works outside of a circuit, but once the resistor is soldered on the circuit board, current is flowing everywhere so you’re not measuring anything valid at all…

…ok

some of them are correct though…

so the only real way to check now is by looking at the bands on the resistors?
this is fun!