Noise/filter Infra Red out level

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Awazleon
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Location: Nanterre, France

Noise/filter Infra Red out level

Post by Awazleon » Sun Nov 15, 2015 10:34 am

Dear all,

After to finish this new working module, I started to set the trimmer. Nothing complicated, only 2.
White Noise and Pink noise are sounding both very nice.
I have a white noise level swinging between approximately -/+ 6V and peak reaching +/- 10V that seems good and pink noise between +/- 5V (not easy to say because it swings a lot with peaks above 5V.

I tried to set the Infra Red ADJ trimmer as described in the doc but I get only a signal moving between +/- 1,2V that seems not good at all
I checked component value and didn't find any mistake. I also exchange U8 and U9 in case of failure but nothing moved.

I did some other measures :
U8-1 : +14,5 / -13,5 V
After R66 : +/-4V
U8-6 : around +/- 1,2V
U8-7, U9-3 and U9-1 : almost same as U8-6
Infra red Out : +/-1,4V

It seems that U8-1 out is good but after the level becomes to decrease.

Based on the Tony's doc, if I use the Multimix LED to set the balance through the ADJ trimmer, I must get Red and Green LED equal times on but of course because the low signal level nether Red or Green blink. I used my scope to chase for the signal levels.

I'll double check again the component values and for any short circuit but if one of you has any advice, this can also help me.

Have a nice day
Pascal

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Synthbuilder
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Post by Synthbuilder » Mon Nov 16, 2015 4:48 am

Hi Pascal,

The 'quality' of the noise will affect the maximum swing from the IR output. By quality I mean whether the white noise sounds clean, free from pops and odd clicks. It may be worth trying another transistor in Q1 and see what happens.

I usually have to try several transistors to find the one with the nicest sounding white noise. And loudest is very rarely the best.

Tony

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Awazleon
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Post by Awazleon » Tue Nov 17, 2015 2:11 am

Hi Tony,

Thx for your advices.
I tried some other guys and found one a bit better. Unfortunately I only have 5. I have to buy some others to extand the tests/selection. I could be get a better one.

Anyway, as usual this module sounds perfectly and the Infra Red is very nice to slightly "swing" a filter.
Last question : which other module can also do that ?

Pascal

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Synthbuilder
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Post by Synthbuilder » Tue Nov 17, 2015 2:21 am

Awazleon wrote:I tried some other guys and found one a bit better. Unfortunately I only have 5.
You may wish to try out other NPN transistors with the same pin out. BC547, BC548, BC549, BC550, etc.
Last question : which other module can also do that ?
To add randomness? If so I think you'll find the sample/slew module very interesting.

Tony

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terjewinther
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Post by terjewinther » Tue Nov 17, 2015 2:48 am

Synthbuilder wrote:You may wish to try out other NPN transistors with the same pin out. BC547, BC548, BC549, BC550, etc.
Tony´s advice is very good. In fact: you can use almost any NPN transistor. I have a bag of some very old transistors I got from a friend once, and they are mostly useless for anything. Except each time I make a noise module: I just pick out some random transistor from this bag and put it in, wait for a minute until the noise process in the module have stabilized, and then listen to the noise and do some measuring. Last time I build the Oakley noise module I ended up using an old odd-looking japanese transistor (that I can´t even remember the number on anymore). Works like a charm, and all the various noise outputs are perfect for my needs.

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Awazleon92
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Post by Awazleon92 » Wed Nov 18, 2015 2:03 am

Tony,

I have some NPN transistors in my stock. I'm going to test it to see if I can find a better one.
Btw, I'm impatient to start to build the S&H module :hihi:

Thx to all for your advices
Have a nice day

Pascal

PS : I don't know why but I can't access anymore to my Awazleon account. So I created this new one.

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