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Re: Noise section trimmer voltage?
Posted: Jul 4th, '14, 04:46
by lsdave
i am only getting around 8mV RMS on my pin 1 of my Noise section 4558C. Adjusting the TM4 doesn't do much. I am getting 30v between pin4 and pin 8 on the opamp.
I did accidentally have U13 in backwards in my snare drum. Could that have damaged the 4558C in the noise section?
Re: Noise section trimmer voltage?
Posted: Jul 4th, '14, 04:57
by lsdave
What are some of your guys voltages on pin 2 and 3 of the opamp?
Re: Noise section trimmer voltage?
Posted: Jul 4th, '14, 05:35
by lsdave
seems like i had a bad q35. I replaced it with another NPN with the same ECB pinout and now i get between 200-750mV. I'm going to play with R127 now to see if i can get it to 130mV.
Re: Noise section trimmer voltage?
Posted: Jul 5th, '14, 15:11
by ikke
27kOhm at R127 did the trick for me.
Re: Noise section trimmer voltage?
Posted: Oct 7th, '14, 17:00
by jooks
Is it ok to trim after building the whole kit or does it put a load on it so it shows different values? My guess is it should be ok but Im not 100% sure...
Re: Noise section trimmer voltage?
Posted: Oct 7th, '14, 17:26
by ElSchtroumpf
jooks wrote:Is it ok to trim after building the whole kit or does it put a load on it so it shows different values? My guess is it should be ok but Im not 100% sure...
I built the whole kit before calibrating anything. I had to change R127 to get the correct voltage but now everything sounds fine.
Re: Noise section trimmer voltage?
Posted: Oct 7th, '14, 17:58
by jooks
ElSchtroumpf wrote:jooks wrote:Is it ok to trim after building the whole kit or does it put a load on it so it shows different values? My guess is it should be ok but Im not 100% sure...
I built the whole kit before calibrating anything. I had to change R127 to get the correct voltage but now everything sounds fine.
Thanks for confirming!
Re: Noise section trimmer voltage?
Posted: Oct 25th, '14, 10:40
by jonathanfb
jmx303 wrote:Just another question for clarification, as I am also measuring approximately 260mV at least (and I am absolutely sure that I did not pick the wrong parts (R127 is 4.7k for now):
Is it really correct to change R127 already now to 47k, at this point, even if the Noise part is the only part finished so far (besides the Power Supply of course)? Wouldn't the value measured change under load (i.e. if the rest of circuits are finished)? In that case I would continue building the rest first and check again at the end. But if I am getting this wrong and the value does not change under load, it would make sense to change the value now.
When did you guys change your R127? Right at the point you measured for the first time or after everything was built?
How should I proceed?
Cheers,
jmx.
How did it go with this jmx? I'm getting similar readings. 260mv rms on expensive mm but 130mv in AC mode on cheap mm with R127 value of 47K. Don't want to get too bogged down with this so early in the build.
jon
Re: Noise section trimmer voltage?
Posted: Nov 10th, '14, 07:02
by Djvinc
Hi there,
I've been trying hard to get this 130mV RMS, but the best I can do is...lower : 80mV at best, which is not enough sound-wise.
To get as high as 80mV I shorted R127 and TM4 (other values only get me lower). I also tried other 2SC828 without success.
What should I try now ? Change R129/R130 ? Or maybe R131 ?
Thx.
Re: Noise section trimmer voltage?
Posted: Nov 10th, '14, 09:06
by pato
Hi,
There was a modification on the original TR-808 which has not been respected in the Yocto. Have you tried it? It worked for me.
Replace R129 (330k) by a jumper (0) and replace R311 (330k) by a 100k. Also replace R127 (47k) by a 10u capacitor.
Have a look page 15 of the TR-808 service manual.