Noise problem on the last batch

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Noise problem on the last batch

Postby Azzer » Apr 24th, '17, 12:11

Hi,
I know there is a lot of info regarding the Noise calibrating issue here in the forum and have read all the posts but still cant get it working so would apreciate if somebody could try and help me out.
I bought 2 Yocto kits from the latest batch a couple of months ago.
From the beggining I built both directly with the Roland Noise mod but couldnt adjust it by the trimmer lower than 640mV in AC mode ( In mV AC mode 500mV ).
I decided to change one of the units so the Noise part was built like the turorial. It didnt make any diference but got worse. Checked all parts and cant find anything wrong there.
I changed R127 from 4K7 to 47K. It got lowered a bit but far from where it should be. I installed a 100k trimmer in R127 and when its maxed out giving me a value of 94k Im still not there.
So with a resistance at R127 of 94k Im getting the following values.
When mulitmeter is set in AC mode it gives me 133 mV. When its set in mV ac mode it gives me 418mV Ac.
These values are meausured by a better multimeter as I wanted to be sure to get the rights values. Its a Fluke 115 with true RMS.
Could somebody please be kind and let me know why the 2 modes ( normal AC mode and mV AC mode) give me so diferent values?
Azzer
 
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Re: Noise problem on the last batch

Postby tupinamba » Jun 10th, '17, 11:14

Hi,
I have the same issue with the Noise section...
I have two built Yoctos, and with one I cannot get below 700mV AC on Pin 1, and with the other Yocto, range is btw 16mV and 20mV AC.
I built both Yoctos in parallel, so that is really weird...
Both 4558 are properly powered (approx. +15v/-15v)

On the first Yocto, the consequence is crappy-sounding Cymbal, Clap and Snare
On the second Yocto, same thing, with nearly no decay on the clap and on the Snare.

Here are pictures of the two Noise circuits :

First Yocto (700mV AC) :
Image


Second Yocto (20mV AC) :
Image

Thanks in advance for you help!
tupinamba
 
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Re: Noise problem on the last batch

Postby BastienL » Jun 10th, '17, 12:02

Hi guys,

I got the same issue yesterday with a Yocto a guy brought me, there's was no "snare strainer" (no pink noise) and the clap was pretty low in volume. So i tried to calibrate the noise but cannot get anything good, so I did the mod suggested on page 15 of the service manual (http://www.ericarcher.net/wp-content/up ... vc-man.pdf) and it's also mentionned on Masuto's website https://masutopedals.wordpress.com/2016 ... ding-tips/.

To resume
- R129 is replaced with a jumper,
- R131 (originally 300K) is replaced with 100K,
- R127 (originally 4.7K) is replaced with a 10uF polarized cap (Masuto show the correct orientation, negative side on the right side of R127, going to the ground)
- add a 22pF cap in parrallel with R130

After the mod, I was able to dial 130mV from the noise section, hope it solves your tuning issues!

It's weird cause on the first yocto I built (from the first batch), I didn't had to do any mod for the noise section.
BastienL
 
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Re: Noise problem on the last batch

Postby tupinamba » Jun 10th, '17, 23:00

Hi everyone, hi Bastien!

I did the mod but still wasn't able to perform a proper calibration.

So what I finally did was using the ear calibration:
1. tweaking TM3 until the clap attack was as I wanted to hear it;
2.tweaking the noise trimmer until I found the sweat spot between "I cannot hear the clap reverb" and "I sounds like sh*t".
3. verifying this setting with the Snare drum (and, of course, it also sounded nice)

So my advice if you have difficulties calibrating is : trust your ears! ;)

Cheers to you all!
tupinamba
 
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Re: Noise problem on the last batch

Postby Masuto » Jul 7th, '17, 02:35

I would recommend to build also a little daughterboard to control noise for the relevant sounds.. so handy.
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Re: Noise problem on the last batch

Postby Masuto » Jul 7th, '17, 02:36

I would also get a batch of sc828 and try different hfe'd transistors for the noise section.
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Re: Noise problem on the last batch

Postby BastienL » Jul 7th, '17, 15:12

Masuto wrote:I would also get a batch of sc828 and try different hfe'd transistors for the noise section.


It doesn't seems related to hfe, I tried around 30 sc828 and only found two that gave a good result (all others were over 500mV RMS with TM4 at minimum), I mesured some "good" and "bad" ones and the difference in hfe didn't seems to have an incidence. Those transistors came from eBay, I ordered some others from Reichelt, I'll test to see if there's a difference.

Before getting ordering those sc828, I tried with a 2SC945 as suggested in another topic of the forum, and I found one that suit more easily than with the batch of sc828 I had after. I'll check if there's a difference in sound but it seems pretty close.

I'll do some other test soon and post the result here.
BastienL
 
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Re: Noise problem on the last batch

Postby Frotje » Jul 19th, '17, 16:41

Hi,

Also had trouble adjusting the noise level. Only adj. 20-70mV.
But after modification mentioned earlier in this topic, it was Ok.
Checked also with scope, Nice random noise...

Regards,

Hans
Frotje
 
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Re: Noise problem on the last batch

Postby gihaume » Dec 19th, '17, 21:44

You need to put a 2SC828 with a hFE of at least 300.
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Re: Noise problem on the last batch

Postby tupinamba » Jan 14th, '18, 18:15

Hi !
I replaced the 2SC828 with another one, from another manufacturer, and the awfull-sounding claps and toms are now perfect. Old 828 hFE was 282, new 828 hFE is 350.
So in my (narrow) experience, there's a connection btw hFE and sound.
tupinamba
 
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