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crashlander42
Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)
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 Posted: Sat Jun 07, 2008 11:14 am Post subject:
Problem with Yusynth Sample an hold |
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What would cause the range on my Yusynth sample and hold to become very narrow (if that makes any sense). I built two of these and I'm not getting very wide swing to my signal. I breadboarded one of these a long time ago and it sounded awesome. I just can't figure out what I've done different.
Which part of the sample and hold circuit would effect the range of the output? I thought it might have been a cap I substituted for C6, but I've replaced that with an exact component and it still sounds the same. Any ideas?
Any help would be greatly appreciated.
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crashlander42
Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)
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crashlander42
Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)
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yusynth
Joined: Nov 24, 2005
Posts: 1314
Location: France
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| Posted: Sat Jun 07, 2008 12:29 pm Post subject:
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Hi
I've just seen your message but it seems you solved it all already 
Yes nowadays you have to select the tranny to find the nosiest when 30 years ago one would select the quietest 
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Yves |
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frijitz
Joined: May 04, 2007
Posts: 1734
Location: NM USA
Audio files: 54
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| Posted: Sat Jun 07, 2008 2:07 pm Post subject:
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| crashlander42 wrote: | | Never mind. Problem solved. When the instructions say to pick the noisiest transistor you should listen. I somehow selected the two quietest transistors I had. |
I need to weigh in, again, on this question. There is a serious (IMO) problem with picking your noisiest transistor. The problem is that the noisier they are, the more popcorn noise they have. I once went through a bag of 50 2N3904's, looking for the ones that gave a flat spectrum at low frequencies. I found only 2 devices that gave a flat, i.e. smooth-sounding, noise spectrum. These both had very low outputs. It's an easy matter to increase the circuit gain to compensate.
Ian |
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yusynth
Joined: Nov 24, 2005
Posts: 1314
Location: France
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| Posted: Sat Jun 07, 2008 2:17 pm Post subject:
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Yes Ian, that's why on the web page of my noise generator-S&H module one can read in the trimming section: | Quote: | | The trimming is quite simple, it consists of taking a batch of BC547 transistors and selecting among these one that gives the highest white noise level while being symetrically balanced around 0V level, with the flatest spectrum. In order to do so, it is a good idea to use a transistor socket for Q2, this way one can swap easily the transistors to find the best one. It is a good practice to wait about 1min before checking the noise level and quality of white spectrum in order that Q2 has reached a steady temperature. |
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Yves |
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crashlander42
Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)
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softfin
Joined: Oct 11, 2006
Posts: 271
Location: Far in the north
Audio files: 1
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| Posted: Sun Jun 08, 2008 8:44 am Post subject:
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I built my Yusynth S&H+noise last winter. I have found the noise source to be a bit on the weak side as well (I used a bc109c transistor). Fortunately I put a socket for the noise transistor so perhaps I should start testing different types of transistors to get stonger and flatter noise.
If anyone has had particularly good results with some specific transistors, please share the knowledge  |
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frijitz
Joined: May 04, 2007
Posts: 1734
Location: NM USA
Audio files: 54
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| Posted: Sun Jun 08, 2008 9:20 am Post subject:
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| yusson wrote: | Yes Ian, that's why on the web page of my noise generator-S&H module one can read in the trimming section: | Quote: | | The trimming is quite simple, it consists of taking a batch of BC547 transistors and selecting among these one that gives the highest white noise level while being symetrically balanced around 0V level, with the flatest spectrum. |
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Yves -- Thanks for the clarification. I was going by what the other post said, without actually reading your instructions. But I have found that the devices with the flattest spectrum have the weakest output. Do you find this to not be the case with the BC547?
Ian |
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Sine
Joined: Sep 10, 2007
Posts: 111
Location: Netherlands
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| Posted: Fri Sep 12, 2008 3:33 pm Post subject:
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| I don't know if its type specific, but i have a few metal can 2n2222's and reversed these are the most noisy transistors EVER ! |
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