[sdiy] Weak VFC output

[Rikard F.]

Link to schematic with my mods (new):
http://www.motorplus.se/bilder/ms20/MS20clone2_modified2.gif




>From: "Rikard F." <rikard_123_321 at hotmail.com>
>CC: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] Weak VFC output
>Date: Mon, 08 Jan 2007 08:45:19 +0100
>
>I found the solution to my problem this morning! The signalgenerator used 
>during my measurements earlier was set to 0.560 mV rms, about 1.6 V p-p. 
>Then I read that a modular VCO normally puts out about 10V p-p (!). When I 
>used a sine this big, It turned out that the output behaved very different:
>
>SVF
>input: 10V p-p
>output @ 10k load:  ~ 5V p-p
>
>VCF (ms-20 clone)
>input: 10V p-p
>output @ 10k load:  ~ 0.65V p-p
>
>With these numbers I calculated the needed amplification of the output OP. 
>When I use the VCF with my soundcard the level is now fine!
>
>Is the last  op-amp in my schematic (U1b) really needed, or could I just  
>just change the value of R16 in the feedback network of U1?
>
>Regards
>/Rikard
>
>
>
>
>>From: harry bissell <harrybissell at copper.net>
>>To: "Rikard F." <rikard_123_321 at hotmail.com>
>>CC: synth-diy at dropmix.xs4all.nl
>>Subject: Re: [sdiy] Weak VFC output
>>Date: Sat, 06 Jan 2007 23:22:36 -0500
>>
>>Do you have a link to the schematic ? That would help in advising you.
>>It could be that the output impedance is quite different than you think it 
>>is.
>>Let's have a look :^P
>>
>>H^) harry
>>
>>Rikard F. wrote:
>>>
>>>I forgot to mention that I've measured the outputs of the filter without 
>>>any load. (The VAC meter has a several Mohms internal resistance i 
>>>suppose) On the SVF output I have 279mv and on the VCF I's 266mV. They 
>>>look almost identical. But when I try to record into my soundcard (input 
>>>imp. >10k) I get a weak level from the VCF. How can that be?
>>>
>>>/Rikard
>>>
>>>
>>>>From: "Rikard F." <rikard_123_321 at hotmail.com>
>>>>CC: synth-diy at dropmix.xs4all.nl
>>>>Subject: Re: [sdiy] Weak VFC output
>>>>Date: Sun, 07 Jan 2007 03:44:55 +0100
>>>>
>>>>Hi Peter,
>>>>
>>>>When I'm measuring I am using a signalgenerator, a VAC meter and an 
>>>>oscilloscope. I've learned that when measuring on a sound system it's 
>>>>appropriate with a 50 ohm load on a line output. Should I try with a say 
>>>>10k instead?
>>>>
>>>>/Rikard
>>>>
>>>>
>>>>>From: Peter Blackett <dragon.servicing at virgin.net>
>>>>>To: "Rikard F." <rikard_123_321 at hotmail.com>
>>>>>CC: synth-diy at dropmix.xs4all.nl
>>>>>Subject: Re: [sdiy] Weak VFC output
>>>>>Date: Sat, 06 Jan 2007 10:16:00 +0000
>>>>>
>>>>>HI, Rikard F,
>>>>>hope you don't mind me asking but what are you using to measure the 
>>>>>signals ?
>>>>>a load of 47 Ohms seems a bit low for most audio equipment.
>>>>>regards Peter
>>>>>
>>>>>wrote:
>>>>>
>>>>>>I have two different filters I use in my studio for processing sounds 
>>>>>>with. (One of them is the Oakley SVF and the other is a MS-20 VCF 
>>>>>>clone.) With my VCF, I have a low output level when I want to record 
>>>>>>the output into my music software. The Oakley has a perfect level. I 
>>>>>>have done some measurements on them both (see below). I can’t figure 
>>>>>>out why they differ so much in this aspect, the measurements doesn't 
>>>>>>show this.
>>>>>>
>>>>>>* The output impedance of both filters is 1k ohm.
>>>>>>* With a sine wave on the input of 590mV rms and a load of on the 
>>>>>>output 47 ohm, I get about 10mV over the load (both filters).
>>>>>>* The output current in this case is about 0.2 mA (both filters).
>>>>>>
>>>>>>The input impedance on my soundcard is specified as “over 10 kohm”.
>>>>>>
>>>>>>How can the output be weaker on the VCF filter when I try recording 
>>>>>>it? How do I measure to find it? I’m pretty new to analyzing circuits, 
>>>>>>so I would be greatful for any tip here..
>>>>>>
>>>>>>/Rikard
>>>>>>
>>>>
>>>>_________________________________________________________________
>>>>Express yourself instantly with MSN Messenger! Download today it's FREE! 
>>>>http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
>>>>
>>>
>>>_________________________________________________________________
>>>FREE pop-up blocking with the new MSN Toolbar - get it now! 
>>>http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/
>>>
>>>
>>>
>
>_________________________________________________________________
>Express yourself instantly with MSN Messenger! Download today it's FREE! 
>http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
>

_________________________________________________________________
Don't just search. Find. Check out the new MSN Search! 
http://search.msn.com/