[sdiy] Weak VFC output

[Rikard F.]

Hi Harry,

Here is the schematic I originally used:
http://www.motorplus.se/bilder/ms20/MS20clone2.gif

When I measured on this filter the output impedance was about 4 ohms (!). I 
added a output buffer stage and 1k resistor. I wanted a volume control on 
the input and added a input buffer with a 100k pot. This is my current 
setup:
http://www.motorplus.se/bilder/ms20/MS20clone2_modified.gif

Any advice would be appreciated.
/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
>>>>>
>>>
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>>

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