vref or 1/2v for multiple pedals in one box?

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vref or 1/2v for multiple pedals in one box?

Postby jorri » 29 Jul 2011, 21:56

I am making a single box with three of these splitter-blends http://www.runoffgroove.com/splitter-blend2.png (except with gain and pad mods on the wet signal).
and the baja limiter as found on here.

Do i need to really replicate the VREF part of the circuit that is separated, or can i use one for all the pedals? how about for the baja as well- can i switch to the same one that can supply 1/2v to all of them?

been a bad day of pedal building today, working out that this can't all fit the perfboard, mostly because i was using 2w resistors i mistakenly ordered thinking they were 0.2w-dunno what i was thinking! i understand this might be simple- but this is such as headache, and i have looked for the answer already.
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Re: vref or 1/2v for multiple pedals in one box?

Postby DrNomis » 29 Jul 2011, 22:08

jorri wrote:I am making a single box with three of these splitter-blends http://www.runoffgroove.com/splitter-blend2.png (except with gain and pad mods on the wet signal).
and the baja limiter as found on here.

Do i need to really replicate the VREF part of the circuit that is separated, or can i use one for all the pedals? how about for the baja as well- can i switch to the same one that can supply 1/2v to all of them?

been a bad day of pedal building today, working out that this can't all fit the perfboard, mostly because i was using 2w resistors i mistakenly ordered thinking they were 0.2w-dunno what i was thinking! i understand this might be simple- but this is such as headache, and i have looked for the answer already.




If they are all powered from the same power source, you should be able to use just the one 1/2 Vref for each circuit provided that it's fed to each op-amp via a 1M resistor, you could even use a spare op-amp to buffer the 1/2 Vref so that it doesn't get too heavily loaded..... :thumbsup
Genius is not all about 99% perspiration, and 1% inspiration - sometimes the solution is staring you right in the face.-Frequencycentral.
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Re: vref or 1/2v for multiple pedals in one box?

Postby Greg » 30 Jul 2011, 01:45

I would think you should really isolate and filter for each circuit.
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Re: vref or 1/2v for multiple pedals in one box?

Postby DrNomis » 30 Jul 2011, 04:14

Greg_G wrote:I would think you should really isolate and filter for each circuit.




You're right, filtering of any supply rail in a circuit is actually always a good thing to do,isolating as well, stops the circuit from doing things like motor-boating and squealing..... :thumbsup
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Re: vref or 1/2v for multiple pedals in one box?

Postby jorri » 30 Jul 2011, 12:41

thanks for the information. its only really 4-5 components each so not a problem to put back in. can always wire the resistors vertically for the extra space.
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Re: vref or 1/2v for multiple pedals in one box?

Postby Dirk_Hendrik » 30 Jul 2011, 13:07

Unless you're absolutely certain the impedance of your Vref approaches 0 you're more on the safe side when giving each circuit it's own Vref supply. If not 0 it does provide an audio path which can lead to noise and oscillations from one circuit into another one. Especially in the case of high gain effects. There's many commercial high gain designs with multiple gain stages which have their own vref supply per gain stage for this reason. If you want to make a stable vref supply buffer it with an opamp which will, actively, supress possible oscillations and such.


As for the power supply.
When you look at, as an example, an Ibanez SM9/SML/MS10 (same thing, different box) the individual dual opamps also have their own power supply filtering for the same reason. One cannot trust the power supplies impedance to be low enough to effectively avoid oscillations.
Sorry. Plain out of planes.

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