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Post new topic Buffer switching option ...advice needed
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Author Topic:  Buffer switching option ...advice needed
Dave Hepworth

 

From:
West Yorkshire, UK
Post  Posted 11 May 2021 6:27 am    
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Hi Folks,
I built a homemade buffer ( end plate plug in design) a while ago.It works amazingly well and I gig with it.
I was wondering if I could put into the circuit an SPDT type switch to effectively give the unit a true bypass.This is because I was thinking of putting in a passivec tone cut pot/ cap on the true bypass side.This would give me an Eric Clapton type muted sound for an instrumental I have in mind.
If this could be achieved would I need a cap somewhere to stop a crack being generated on switching between active and passive output.The buffer is turned on by completing the circuit to earth using the output jack and plugging in.If you could advise with plus a diagram that be an enormous help.Thanks in advance.
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ajm

 

From:
Los Angeles
Post  Posted 11 May 2021 6:47 am    
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Dave: To really answer your question we need a schematic of what you have.

And unless I missed something, an SPDT switch by itself will not give you TRUE bypass.
It will/can give you MECHANICAL bypass, which is not the same.
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Dave Hepworth

 

From:
West Yorkshire, UK
Post  Posted 11 May 2021 8:22 am    
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Hi Ajm
Thanks for the reply.Unfortunatly I don't have a schematic and it was done on a vero board which is now sealed !looks like a thumbs down on things.
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Cappone dAngelo


From:
Vancouver, BC, Canada
Post  Posted 11 May 2021 7:08 pm    
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Is there a reason you can't use a DPDT instead?

The only way I can think of doing true bypass with a SPDT is if it's switching a relay or other multi-pole electromechanical switch which then does the actual true bypass switching.
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Dave Hepworth

 

From:
West Yorkshire, UK
Post  Posted 12 May 2021 2:21 am    
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Hi again folks ,
This is what I was thinking of.I know that the buffer would still be on on the output of the socket even when input to buffer is closed off,but the buffer wouldn't see the input ,so would it matter.
I have omitted earthings and the pot on my diagram.
Any comments would be welcome thanks for looking.
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post  Posted 12 May 2021 4:05 am    
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You have to separate your buffer at both ends – using a DPDT switch – from whatever you want to put on the "other" line. As you have drawn it the buffer's output will short-circuit the "other" line, resulting in total failure.
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Dave Hepworth

 

From:
West Yorkshire, UK
Post  Posted 15 May 2021 1:25 am    
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Hi again,
Could I dispense with the switch and just put a tone pot in line with output of guitar before it goes into the buffer ? Thanks
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post  Posted 15 May 2021 2:51 am    
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Dave Hepworth wrote:
Could I dispense with the switch and just put a tone pot in line with output of guitar before it goes into the buffer ?
Yes, that should work fine with the right pot and cap values, same as older steels with built-in tonepot. You may also rig the pot as a vary-Z control, with just the pot connected via a resistor to GND for a fixed lowest-Z value.
However, most of the old steels also has a switch to connect such a tonepot or vary-Z pot in/out of the signal-chain, and you may need one too.
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Dave Hepworth

 

From:
West Yorkshire, UK
Post  Posted 17 May 2021 1:57 am    
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Hi Georg,
I have used the switch and tone pot as you suggested.It works fine in principle. However I don't seem to get a smooth muted transition on the sweep of the pot ....it is mostly at the end.I have tried a 500 and a 250 K pot.What values do you suggest....is because of the signal going into a buffer ? BTW the pot is marked A so I presume it is audio taper.
Here is a diagram of what I have done.Thanks again for any advice.
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post  Posted 17 May 2021 3:41 am    
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The buffer has nothing to do with how your tone control behaves. What you observe is normal.

For that type of passive tone control, log pots will work better – have a wider useful rotary range – when connected "in reverse". Your sketch does not tell, but easy to test by disconnecting the GND from the lug you use now, and connect the log on the other side/end to GND instead. Then you must of course use the pot in reverse also.

FWIW: I usually "modify" the pot-taper for such passive controls by adding parallel resistors between the lugs of linear or logarithmic pots of a much higher value – often in the M-ohm range. I always modify them "by ear", as various PUs react different to varying load.
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Ken Morgan

 

From:
Midland, Texas, USA
Post  Posted 17 May 2021 4:28 am    
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Something like this would do it. Completely removes the effect from your signal path.
_________________
Ken Morgan
Midland, TX
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Georg Sørtun


From:
Mandal, VA, Norway & Weeki Wachee, FL, USA
Post  Posted 17 May 2021 5:42 am    
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Ken Morgan wrote:
Something like this would do it. Completely removes the effect from your signal path.
The effect is as removed as it can possibly be, by a switch.
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Dave Hepworth

 

From:
West Yorkshire, UK
Post  Posted 17 May 2021 7:18 am    
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Hi All,
Thanks Ken for the suggestion..however I like the idea of a compact " end plate" buffer" ..less hassle and wires etc.
However I seem to have fixed the sweep problem by using a 100K log pot .Lower than the normal 250 to 500 pots but it does work great with a gentle progressive sweep,thanks for the advice Georg.
Regards Dave
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