# If Making A Passive Volume Box, 500K vs 250K Pots?



## Guest (May 20, 2019)

I have been using a passive volume pedal at the end of my chain to keep the signal from my pedal board from being too hot when going into my amp. The amp (Bruno Underground 30) is very input volume sensitive. So if the amp volume is really really low (.5 to 1 on the dial) the amp will be low enough to hear my electric guitar strings. If I slam the input the thing will go very loud, as if the volume is cranked. So the passive volume pedal after all my pedals works great. 

So I want to make a small box to replace the volume pedal. Reasons: The size of the volume pedal. Plus the treadle is hard to get to just the right spot. Touchy. So if I can turn a knob and it will stay there- perfect.

I looked at the volume pedal (Dunlop High Gain GCB-80) and it is a big 500K pot going directly to the input and output jacks. I have another Dunlop High Gain GCB-80 but it has a 250K pot but must be newer. The pot is a 250K, but there is a small board with a wiring harness attached to the pot, which goes to a pcb board that the jacks are mounted to. I am not sure if there are any other goodies in it as the boards seem to just make the wiring harness easy automate the manufacturing. 

So... what would the difference be if I use a 250K pot instead of a 500K?

250K with wiring harness:


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## oldjoat (Apr 4, 2019)

not much


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## mhammer (Nov 30, 2007)

oldjoat is pretty much right. When it comes to guitar volume controls, the received wisdom about higher-value pots preserving more treble is correct. But as I keep harping on about, it is most correct when the volume control is up full. Once you start turning the control down, the loading starts, regardless of what the pot value is. And since your goal is to turn the volume down by a predetermined amount, I have to ask what your tonal goals are. If you use your volume pedal and try to set it at less than max, is the resulting amp tone to your satisfaction, or do you find you're missing something?


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## Granny Gremlin (Jun 3, 2016)

Building on what mhamer said:

- Id use at least 500 k and consider adding a treble bleed bypass cap ( google it, common mod to guitar tone controls). If your chain has a buffered pedal in it this makes less difference and it may be best to go with a 1 meg pot ( like your amp’s preamp volume control).

- if you know that there is 1 to 3 specific amounts of attenuation you need ( eg 6/12/18 db) it would be much better to put in fixed resistive pads. Pads can be made to not load the signal chain at all (not change the impedance of the signal between the pedalboard and amp vs a pot which will add resistence progressively as you attenuate). Still simple and passive; a stomp. Switch for each level of atten. If you do not know how much attenuation or the need to change the amount depending on fx engaged ( and pedalboard changes over time) you can use a rotary switch to make a stepped attenuator wich will cut in (eg) 6 or 12 db steps per stop or detent. Essentially a variable H pad and the same benefit of not loading the chain applies. Additionally totally repeatable vs a pot which you can just get back in the ballpark and may drift ( eg knob knocked around in transport).


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## ezcomes (Jul 28, 2008)

I did what you are doing twice...
I made one with a 500k and put it in front of the amp...worked ok
I made a second, and used it more...in the loop with a 25k...put it in bypass, and set my lead volume, then turned it on and tuned my rhythm level
Good luck!


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## mhammer (Nov 30, 2007)

Granny Gremlin said:


> Building on what mhamer said:
> 
> - Id use at least 500 k and consider adding a treble bleed bypass cap ( google it, common mod to guitar tone controls). If your chain has a buffered pedal in it this makes less difference and it may be best to go with a 1 meg pot ( like your amp’s preamp volume control).
> 
> - if you know that there is 1 to 3 specific amounts of attenuation you need ( eg 6/12/18 db) it would be much better to put in fixed resistive pads. Pads can be made to not load the signal chain at all (not change the impedance of the signal between the pedalboard and amp vs a pot which will add resistence progressively as you attenuate). Still simple and passive; a stomp. Switch for each level of atten. If you do not know how much attenuation or the need to change the amount depending on fx engaged ( and pedalboard changes over time) you can use a rotary switch to make a stepped attenuator wich will cut in (eg) 6 or 12 db steps per stop or detent. Essentially a variable H pad and the same benefit of not loading the chain applies. Additionally totally repeatable vs a pot which you can just get back in the ballpark and may drift ( eg knob knocked around in transport).


At the risk of beating it to death, having a higher-value pot (like 1meg) is great if it is going to be set up full most of the time. But since the intent is to use it to_ reduce_ the output, that means that much of the time a portion of the pot's resistance will be placed in series with the guitar's output. If the box is followed by a lengthy cable to the amp, that will increase the impact of the cable capacitance.

But this brings up an important aspect not yet raised: _where i_n the signal path is this box intended to go? Is it going to be the only thing between guitar and amp? The first thing? The last thing? Will there be any other devices between guitar and box or box and amp, that will provide a buffering effect?

Mark


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## Granny Gremlin (Jun 3, 2016)

Thought he said last before amp


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## dtsaudio (Apr 15, 2009)

If put at the end of the chain, then either of those pots is too large unless your guitar cord is really, really short. The added resistance will cause a roll off of the highs.
The low output impedance of most pedals will drive a lower value pot, and the lower resistance pot will give a lower source resistance for the amp and cable. 10k to 25k log taper is all that is needed.
Ezcomes idea is also an option.


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## Granny Gremlin (Jun 3, 2016)

Right. Total brain fart above.


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## Guest (May 21, 2019)

Thanks for all the comments and informed suggestions. The volume pedal I use goes just before the amp, after all my pedals. I don't think it is draining much tone, and if it is, I like what it is doing. I think I will make a little passive volume box with a 500K, because that's what the volume pedal is using.


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## CathodeRay (Jan 12, 2018)

dtsaudio said:


> If put at the end of the chain, then either of those pots is too large unless your guitar cord is really, really short. The added resistance will cause a roll off of the highs.
> The low output impedance of most pedals will drive a lower value pot, and the lower resistance pot will give a lower source resistance for the amp and cable. 10k to 25k log taper is all that is needed.
> Ezcomes idea is also an option.


Late to the party, but I agree with @dtsaudio .
IF the pedal chain has a buffer in the path (always on, or not 100% true bypass) & the volume control is at the end of that chain, stick to a lower resistance (<200k) if you have the luxury of choice.
Less noise, better treble retention.
To a limit... too low (<10, 20K?) and you gain nothing, you risk loading the last pedal in the chain in a way it was not designed for, and even suck a bit more power.
I used 25K on mine.


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## mhammer (Nov 30, 2007)

I guess this is why companies that make volume pedals have low-resistance versions as well.


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