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SurfGuitar101 Forums » Gear »

Permalink The Surfy Bear Fet Reverb

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Today I added a kill dry switch - an SPDT switch between the PCB and lug 1 of the Mixer knob. I fried a lug on the first switch but luckily I'd bought two. Second time's the charm!

A Sunday well spent if I say so myself. Now if Amazon would graciously ship me that damn toolbox...

Hi all, so I built a little foot switch box to control the reverb level. Just a simple 5kb pot across +/- of the reverb pan out. Works great, but it cuts the treble of the reverb a good amount. Anyone know how to stop the treble cut from happening?

Wiring is Lug 1 to ground and Lugs 2/3 to hot. I tried putting cap across the pot but doesn't to seem help.

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Last edited: Mar 22, 2021 16:04:00

Are you sure that it's cutting the treble and not just boosting the mids/bass? I'm not sure how this mod works exactly. (Is it boosting or cutting the reverb level?)

If it is boosting, I wonder if you could change it to cut the reverb level and then use a treble bleed to make up for lost treble. You might not even need the battery at that point as maybe you could just have it be a footswitchable pot. You would need to set the base reverb level higher and then use the switch to choose your lower amount instead of vice versa.

I could be wrong about all of this, I'm just throwing out a not completely informed idea.

-Eric

New music coming soon!

Also:
https://theverb.bandcamp.com/
https://www.facebook.com/theverbseattle/

Its just a pot across the reverb output. So it cuts the reverb level. Dry signal is unaffected. But it cut a bit of treble as you dial it back. Looking to remedy that if possible. Not a huge deal though.

The battery is just there for the indicator LED. The "circuit" is completely passive otherwise.

Ah, could the old fashioned treble bleed still work? Is the treble cut more the lower the pot is turned?

-Eric

New music coming soon!

Also:
https://theverb.bandcamp.com/
https://www.facebook.com/theverbseattle/

Nope, treble bleed does not work. And yes, the more you dial back the knob (more attenuation), the more the treble is cut.

Ok, I saw that you said that you put a cap across it. I'm assuming that you did the resistor alongside it? If so, then I'll shut up because that was my only idea.

-Eric

New music coming soon!

Also:
https://theverb.bandcamp.com/
https://www.facebook.com/theverbseattle/

I did. I tried a number of methods.

I'm sorry. The only other thing might be the cable length. I wonder if the loss in capacitance due to the instrument cable is cutting the treble. Have you tried it with patch cables to see if there is a difference? Then I swear I'm out of ideas.

-Eric

New music coming soon!

Also:
https://theverb.bandcamp.com/
https://www.facebook.com/theverbseattle/

I have!

Confused Yikes.

Hopefully someone more knowledgeable than me answers then. Good luck!

-Eric

New music coming soon!

Also:
https://theverb.bandcamp.com/
https://www.facebook.com/theverbseattle/

kinski wrote:

Just a simple 5kb pot across +/- of the reverb pan out. Works great, but it cuts the treble of the reverb a good amount. Anyone know how to stop the treble cut from happening?

The reverb output transducer is like a single coil guitar pickup with one pole piece.
Depending on the type of guitar pickup it likes a 250k (Strat), 500k (LP), 1M (Jazzmaster) volume pot.
The higher the pot value, the brighter the pickup will sound. The lower, the darker.
A 5k pot is way too low. It loads down the reverb output transducer. It lowers the resonance peak (where the treble is) significantly.
A treble bleed is not going to help with such a small value pot. It will sound dull even when on full volume.

Here you can see the effect of the load (volume pot value) on the frequency response of a passive guitar pickup (or reverb output transducer):
https://i.postimg.cc/SQWxWYtK/Screenshot-2021-03-22-232022.jpg

Try at least a 100k pot.

kinski wrote:

I tried putting cap across the pot but doesn't to seem help.

If used as a treble bleed it will help to prevent treble loss when turning down the volume pot.
When connected accross the pot (lug 1 and 3) it will shift the resonance peak of the frequency response. I think someone called it the 'color mod' or something somewhere in this thread or another thread on this forum.

Here you can see the effect of a a different capacitive load on a passive guitar pickup or reverb output transducer:
https://i.postimg.cc/qvgtXM3Z/Screenshot-2021-03-22-233527.jpg

A different volume pot value will affect the amplitude of the peak, while a different capacitive load affects the frequency of the peak.

(Graphs copied from here: http://www.buildyourguitar.com/resources/lemme/)

Last edited: Mar 22, 2021 17:41:06

Ah! This is super helpful. I’ll try some other pot values! Thanks!

Updated my post with some additional info...

So I tried a whole bunch of pot values using both audio and linear. The different values offered no improvement with the treble response and the sweep of the pot got more and more useless as the value went up. 5kB easily has the best sweep of them all. 10kB is fine too. I found even 25k was too much. So obviously 100k, 250k and 1M were not good at all. Lots of dead space in the sweep and nearly impossible to dial in lower reverb levels with any precision. And the treble cut was basically the same.

No worries, I can live with the treble cut. In a way it’s cool to have a big drippy bright reverb and then switch to a shorter dark reverb.

Last edited: Mar 23, 2021 12:40:30

kinski wrote:

Wiring is Lug 1 to ground and Lugs 2/3 to hot. I tried putting cap across the pot but doesn't to seem help.

Are you making a voltage divider or load pot?
This is how you should connect a volume pot as a voltage divider:

image

Thanks for this. I think im gonna stop messing with this idea and leave it as it is. Im fine with the tone rolloff.

With the way things are currently wired, and my enclosure is set up, it would take a bunch of alterations to try out the voltage divider wiring. So I'll leave it. But thanks so much!

Three years later I finally finished my tank! Having two kids in the meantime has made finding the time difficult but also little experience with electronics worried me. In the end I couldn't wait any longer to hear those springs. Oh and special thanks to SandBug for his picture dating back to December of 2016, that was the clincher as to how to wire up the the lamp and switch between the board and the DC jack.
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Wow, Odrigo! That's such a cool build, I love that trippy grill cloth. And it makes me happy that someone found my pic of the wiring helpful. Congrats on the reverb and your expanding family, good times!

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