Question about pre-clip bass control on FX pedal

[Steve A.]

I just picked up a Wampler Ectasy/Euphoria pedal mainly because of its transparent low gain sounds in the Open mode. I'd like to use it in the Dumble Smooth mode as well but there is too much bass with a neck humbucker. I would like to modify the pedal for less bass in the Smooth mode when the Bass control is set to 0, yet be able to turn the control up a little bit to get the stock sound in Open mode when set to 0.

Here is the schematic with the 10k bass pot shown as a plain resistor.



Question #1. What value for the Bass variable resistor cuts the bass: 0 or 10k?

Question #2. Will increasing the value of the 2.2uF cap increase or decrease the bass?

Question #3. I assume that the guitar input is indicated by V1/Sine. Is that correct?

Thanks! I'm still trying to wrap my head around ss circuits.

Steve Ahola

P.S. Here is a schem of Timmy which also uses a pre-clip bass cut control but unlike the Wampler fully CW is max cut...

[Richard]

I'm just playing along at home and am not sure but it looks like the bass control is in the negative feed back circuit. In a standard Fender style circuit the undesired frequencies are bled to ground, in a NFB circuit they are fed back to the inverting input where they cancel out. I would guess that the 10K value keeps the bass in the NFB loop therefore decreasing bass. As far as the capacitor value goes I don't know, I would guess smaller would keep more bass in the NFB loop and therefore reduce the amount of bass present.

[J M Fahey]

Question #1. What value for the Bass variable resistor cuts the bass: 0 or 10k?

Question #2. Will increasing the value of the 2.2uF cap increase or decrease the bass?

Question #3. I assume that the guitar input is indicated by V1/Sine. Is that correct?

Thanks! I'm still trying to wrap my head around ss circuits.

Steve Ahola

The main NFB loop and which defines stage gain and frequency response is basically "Gain" variable resistor (plus series R3 which is basically so it can not reach 0 ohms) and should be 1M Audio for a smooth response) and R4 .
So gain can roughly go from 10X to 1000X .
The latter will be *severely* lacking highs because the Op Amp runs out of open loop gain above ~100X or so.

Now low mids and lows are *severely* cut (nothing subtle in distortion pedals) by classic 47n C3 , just do the Math: 47n and 1k cut at 6dB/oct below 3 kHz

Which of course is done on purpose to keep distortion "clean" instead of muddy/farty/dull.
FWIW Tube Screamer, MXR Dist + and most "classics" use 47n and 4k7 for ~750Hz cutoff.

This pedal uses a more extreme low cut but at the same time bypasses it with 2.2uF cap, how much is bypassed is controlled by "bass" 10k pot.
Best curve there is Reverse Log, but since they are hard to source, I use regular Log and remember it will work smoothly but "backwards" ... which afrer all is just a convention.
You might even write numbering the reverse (but in this case proper) way, as in going from 10 to 0 (no kidding).

I bet that just 10k in series with C5 will let way too much Bass, even on "0" (which actually means maximum resistance) , I woukld use a 100K Log or Reverse Log (with proper scale numbers) there for a more useful range.

Or add a mini rotary switch, say 10/12 steps, with the proper resistor string, so you get a "stepped pot" with any curve you wish.

Or you may switch different caps, as in: 47n , 100n , 220n , .47uF, 1uF , 2.2uF , with results similar to Orange FAC control ... which is exactly the same.

[Mick Bailey]

Tayda does Alpha rev.log pots - I usually add a couple every time I order just so I get a few in stock for pedal builds.

[Steve A.]

This pedal uses a more extreme low cut but at the same time bypasses it with 2.2uF cap, how much is bypassed is controlled by "bass" 10k pot.
Best curve there is Reverse Log, but since they are hard to source, I use regular Log and remember it will work smoothly but "backwards" ... which afrer all is just a convention...

I bet that just 10k in series with C5 will let way too much Bass, even on "0" (which actually means maximum resistance) , I would use a 100K Log or Reverse Log (with proper scale numbers) there for a more useful range.

Or add a mini rotary switch, say 10/12 steps, with the proper resistor string, so you get a "stepped pot" with any curve you wish.

Or you may switch different caps, as in: 47n , 100n , 220n , .47uF, 1uF , 2.2uF , with results similar to Orange FAC control ... which is exactly the same.

Juan, thanks for such a comprehensive answer. So increasing the value of the 10k pot (and the 2.2uF C5 cap, too?) would increase the bass cut?

Instead of replacing the 10k pot with a 100k pot I guess I could use a mini-toggle switch to insert a resistor in series. Perhaps 47k? I guess even better would be a 100k trim pot used at least temporarily to determine the desired value.

BTW looking at the schematic for the Timmy clone it looks like they have
the bass control drawn up to boost the bass as you turn the control CW (on the real control it would cut it.) Am I reading that correctly?

Thanks again!

Steve Ahola

[Steve A.]

Tayda does Alpha rev.log pots - I usually add a couple every time I order just so I get a few in stock for pedal builds.

I just checked and see that Tayda is in Thailand. Can anyone tell me about their shipping costs and delivery time to the US? How would they compare to Mouser?

Thanks!

Steve Ahola

[Steve A.]

Juan:
Decisions, decisions...
I have an Alps C50k pot in hand and the C100k pot recommended by you coming in a week. Should I first try out the C50k pot or just wait for the C100k one?
The pedal inards have been removed from the case although that really isn't an issue...

Steve Ahola

P.S. I learned that Brian Wampler prefers telecasters which could explain why I think that the pedal has too much bass with a Les Paul in the Dumble-ish "Smooth" mode. Just think if this mod goes well Brian might call it the "J M Fahey Ectasy/Euphoria Mod" on his podcasts!

I don't see why it would not work well as the stock settings would still be available. Thanks!

[J M Fahey]

Oh, please try the 50k-C , might be all you need

[rjb]

I just checked and see that Tayda is in Thailand. Can anyone tell me about their shipping costs and delivery time to the US? How would they compare to Mouser?

It's been a while since I've ordered from Tayda, and I don't have the records on hand- but shipping was pretty inexpensive and surprisingly quick. They have warehouses in Thailand, Singapore, and Colorado. If I recall, one order came by China Post, and another was drop shipped from somewhere in the U.S.

Determining the shipping cost can be a bit of a hassle- I think it is calculated by weight, and they don't tell you the break points. You have to tally up your order and calculate postage online- you might find that if you add a 3 cent part, the shipping suddenly jumps a few bucks. (Then you have to agonize over which parts you don't really need!)

For me, ordering from Mouser can be maddening. Online tracking shows the package shipped overnight from Texas to BWI Airport, about 2 miles from here. Then it gets trucked about 20 miles south to Laurel sorting facility. Stays overnight in Laurel; about 4:30 PM, package is literally driven past my house to the Linthicum distribution center- about 6 miles north of here. Overnight in Linthicum; sent out for delivery in the morning. Since commercial deliveries are made first, and I work at a residential address, package arrives around 6 or 7 PM.

How is your Mouser experience?
On second thought, don't tell me.

[Steve A.]

I googled the Alpha number (C100k) and found them at Pedal Parts Plus in Louisiana. I ordered 5 pots I needed for about a buck apiece. They recommended priority shipping so they should be here tomorrow!

http://www.pedalpartsplus.com

Steve Ahola

P.S. I remember when C taper was audio (similar to A) and D was reverse audio... kinda threw me off looking at the C pots in a dirt-cheap second-hand home-made Timmy clone I bought on eBay.

P.P.S. I haven't ordered anything from Mouser for a few years. No complaint about their shipping but there were so many different parts in their catalog that I would often order the wrong ones...

[rjb]

P.P.S. I haven't ordered anything from Mouser for a few years. No complaint about their shipping

I can't complain about Mouser's shipping either- they generally get the parts from Texas to Maryland overnight.
But the local UPS & USPS.....

[MarkusBass]

I'm not sure how the pot is wired (you showed it as a resistor on the schematic). Depending on how the pot is wired (pins 1 and 2 shorted, or pins 2 and 3 shorted), it is possible to use audio pot (in case when pins 2 and 3 are shorted).
I assume that the pot is labeled as "BASS CUT" - meaning: the more you turn it clockwise, the more bass cut you get. If this is the case, you may use 20k audio pot. Here is requency responce of the input circuit:

You can see that audio taper of the pot results in "linear" bass cut changes - you get 21dB change at 100Hz. With increase pot value to 50k the range of bass cut increases to 22.5dB (just by 1.5dB) so I'm not sure whether it will be audible (but it's worth to try).
Just for reference, this is schematic I used (to show you the pot connections).


Mark

[Steve A.]

Well I finally got around to modding my Wampler pedal with the C100k bass pot. I decided that it was a little extreme so I put a 100k resistor across the outer terminals to bring the net value down to 50k.

The replacement pot had solder logs so I used solid wire to reach the pcb. Any idea where to order the Alpha pots with the flat blade pcb standoffs?

Reassembling the pedal was a struggle until I used a tapered reamer to enlarge the pot holes a little bit...

Steve Ahola

P.S. The pedal works better for me but now I wish to cut the tone (treble) a little bit. Any suggestions? The tone pot is misdrawn in the drawing...

I finally got to use my brand new...

Joe Knows Electronics 1/4W 86 Value 860 Piece Resistor Kit

http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1



I put together my own collection of 1/2W metal film resistors for tube amps using those expensive packages with maybe 6 pieces per card from TRF or NTE...

[Steve A.]

I'm not sure how the pot is wired (you showed it as a resistor on the schematic). Depending on how the pot is wired (pins 1 and 2 shorted, or pins 2 and 3 shorted), it is possible to use audio pot (in case when pins 2 and 3 are shorted).

The reverse-engineered drawing has many errors. The 10k resistor labeled BASS is actually a variable resistor with 0 ohms being full bass.

I suspect that the TONE control has the tail going to the cap and the wiper going to the VOLUME control and with a 100k* trim pot between the wiper and the cap I could dial back the treble...

* Just a guess...

Steve Ahola

[Steve A.]

Question: I want full range of 25k reverse audio Tone pot to cover what is now roughly 12:00 to 5:00. I think that putting a 27k resistor between T1 & T3 (or T2 & T3) would get me closer to that goal. Better yet, how about a 50k-100k trim pot to dial in desired Tone (= treble) setting.


Any guesses before I tack solder a trimpot to Tone pot leads?


Observations:
1.T3 goes to ground through series capacitance of 5.5uF
2. V1 goes directly to ground


Wampler Ectasy Tone/Vol readings (T/V)


T max / V max
T1 . V1 - 96k
T1 . V2 - 0
T1 . V3 - 0
T2 . V1 - 120k
T2 . V2 - 22k
T2 . V3 - 22k
T3 . V1 - 120k
T3 . V2 - 22k
T3 . V3 - 22k

T min / V min
T1 . V1 - 96k
T1 . V2 - 96k
T1 . V3 - 0
T2 . V1 - 96k
T2 . V2 - 0
T2 . V3 - 0
T3 . V1 - 120k
T3 . V2 - 22k
T3 . V3 - 22k

T min / V max
T1 . V1 - 96k
T1 . V2 - 0
T1 . V3 - 0
T2 . V1 - 96k
T2 . V2 - 0
T2 . V3 - 0
T3 . V1 - 120k
T3 . V2 - 22k
T3 . V3 - 22k

T max / V min
T1 . V1 - 96k
T1 . V2 - 96k
T1 . V3 - 0
T2 . V1 - 120k
T2 . V2 - 120k
T2 . V3 - 22k
T3 . V1 - 120k
T3 . V2 - 120k
T3 . V3 - 22k