Building the Andy Timmons madbean pedal but only have a 50k pot for volume,gain

[Belanger]

OK so I'm building the Andy Timmons madbean circuit and it calls for a 100k volume and gain. Is this one of those instances I can get away with using the 50 K put or is this a situation where I should put a 50 K resistor in series with the pot( if that's even right) to make it a 100k pot.  Thanks a lot for taking the time to help and I'll also post a pic of the schematic below

[GibsonGM]

I'd put a 50k in series with the gain pot, and see what the 50k for volume sounds like...you might lose some highs or something, but it shouldn't be TOO bad....the gain pot, tho - you won't get full gain unless you have 100k total....

I'd swap them out for the real value pots when you can...won't hurt anything at all to use them for now, tho (don't forget to remove 50k resistor if you put it in there, when you get a 100k, LOL, altho it will only give you more gain!).     Also, if you put in a hard-wired resistor, you won't be able to dial  down LESS gain that what the 50k gives you, of course...

[Belanger]

Thank you so much for the help on this one, your a life saver lol. I was so excited to try out the pedal and I swear I had the correct values in stock but I was very wrong    Atleast I can still play it while I wait for the shipment from small bear(shameless plug)

[GibsonGM]

Oh sure man!  Yeah, if you look - see the 100k pot (+1k resistor) in the feedback loop of the opamp?  Call that R2.

That sets the gain of the opamp, along with the 1k to ground to its left, which we'll call R1.  So, its gain is the gain formula for a noninverting opamp, 1+ R2/R1, or 1+ 101k/1k.... = 101 +1 = 102.  Saying gain of 100 is close enough

Just your 50k pot won't get you enough resistance to get the gain that high, which I'm sure is characteristic to the sound desired, so add that ~50k in series with it (47k....).       

The 100k output helps match the pedal's output impedance to the next pedal or amp's input impedance.  If 50k sounds odd, add another 50k to ground at the cold (ground) end of the pot.  You may not notice a thing...I often run 'em with NO pot on the output til I decide if I like the thing, and use just the amp's volume.

Small Bear'll treat you right, they are great  

[Belanger]

Seriously I'm learning so much from you guys and this site. I never would of been able to start diving into this if it wasn't for this forum and guys like you who are willing to train us young grasshoppers lol

[GibsonGM]

Some older guys trained us, too    And we're not always right, ha ha!  But 'group learning' like this seems to work best for many!!

[ct_anthony]

Just another question regarding the above schematic... asuming comp switch in pos 1, so that it selects the 2N7000 as clippers... won't the red led (always connected) prevent the 2n7000 from being used?

I would have thought it the other way around... the 2n7000 always to ground and the red led and the bat41 on the toggle...

[antonis]

Just another question regarding the above schematic... asuming comp switch in pos 1, so that it selects the 2N7000 as clippers... won't the red led (always connected) prevent the 2n7000 from being used?
I would have thought it the other way around... the 2n7000 always to ground and the red led and the bat41 on the toggle...

Not quite right...

Red LED's forward voltage drop is about 2V which is greater than Si diode's one (650mV) so LED's clipping threshold is allways dominated (either by MosFet clipper or Si diode clipper).

The above is true even in the case of negative asymmetrical clipping (Q1 + BAT) because their total voltage drop is still lower than LED's one..

P.S.
Sir Mike  could add to his amplification analysis the possibility to use 50k Gain Pot by lowering R5 to 470R (for keeping same gain width) and raising C4 to 470nF (for keeping same low cut-off frequency)
You optionally may lower C3 to 47pF (to keep high cut-off frequency) but don't bother too much with it because it's original freq is about 16kHz which lowers to about 8kHz with the 50k Pot..

[ct_anthony]

Just another question regarding the above schematic... asuming comp switch in pos 1, so that it selects the 2N7000 as clippers... won't the red led (always connected) prevent the 2n7000 from being used?
I would have thought it the other way around... the 2n7000 always to ground and the red led and the bat41 on the toggle...

Not quite right...

Red LED's forward voltage drop is about 2V which is greater than Si diode's one (650mV) so LED's clipping threshold is allways dominated (either by MosFet clipper or Si diode clipper).

The above is true even in the case of negative asymmetrical clipping (Q1 + BAT) because their total voltage drop is still lower than LED's one..

P.S.
Sir Mike  could add to his amplification analysis the possibility to use 50k Gain Pot by lowering R5 to 470R (for keeping same gain width) and raising C4 to 470nF (for keeping same low cut-off frequency)
You optionally may lower C3 to 47pF (to keep high cut-off frequency) but don't bother too much with it because it's original freq is about 16kHz which lowers to about 8kHz with the 50k Pot..

Ok... It thought that the body diode of the mosfets is like a conventional silicon and the "mosfet special clipping" (like used here, gate+drain to source) goes up to 3-4v before "max" clipping...

[Belanger]

Thank you so much.  It's easy to understand what you guys mean and learn from this when its a pedal I've actually worked on

Just another question regarding the above schematic... asuming comp switch in pos 1, so that it selects the 2N7000 as clippers... won't the red led (always connected) prevent the 2n7000 from being used?
I would have thought it the other way around... the 2n7000 always to ground and the red led and the bat41 on the toggle...

Not quite right...

Red LED's forward voltage drop is about 2V which is greater than Si diode's one (650mV) so LED's clipping threshold is allways dominated (either by MosFet clipper or Si diode clipper).

The above is true even in the case of negative asymmetrical clipping (Q1 + BAT) because their total voltage drop is still lower than LED's one..

P.S.
Sir Mike  could add to his amplification analysis the possibility to use 50k Gain Pot by lowering R5 to 470R (for keeping same gain width) and raising C4 to 470nF (for keeping same low cut-off frequency)
You optionally may lower C3 to 47pF (to keep high cut-off frequency) but don't bother too much with it because it's original freq is about 16kHz which lowers to about 8kHz with the 50k Pot..

Ok... It thought that the body diode of the mosfets is like a conventional silicon and the "mosfet special clipping" (like used here, gate+drain to source) goes up to 3-4v before "max" clipping...

[antonis]

Thank you so much.  It's easy to understand what you guys mean and learn from this when its a pedal I've actually worked on

Ahaaa...!!! 
(let's test you a bit..)

1. What's the purpose of 10KC ME2 Pot..??

2. Despite of question 1., is the specific Pot correctly wired..??
(justify your answer..!!)



P.S.
Beware of your answers...!!
(if they are right they will be followed by additional "harder" questions..)

[Belanger]

To be Truly honest I don't but can you please help me learn the purpose of it.  I find all of this so interesting, I just want to learn as much as possible    Hopefully next time you quiz me I'll have the answer.   Also thank you for all the information you've posted here it's EXTREMELY helpful

Thank you so much.  It's easy to understand what you guys mean and learn from this when its a pedal I've actually worked on

Ahaaa...!!! 
(let's test you a bit..)

1.What's the purpose of 10KC ME2 Pot..??

2. Despite of question 1., is the specific Pot correctly wired..??
(justify your answer..!!)



P.S.
Beware of your answers...!!
(if they are right they will be followed by additional "harder" questions..)

[antonis]

I presume you've understood that I was kidding..

But I think that going through the building blocks of a circuit it's always a good idea - it helps a lot on later debugging and partially modification of another circuit..

[duck_arse]

antonis can learn both of us then.

1) it appears the ME2 pot is forming a low-pass filter with the C8 22nF cap.

2) the specific pot, being reverse log taper, will change (resistance with rotation) faster near the CCW end than the CW end. the little arrow indicates the terminal marked "1" would be the CCW end, so as the pot is rotated further clockwise, due to the wiper being short to the CCW, the total resistance in the RC will drop, making this control an apparent treble boost, as it will cut less treble with less resistance. I don't know if the "C" taper will offer a better control-feel or not.

teacher?

[antonis]

I don't know if the "C" taper will offer a better control-feel or not.

Neither do I.. 

teacher?

Nothing to add (or subtract)...!!
(except that, when pot is Full CW, C8 also acts as a clipping curve's edges "softener"..)

[GibsonGM]

Sir Mike  could add to his amplification analysis the possibility to use 50k Gain Pot by lowering R5 to 470R (for keeping same gain width) and raising C4 to 470nF (for keeping same low cut-off frequency)
You optionally may lower C3 to 47pF (to keep high cut-off frequency) but don't bother too much with it because it's original freq is about 16kHz which lowers to about 8kHz with the 50k Pot..

No royalty here, ha ha!!  Often I am as in the dark as anyone else about the 'finer points' that are built into a circuit - which is what makes this hobby so interesting and addictive!  If I were a blue blood, I'd never come here to see how the commoners are getting along in understanding what the techno's have built for us to look inside...

But of course - at times we may scale our resistances and capacitances to achieve the same outcome.  We do this often with tube circuitry - reduce resistances to reduce the thermal noise that they impart into a circuit.  But there ARE times when this can't be done much, if the components are also related to impedance relationships.    And it's those "at times" that still sometimes confuse me, too      Because we're testing all of our changes on breadboard (!), we see pretty quickly whether doing this is harmful or not...

That 10kC is a neat control, I like that - if you adjusted it, maybe you could call that the "Shrill" control? 

[Groovenut]

The differing clipping diodes are primarily going to give the impression of differing headroom options (hence the label Comp). Most of the clipping is going to come from the opamps as rail clipping.

I see ME2 as a standard Rat style tone control. CW, pin 3, would give the least high frequency rolloff with a knee of 15.4KHz. The C taper should place the usual B noon setting at about 10 o'clock. At full CCW rotation the LPF knee will be 691Hz. The clipping diodes, as wired are always connected directly to R8.

The Hair control that follows is a redrawn version of the SWTC3 (simply wonderful tone control) Jack Orman has on his site here http://www.muzique.com/lab/swtc3.htm which is actually from the early 70's. The difference being the upstream resistor is split into two components and made adjustable (R8 & ME2) aka Rat Harmonics control. With the Hair control at CCW you essentially have the rough equivalent of a two pole filter with different knee points. Examples of this application can be seen in many ROG designs as the double RC filter right before the circuit output for shaving off all the crazy high frequencies generated during clipping.

This circuit is primarily a clone of a clone with tweaks. The first iteration I saw was the MI Audio Crunch Box, then Suhr cloned it and added the choice of clipping diodes, now we have the JHS @ (which is a variation on the Angry Charlie).

I would be interested to know what the actual JHS @ circuit looks like as this is only Brians guess (according to him) of what the circuit is.

My interpretation any way 

[Belanger]

Wow.  Give me your knowledge lol! Seriously that's amazing   I'm just starting off so hearing you guys explain things like this really realllly helps.   Now I'm going back j we everything you've said over and over until it makes some sense in my head on how you managed to figure this all out lol.      I've been reading the formulas and what not but I may as well be reading Latin

The differing clipping diodes are primarily going to give the impression of differing headroom options (hence the label Comp). Most of the clipping is going to come from the opamps as rail clipping.

I see ME2 as a standard Rat style tone control. CW, pin 3, would give the least high frequency rolloff with a knee of 15.4KHz. The C taper should place the usual B noon setting at about 10 o'clock. At full CCW rotation the LPF knee will be 691Hz. The clipping diodes, as wired are always connected directly to R8.

The Hair control that follows is a redrawn version of the SWTC3 (simply wonderful tone control) Jack Orman has on his site here http://www.muzique.com/lab/swtc3.htm which is actually from the early 70's. The difference being the upstream resistor is split into two components and made adjustable (R8 & ME2) aka Rat Harmonics control. With the Hair control at CCW you essentially have the rough equivalent of a two pole filter with different knee points. Examples of this application can be seen in many ROG designs as the double RC filter right before the circuit output for shaving off all the crazy high frequencies generated during clipping.

This circuit is primarily a clone of a clone with tweaks. The first iteration I saw was the MI Audio Crunch Box, then Suhr cloned it and added the choice of clipping diodes, now we have the JHS @.

I would be interested to know what the actual JHS @ circuit looks like as this is only Brians guess (according to him) of what the circuit is.

My interpretation any way 

[duck_arse]

and a late happy birthday, belanger.

[POTL]

it is 100% correct scheme
knowing JHS seems to me to be 3 clipping mode
1) Silicone diodes
2) LED
3) Open clipping

here the third mode is FETs with the diode
is exactly right?