Paul Cochrane - Timmy  [traced]

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Post by Ben N »

Not an exact analogy, but I tried 18v (using an 18vdc supply, not a charge pump or doubler) with my Barber DD, being as Barber advertises that his components are rated for it. I found the difference in headroom to be negligible to nil, so I got rid of the extra wall wart. Seems the design itself imposes limits on headroom (unlike, say, a micro-amp or such, which will theoretically stay clean until it gets within clipping range of the rails). Besides, Paul says that he designed the Timmy for a clean boost with the G,B&T controls at 0, so what benefit would there be to add more headroom?

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Post by soulsonic »

With diode clipping circuits it's hard to get any increased headroom at higher voltage because the diodes determine the maximum headroom.
If you have a switch to remove then diodes from the circuit... then you'd likely get a big boost in headroom.
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Post by briggs »

Like soul says - the diodes are the headroom imposers in this design. Increasing the headroom on something like a jfet circuit will have much more impact - overall gain will increase as will the "dynamic" headroom - I find that the 18v runoffgroove supreux deux sounds like god compared to it's 9v little brother the supreux.
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Post by blanik »

briggs wrote:Like soul says - the diodes are the headroom imposers in this design. Increasing the headroom on something like a jfet circuit will have much more impact - overall gain will increase as will the "dynamic" headroom - I find that the 18v runoffgroove supreux deux sounds like god compared to it's 9v little brother the supreux.
but doesn't the klon also uses diodes (1N34A) for the clipping?

when i was saying the klon had more headroom, it was in the sense that when the Timmy has gain to zero and T, B and Vol maxed, it becomes a very good clean boost but the volume is maxed (to compensate for the drive at zero) but the output of the pedal isn't that much higher than the bypassed signal so the only way to push harder is with the gain knob (although the taper of the gain pot allows for a fairly "clean" signal boost, it's still gainy) where the klon at zero drive and neutral EQ as a lot of output on tap from the volume pot to drive a clean tube amp without using the gain pot... nonetheless i prefer the Timmy to the klon

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Post by Ben N »

Just out of curiosity, does anyone know how Paul implemented the boost in the Tim, and is it clean? I mean, does it just add resistance to the NFB loop of the second opamp stage, is there an additional transistor boost, is it just a psuedo-boost, a la Fulldrive II, whatever? Maybe the answer is a clue to getting a biogger clean boost with the gain turned down.

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Post by briggs »

blanik wrote:
briggs wrote:Like soul says - the diodes are the headroom imposers in this design. Increasing the headroom on something like a jfet circuit will have much more impact - overall gain will increase as will the "dynamic" headroom - I find that the 18v runoffgroove supreux deux sounds like god compared to it's 9v little brother the supreux.
but doesn't the klon also uses diodes (1N34A) for the clipping?

when i was saying the klon had more headroom, it was in the sense that when the Timmy has gain to zero and T, B and Vol maxed, it becomes a very good clean boost but the volume is maxed (to compensate for the drive at zero) but the output of the pedal isn't that much higher than the bypassed signal so the only way to push harder is with the gain knob (although the taper of the gain pot allows for a fairly "clean" signal boost, it's still gainy) where the klon at zero drive and neutral EQ as a lot of output on tap from the volume pot to drive a clean tube amp without using the gain pot... nonetheless i prefer the Timmy to the klon
The Klon has two dual opamps - the clipping amp runs off 9v and uses Ge diodes to clip, increasing the voltage here would render no real change as the Ge diodes clamp everything out (although the opamp will probably be adding some clipping of it's own before the signal hits the diodes). The Boost/Tone section is run at dual polarity +/- about 16 volts, that is your extra headroom

The boost section in the Timmy is the second op amp stage, increasing the voltage will allow you to increase the gain in that section without the op amp clipping.
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Post by Ben N »

Sorry, Briggs, did you mean the Timmy or the Tim afa the boost?

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Post by briggs »

The schematic of the Timmy. Check it out - the first opamp is the main clipper with those diodes, the 2nd boosts the volume by a factor of 2...
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Post by paulc »

soulsonic wrote:With diode clipping circuits it's hard to get any increased headroom at higher voltage because the diodes determine the maximum headroom.
If you have a switch to remove then diodes from the circuit... then you'd likely get a big boost in headroom.
Actually that's not totally correct in this type of circuit.

While you'd think that the diodes would limit the signal there is an odd side effect of the non inverting opamp/current limiting diode setup. Some of the input signal "leaks" (for lack of a better word) into the output. The larger the input signal the more shows up on the output. This can be seen on a scope. Run a signal into a circuit like this, and crank the gain. At low input levels you'll see a nice square like wave, but as you bring up the input level you'll start to see it sort of sine back out. The peaks will increase in amplitude, and with really loud inputs like what you'd get stacking a pedal into it you'll hit rail clipping even though there are diodes in there. This can also cause rail clipping in the output stage.

This effect is what that whole clean sound riding in the mix thing is about. The higher the B+ the greater this effect can be.

Running the pedal at higher voltages will cut down on the chance to clip the rails with hot inputs. The pedal was built around single coils, so it's not a problem, but if you're using really hot buckers you might like the sound of pumping it up. It also depends on the op. For myself I think it get's a little colder sounding with the stock 4559, but with a lm1458 it's nice.

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Post by guiltyspark »

Paul, on another subject, would you mind telling us what kind of clear coat you're using on your pedals? It seems to be pretty tough and shiny. I'm using some clear now that seems kind of "plastic-y", I'd like a more professional finish. I assume you're using a 2 part self hardening auto type clear and a spraygun.

Thanks in advance-

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Post by paulc »

guiltyspark wrote:Paul, on another subject, would you mind telling us what kind of clear coat you're using on your pedals? It seems to be pretty tough and shiny. I'm using some clear now that seems kind of "plastic-y", I'd like a more professional finish. I assume you're using a 2 part self hardening auto type clear and a spraygun.

Thanks in advance-

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To be honest I'm not sure! The pedals are painted by a friend at a toyota body shop. It's whatever he uses for the cars.

It can chip though - it's not as tuff as powder coating, and it costs more than that. I've got some new things I want to have out this summer, and those will be powdercoated.

Later, Paul

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Post by gght »

Geez, better get on the list now!!!! Whatever it is!

:lol: :lol:

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Post by paulc »

gght wrote:Geez, better get on the list now!!!! Whatever it is!

:lol: :lol:
:thumbsup

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Post by guiltyspark »

paulc wrote:
guiltyspark wrote:Paul, on another subject, would you mind telling us what kind of clear coat you're using on your pedals? It seems to be pretty tough and shiny. I'm using some clear now that seems kind of "plastic-y", I'd like a more professional finish. I assume you're using a 2 part self hardening auto type clear and a spraygun.

Thanks in advance-

Guiltyspark
To be honest I'm not sure! The pedals are painted by a friend at a toyota body shop. It's whatever he uses for the cars.

It can chip though - it's not as tuff as powder coating, and it costs more than that. I've got some new things I want to have out this summer, and those will be powdercoated.

Later, Paul

Thanks Paul!

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Post by forestcaver »

Just wanted to say thank you to Paul for his tolerance and help in this topic - correcting the schematic was a very big thing to do. BTW, I think he was pretty restrained having read the topic all the way through :-)
I was curious about how a Timmy worked, having read about them but never played one. I will probably build/breadboard one some day to see what it is like. I don't think I am depriving him of income as I would almost certainly never have bought one (although perversely I am much more likely to now - having seen the price and his attitude on this board).

Thank you...

Cheers,
Andy

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Post by gght »

Just wanted to say thank you to Paul for his tolerance and help in this topic - correcting the schematic was a very big thing to do. BTW, I think he was pretty restrained having read the topic all the way through

+1

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Post by Ben N »

Here is my not-so-clever proposal for adding a switchable boost to the Timmy with only 4 (6 with LED) added components, all of them off-board. Any comments? Specifically, any suggestions as to values? TIA
Timmyboostmodfrag.GIF
Timmyboostmodfrag.GIF (11.34 KiB) Viewed 1822 times

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Post by paulc »

Ben N wrote:Here is my not-so-clever proposal for adding a switchable boost to the Timmy with only 4 (6 with LED) added components, all of them off-board. Any comments? Specifically, any suggestions as to values? TIA
Timmyboostmodfrag.GIF

The output of the second stage is already pretty much maxed out for headroom. Because of the output level of the 4 diode clipper any more gain will cause the stage to go into nasty rail clipping. Not a good sound at all... If you do that you might want to look into pumping up the voltage to give you more headroom.

A better way is to mess with the output. I've got a new version of the pedal coming out soon, and one thing it does is it selects between two volume controls.

Later, PaulC
tim/timmy pedals

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Post by Ben N »

Thanks for replying, Paul. I was thinking about that, but figured that by trimming the bass a little (the .1u) and keeping the gain within reason (50k pot) I could avoid most of that. I also thought about adding a couple of diodes (LEDs?) to the feedback loop, less as clippers than as a limiter, for the same reason. I also thought about just kludging in a transistor booster, like Gus Smalley's overdrive or an LPB-1. But the elegance of getting it from the existing components is attractive to me, as is the subtle tonal shaping you can do (at least more easily) with an active boost rather than switching between output pots. But I hear you.

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Post by paulc »

Ben N wrote:Thanks for replying, Paul. I was thinking about that, but figured that by trimming the bass a little (the .1u) and keeping the gain within reason (50k pot) I could avoid most of that. I also thought about adding a couple of diodes (LEDs?) to the feedback loop, less as clippers than as a limiter, for the same reason. I also thought about just kludging in a transistor booster, like Gus Smalley's overdrive or an LPB-1. But the elegance of getting it from the existing components is attractive to me, as is the subtle tonal shaping you can do (at least more easily) with an active boost rather than switching between output pots. But I hear you.
If you think the stock design is loud enough, and you're just wanting some volume changes out of it than you might look into doing it "backwards". Change the gain from a unity buffer to the max amount instead of adding to the max. I'd go with a 10k pot for the feedback resistor, and a 10k for the inv input. Pick a cap for that section based on taste. .47uf will be big enough to keep the low end flat. Make it smaller for a roll off. Then just short out the pot for unity, and bring it back in for boost.

A unity gain output stage still has a boosting effect because of the 4 diode threashold from the clipping stage, so maybe this will work for you.

Later, PaulC
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