I just got back from Nashville,and i saw all of these guys using Tim/Timmy pedals.What's the big hoopla about these pedals?
Quote from: soupbone on October 25, 2013, 10:22:29 PM
I just got back from Nashville,and i saw all of these guys using Tim/Timmy pedals.What's the big hoopla about these pedals?
Build one and find out:)
Quote from: pappasmurfsharem on October 25, 2013, 10:43:44 PMBuild one and find out:)
Think I might!
This may have been talked to death somewhere, but I can't figure out how to search for it...
What's the deal with the wire between the two sets of diodes? You know, the one that connects the junction of the "this way" diodes to the junction of the "that way" diodes. I can't figure out how that would do any damn thing at all. ???
Quote from: ashcat_lt on October 26, 2013, 12:27:44 AM
Quote from: pappasmurfsharem on October 25, 2013, 10:43:44 PMBuild one and find out:)
Think I might!
This may have been talked to death somewhere, but I can't figure out how to search for it...
What's the deal with the wire between the two sets of diodes? You know, the one that connects the junction of the "this way" diodes to the junction of the "that way" diodes. I can't figure out how that would do any damn thing at all. ???
I'm not sure what you mean pic?
http://i76.photobucket.com/albums/j6/IvIark_2006/Layouts/Schematics/timmyver3wj0.png
Quote from: nocentelli on October 26, 2013, 09:10:22 AM
http://i76.photobucket.com/albums/j6/IvIark_2006/Layouts/Schematics/timmyver3wj0.png
Hmm I have no idea on that one never saw the scheme before.
the top 4 diodes are a basic back to back diodes arrangement 2 diodes in series one way 2 diodes in series going the other way, the 2 diodes into the switch allows you to use just a single diode for one way or the other or both or neither. asymetrical clipping if only one of the 2 switches is on.
Quote from: Quackzed on October 26, 2013, 12:09:20 PM
the top 4 diodes are a basic back to back diodes arrangement 2 diodes in series one way 2 diodes in series going the other way, the 2 diodes into the switch allows you to use just a single diode for one way or the other or both or neither. asymetrical clipping if only one of the 2 switches is on.
But what about the junction between the back to back diodes?
thats a matter of debate... but most agree that it doesn't really matter, leave it in, leave it out, no real difference either way.
Several years ago on the other forum, Paul C chimed in to correct the schematic. In theory, that diode junction does nothing, but he claims a small audible difference. Same with the off-center bias (that would matter if the opamp clipped but shouldn't matter in a diode-clipped arrangement).
I will note here also that he was not happy about his schematic being posted, but since it was already up he wanted it to be accurate so his design wouldn't be misrepresented. He is a former member here, so you won't find much discussion of his on this site.
What's supposed to be cool about the Timmy is that since it has higher headroom than a TS due to the extra diodes and since it has control over the amount of bass dumped in the gain circuit, you can tailor an overdriven sound that's closer to your guitar's natural sound than you can with overdrives that have a low clipping threshold and significant fixed filtering in the gain stage. As far as I can tell, this is the pedal that started the "transparent overdrive" trend, but I'm pretty late to that party, so that may be inaccurate. I haven't heard one in person, though I've had one half-built for about 18 months now. :icon_redface:
Quote from: Keppy on October 26, 2013, 12:59:05 PM
In theory, that diode junction does nothing, but he claims a small audible difference.
Could it be something to do with the junction capacitance of the diodes?
Quote from: psychedelicfish on October 26, 2013, 09:57:17 PM
Quote from: Keppy on October 26, 2013, 12:59:05 PM
In theory, that diode junction does nothing, but he claims a small audible difference.
Could it be something to do with the junction capacitance of the diodes?
Maybe. Any difference would have to be due to some sort of secondary effect, rather than the basic action of a theoretically ideal diode. Based on the way diodes are
supposed to work, that connection should not affect anything. I haven't studied junction capacitance or any other non-ideal diode behavior, so I really don't know why it would make a difference, nor have I built the pedal to find out if it does in fact make a difference.
Maybe Paul was messing with the FSB guys and that connection just made the internal DIP switches easier to wire. :D
Quote from: psychedelicfish on October 26, 2013, 09:57:17 PM
Quote from: Keppy on October 26, 2013, 12:59:05 PM
In theory, that diode junction does nothing, but he claims a small audible difference.
Could it be something to do with the junction capacitance of the diodes?
There is the hypothetical consequence of such connections, and there is the audible in-the-field effect. Some effects which are heard ARE illusory, and the byroduct of human expectations. But some effects are real, only the byproduct of either rare, or special circumstances; this kind of pickup, with these guitar or pedal settings, and that kind of amp at that volume level. I won't dispute the musical relevance of such unusual combinations of factors, since many of the recorded sounds lodged in our collective memory as benchmark tones DO come from "one-off" circumstances. But the average player in the average playing situation, whether bedroom, bar, music store auditioning room, or basement band, is not going to notice.
Assuming all schematics posted around are accurate, the Timmy is distinguished by three things:
1) The use of a 2+2 diode complement, resulting in less clipping (or at least clipping more confined to initial pick attack), and more output level.
2) The variable "ground leg" of the clipping stage that alters bass response of the unit.
3) The use of a variable lowpass filterfor tone control, instead of the complementary treble-cut/treble-boost control of the TS-9/SD-1/similar.
The reason the Timmy is so appreciated by players is that these three features allow for one to push the amp a little harder and use the amp's overdriven sound in tandem with the pedal's, allow the bass content to be matched to the pickups and amp settings, and allow for a "smoother" sounding output with more dialable treble-cut.
I forgot I posted this thread!I have "Attention Dave Disorder".lol Good stuff!Might have to build me a Timmy now. :icon_biggrin:
Some time ago...a few individuals on the "other" site were working at reverse engineering the Tim pedal.
A Timmy schematic was already available on the internet.
Paul Cochrane chimed in to clarify a few of the details and stated that the Timmy was nothing more than a chopped down version of the Tim.
Paul also clarified details pertaining to the differences of the two pedals such as the "Boost", "Boost Tone", Send, and Return features.
The Timmy pedal originally used a board mounted dip switch to add/cut diodes to select between different clipping configurations.
The Tim used a push/pull switch attached to the "Boost Drive" control for the same purpose. Both pedals eventually switched over to a top mounted toggle switch.
Paul outlined the following details about the toggle switch/clipping diode configuration:
"The clippers are wired a little different now due to the 3- way toggle"
"The toggle is just a spdt on/off/on. One leg goes to the junction of the 4 diodes shorting out two of them. The other leg brings in a single diode which then parallels the 4 for a 2/1 setup."
"The diodes go 4 in the middle position, 3 (2/1) in the up, and 2 in the bottom. 5 diodes total."
Armed with this info...I came up with this configuration:
(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/Tim%20clipping%20diodes.jpg)
In the "up" position D5 in parallel with the 4 diodes "cancels" D4 and D3.
In the "middle" position you get the 4 diodes unabated.
The "bottom" position D1 and D4 are taken out of the loop for two diode clipping.
Is my interpretation of Paul's description correct?
Yes.
Thanks for the reply Leo.
Now...I was just looking at my drawing...and it occurred to me that by reversing the polarity of D5 that would cancel D1 and D2.
To keep me from searching the web...two questions:
One set of series diodes will clip the positive side of the signal, and the other set will clip the negative side.
Which set does what?...and is there any preference to clipping the top versus the bottom or vice versa?
Pretty sure D3 and D4 are the positive side. Diodes conduct when the triangle points toward the lower voltage. But no, it doesn't really matter. Polarity is arbitrary. I mean, we can go back to what Mark said about maybe on one specific guitar into one specific amp, but...
Thanks for that Ash!
> As far as I can tell, this is the pedal that started the "transparent overdrive" trend, but I'm pretty late to that party, so that may be inaccurate
No, there were many pedals before that.
Quote from: Keppy on October 26, 2013, 12:59:05 PM
In theory, that diode junction does nothing, but he claims a small audible difference. Same with the off-center bias (that would matter if the opamp clipped but shouldn't matter in a diode-clipped arrangement).
I've simulated the circuit in LTspice for both the diode junction and the off-centre bias.
1] The junction between the back to back diodes indeed conducts no current other than a few fA of noise (normal wire).
2] The off-centre bias would work if the negative I/P was not left DC floating. When it's set, some
VERY interesting asymmetry results... second harmonics galore. This can be approached at least two different ways.
I can post a screen capture of circuits & O/P if anyone's interested.
-- Edited --
Screen capture of 2 off-centre biasing schemes & resulting asymmetry:
(http://aff-media.s3.amazonaws.com/Timmy-OD-asym.png)
Oh please post screenshots of everything!
A local member of a different forum brought his Timmy over to my place because he had read that swapping op-amps improved the tone. In particular, a 1458 dual op-amp - normally a less-preferred chip - was dubbed as the ideal replacement for the 4560 or whatever that the pedal comes with. I was sceptical, but we installed a socket and subbed a variety of alternatives - TL072, JRC4558, CA3240, CA3260, OP275, etc. - and darn if a 1458 didn't sound sweeter and less harsh than the original and any of the alternatives tried.
Live and learn. I forget which brand of 1458 it was.
So fun and easy to swap out IC op amps! Also discrete versions.