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Vintage threads from the first ten years

Another Tube Screamer Question

10/30/1999 7:44 AM
Jim O	Another Tube Screamer Question OK- I have been following the T.S. threads here for a few nights now and have one more question. I have a T.S.9 reissue that I did the T.S.9 TO 808 MOD (changed the output resistors) as posted @R.G.KEENS. My reissue's chip is a TA75558P. Is it worth hunting down a JRC4558? Is it a big differance in sound? I have to admit, this mod made a BIG difference-love the sound now. Jim O

10/30/1999 7:44 AM

Jim O

Another Tube Screamer Question

OK- I have been following the T.S. threads here for a few nights now and have one more question. I have a T.S.9 reissue that I did the T.S.9 TO 808 MOD (changed the output resistors) as posted @R.G.KEENS. My reissue's chip is a TA75558P. Is it worth hunting down a JRC4558? Is it a big differance in sound? I have to admit, this mod made a BIG difference-love the sound now.
Jim O

10/30/1999 2:59 PM
Joe Z.	I think it's worth it. The 4558 just sounds better, so do a host of other op-amps. While we're talking about tube screamers, I have a question about the clipping diodes. I changed one side to a single germanium. I'm not convinced I like the sound, should I have used two one side? Also, as the note fades out, I percieve "waves" in the signal, is that because the two sides are too mismatched? Thanks for the help. Joe

10/30/1999 2:59 PM

Joe Z.

I think it's worth it. The 4558 just sounds better, so do a host of other op-amps.

While we're talking about tube screamers, I have a question about the clipping diodes. I changed one side to a single germanium. I'm not convinced I like the sound, should I have used two one side? Also, as the note fades out, I percieve "waves" in the signal, is that because the two sides are too mismatched? Thanks for the help. Joe

10/30/1999 5:12 PM
marrk	I have done a lot of TS experiments. Definitely hunt down a JRC 4558 for a great blues tone. I am working on a friends little Fender Sidekick amp and it has 2 of them in there. Try a Texas Instruments TI4558 for a prettier, lower gain tone. Look in any electronics from the early to mid 1980's. My personal favorite diodes are 1n4002. I went crazy and put the whole thing in a 1590BB enclosure with rotary switches to select different diode and cap settings. Good luck, Mark

10/30/1999 5:12 PM

marrk

I have done a lot of TS experiments. Definitely hunt down a JRC 4558 for a great blues tone. I am working on a friends little Fender Sidekick amp and it has 2 of them in there. Try a Texas Instruments TI4558 for a prettier, lower gain tone. Look in any electronics from the early to mid 1980's. My personal favorite diodes are 1n4002. I went crazy and put the whole thing in a 1590BB enclosure with rotary switches to select different diode and cap settings. Good luck, Mark

10/31/1999 4:49 AM
Jim O	Re: OTHER 4558's Ok, i just pulled apart an old non-working chorus ped and it has a couple of NEC-C4558C (PO623E)in it. Anybody have any experiance with these? I will hunt for the JRC's in the meantime

10/31/1999 2:30 PM
marrk	I just ripped a similarly marked chip from a 1980's stereo "donated" by a friend. It is marked "N Malaysia C4558C". Any of these are fair game for the TS circuit. Try them all and use the one(s) you like best.

10/30/1999 5:56 PM
Ed Rembold	Re: Another Tube Screamer Question Joe, If your using 1N60, use 2 on one side. If using 1N34A use 2 or 3 on one side. personally, I like a 1N4007+1N60 on one side, and a 1N4148 on the other. Ed Rembold

10/31/1999 11:52 PM
Mark Hammer	Each diode path determines the clipping threshold of one half of the waveform. Diode types vary with respect to the actual threshold at which they clip, and how quickly they change at that threshold point. You can vary the clipping characteristics by switching diode types (GE has a lower threshold than SI), or by switching the number of diodes in series (more diodes = higher clipping threshold). GE diodes seem to be preferred in some circuits. You can also vary the clipping characteristics by making the two diode paths dissimilar (e.g., GE one side, SI on the other, or 2 diodes one side, 1 diode on the other). Asymmetrical diode arrangements tend to produce more even harmonic content, which is a small part of what people seem to like about tubes, so folks find that a 2+1 diode arrangement gives them a "sweeter" tone. That being said, use of an asymmetrical set of low threshold diodes, driven by a very high gain signal, can mush out in ways that are very UN-sweet. The pleasantness of the diode arrangement is very much a function of what you are pushing through them or trying to get them to do. My best advice is to either borrow one, or splurge for a cheapo DMM that measures diodes. This will let you identify the clipping threshold of individual diodes and make good selections. Given that your standard bubble pack of germanium or silicon diodes from Radio Shack can span a wide range around a "standard value", it is important to know the diode rather than just the diode type. E.g., SI diodes of the same type can range between 0.5v and 0.7v clipping thresholds. If you accidentally pick two of the lower value for the 2 part of your asymmetrical combo, and a 0.7v one for the other side, you've got clipping thresholds of 1.0v on one side and 0.7v on the other; not a huge difference, if that was what you were looking for. In circuits like the TS-9/808, people like the softer, unbuzzy distortion it produces. Part of this is because of the tone shaping around the distortion stage, but part is because of the combined clipping circuit and gain characteristics. Since clipping depends on both, you can get a fuzzier sound by changing to diodes (or diode combos) with a lower threshold, or by upping the gain so that the signal spends more time above the threshold of clipping. Conversely, if you reduce the gain, there is less clipping, or if you change the diode combo (e.g., by increasing the number of diodes, or by installing the same number of diodes with a higher threshold) to one with a higher threshold, then there will be less time that the signal is above clipping threshold. The only caveat to keep in mind here is that unless you follow the clipping circuit with some kind of adjustable gain stage, you maximum output volume will be limited to that of the clipping threshold. Conversely, if you raise the clipping threshold, the maximum output volume will be raised. As several threads have attested to here, this is quite noticeable when one changes diode types in the MXR Distortion +.

10/31/1999 11:52 PM

Mark Hammer

Each diode path determines the clipping threshold of one half of the waveform. Diode types vary with respect to the actual threshold at which they clip, and how quickly they change at that threshold point. You can vary the clipping characteristics by switching diode types (GE has a lower threshold than SI), or by switching the number of diodes in series (more diodes = higher clipping threshold). GE diodes seem to be preferred in some circuits.

You can also vary the clipping characteristics by making the two diode paths dissimilar (e.g., GE one side, SI on the other, or 2 diodes one side, 1 diode on the other). Asymmetrical diode arrangements tend to produce more even harmonic content, which is a small part of what people seem to like about tubes, so folks find that a 2+1 diode arrangement gives them a "sweeter" tone. That being said, use of an asymmetrical set of low threshold diodes, driven by a very high gain signal, can mush out in ways that are very UN-sweet. The pleasantness of the diode arrangement is very much a function of what you are pushing through them or trying to get them to do.

My best advice is to either borrow one, or splurge for a cheapo DMM that measures diodes. This will let you identify the clipping threshold of individual diodes and make good selections. Given that your standard bubble pack of germanium or silicon diodes from Radio Shack can span a wide range around a "standard value", it is important to know the diode rather than just the diode type. E.g., SI diodes of the same type can range between 0.5v and 0.7v clipping thresholds. If you accidentally pick two of the lower value for the 2 part of your asymmetrical combo, and a 0.7v one for the other side, you've got clipping thresholds of 1.0v on one side and 0.7v on the other; not a huge difference, if that was what you were looking for.

In circuits like the TS-9/808, people like the softer, unbuzzy distortion it produces. Part of this is because of the tone shaping around the distortion stage, but part is because of the combined clipping circuit and gain characteristics. Since clipping depends on both, you can get a fuzzier sound by changing to diodes (or diode combos) with a lower threshold, or by upping the gain so that the signal spends more time above the threshold of clipping. Conversely, if you reduce the gain, there is less clipping, or if you change the diode combo (e.g., by increasing the number of diodes, or by installing the same number of diodes with a higher threshold) to one with a higher threshold, then there will be less time that the signal is above clipping threshold.

The only caveat to keep in mind here is that unless you follow the clipping circuit with some kind of adjustable gain stage, you maximum output volume will be limited to that of the clipping threshold. Conversely, if you raise the clipping threshold, the maximum output volume will be raised. As several threads have attested to here, this is quite noticeable when one changes diode types in the MXR Distortion +.

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