I’ve been doing a lot of looking into Tube Screamers in preparation for a project thats’ tentatively titled The Omni Screamer. An expansion on the old MohoMods MultiScreamer. Anyway, here’s a collection of my notes in a somewhat coherent format.
I don’t know how official this schematic is, but it looks like a factory schematic and not one some internet dudes drew, so I’ll take it as canon.
Ibanez/Maxon hasn’t always been consistent with what op-amps they use in all the TS variants. The factory schematic for the TS808 seems to call for an RC4558 (Texas Instruments?), but they mostly shipped with JRC4558s. Some other op-amps show up too, mostly 4558s from other manufacturers. The TS9 was all over the place, ‘seemingly random’ according to Analogman. For the reissues, Ibanez seem to have settled on the JRC4558D for the TS808, and the TA75558P for the TS9. This is likely to justify the higher price point of the TS808 and keep it mojotastic. Ultimately, the JRC4558 seem to be THE Tube Screamer IC. Yeah, there were other 4558s, but current production models only ship with the JRC or TA75558P.
The Output Resistors.
The TS808 has a 100R series resistor and 10k shunt resistor at the output. The TS9 and pretty much every other TS variant have a 470R series resistor and 100k shunt resistor. Does it matter? Honestly, I’ve played with these on switches and hear no difference. I’ll take either pair. But this does help us classify the circuits. Since the op-amps do vary, we can define a TS808 circuit as one with 100R/10k and a TS9 circuit as one with 470R/100k. Because those are the only parts that differ.
This thread has some discussion on whether or not they matter: http://www.diystompboxes.com/smfforum/index.php?topic=108501.0
The Clipping Diodes
The diodes don’t get a whole lot of discussion, as everyone is focused on the op-amps and output resistors when they do their 808-spec mods. Most DIY clones use 1N4148s or 1N914s, which should be similar to what come stock in real TS’s. Early TS808s seem to have has 1S1588s (orange with a blue stripe marking the cathode), though the schematic I posted above calls for MA150s. Most of the other TS variants, including Maxon’s current offerings, use MA150s or something that looks the same, orange with a white stripe. The TS5 is notable for having 1N4148s. The diodes are hard to identify because they’re not labeled on the body. We have to go by what the schematic calls for, and we know that they didn’t always use the specified parts when populating the PCBs at the factory. Or we go by appearance of the diode and take an educated guess. So I’m going to say the definitive TS diodes are 1S1588 and MA150.
Does this matter? I’d expect 1N4148s to have similar, if not identical, clipping characteristics. This is something I’ll have to experiment with.
The Input and Output Buffers
All official TS variants have input and output buffers. Even the OD9, which is true bypass, maintains the buffers. Some clones strip these off, because they’re unnecessary with TBP. The TS808 and TS9 buffer configuration is made up of two discrete transistors. That means that they’re individual parts. A very early version of the TS808 (the narrow box) used both sides of a dual op-amp for the buffers instead of individual transistors. The TS10 has an extra buffer coming off the input buffer. The ST9 and STL both use one half of a dual op-amp for the input buffer and the other half for the mid boost part of the circuit, then the output buffer is a discrete transistor. For the most part, all official TS variants have the same stuff between the buffers. Even the TS808/9 output resistors are part of the output buffer.
1979 TS808 Narrow Box / Original Maxon OD808 / TS808 35th Anniversary Reissue
These three pedals are all pretty much the same. They even share the same PCB layout. The input and output buffers are both halves of a dual op-amp instead of discrete transistors. If Matsumin’s schematic for the OD808 is to be believed (and expanded to include both TS808s), they have a 220R series resistor where the later 808s have 100R, but they do have the canonical 10k shunt resistor. Everything inbetween the buffers is the same as every other official TS, save for the op-amps. The OD808 and ’79 TS808 had two MC1458Ps, and the 35th Anniversary has two JRC4558Ds.
TS9 / TS9DX / TS7 / TS5
The things that define a TS9 in comparison with the TS808 are output resistors. Other TS versions are essentially TS9 variants, sharing the same output resistor values. I consider the TS9 the branching point for most of the other variants.
The TS9DX is exactly like a TS9 when the mode switch is set to the TS9 position. The earliest run of these pedals had the drive pot connected incorrectly, resulting in less gain than a typical stock TS9, but this was fixed on previous production runs. It uses the same PCB layout as the TS808 and TS9, with an additional daughter board for the parts that the switch controls. It seems to ship with the TA75558P most of the time, but units with JRC4558Ds have been known.
The TS7 is a TS9 circuit with a Hot switch. Despite being lower-end gear than the TS9, they usually come with JRC4558Ds straight from the factory. It has a B20k tone pot instead of the usual W20k or G20k (same thing). The PCB is unique to the TS family, as the ToneLok series of pedals have lots of daughter boards crammed into the box, with way more solder pads than are necessary so multiple circuits can be built on the same boards.
The TS5 comes with the TS75558P. While most of the other TS’s have what look like MA150s for clippers, this guy has 1N4148s. The tone pot is G20k, surprising for a cheaper pedal. I also found that the 51pF cap is 47pF. Not a big deal, it was probably just what the factory had on hand. I have gone over it enough to find any other differences, but it’s pretty much a cheaper TS9 in a crappy plastic enclosure. Some very early runs had metal enclosures.
The TS10 has always interested me because, for years, believe my OD808 reissue was actually a TS10 circuit. Well, the TS10 has the TS9 output resistors. Sometimes it shipped with an MC4558 and sometime with a JRC4558. It also has an extra transistor, an emitter follower off the input buffer going to the bypass. In the effect portion of the circuit, the only difference between a TS9 and TS10 is that the TS10 has a 220R resistor in series with the input of the op-amp.
Maxon OD808 Reissue / OD9
The OD808 reissue has the TS9 output resistors, not those of the TS808. Maxon claims they also reversed their positions to reduce noise levels. The IC is a JRC4558. There is no 220R from the TS10 circuit, though the input buffer does have the TS10 emitter follower tacked onto it. So we can call it a hybrid TS9/TS10, but the effect portion of the circuit is just a TS9.
The OD9 is a TS9 with a JRC4558D and true bypass. It shares its PCB layout with the TS808 and TS9, but leaves out all the switching circuitry.
When the pedals are on, the OD808 and OD9 are exactly the same. The only difference is in the bypass.
ST9 /STL / Maxon ST-01
Theses guys all have the same mid boost circuit spliced into the regular TS circuit. The mid boost includes one half of a dual op-amp, and the other half is used for the input buffer. A transistor is then used for the output buffer.
The ST9 has its Mid Boost circuitry in front of the clipping section of the TS circuit. On the STL, its after the clipping section. But the Mid Boost stuff is otherwise identical.
Both the ST9 and STL seem to mix the 808 and 9 output resistor values. They have a 470R series resistor and a 10k shunt resistor. The positions are reversed like in the OD808.
The ST9 has a G100k tone pot, according to Dirk Hendrik’s tracing. The STLs is the typical TS tone pot, G20k, according to the factory schematic.
I have no idea whether the Maxon ST-01 is an STL or ST9, but it seems to be one of the two.
OD9 Pro Plus / TS9B / TS808DX
I’m grouping these together because I don’t know what’s in ’em. The OD9 Pro seems to have some boost circuitry, and it sounds like there’s an internal charge pump. Rumor has it that the TS9B is not a true TS circuit, but I haven’t seen gutshots yet. The TS808DX also seems to have some charge pump stuff going on in it, in addition to boost circuitry.