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Editor''s Note: The information contained in this article is extremely technical, and involves working closely with complex circuits. Please have an experienced technician assist you unless you feel experienced enough to understand the information.
One of the most discussed, and surely the most modded, stompbox circuits ever is the good ol'' Ibanez Tube Screamer 808. Players like Santana and Stevie Ray Vaughan have plugged into a Tube Screamer, and I´m sure that Ibanez will never stop producing it. In addition, many more or less accurate TS clones have appeared on the scene, and it seems that almost every electric guitar player owns such a unit.
Over the years, plenty of TS-related discussion appeared on the Internet, and over time, lot of myths and urban legends were created. When Robert Keeley and Analogman began converting modern TS versions to the original 808 specs and sprucing up the circuit with different, cool modifications, a real boom started, which continues today. Try Googling this subject and I´m sure you will find more webpages than you can read in a month!
Modding Later Ibanez TS Versions
The original Ibanez 808 from the early ''80s is no longer in production, but a reissue is available today. Besides this, Ibanez produced a lot of follow-up versions over the years and all these versions can be modded to original 808 specs. This mod is usually referred to as "the Tubescreamer 808" mod, and is a simple swapping of two resistor values in the output section.
In terms of what resistors are best for this mod, my personal advice is to let your own ears decide what you like best. Some prefer NOS carbon comp resistors because the old 808 boxes used them. I think that it´s the change of the value that matters and really influences the tone, not the material of the resistors, but that is my humble opinion.
Keep in mind that carbon comp resistors are notorious for a high thermical noise factor and high tolerances in value; that´s why I prefer metal film resistors with only 1% tolerance in my own Tube Screamers. You can simply desolder those two resistors and replace them with a socket, so it´s easy to try different resistor materials and to decide what you like best. Check out Small Bear Electronics, where you can get everything you need at a fair price.
Having said all that, here we go for a complete listing of all versions and how to mod them to 808 specs. The number of the resistors are referring to the imprint on the PCB and the values they should be replaced with:
TS5 (Soundtank series): R34 = 100 ohm and R35 = 10k
TS7 (Tonelock series): R55 = 100 ohm and R58 = 10K
TS9 / TS9 DX / TS808 reissue: R15 = 100 ohm and R13 = 10k
Modding the TS10
The TS10 is a very special box and requires a lot more work to convert it, but on the other hand, early TS10 models are often loaded with the magical IC chip from the famous 808 Tubescreamer, the ''80s version of the JRC4558D. Here are what you''ll need to do to mod out your TS10:
- Remove R40 (10k) and run a jumper from the end of the R39 1K resistor furthest from Q6 to the end of C15 nearest Q6
- Remove the Q6 transistor
- Change R21 (470 ohm) connected to the output socket via a 10uF cap to 100 ohm
- Change R22 (100k) to 10k
- Short out R6 and C11
- Remove R17
- The input section before the first transistor is biased to +4.5V through a single 510K resistor. Remove R2 and R3 so one end of the 510K resistor will now not be connected to anything. Now you must connect it to 4.5V. The PCB 4.5v tracks are labeled "4.5v."
The Original 808 IC Chip and Variants
As mentioned above, the original 808 Tubescreamer was loaded with the ''80s version of the JRC4558D IC chip, and is one of the holy tone grails that everyone seems to search after today. A modern version of this IC is still available but some people claim that it''s too different from the old ones. You can find the old original ICs on eBay, but they are very expensive. If you want to convert your Tubescreamer as close as possible to the original specs, then this is the way to go.
A little hint: this IC chip was very common around the early ''80s and was used in a lot of consumer electronic products, like TVs, radios, tape recorders, and so on. If you have the gumption and the time to canabalize old, worn out devices, chances are good that you will find some of these old ICs for free! If you want to learn more about this magical IC, check out Andreas Möller''s webpage.
Some people say that the influence of the IC on the overall tone is not especially significant, but to my ears it really makes a difference, so it''s best to let your own ears decide. Personally, I think one of the best TS mods is to desolder the IC chip and replace it with a high-quality IC socket with gold inserts for the best possible contact.
You can try different ICs to find the tone you want. Here is a list of IC chips I tested; you can also do your own search and try every standard dual op-amp IC you like:
JRC4558D (current production) - classic TS chip, follow-up of the original IC, smoother than the RC4558P
JRC4558DD - high gain version of the classic chip
RC4558P - made by Texas Instruments, sounds warm and soft, but rawer than the current production JRC4558D. Robert Keeley´s first choice, also my favorite IC for Tube Screamers
RC4558 (generic) - no-name clone of the TI RC4558, sounds edgier than the original
RC4559 - high-performance dual opamp, used in many quality audio preamps
LM833N - low noise dual opamp, known to sound good in TS circuits
MC1458 - low noise, soundwise somewhere in between the JRC4558D and the TI RC4558P
TL072 - used in a variety of commercial TS clones
TL072IP - Low noise version of the TL072, more hi-fi sounding
TLC2272 - increased dynamic range, high drive
NE5532AB - audio opamp, low distortion, high slew rate
NE5532AP - audio opamp, very low distortion, high slew rate
Burr Brown 2134 and 2234 - audiophile audio opamps, very clean and transparent
The Tube Screamer on Steroids
To close this article I would like to leave you with a very special TS mod I developed some time ago, called the "Tube Screamer on Steroids" mod. This mod will make your sound really stand out and turn your TS into a roaring beast.
It´s based on the common "asymmetrical clipping" modification that you can find all over the web. The signal clipping in the TS circuit is not done by the IC, but by the two 1N914 clipping diodes, D1 and D2. When you take a look at the circuit drawing, you will notice that both diodes are orientated to exactly opposite sides; that´s what we call a "symmetrical clipping," that is often considered somewhat hard, raw and harsh sounding.
To smooth out the overall tone, a third diode, D3, which is orientated the same way as D1 can be added; that´s what we call an "asymmetrical clipping," and is considered to be smooth and much more natural, tube-sounding. The easiest way to do this mod is to throw in a third 1N914 diode, as most PCBs are prepared for this. If you want to be more flexible, you can wire this third diode on a switch to have the possibility to change from the standard symmetrical to the new asymmetrical clipping mode.
A prime example for this mod can be found on the General Guitar Gadgets webpage; I highly recommend studying this page to get some deeper knowledge about the TS circuit. There you will also find a link to the webpage about the TS technology from R.G. Keen, published on his Geofex webpage and perfect for the advanced DIY builder.
Another field to experiment, which I use, is to use different types of clipping diodes to change the sound. For my "Tube Screamer on Steroids" mod, you need six 1N60 germanium diodes and a standard on/off switch; it doesn´t matter if you use current production or NOS 1N60 diodes. Solder all the diodes in series and connect them to the switch as shown on the included diagram. This way all the connected diodes work as one big D3 diode; the result is marvellous.
Take care while soldering all the diodes together, as germanium diodes don´t like a lot of heat from the soldering iron. I highly recommend using a heat sink and to avoid overheating them with long soldering times. I know people that go so far as to store the diodes in the fridge for some days before soldering them!
When you use the switch now, you will hear a big, impressive and very smooth, tube-like TS tone that really sounds like a TS on steroids. It''s perfect for beefing up every solo line.
Now you might ask why the hell he uses that many diodes in series; here´s the technical background for those who are interested in it.
First of all, it´s important to realize that D1 and D2 are standard 1N914 silicon diodes, while the 1N60 is an old-style germanium diode type. With only one 1N60 diode for D3, you will not hear any change in the sound. From a static point of view, one 1N60 diode raises the effective threshold voltage of the silicon value (approx. 0.55v) only about 0.1v (approx. 20%), which is almost inaudible. In addition, the little germanium value is dominated by the much bigger silicon value, because germanium has a different exponential coefficient compared to silicon.
If you want to have the typical germanium tone, you have to make sure that the D3 germanium diode is dominating the threshold voltage. If you only want the threshold voltage effect, you need a minimum of two 1N60 diodes in series (three is better); if you want the germanium tone, you''ll need approximately six 1N60 diodes in series to cascade enough diodes to significantly dominate the threshold voltage of the silicon diode.
If you want to be even more flexible, you can also use a 6-way rotary switch to cascade the 1N60 diodes step by step; this way you can blend in the germanium tone from hardly noticeable to full throttle. With this background, you can also experiment with different germanium diodes (eg. 1N100, 1N34a, 1N270, etc.) and also other clipping devices like LEDs, transistors and different silicon diodes (eg. 1N4148, 1N4001, 1N5818, etc.) - just do the math and rock away!
I hope you enjoyed this one; until next month, God bless and happy soldering.
Dirk Wacker has been addicted to all kinds of guitars since the age of 5 and is fascinated by anything that has something to do with old Fender guitars and amps. He hates short scales and Telecaster neck pickups, but loves twang. In his spare time he plays country, rockabilly, surf and Nashville styles in several bands, works as a studio musician and writes for several guitar mags. He is also a hardcore DIY guy for guitars, amps and stompboxes and also runs an extensive webpage (singlecoil.com) about these things.