(Image courtesy of the Tube Screamer Technology Page with red stuff added by me)
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Tube Screamer pedals all have this transistor circuit used as an output stage:
(Image courtesy of the
Tube Screamer Technology Page
with red stuff added by me)
The most common Tube Screamer mod is to change the values of the resistors higlighted in red.
The original TS-808 had:
Rb = 100 ohms
Rc = 10K ohms
Later versions of the Tube Screamer (including my TS7) have:
Rb =
470 ohms
Rc = 100K ohms
On the TS7, the resistors referred to above as Rb and Rc are designated R55 and R58, respectively:
The prevailing wisdom is that changing the resistors on a newer Tube Screamer to the values in the older TS808 (often referred to as an "808 mod") gives a better sound.
For the "non-808-modded" recordings, I had carbon film resistors in the output circuit with
these measured values:
Rb = R55 = 468 ohms
Rc = R58 = 99.2K ohms
I had done
some experimenting with these earlier, so they were not the actual resistors that came with the TS7. But they
were similar carbon film resistors with the values shown above.
For the "808-modded" portion of the test, I changed the two output resistors to carbon composition resistors
(as opposed to carbon film) with the 808's resistor values, since this is how it's usually done. The new resistors had
these measured values:
Rb = R55 = 102.1 ohms
Rc = R58 = 10.00K ohms.
In each section below, made with Test Rig 1, one of the recordings was done with the 808-modded TS7 and one was done with the non-808 modded TS7. They have been mixed randomly. Select the recording you think has the 808 modification.
| Section 1: Blues Riff | Recording A (2889K wav) | Recording B (2689K wav) |
| Section 2: Long Power Chord | Recording A (1868K wav) | Recording B (1843K wav) |
| Section 3: Short Power Chord | Recording A (243K wav) | Recording B (229K wav) |
| Section 4: Lead with Dynamics | Recording A (2896K wav) | Recording B (2894K wav) |
| Section 5: Long Single Note | Recording A (935K wav) | Recording B (962K wav) |
| Section 6: Short Single Note | Recording A (173K wav) | Recording B (173K wav) |
| Section 7: Long Fourth | Recording A (1201K wav) | Recording B (1239K wav) |
| Section 8: Short Fourth | Recording A (136K wav) | Recording B (130K wav) |
The average score so far is 7/8 correct.
