Tube Screamer on a Breadboard

I think there is no need for a long introduction for Tube Screamer pedal. It’s been around since 70’s and featured on many-many-many guitar player pedalboards. While maybe identified a lot with blues, it is used in all possible music genres – blues, rock, grunge, heavy metal, trash metal, metal core … I mean, all sorts of metal 😁 … and the list goes on.

A pedal copied in one way or another by probably every major pedal manufacturer, and nearly all boutique ones.

Here I cover the basic schematic for the circuit, cover some interesting details, there’s even SPICE simulation if you want to do some analysis yourself. I’ll move on to put the effect on a breadboard and try it out. I also added bill of material (of components that I used for breadboarding).

In this post I do cover only TS808 version of the pedal, but I plan on covering lots more. I’ll be looking into derivatives as well – like Boss’ OD-1 and SD-1, MXR Zakk Wylde and GT-OD pedals for example.

They all have nearly identical circuit topology, but they definitely do not sound the same. Having said that, because they have very similar topology, with rather small tweaks you can get the same circuit to sound like either of them. Anyway, let me get started 😊.

Schematic

I got the basic schematic from Electrosmash and geofex, here’s my version of it:

Op-Amp Difference

I should probably note that this is not 100% TS808 vintage schematic, I did adapt it a bit to use components I had available. The most notable difference is the op-am. I used NE5532 which is a great low-noise BJT op-amp.

The original, of course, uses “magical” JRC4558/RC4558, which is not really magical at all – very similar to μA741 op-amp (LM741). The magic is in the circuit itself and that’s what makes Tube Screamer what it is, and that’s why the topology itself was copied so much.

The likelihood of the pedal sounding different due to an op-amp is smaller than, say component tolerances. Some caps have up to 20% tolerance, and even 10% tolerance in C3 above makes the quoted 720Hz cut-off frequency really be anything between 650Hz and 800Hz. That is probably a difference you might be able hear at far ends of the tolerance.

Anyway, long way of saying, there should be no difference in sound. But I guess I’ll have to try comparing the actual pedal and this version at some stage 😉.

Transistor Differences

I used BC549C transistors instead of 2SC1815 (there were different ones used throughout the years). This should not make any difference either, because the transistors are used as unity gain buffers.

True Bypass Version

Oh, I should probably mention that this is a true bypass version. The original pedal uses JFETs for switching. The switching system probably constitutes half of all the components used. Doing true bypass version gets rid of lots of parts.

Interesting Bits

For in-depth analysis go to Electrosmash, I can’t do anything better 😊. I’ll just point out some interesting things about the circuit.

Here are the sections of the circuit – and I breadboarded the effect section by section in the video below:

Power supply is self explanatory, but more interesting are input and output buffer. While totally transparent unity buffers, they are helping with input impedance and output driving. Also, they are needed for the JFET switching to isolate the circuitry from whatever comes before and after the effect.

This means that, even when the effect is disengaged, the guitar signal goes through the buffers. This also means that you cannot run the original pedal without power supply – even when not using it.

When using true bypass, with slight modifications to the circuit, we could get rid of input and output buffers, thus greatly simplifying the circuit. I’ll do that in one of the next posts, so stay tuned.

SPICE

Here’s a handy SPICE circuit diagram you can play with:

What is probably interesting to see is how tone pot taper affects the tone control. Now, having linear taper (B) or G taper (B4) makes no difference to the tone. The difference is in the level of control you get with them. Look at these frequency responses of the two tapers:

You can notice that at the maximum and the minimum values – the curves are identical, but the linear curves are totally squashed (each curve corresponds to 10% knob turn).

Here’s how various B tapers look like in Bourns’ datasheet:

Highlighted in green are 4B and B tapers. The way the tone section is designed, pretty much requires 4B taper or similar to give decent control over tone.

Breadboard Diagram

Let me prepare a breadboard diagram for this. As usual, I used DIY Layout Creator. Here’s a possible layout:

If you want to experiment yourself with the layout, here’s the DIY file I used:

Bill of Material

Here’s the list of components I used for breadboarding:

Designators	Component	Notes
	Breadboard	Any breadboard will do, I used full size breadboard. You probably don’t want anything smaller than that.
	Jumpers and wires	As many as you need. I got some online, but 24 AWG solid core wire will do just fine. I used some crocodile clips for pots so I didn’t need to solder anything.
	9V battery	I used 9V battery snap with Dupont wire.
	DPDT push button	I used ALPS SPPH410100 latching push button for bypassing the effect – totally optional.
IN	Switchcraft 12B	In – stereo jack (mono will do too)
OUT	Switchcraft J111	Out mono Jack
RV1	Alpha 16mm 500K log pot	Any 500K log pot will do for Overdrive
RV2	Alpha 16mm 20K-tone pot	I actually used 25K linear pot … that’s what I had, that’s what I used 😊
RV3	Alpha 16mm 100K log pot	Again, any 100K log pot will do for Level control
C1	22n (0.022uF)	Metal film PET cap (original uses 20nF, no difference to the sound)
C2, C7	1 uF	Metal film PET cap (Electrolytic will do fine here, just mind the polarity)
C3	47nF (0.047uF)	Metal film PET cap
C4	47pF	Ceramic C0G (NP0) – (original uses 51pF – within tolerance quite frankly)
C5, C6	220nF (0.22uF)	Metal film PET cap
C8	100nF (0.1uF)	Metal film PET cap
C9	10uF	Electrolytic cap 25V
C10	100uF	Electrolytic cap 25V
C11	47uF	Electrolytic cap 25V
C12	100n (0.1uF)	Ceramic X7R
D1, D2	1N4148	Small signal diode for clipping
D3	1n4002	Reverse polarity protection, 1N4001, 1N4007 and likes will do, I didn’t bother using it for breadboarding
R1, R7, R9, R11	1K	1% 250mW metal film
R2, R12	470K	Original used 510K, no difference to the sound, used for biasing
R3, R5, R10, R13, R15, R16, R17	10K
R4	4.7K
R6	51K
R8	220 ohm
R14	100 ohm
Q1, Q2	BC549C	Original used 2SC1815
U1	NE5532	Original used JRC4558/RC4558

Breadboarding It

Let’s do the actual breadboarding and hear what the effect sounds like.

I think the pedal sounds great. There’s a lot of noise due to high gain of the pedal and lots of wires and this being a breadboard. But if you get past that, it actually sounds quite good.

And, funnily enough, I tried convincing everybody earlier that the op-amp does not matter. Well, don’t use LM358 … it sounds horrible in this circuit. NE5532 and TL072 sound pretty much the same though. Have a look and let me know what you think.