Early 80s Distortion

Manfred · Post by **Manfred** » 30 Nov 2012, 13:12

I found this construction guidance in one of my old folders.
As a far as I can remember the guidance was puplished in the early 80s on a German electronic journal.
I noted down following information.
I was named Tube-Box.
The circuit was developded by trial and error.
Therefor the distortion output fed in a "Roland Jazz Chorus 60" amplifier,
the sound have been compared with a "Mesa Boggie Mark II + 12 Electro-Voice" speaker combo amplifier.
The parts have been changed until there was no more audible difference.
The size of the PCB is 2,5" by 2,125"

Manfred · Post by **Manfred** » 01 Dec 2012, 07:08

Sorry,
the is a mistake in the wiring layout,
input and output labeling are interchanged.
Here the corrected layout.

roseblood11 · Post by **roseblood11** » 01 Dec 2012, 09:51

Doesn:t the 1n in the feedback loop kill a lot of treble?
On the other hand it might work quite well with a Jazz Chorus...

Manfred · Post by **Manfred** » 01 Dec 2012, 22:58

Doesn:t the 1n in the feedback loop kill a lot of treble?

I built this project in 1986 as point to point wiring on a perfored board for testing.
As a far as I can remember the "Tube Box" sounds god.
Unfortunately, the device is not available anymore, so I cannot test it again.

mictester · Post by **mictester** » 02 Dec 2012, 03:05

The maximum output from this is going to be about 0.2V p-p, because of the germanium diodes to ground. This is going to be "quiet" compared to many effects these days.

okgb · Post by **okgb** » 02 Dec 2012, 04:48

Can we say it predates " fuller's of myself " pedals with the two sets of diodes ?
curious , of the mesa mark series , the IIC+ 's do sound better than the others , a nicer grind
I 'll put this in my que to try , thanks

Manfred · Post by **Manfred** » 02 Dec 2012, 07:15

The maximum output from this is going to be about 0.2V p-p, because of the germanium diodes to ground. This is going to be "quiet" compared to many effects these days.

Add a common Buffer with gain for more output.

On the other hand, this is a distortion unit, it generates the desired distortion sound in itself.
So it is not necessary to feed in the tube amplifier to generating the overdrive sound as a overdrive pedal do.
The tube amplifier could remain in the clean range, for this the 0.2 V p-p is sufficiently.

HENK · Post by **HENK** » 02 Dec 2012, 10:51

I build One in the Eightees;
It`s from ELEKTOR.
Nice sounding with a lot sustain.

tube-exorcist · Post by **tube-exorcist** » 02 Dec 2012, 12:30

HENK wrote: It`s from ELEKTOR.

Wrong - this is from ELRAD, September 1983/ETI (Electronics Today International) by Christian Persson.

HENK · Post by **HENK** » 02 Dec 2012, 14:32

tube-exorcist wrote:
HENK wrote: It`s from ELEKTOR.
Wrong - this is from ELRAD, September 1983/ETI (Electronics Today International) by Christian Persson.

Right...
long time ago..

Manfred · Post by **Manfred** » 05 Dec 2012, 05:48

I created a SprintLayout-6.0 project for the TubeBox.
If anybody might be interested in that SprintLayout file, give me a PM, then I will send it.

Manfred · Post by **Manfred** » 08 Dec 2012, 07:19

Now as stripeboard too.

Manfred · Post by **Manfred** » 27 Dec 2012, 23:25

The PCB from this kit can use to build the Tube Box with little mods.
http://www.musikding.de/Kits/Musikding- ... :2514.html
The PCB is availabel without kit too.
http://www.musikding.de/Circuit-boards/ ... ::602.html

jymaze · Post by **jymaze** » 29 Dec 2012, 15:02

The practical threshold of germanium diodes is more about 0.3V (starting at 0.2, but soft knee), therefore the output signal should be about 0.6 p-p (not 0.2 p-p as stated above).

Therefore, it is probably going to be about the same volume as bypass, or a little more even (unless you have high output pickups or some active electronics with gain).

mictester · Post by **mictester** » 29 Dec 2012, 22:43

jymaze wrote:The practical threshold of germanium diodes is more about 0.3V (starting at 0.2, but soft knee), therefore the output signal should be about 0.6 p-p (not 0.2 p-p as stated above).

You're quite wrong. Germanium diodes start to conduct at about 0.18V at room temperature, and fully conduct at 0.22V. There are two of them wired in anti-parallel in this circuit, so will clamp the signal at slightly over 0.2V p-p. In modern terms, this is quite a low output level.

jymaze · Post by **jymaze** » 30 Dec 2012, 14:35

Look at the curve under here for 1N34, it even goes way beyond 0.4V for higher current (to be expected with clipping to ground with a modest resistor of 3.3k before it). It is not only about the threshold, but what is after it too (the knee, the asymptotic value, etc...). Actually, the asymptote is more relevant in a lot of cases since there will be more than a mA conducted to ground from the opamp having its output clipping at the rails. You can note that a 1N914 have a very sharp knee to an almost vertical asymptote (so threshold and asymptote are close together), contrary to a 1N34 which start early and takes a while to reach the asymptote (soft knee):

: Diodes.jpg (32.52 KiB) Viewed 3116 times

In practice, a germanium diode will have a voltage drop somewhere between 0.2 and 0.4 volts usually, depending on the current flow.

Also, whatever you may believe the threshold is, the peak-to-peak will be twice the threshold/asymptotic value since there is a positive and a negative part to the wave, and that is not really debatable!

b-spot · Post by **b-spot** » 10 Jan 2013, 01:22

Can you guys help me? This is my first attempt at building a pedal. I've done everything on the stripeboard, but do not know what connects to IN, G2, 9V, G1, V3 and 0V.
I'm also using 1N4148T's in place of all four diodes and a 100nf in place of C3. Will this still function?

Any help would be appreciated, thank you.

jymaze · Post by **jymaze** » 10 Jan 2013, 13:05

Hello,

"IN" is where the signal gets in (input jack)

"OUT" is where the signal gets out (output jack)

"OV" is the negative pole of the battery/power supply while 9V is the positive pole

G1, G2, V3 refer to the lugs of the gain pot and volume pot.

You can use all 1N4148 but the sound will be different compared to using germanium diodes to clip (less distortion and compression).

100nF for C3 will work, but it may be too dark of a sound so sticking to a lower value should be better.

b-spot · Post by **b-spot** » 10 Jan 2013, 14:26

Forgive me if I'm missing something obvious, but I am still unsure where to connect the grounds to and where to connect the output to. I am not using a switch at this moment, so please remove it from the equation. Thanks again.

jymaze · Post by **jymaze** » 10 Jan 2013, 15:46

In this circuit, ground and 0V are the same, tied together.

I think you should check these articles, you need to understand things better or you are heading for a failure here:

http://www.generalguitargadgets.com/tech-pages

We all started somewhere, it is normal to be a little lost at first if you don't know much about electronics.