Throbak Overdrive Boost Schematic  [traced]

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Re: Throbak Overdrive Boost Schematic

Postby bc108 » 17 Aug 2017, 16:13

Anyone have the pcb layout, eagle files, etc. for this one?
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Re: Throbak Overdrive Boost Schematic

Postby crazyhendrix » 23 Aug 2017, 16:18


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Re: Throbak Overdrive Boost Schematic

Postby Manfred » 21 Sep 2017, 19:41

I am astonished that the resistor which is connected to the bass potentiometer taper is 39 Kiloohms at all Colorsound Overdriver schematics.
In the Throbak Overdrive Boost schematic above the value appears with 3.9 Kiloohms.
It is possible that there is reading error occurs while tracing?
Which value is applied at the original Throbak circuit?
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Re: Throbak Overdrive Boost Schematic

Postby Manfred » 01 Oct 2017, 20:35

I bought a 2N404A (Texas Instruments) and made some curve traces using the PEAK Atlas DAC75 Pro.

The base-collector diode trace which is applied in the circuit.
2N404A_Base-Collector-Junktion.jpg


You can find more traces in the PDF file which you can download:
2N404A data.pdf
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Re: Throbak Overdrive Boost Schematic

Postby Manfred » 02 Oct 2017, 01:37

I traced a lot of different Germanium PNP transitors types I own and found only two types as substitution for the 2N404A applied as collector-base diode,
namely AF105 and TFK306.

2n404A_comparison.jpg
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Re: Throbak Overdrive Boost Schematic

Postby Manfred » 02 Oct 2017, 11:04

I forgot to trace the OC44 Transistor, the trace is almost identical to the 2N404A curve.
I traced some Schottky Diodes too and found the BAT48 with the suitable knee voltage,
but the gradient of the curve was too steep.
Therefor, I wired a 8.2 Ohms resitor in series with, to to achieve the same forward resistance as with the transistor curve.
The curves overlap is quite good, so that the serial circuit could be a good suited approach.

2n404A_comparison_2.jpg
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Re: Throbak Overdrive Boost Schematic

Postby Manfred » 02 Oct 2017, 21:20

I traced some Schottky Diodes too and found the BAT48 with the suitable knee voltage,
but the gradient of the curve was too steep.
Therefor, I wired a 8.2 Ohms resitor in series with, to to achieve the same forward resistance as with the transistor curve.
The curves overlap is quite good, so that the serial circuit could be a good suited approach.


In the clipping circuity of the Throbak Overdrive Boost the 8.2 resistor can be omitted,
because the output resistance of the of the feeding Emitter circuit is much higher.
Therefore, in this case, the BAT48 could substitute the 2N404A CB-diode.
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Re: Throbak Overdrive Boost Schematic

Postby Manfred » 09 Oct 2017, 07:37

I made some test by means of an oscillographed measurement of the clipping curves.
The results confirmed the assumption taken,
the BAT48 could substitute the Collector-Base-Diode of the 2N404A.
The clipping shapes are very similar, the 8.2 Ohms resistor has no influence on.
The amplitude is a little higher when using the BAT48, but the clipping curve shape is very similar.
In these cases there will be negligible differences between the clipping curves.
Therefore, in my opinion, the BAT48 is a very good substitute for the 2N404A in this application.

Test circuits:
ClippingDiodesTestCircuits.JPG



Clipping curves oscillograms:
ClippingDiodesTests.JPG
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