Protone - Blasko Bass Overdrive  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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G.Bisson
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Post by G.Bisson »

Protone Blasko Bass Overdrive
Designed for Blasko while touring with Ozzy Osbourne. Produced in limited quantities in 2011. Features a Baxandall tone stack and 2N5457 JFET clipping.
Blasko_BassOverdrive_pcb trace_G.Bisson.jpg
Blasko_BassOverdrive_schem_G.Bisson.png

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NegationOfNegation
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Post by NegationOfNegation »

Hi,
maybe its late for an answer, but two notes are usefull i.m.h.o:

1.) You measured with a voltmeter with an impedance of 1Meg?
So it make sense that behind a bias voltage divider of 1Meg to 1Meg
(e.g. R17 to R18) 1/3 of supply voltage was measured. (In use as
overdrive, that means, if not measured, that means without voltmeter,
it should be 1/2 of supply voltage).

In earlier years, measuring condition had been noted on (service) schematics.

2.) Looks like, there is one connection missed in schematic --
between Q2s gate an the connection between C2 and R6.
If this connection exists, there is an bias voltage divider
on Q2s gate (as well as on Q5s gate and Q7s gate) and
an capacitor between Q2s source and gate -- just like on the
other µ-amps.

Cheers and happy weekend

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G.Bisson
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Post by G.Bisson »

Thanks for another set of eyes to check it.

1. I'll check the specs on my multimeter later.

2. I checked connections to Q2 gate while I had the pedal apart because the schematic doesn't look like a typical mu-amp configuration. Now that I look at the photos again, your assumption appears correct. I'll probe for continuity between R6,C2,Q2 and update the schematic if I can confirm the connection.
Protone_Blasko_BassOverdrive_pcb trace_G.Bisson_markup.jpg

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G.Bisson
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Post by G.Bisson »

1. Confirmed voltmeter impedance as 1M Ohm by creating a voltage divider on a fresh 1.5v AA battery in series with a 1M Ohm 1/4W 1% resistor. Battery voltage measured at 1.546v, when in series with resistor it measured 0.773v.

2. Confirmed connection between R6 and Q2 gate by probing for continuity.

Revised C2 and R6 on the schematic diagram. Also added a little more description to capacitors and cleaned up some text.
Protone_Blasko_BassOverdrive_schem_REV1_G.Bisson.png

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