Rangemaster voltage

[Bosco Birdswood]

Hi guys, I had a BYOC Overdrive 2 kicking about whose boost section I decided to mod to be a Rangemaster clone using the BYOC Germanium Boost schematic as a reference.

It essentially works but there's a fair amount of hiss. I wanted to check the bias as per the instructions I've found elsewhere online, but while these seem to have the same schematic the collector bias voltages they talk about are in negative voltages, whereas mine are positive. I read this is to do with the Rangemaster being negative ground, but I can see no difference in the schematics regarding electrolytic orientation etc. Any insight here would be great. Am I ok with my positive collector voltage? I'm using an OC44.

Secondly, in order to get the voltage up to 7v I have to significantly reduce the 3k6 resistor's value - the 100k trimmer doesn't give me enough range. I've read that this indicates that the OC44 is too leaky or too low Gain. Is there any way to corroborate this?

Sorry for the lack of diagrams- I'm on my phone


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[alfafalfa]

It essentially works but there's a fair amount of hiss.

If it sounds like the sea, you have bad transistor, just try to get a better one.
I had the same experience.

Good luck.

[Bosco Birdswood]

Here's the OD2 schematic pre boost modification

http://byocelectronics.com/od2schematic.pdf

And here's The Rangemaster clone circuit

http://byocelectronics.com/germaniumboostschematic.pdf

[tonyharker]

OC44 is PNP and needs NEGATIVE collector voltage!

[duck_arse]

Code Select Expand


[img]http://byocelectronics.com/od2schematic.pdf[/img]
[img]http://byocelectronics.com/germaniumboostschematic.pdf[/img]


bosco - you can't link to pdf's as images. you would need to just hyperlink to them, they don't embed in the page, if that's the right terminology.

[anotherjim]

Can you get an NPN Ge transistor? That would be a far easier option that putting a positive ground circuit in a negative ground box.

This is an often used NPN circuit. The Ge diode is optional, can offset misbehaviour of a leaky transistor.

Positive ground circuits can, and often are, drawn the same way up as negative ground. They are usually battery powered and if you follow the wiring to the battery you can see the difference. But the electro caps should have polarity flipped if they connect to power or ground.


Note that simple transistor circuits can seem to pass some signal with power reverse (or off altogether) - Unfortunately, it doesn't mean they perform as they should.

[Electric Warrior]

OC44 is PNP and needs NEGATIVE collector voltage!

It's more complicated than that. The rest of the pedal is negative ground, so just wiring it up positive ground using the same power supply is not an option.
I guess using an NPN germanium is the easiest solution to the problem.

[Bosco Birdswood]

Can you get an NPN Ge transistor? That would be a far easier option that putting a positive ground circuit in a negative ground box.

This is an often used NPN circuit. The Ge diode is optional, can offset misbehaviour of a leaky transistor.

Positive ground circuits can, and often are, drawn the same way up as negative ground. They are usually battery powered and if you follow the wiring to the battery you can see the difference. But the electro caps should have polarity flipped if they connect to power or ground.


Note that simple transistor circuits can seem to pass some signal with power reverse (or off altogether) - Unfortunately, it doesn't mean they perform as they should.

OK, this is starting to make sense based on your comments and a little clarification on positive ground circuits. What BYOC have done is flipped the circuit on its head so that what they're labelling as V+ in their diagram (link now added above in place of my failed image insert) is in fact technically ground, and what they're labelling as ground is actually -9v (relative to ground). I was using the chassis as my ground point to measure collector Voltage whereas I should have been using V+ as my ground reference I guess. Am I right in saying this?

[anotherjim]

Is this the BYOC scheme?

They have flipped it upside down. That is how you would have to do a PNP with negative ground.
Should work.

A positive ground PNP collector voltage would be measured between collector and ground. To keep things things similar, the BYOC schemes way, would be to measure between collector and +V.

I find the bias trimmers best setting is checked by ear. Tweak for 4.5v on collector (don't matter what you use for ground, 4.5 is half supply either way. Then slowly adjust while playing through it into a clean amp. The sweet spot is where it chimes best.

[Bosco Birdswood]

Yeah that's the one.


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