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Increasing power supply to ROG's Umble - any harm?

Started by Aleksandar, May 02, 2018, 10:52:05 AM

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Aleksandar

After awhile, I am thinking about building a new solid state amp, that would suit my needs. The reason - my beloved tube amp is oh so gentle, and go into rattling snake/tamburine mod after a year or so! So, there are three paths I'm considering:

1. Building the "Blackface" preamp from RED circuits and  making its power supply switchable from 30 to 12 volts.

2. Doing the same thing with ROG's "Umble" preamp.

3. Maybe even doing them both as switchable channels.

My questions:

- What are your opinions on these circuit designs?

-  Can I increase the Umble's power supply, without doing any harm. Also, I read that the circuit is a bit noisy, is there a way to fix that?

Loudthud

The first preamp was discussed in these threads:

https://www.ssguitar.com/index.php?topic=304.0

https://www.ssguitar.com/index.php?topic=3373.0

It will run on higher Voltage if you get the right JFETs. You want an Idss of 10mA or less. I highly suggest that you install sockets for your JFETs so you can swap them around until you find some that work. The same generally applies to the second circuit but you may need to swap out some of the trim pots to get everything working.

Aleksandar

#2
Thank you! One more question, not exactly related to the preamp section of the forum, but yet related to my amp building plans. What do you think of this design?

http://redcircuits.com/Page123.htm

It's really simple, I hope its not too simple. But it's a single supply and  that would suit most the preamps in the previous posts. Also what exactly is the purpose of the bipolar transistor there, and can it be replaced with a fet or mosfet transistor?

Loudthud

Quote from: Aleksandar on May 05, 2018, 05:50:52 PM
What do you think of this design?

http://redcircuits.com/Page123.htm

That circuit has some problems.
1) It's easy to smoke the FETs if you adjust the trimmers wrong. Slight circuit revision would fix it.
2) The reason for the regulated power supply was probably that the circuit Hummed without it.
3) The LM317T in the power supply is a 40V part in a 50V circuit. It could fail and cause the circuit to hum.

Quote from: Aleksandar on May 05, 2018, 05:50:52 PM
It's really simple, I hope its not too simple. But it's a single supply and  that would suit most the preamps in the previous posts.

Single rail amps get a bad rap here. I think they sound more like tube guitar amps.

Quote from: Aleksandar on May 05, 2018, 05:50:52 PM
Also what exactly is the purpose of the bipolar transistor there, and can it be replaced with a fet or mosfet transistor?

Yes it can be replaced by a MOSFET. Some adjustments to the circuit will be required. See the circuit I posted in this thread:
https://www.ssguitar.com/index.php?topic=3747.0