Question regarding Merlin Blencowe's Tube Premp Book- Ch. 14 Topologies Opinions??

[silverfox]

Wrecked OverDrive Concept

Thanks for the submission. Don't take this a sarcasm- I checked out your sch and then saw the others posted on your photo-bucket. Is there a method to the designs or are you just combining schematics? Have you built any of the other designs listed?

I'm in the process of completing a prototyping chassis system (here: http://music-electronics-forum.com/t35423/), and when complete I want to try to merge a Dumble OD circuit with a Train Wreck channel. This would become the Dumble OD circuit. Then I'll try a build of the Dumble 124 to go with it. Basically a Dumble 124 with a Wrecked OD. Both outputs could be run simultaneously and sent to a line out for mixing on a mixer board, then brought back to the power amp in. Looking for more of a metal overdrive to go with the Dumble clean channel.

Is that crazy talk??

Silverfox.

[printer2]

Thanks for the submission. Don't take this a sarcasm- I checked out your sch and then saw the others posted on your photo-bucket. Is there a method to the designs or are you just combining schematics? Have you built any of the other designs listed?

I'm in the process of completing a prototyping chassis system (here: http://music-electronics-forum.com/t35423/), and when complete I want to try to merge a Dumble OD circuit with a Train Wreck channel. This would become the Dumble OD circuit. Then I'll try a build of the Dumble 124 to go with it. Basically a Dumble 124 with a Wrecked OD. Both outputs could be run simultaneously and sent to a line out for mixing on a mixer board, then brought back to the power amp in. Looking for more of a metal overdrive to go with the Dumble clean channel.

Is that crazy talk??

Silverfox.

Some of the ideas I have breadboarded, a couple of amps have done are documented in the pictures. As you found, a lot of schematics where
i have been combining schematics seeing what is common and what would be needed to do to fit them both together. Kind of a progression on my wayward path. Got a little sidetracked with the guitar building but am returning to some of these projects.

[kg]

I don't have extensive experience with this however, the Peavey Road Master I played through prior to donating to scientific purposes seemed to switch very nicely using LDR's. With all due respect, what are your thoughts on that?

Silverfox.

they, like everything else we build with, have compromises.

they have a rather slow on/off characteristic. as i said before, they have quite miserable isolation, ie "on resistance" vs. "off resistance." while not terribly fragile, they're a hell of a lot more prone to deterioration or destruction than say an electromechanical relay. they're expensive. there aren't a lot of different characteristics to choose from. they have low power dissipation ratings.

BUT

they DO switch noiselessly. there is no contact bouce. there is no inductive flyback. the slow(er) transition is plenty fast enough for audio switching, and helps smooth the response and PSRR.

sometimes their use cannot be avoided, and they are the most elegant solution. however, due to the above issues i'll attempt an electromechanical relay first every time (if the circuit allows it... obv. you can't use an electromechanical relay to introduce a simple tremolo circuit for example).

jm2c
ken

[cyclone]

No offense, but I don't think you'll get enough grunt out of that cold clipped stage taking the output off the cathode without rearranging the anode and cathode resistances, then its not a "choppa" as my pal from Rhode Island says. By grunt, I mean voltage gain. Won't sound like a trainwreck for sure. It would also be non inverting unlike the TW stage. Hmmm, wonder how a cathode follower with unequal cathode and anode resistors with the same cumulative resistance but say a larger cathode resistor would work as a slightly less than unity chopper ckt? You'd still need a stage in front of it for voltage gain or a regular chopper and a cathode follower after it. Def. not a trainwreck ckt at that point. Might have potential, dunno. Why is a carrot more orange than an orange? Don't know that either but I like them both)

[Mick Bailey]

they, like everything else we build with, have compromises. they have a rather slow on/off characteristic. as i said before, they have quite miserable isolation, ie "on resistance" vs. "off resistance."

Isolation is the electrical separation between the 'sides' of the device, the LED and LDR, and is typically 2kV The latency between fully on and fully off is transition or rise/decay time.

The on/off resistance varies a lot with devices. The ones I currently use have an on resistance of around 50 Ohms and off resistance of a round 30M Ohms, so the on-off ratio is good enough for most amp applications.
The greater problem in choosing a suitable device is the LDR voltage capability. Many excellent devices in all other respects won't handle the high voltages in tube amps and can only be used for signal switching, or switching 'floating' voltage level changes, where the device only sees the difference between switched voltages and not the voltage to ground.

A power MOSFET would be a better choice for HV switching.

Mesa has used LDR switching for years - the Tremoverb has 29.