Is this possible? I was going to put together one of Marks tube preamps into one of his low power tube power amp modules (https://frogpedals.com/). Then I got to thinking. Maybe I could also put in one of the little 10 Minute chipamps in there as well (10 Min Amp - AUD $7.00 : diyguitarpedals.com.au, A shop for all diy guitar pedal enthusiasts!). Then I would have a .75-2.5W tube amp and a 7-8W chip amp for testing my pedal builds and such.
Only problem is I'm not sure if it will work. I was going to run the output of the preamp into a switch to choose between the tube/SS sections each with a separate master volume or I could put a switch between the outputs of the power sections and put a dummy load on the tube OPT when switched to the SS side.
Any ideas?
Only problem is I'm not sure if it will work. I was going to run the output of the preamp into a switch to choose between the tube/SS sections each with a separate master volume or I could put a switch between the outputs of the power sections and put a dummy load on the tube OPT when switched to the SS side.
Any ideas?
For the 10 Min Amp Paul states:
"Adding a boost circuit and EQ / Tone Control to the front of the amp increases its versatility and volume output significantly and is a recommended addition to your amps input signal chain. "
That is essentially what the "preamp" that Mark designs does. As well as adding clipping options for dirt.
I know the STA-540 chip used in the Orange micro terror is a Class AB same as the TDA7266M in the 10 minute amp so I'm hoping it will work.
What would I measure to see if there might be an issue?
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If no schematics, just check operationally. With multiple stages, check for clipping and bass loss
immediately after each stage, both with and without the loading effects of the next stage.
Most tone circuits are passive and lose a lot of signal level, so the previous stage may be forced into clipping.
The power amp itself should work, it's the gain structure and interface that may cause problems.
immediately after each stage, both with and without the loading effects of the next stage.
Most tone circuits are passive and lose a lot of signal level, so the previous stage may be forced into clipping.
The power amp itself should work, it's the gain structure and interface that may cause problems.
The 10 Min amp has a low impedance (10K) input, so yes, it would need at minimum some kind of buffering between the guitar and the power stage. If you're planning on using the Alembic style tube preamp, it has lots of signal but relatively high output impedance, so probably need to attenuate the signal and run it though a buffer circuit before hitting the power amp stage. Cheers
Thanks. That's helpful. I should have all the PCB's here shortly so hopefully I can cobble it together this summer and go from there.
I designed a couple of tube/chipamp amps a few years back.
One used 12au7 front end in inverting config.
The 2nd one used 12au7 in cathode follower config.
Sounded very good.
I tried to reduce gain of chip amp but it just oscillated.
Spec says you need to have min gain on TDA7294.
So put 1000pf across chip amp inputs and that fixed it.
I used +/- 35volts for chipamp and also for valve stage.
One used 12au7 front end in inverting config.
The 2nd one used 12au7 in cathode follower config.
Sounded very good.
I tried to reduce gain of chip amp but it just oscillated.
Spec says you need to have min gain on TDA7294.
So put 1000pf across chip amp inputs and that fixed it.
I used +/- 35volts for chipamp and also for valve stage.
I am wondering if it may be a useful approach to take a portion of the signal output of the tube power amp and feed that to the SS power amp. So instead of switching between tube or SS power, you either run the tube amp output through the speaker, or it goes through a power load resistor and voltage divider to send that to the SS amp. The point is to get the whole tube amp sound re-amped at higher wattage of the SS amp.
Possibly. Definitely something I hadn't really thought about but makes sense. First I'll have to see if the preamp will push enough current to drive the tube power amp. If not I'll need to get a separate PS board for the tube amp. This is all really just an experiment. IF it doesn't work I know I can build the pre, tube power, and SS power into their own little pedal formats as they were designed.