Dumble-ish preamp project

[dcribbs1412]

Nicely Done!
Great sounding amp and very nice playing Rootz.
Appreciate sharing your findings and info.

D

[10thTx]

Thanks for sharing your sound clips!! You are a remarkable guitarist and that's one great sounding amp design! Bravo.

With respect, 10thtx

[donvan]

Nice job on your amp Rootz! I like the idea of being able to switch the HRM in and out.
I see that to disable the lnfb in the 2nd stage you have a switch that takes C11 and R38 to ground. I've seen others disable lnfb by using a switch to open the lnfb circuit. Are their advantages to doing it one way or the other?

[rootz]

Thanks guys! I should do a better demo with a proper mic. Tried it today with a SM57, Audient ID14, and Logic Pro. Didn't get the sound quality I want. I need to learn more about home recording.

Anyways, I feel I can get really close to the non-HRM sound with the tone stack switched in, just less polite than non-HRM. The low value of snubbers on the OD triodes when compared to a #124 made me suspect the amp would be bright, or at least brighter than #124. It isn't at all. Very smooth OD sounds here.

I play this preamp mostly with the LNFB on V1b switched off, but swap to LNFB occasionally. There is a reason for doing it this way, switching the cap and 22meg resistor to ground. At point where the switch is there is no DC due to the 47n cap being on the side of the anode. So, only AC switching and any small toggle switch would be good enough. Also, the 47n cap always has a path to ground. This way I essentially switch between ground potential at the grid and real ground. That is important, because rapidly discharging caps would probably introduce a pop (or at least that is what I'm trying to prevent). I guarantee this solution does not pop! The only disadvantage I can think of is that tis solution marginally loads the circuit in two places. Probably nothing you would ever hear as the loading is very small due to the 22meg resistors.

[donvan]

... there is no DC due to the 47n cap being on the side of the anode. So, only AC switching and any small toggle switch would be good enough. Also, the 47n cap always has a path to ground. This way I essentially switch between ground potential at the grid and real ground. That is important, because rapidly discharging caps would probably introduce a pop (or at least that is what I'm trying to prevent).

That makes perfect sense. Thanks for answering my question!

[rootz]

A quick follow up.

Preamps are fun, because they provide me with new possibilities. I use Logic Pro for recording. Never liked any of the standard amp models in that software. They always sound fake to my ears. Now I can plugin to the preamp and wire that directly to Logic Pro X via my Audient ID14. In Logic I just have to use a neutral amp and cab sim. I prefer to use the IR's of Ownhammer, but lost them all in a computer crash. Luckily Logic has the Brown 4x12, which sounds like a bunch of G12H's or 65's. Some late night takes, a bit of EQ and lots of reverb later, this is the result.
https://soundcloud.com/user-433489378/d ... ogic-pro-x

[rootz]

Not very sure how I recorded this. Definitely Sm57 on Neo creamback. Sounds like the preamp was in HRM mode.

https://soundcloud.com/user-433489378/48khz-test

[10thTx]

Really incredibly great playing! Tone on the Logic Pro recording is superb, IMO.

Thanks for sharing your success and talent. With respect, 10thtx

[Guy77]

Sounds great ! Thanks for sharing your projects here.

Cheers

Guy