(02-21-2024, 04:14 PM)coco Wrote: Looking to share build experiences. I am about to start one and connect it to a low watt amp.
I built the D-PRE and connected it to a 6CM6 small pentode 9 pin power tube, single ended. I designed a power supply to drive both. Runs at about 250 V B+
As built it, I measured every component before installing onto the board so I know the board was built correctly.
I added a Master Volume after the channels are relay switched so essentially there are three level controls. I didn't use the tiny PCBs for volume control and jacks. At full power getting about 5 watts rms which is about what I was after.
It is housed in an 11” X 4” X 2.5” chassis so very compact.
I have built and heard many full size Dumble #124 style amps so I can make some comparisons.
It drives the 6CM6 pentode power tube very well.
There is decent cleans when using the clean channel
It is decently touch sensitive.
The Mid boost and Jazz/Rock do what they’re intended to do.
The Treble and Mid controls are extremely subtle.
The Mid control is hardly noticeable. Such that I confirmed it was working using my o’scope.
The Early Drive (AKA Trim) does as expected but it goes into OD very quickly. Not much range at all. Same with the Late drive (AKA Level) , goes into OD quickly, not much range.
Between the Early and Late OD Drive though, you can find a nice saturated OD that resembles a Dumble.
Having an OD level and Master Volume allows the player to adjust the OD to match the clean channel which is very useful.
I used one relay for channel switching and for muting the second OD triode. Muting the 1st OD triode is suggested but space was limited and I didn't want the added complexity of a second relay.
KOC was helpful in a couple of emails. Some parts were missing and he confirmed my substitutions.
The PCB is small and parts are very small. Service and mods will be challenging.
This is not kit for a beginner. There is minimal and only basic documentation.
FWIW, if I was designing this, the board would be larger, less compact, use 1/2 W metal film res. and fewer radial caps. I would probably try to put the pots on board.
This was an experiment to see how close I could get to my 6L6 #124 at much lower volume levels. I will continue to work on the project (Fx loop) and also see what other players think of it. There is still some work to do but it was a decent start.