Brown Dual Pre with Vibro

Hi

Been working for several weeks on a great project - a 2u box  :

first    channel of brown fender super      preamp + harmonic vibrato and an additional gain stage
second channel of brown fender bassman preamp

each with a white cathode follower line amp output.

Edcor power traffo and 15K:600 op traffos.

Really an interesting journey, from the 68K input resistors to the tone stack to the
2.5 tube vibrato to the la2a output stages.

I have been trying different stuff out - learning and relearning the basics, but especially
playing, listening and watching the analyser ... all thru a Motu 2408MkII to old EL84 pp hifi amp
and cheapish but OK 3way hifi speakers.

I have to say - for a 48 year old design, the sound is simply amazing.

The harmonic trem is outstanding.

Enough good to sustain several weeks of tweaking and learning the fender brown basics first hand.

I plan to use it with 2 chns of sta-level compression and effects pedals.

The experience has made me feel stupid, smart and lucky!

Man it's good to be alive and diy!

Put some pics up shortly.

So happy 

some pics







I used bits and pieces I had lying around and a cheap rack.

The bassman channel is from the fender/marshall (jtm45) with an la2a amp added

The vibrotwin is from the fender brown super/twin, the one with the tapped treble pot
in the tone stack and the 2.5 tube "harmonic vibrato", again with the la2a amp section added
and some switching.

I wanted to use a tube rectifier and choke and all that, even tho it's not needed.

I use it as a clean channel and an effects channel by bridging the inputs and taking the
outputs to a mixer.

Just have to complete the gain staging in the vibro twin and button it up
(clean up the B+ wiring and resistors)

Pretty cheap to do and absolutely sounds great. Noise is pretty reasonable
at typical usage setup for 22dB overall gain with -68dBu noise floor.

I really wanted to see how quiet a hastily wired box with lots of interconnects
and unshielded edcor traffos would be with a decent sized edcor power traffo
(75mA 300-0-300V, 3A 6.3V, 2.5A 5V). It uses about 45mA of HV all up.

I was pleasantly surprised. I imagine better layout and wiring would drop
that a couple of dB, but perfectly fine as it is.

PSU decoupling was very important due to the vibro oscillator - hence all the B+
wires so I could try out a bunch of schemes. Still could benefit with the HPF
from the voxac30 tacked to output of vibro to reduce the oscillator punching
thru into audio.

Surprisingly stable grounding - moving grounds around made virtually no
improvement or detriment. Noise optimising was all about PSU decoupling.

I really love using eyelet board and wires.

Next stop - a dual sta-gates style limiter to go with it

Thanks for checking it out!

a little busy but looks good
and if it gets you to play more
than Success !  , nice work

Gorgeous work! I will I had the skills to do something like this.

Thanks for the peek at the insides.