Badger rack preamp

[fred.violleau]

Hey guys,

Been busy lately on a badger 30 preamp put in a rack.
Got already a few amps and I am trying to keep the real estate efficient.

Build my own layout and used schematic provided by a fellow member on the SLO clone forum.

Only liberties I took were the following:
- elevated heaters
- line out dedicated output (not sure it is really needed though)
- separate gain controls for more flexibility (former badger uses a single dual pot for the gain control)
I used an Astek AS05T200 as power transformer, very affordable and small footprint that fits in a 1U rack.

This is my first jab at rack preamp, so cable runs could be better.

Here are a few pics of the process:

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Learnings : not all FX loops are created equals.
When I plug the preamp in a return FX loop there is sometimes a huge 60 cycle hum, and sometimes it's OK.

I suppose it is related to the receiver amp grounding scheme for the FX loop, since nothing changes on my build.

The drive pot (far right from above) is the overall master volume. When it is 100%, there no hum, only the preamp hiss is audible. As soon as I turn down the output, hum starts to be audible. Do you know why?

My grounding scheme is simple: I have 4 grounds
-IEC far right upper corner
- Power supply and elevated heaters (next to PT)
- FX Loop and output jacks (line out and Master Volume) in front of FX jacks
- Preamp Audio ground at Input jack (bottom left)

Do you see anything that would explain the hum when lowering master volume output?

Thanks again for your help!

Fred.

[Reeltarded]

I love that thing! Splitting the gains is the best, huh?

This hum thing.. I have had that happen. Umm but.. One time I separated a bus bar and grounded both parts separately, but that was to isolate the NFB end, and a few times it was a bad pot, or a bad ground ref on a stage in a cathode. I think. Been a while.

[xtian]

Great looking as usual, Fred! Did you fab your own noval socket holders? How?

[fred.violleau]

I love that thing! Splitting the gains is the best, huh?

Yup, I really like it, the two drive pots, how they have a very different flavor and the way they interact.

This hum thing.. I have had that happen. Umm but.. One time I separated a bus bar and grounded both parts separately, but that was to isolate the NFB end, and a few times it was a bad pot, or a bad ground ref on a stage in a cathode. I think. Been a while.

I have to check again the grounding, I metered every connection, and each was about .1 ohm. The devil hides sometimes in small things... I have redone the heaters wiring because my first run was going under the line out pot, and it added hum.

@xtian thanks man, borrowed your upside down cap setup yes I did repurpose a metal corner (probably some patio piece) into a noval socket holder, works pretty well. Had done this first for D-Lator in a pedal. The good news is the metal piece is very cheap too!

Fred.

[WhopperPlate]

I love this , very cool

[fred.violleau]

Quick update, the layout of power cables is quite critical.
Since I moved signal AND ground cable away from these, the Master volume works like a charm, no hum anymore!

This things is a beast when plugged into a 50w with EL34.
Will try to record something on Monday when wife and kids are away. I don't have any airbrake or load box so it's quite loud, but man it sounds glorious.

I was not a big fan or the typical Marshall tone stack (100k slope 250p, .22uf .22uf), but this preamp got me. I like the way treble really sculpts the tone Mids are interesting too. Bass is a bit too furry sometimes, need to play more with it and different guitars as well.

Cheers;

Fred.

[Colossal]

I was not a big fan or the typical Marshall tone stack (100k slope 250p, .22uf .22uf), but this preamp got me. I like the way treble really sculpts the tone Mids are interesting too. Bass is a bit too furry sometimes, need to play more with it and different guitars as well.

Cheers;

Fred.

Hi Fred,

The Marshall stack values are usually 33k or 56k for the "slope" resistor, not 100k, and 500p or 250p respectively for the treble cap. Bass and mid caps are 0.022uF (22n).

Looks like a great build.

[fred.violleau]

Colossal, absolutely right, my quote is a terrible mess, thanks for the clarification.

Did a quick clip of what this thing can do, I think it captures the essence of it, despite my poor attempt at playing way above my pay grade

And this is a recording through my phone, so it sounds as good as what a phone can capture...

https://youtu.be/cRVCCyMxx_U?feature=shared

Fred.

[Reeltarded]

Colossal, absolutely right, my quote is a terrible mess, thanks for the clarification.

Did a quick clip of what this thing can do, I think it captures the essence of it, despite my poor attempt at playing way above my pay grade

And this is a recording through my phone, so it sounds as good as what a phone can capture...

https://youtu.be/cRVCCyMxx_U?feature=shared

Fred.

It's a Monster!

Also YOU MONSTER! Turning off replies!

Rig sounds excellent.

[fred.violleau]

Hey Miles,

Glad you liked it!

Fred.

[nworbetan]

There are so many things I like about this build that I feel bad that my comment about it is a suggestion for an improvement in the layout. One of the specific things I like (and I'm planning to do the same thing): the divider between the transformer and the audio signal path. One detail that has room for improvement would be moving the power supply board to the transformer side of the divider. A simple way to make it fit would be to use a divider with a 90 degree angle in the middle that meets the front and back panels at 45 degree angles. The power supply board would probably need to be rearranged to fit, but it looks like the space is there for it.

[fred.violleau]

hey Nworbetan,

Thanks for your comment! I had initially planned to move the power supply board on the transormer side, but thought that the EMF could impact the power board, so I decided to put everything on the same side.
It is far from perfect and again cable runs need some improvements.
Planning a friedman Dirty shirley preamp with the twin sister controls in a near future, will try to move everything on the transformr side.
It is quiet thought. The ground lift did not deliver so much, so might revisit this in a different way later.

Happy holidays !

Fred.

[Guy77]

I love the sound of your Badger Fred! You nailed the ACDC sound.
What type of amp are you playing your preamp through?

I heard that the Power knob on the original Badger amp was a part ordered from London Power, their power scaling device.

Cheers
Guy

[fred.violleau]

Hey Guy,

Thanks for listening to the clip.
Signal path is as follow : squier Flame guitar equiped with S&D JB and 59 pickups > badger preamp > the FX loops return of my 50W Dumble EL34 amp > ET90 by WGS
IIRC I read the same thing about the Power scaling solution.

Happy Holidays;

Fred.

[bepone]

And this is a recording through my phone, so it sounds as good as what a phone can capture...

https://youtu.be/cRVCCyMxx_U?feature=shared

great sounds!