Adjusticator Mixer Configure +/- Supply

[chrisaxeman]

Hello Guys,

Long time since I've posted, but sort of been away with life (Wife, Kid etc.).

I need some help, please.

Years ago I built a half-rack interface/mixer/MIDI thru based around the http://geofex.com/circuits/Adjusticator.gif

I used a dual op-amp (just a TL072) from memory, one side for a standard Adjusticator to pad a line level loop down, and the Adjusticator mixer to mix a couple of delay pedals and Boss SE50 in parallel, and then using the mixer to boost the level back up. I still had headroom issues with the line level loop from my amps.

The supply I used was +18-0vdc, but now I would like to modify the supply to a +/-18vdc, so I can use the mixer with line level effects and maximise headroom. I'll bypass the input Adjusticator.

I have a 9vac 1600ma tap available, so I was thinking of a dual doubler circuit, with a 7818/7918 +/- reg either side.

I'm just not sure how to re-configure the power supply connections to the opamp.

Any ideas appreciated.

Cheers

Chris...

[R.G.]

No difficulties. You make +/- (voltage) and apply +V to the + supply pins of the opamps. The -V pins of the opamp are removed from circuit ground and connected to the -V supply. You remove the 10K+10K+10uF bias supply generator, and connect the 100K resistors that used to go to the bias supply instead to the ground in the middle of the two power supplies. All other places that are noted with the ground triangle are also connected to the ground in the middle of the bipolar supply.

Yell if that doesn't help.

[chrisaxeman]

Thanks R.G.

I should do some reading on biasing the power supply.

Know this is a good place to start http://geofex.com/circuits/Biasnet.htm but I like pictures lol.

Any suggestions for further reading?

Cheers

Chris.

[chrisaxeman]

Hi Guys,

Long post warning, but I really need some help to sort this out

After some minor track cutting and shutting and a bit of tidy up, converted the piece over to +/-15vdc, and installed a 4th input into the Adjusticator mixer directly from the input Adjusticator to get a dry signal in parallel with the two delays and pitch shift I'm going to use (effects are set 100% wet to avoid phasing). Ideally I'd like to modify the input Adjusticator to a 2ch mixer in it's own right, so the mixing is dual stage, but........

I'm still not happy with it. Regardless of which amp I use, a really overdriven signal has a "swamping" or "ducking" effect on the delay or effected signals in parallel with the dry. This is the same as what used to happen with it before. Is it a headroom, or impedance issue with the Adjusticator?. How do the guitar Line Mixers like the Bradshaws handle the hot signals from a line level amp fx loop?

So to explain how it's configured:

- The amp effects loop send goes into the input Adjusticator.
- The output of the input Adjusticator gets split to the rear send jacks, which feed the effects inputs, as well as a feed into the Adjusticator Mixer.
- The return Jacks feed the effects returns back to an input each of the Adjusticator Mixer, to be mixed to with the amp dry signal from the input Adjusticator, and then the sum is sent back to the amp effects return.

I did only use 100k trimmers instead of 1M in the feedback path as I wanted unity gain at most. The 100k pots on the mixer were subbed for 100k's to ground for simplicity. I've always got adjustability from the effects units themselves. But high gain is a problem from the amp fx send.

Here's some pictures of the unit. It is a very handy item for quick rig setup and MIDI distribution, and does phantom power to the MIDI controller. Would be a shame to gut it and just turn it into an interface. The added switch at the back is a ground lifter.

The +/-15vdc board is the brown one, the 15vdc regs are bolted to the case for heatsinking, insulated on Mica shields. I'm getting a bit of hum that I never used to get too. It disappeared when I unplugged the SMP on my computer monitor (on the same power line, but physically a good 8 feet away), so did I filter enough on the dual doubler? I put 47uF's on the output of the regs, 4 x 1000uF's in the dual doubler (with enough space to go bigger), with 0.1uf oscillator caps across them all. Raw doubler voltage was around +/- 30-32 volts wrt ground no-load before the regs. The AC adaptor I used was reading around 11vac but that shouldn't matter. Current draw was 300ma on the adaptor at idle.

Any upgrades I can make? I'd love to make this work properly after all the effort I put in (albeit 7-8 years ago).

[chrisaxeman]

Nobody?

[samhay]

Tidy build.
I imagine this will be much easier to debug with a schematic.