Hello!

I completed a SLO-style amp with the excellent PCB:s from Dirks shop and perfect help from Joachims step by step thread.  :topjob:

The thing sounds great, and has worked fine with my band.
I run a switchable 10K volume pot in the effecs loop to make a solo volume function. This is a really useful feature so thought I might incorparate it into the circuit. The question is of course: wehere to put this? My first idea is 1M pot after the tone stack along with the channel volumes. It will then be in parallell to the channel volumes and be switched in/out by a relais. 

The other idea is to use the cables that are alreay out from the PCB to the back of the chassis. The effects loop. This will potentially be a nicer lay out. Maybe if i put 25 K vol pot directly after the cathode follower V3A for example.

What would you do? Anyone tried some approach to this?

Best regards

One obvious place is to put a 1M pot in series with the ground of the master volumes. This will of course workas a solo boost. My objection is that the boost level will be interactive with volume controls. The higer the volume, the less the boost. So boost level will need to be adjusted for different master settings. I experimented a little and the thing works fine but i feel there is a better solution somewhere, also at low volumes it is possible to really get loud volumes with the solo pot by accident...

A standard 25K volume knob pot within the loop circutry is functional, maybe this the best place in the SLO?

Ideas?

Maybe yes

I could also accept a voltage divider in front of the phase inverter, where the ratio can be changes by a potentiometer (switchable) which acts as a solo level.

I tested this in a 2203 Marshall amp and it worked well.

I made the same experience with the boost function in the master level ground wire. It is unsatisfactory if you have more than one master lever control.

Regards

Yes a cut is equally good as a boost in this case, that is good to keep in mind.

The basic principle is: a volume control after the master volume (the 2 channel volumes in the SLO case)?
To refine it that could be A 500K pot but with the ground connected via 470K resistor to stop the amp from go to complete silience? Is that how you did it on the 2203?

Best regards

Hi

In order to have a variable solo boost you need to put a poti in series with the normal volume controls, splitting the ground connection of the normal volume controls.

So you will have the original / normal volume in series with your additional potentiometer connected to ground.

The additional potentiometer then acts as variable resistor (connect the whiper to one solder lug of the pot) and "lifts" the original volume from ground when activated.

Activation is done by not shunting the additional pot - if it is shunted (e.g. by relais) the circuit will remain as original before.

Regards, Stone

Thanks!
Yes. But a variable resistor in the ground will be interactive with the individual settings of the 2 channel-masters. Perfectlyt OK with roughly the same setting of course, but not ideal in all cases.

I thought a little and the best solo boost will probably be an 1M pot wired as a standard vol pot (or 500K pot + 470K resistor to ground to stop soloboost from potentially making amp completely silent) that is switched in with a relais. Position is after the channel masters vactrols.
Not interactive and a clear design. I guess in practise, some care must be taken to make it pop free.
Right?
 

Hi

I would give it a try and wire a 1M pot in series with the lead master volume - so this won't interact on the other one and maybe it is what you are looking for.

The shunt of the resistor by relais should not produce a popping noise - if unsure, take a VTL.

Regards, Stone