AMZ Mosfet Booster as amp Master Volume??

[FunkyGibbon]

Hi,

I have a tube combo, with a very simple effects loop arrangement - in and out sockets with no volume in or out controls.

The loop goes between the Master Volume and the power section. This means that as you turn up the amp master volume, the signal going to the 'post' effects increases.

My post effects are being over-loaded at not even close to 'rocking' volume (about two on the knob!!) - problem. One solution would be to stick the effects in front of the preamp.


I thought a second solution might be to keep the amp master volume below the level where the pedals are being overloaded (at wimpy '2'), and then use an AMZ Mosfet Booster (because it's supposed to be very clean) as a kind of 'recovery stage' or master volume.

Can anybody see any problems regarding 'THE TONE' of the amp if I try this method (sure, the only way to know is to try, but humour me!)?

I know 'amp mojo heaven' is achieved by cranking the master volume of a tube amp way up, but is this not essentially just pushing a high volume signal into the power stage? Can I achieve exactly the same effect by using a solid-state final gain stage before the power amp (aside from any colouration from the Mosfet Booster)?

If no problems, is the AMZ Mosfet Booster the cleanest there is? Would some full-range, hi-fi device (if I were to find one!!) be even better?!




Thanks in advance for your advice,

Christopher

[R.G.]

No single device amplifier will ever be as clean as an opamp in an amplifying setup for audio.

The entire reason that the electronics world invented high feedback amplifying stages is to get low distortion and predictability.

It would be cleaner to use one side of a TL072 JFET opamp to restore the volume from your effects chain.

[d95err]

Sounds like a job for the "Adjusticator":

http://www.geofex.com/circuits/Adjusticator.gif

[FunkyGibbon]

Thanks, R.G. and d95err for the speedy replies!

I'm looking right now for an opamp boost circuit, and was just about to ask if R.G. had one in mind, when the Adjusticator arrived! Looks good!

Thanks again for your help!

Christopher

[FunkyGibbon]

erm... is there an advantage in this situation to having an inverting gain stage?

Thanks again,

Christopher

[ulysses]

The loop goes between the Master Volume and the power section. This means that as you turn up the amp master volume, the signal going to the 'post' effects increases.

this seems like a bizzare setup  what amp is it?

i was going to suggest a volume limiter on the effects out.. but given your description this prob wont work..

cheers
ulysses

[FunkyGibbon]

Hi,

It's a Rivera Pubster 45. The cheaper end of their range, so it's quite basic. Since the master volume is before the output to the effects, it essentially can limit the signal going to the loop effects (i.e. at bedroom volume). Then I just need to bring the volume back up again.

[FunkyGibbon]

So... R.G....

Call me "visuo-spatially-challenged" but I'm not following your post from many years ago on how to use just one side of the Adjusticator as non-inverting boost.

I wonder if you'd mind making it any clearer? Looking at the diagram, I should flip the opamp around, right? But the 2.2M and 0.1uF now go into the opamp (at the + non-inverting input).

Now, what did I have to do with the series 100k and the the 100k that previously went into the non-inverting input??...

Thanks,

Christopher

[slacker]

What are the effects you're trying to use in the loop? If they're stompboxes then the problem is most likely that the effects loop is running at line level which can be too loud for stompboxes. I'd build a pair of adjusticators and run one before the effects to reduce the volume going into them and then another after them to bring the volume back up, that way you'd have total control over the loop and can set the optimum volumes for the effects.

Call me "visuo-spatially-challenged" but I'm not following your post from many years ago on how to use just one side of the Adjusticator as non-inverting boost.

If you want a non inverting opamp booster look at the Micro Amp schematic http://www.generalguitargadgets.com/diagrams/microamp_sc.gif that's probably simpler than trying to explain how to mod the adjusticator.

[FunkyGibbon]

They're stomp boxes (phaser, delay, looper). Loop output to the effects is not necessarily line level, it's tube preamp output level (whatever that may be) after being attenuated by the Master Volume. Since the Master Volume goes before the loop, this will do just fine at attenuating the level to the effects. So I only need one boost, to bring the level back up post effects to a level the same as if I had the Master Volume turned up high... I think!!

I also think I get the non-inverting Adjusticator (apart from the solution of connecting two together in series - although this might be a good idea if I ever need to REALLY crank the amp!!).

The 2.2M and 0.2uF go to the (+) input, also now connecting to the 100k going to Vbias (the 10k). Now the 100k connected to the (-) input is still connected to the (-) input and the 10k and 1M pot at the bottom of the diagram, but the other side of it hops over the circuit input, and is connected to Vbias. Right??...

(Thanks, slacker, for the Microamp suggestion. That helped.)

Thank you again for everyone's interest and help,

Christopher