Guitar into clean buffer, then straight into amp's FX Return ?

[Mackin]

Hello everybody,

I am not finding the clean channel of my amp very friendly for pedals... It breaks up too easily, making chorus and other modulation effects a bit grainy. Lately, I've been noodling around with my guitar, plugged into a Digitech modeler straight into the amp's FX Return. The master volume on the amp has no effect, which I found weird at first - but it got me thinking :

Could I use a DIY clean buffer/preamp instead of my amp's preamp ? I would have things laid out like this : Guitar > Pedals (Dirt, modulation, delay, etc) > DIY clean buffer/preamp (instead of the amp's preamp) > FX loop return.

Thanks for reading 

[anchovie]

How do you normally have your pedals set up? Do you run them all as a chain into the input of the amp or have you tried running just your dirt boxes into the input and putting the modulation effects separately into the loop? Have you only run your Digitech modeller into the FX return or have you added your other pedals too to see if they still sound good?

It would help to know what the actual amp is too.

[Mackin]

Hey thanks for the reply 

The amp is a Marshall Lead 100 Mosfet. I only have a few pedals right now, 3 that I use all the time : Korg tuner, BYOC Shredder and OptiComp. I sometimes use the Digitech (RP100) for delay and chorus just for fun - but when my BYOC Chorus will be finished, I am going to have it on the floor with the other pedals for accessibility (same for an eventual delay).

The reason why I want to do this is that the amp's clean channel can't take much signal before breakup, therefore not allowing the power stage to be driven hard enough. Friday night (I was playing with my band  ) I had the master on 10 with the clean channel volume (gain actually) on 1 and ½. More than that, it breaks up and it's a mess. My pedals are at unity gain too, I play clean in some parts.

[km-r]

your proposal would be good, just put a volume control on your preamp/buffer.
i cant really suggest you a "good" or ready-made buffer but i think a unity or low gain gain buffer with a relatively high input impedance would suffice.

how does a mosfet amp at 10 sound? i suppose it has a limiter of some sort.

[anchovie]

Marshall MOSFET? Yeah, go for it, bypass the preamp run your own into the FX return. The only time I heard one of those amps sound good was when a Death Metal band ran two Shredmasters into it!

[Mackin]

Marshall MOSFET? Yeah, go for it, bypass the preamp run your own into the FX return. The only time I heard one of those amps sound good was when a Death Metal band ran two Shredmasters into it!

Hahaha ! I actually like the amp's sound, it is simply just not doing the trick with effects before the preamp. Plus, mine is old and noisy - except when going straight through the power amp. It's pretty loud too ! Here's the thing :

[km-r]

the cab looks wicked awesome! 
DIY 412?

[Mackin]

i suppose it has a limiter of some sort.

I have no idea, I'd tell you if I knew how to read schematics  There's one available from Dr. Tube (Lead 100 Mosfet, model 3210). Can the power stage or something be damaged by excessive signal levels coming from my pedals ? I don't remember where but I read that having a SS power amp clip was bad for the thing... (I don't know what I'm talking about, so please correct me).

And yeah, DIY cabinet. It's a 4x10, got the speakers cheap on eBay and built the cab with my dad (thanks dad !). 

[Mackin]

Oh, that just made me think -
Here's a reply I got in a thread about my amp over at Harmony Central regarding limiting :

There are back-to-back LED's in the feedback loops of the 2nd and 3rd stage op-amp preamps. I doubt they are there for distortion. More likely, they're using them as limiters. LED2 and LED3 are in the feedback loop of IC1B, which is before the volume pot - not where you'd usually find a distortion circuit.

[Mackin]

Sorry about the triple post -
I am still looking for information about power amp clipping = danger.

Thanks 

[Ripthorn]

The problem might be that that is a Marsnall amp, not a Marshall

[anchovie]

Sorry about the triple post -
I am still looking for information about power amp clipping = danger.

Thanks 

Whoever gave you that reply at Harmony Central is talking rubbish. The LEDs in the feedback loop of IC1B are for distortion, the same loop has even got a pot in it labelled "Gain" - how more obvious could it be?! Diodes in a feedback loop is how the Tube Screamer and countless other distortion circuits are designed for softer clipping. To put the diodes after the volume control would be ridiculous, even if they were set up for hard clipping they would need to be before the volume, before the tone stack even! Anyway, rant over. Give him a virtual-slap from me.

To go back to your original concern - the FX return goes into IC5B which is another op-amp and the output of that goes to the power amp. If you feed in too strong a signal it will hit the rails of the op-amp, and that will act as a hard limiter on the signal to the power amp. It'll most likely sound awful (or brilliant, if your music demands that your tone be mashed up that much) but there's no danger involved in hitting the op-amp rails, that's how the Sansamp generates its distortion by design.

[Mackin]

[...]
(or brilliant, if your music demands that your tone be mashed up that much) but there's no danger involved in hitting the op-amp rails, that's how the Sansamp generates its distortion by design.

Awesome ! Thanks for the information