MOSFET in a pre amp & the effect on pedal input

[Gold star]

A number of tube guitar amps have a MOSFET in the pre amp. The main reason for this is to create gain without the need for an extra tube = or tubes. However, if you input an overdrive pedal or one that colours the basic voicing (amp in a box) will they work as well with the signal being fed into the Mosfet ?

 

[idsnowdog]

Most of the amps that I have seen with a MOSFET booster have multiple inputs and are based on Dumble designs. If you find that pedals don't go well before the booster you could use them with the unboosted inputs or in the effects loop.

 

[Gold star]

Most of the amps that I have seen with a MOSFET booster have multiple inputs and are based on Dumble designs. If you find that pedals don't go well before the booster you could use them with the unboosted inputs or in the effects loop.

my amp, an AC10 C1, has no multiple inputs or loop. Gain & master controls . They put a mosfet in the first position in the pre amp ..

 

[Rex_Rocker]

I wouldn't worry too much about it. What pedal in particular are you concerned might cause undesirable results?

Many of the usual suspect overdrives don't really "boost" the signal all that much, if any. A relatively hot pickup easily puts out higher peaks than the Tube Screamer ever can at 9V, for example. A Tube Screamer only "appears" louder (if it does at all) because it's a whole lot more compressed. So a really hot pickup technically "hits the input stage" harder than a Tube Screamer does most of the time. Most overdrive pedals are like that including the Bluesbreaker, the Blues Driver, the SD-1, etc. So if a hot pickup is fine on your amp, then so will most stompboxes.

A Klon does have A TON of output by comparison, though.

 

[Gold star]

I wouldn't worry too much about it. What pedal in particular are you concerned might cause undesirable results?

Many of the usual suspect overdrives don't really "boost" the signal all that much, if any. A relatively hot pickup easily puts out higher peaks than the Tube Screamer ever can at 9V, for example. A Tube Screamer only "appears" louder (if it does at all) because it's a whole lot more compressed. So a really hot pickup technically "hits the input stage" harder than a Tube Screamer does most of the time. Most overdrive pedals are like that including the Bluesbreaker, the Blues Driver, the SD-1, etc. So if a hot pickup is fine on your amp, then so will most stompboxes.

A Klon does have A TON of output by comparison, though.

The pedals I refer to are SD1 & DS1 . Pickups are single coils, but one one guitar, 1959 Seymour Duncan HB's . It's a 10 watt and the neck humbucker gives a thick sound I don't like I believe Mosfets are put in the pre amp as an alternative to a third or fourth tube. These 'amp in a box' pedals are nonsense I think, where a Fender becomes a Marshall...

 

[Rex_Rocker]

The pedals I refer to are SD1 & DS1 . Pickups are single coils, but one one guitar, 1959 Seymour Duncan HB's . It's a 10 watt and the neck humbucker gives a thick sound I don't like I believe Mosfets are put in the pre amp as an alternative to a third or fourth tube. These 'amp in a box' pedals are nonsense I think, where a Fender becomes a Marshall...

Ah, no. The SD-1 is slightly quieter than the TS, so no worrires there.

The DS-1, I don't know. I had one, and I don't remember it being very loud, but I wouldn't worry about it either.

 

[Gold star]

Ah, no. The SD-1 is slightly quieter than the TS, so no worrires there.

The DS-1, I don't know. I had one, and I don't remember it being very loud, but I wouldn't worry about it either.

Just going back to this, I think I'd be right in saying a MOSFET is put in the pre amp section to boost the gain in preference to using another tube or two in there to do the same. In other words, it's cheaper. how much less I'm not sure

 

[beaubrummels]

Amp-in-a-box pedals generally are not boosts (though some have an additional separate boost on them.). If they are just an amp simulation only, then it's just coloring the sound before the input and shouldn't affect gain staging with the amp.

 

[eclecticsynergy]

I doubt the issue is with the MOSFET.
Vox amps have always been notoriously picky about which gain pedals they'll work well with.

 

[Gold star]

I doubt the issue is with the MOSFET.
Vox amps have always been notoriously picky about which gain pedals they'll work well with.

I believe that chip is put in there as an alternative to an extra tube...false economy IMO, but everything is costed

 

[Rex_Rocker]

Don't worry. It's the same effect as stacking gain pedals, then. Pretty common, and sounds great if you know which pedals to stack.

 

[eclecticsynergy]

I believe that chip is put in there as an alternative to an extra tube...false economy IMO, but everything is costed

My thinking was that the issue with your AC-10 may be more due to the nature of Vox amps in general, rather than the MOSFET itself.
It's fairly widely recognized that Vox amps tend to be pretty choosy about which gain boxes they like, or don't like.