AD30VT and Boost

[marnold]

I've been using my new DVM "Thesis 96" (aka BYOC OD2) with my AD30VT a lot lately. I mentioned this in my review of the pedal, but I think it deserves it's own thread. On the cleaner amph models in general, but the Black 2x12 in particular, the boost function on the pedal works as one would expect it to. Push button, more louderer. So far, so good.

But when I use the higher gain models (from the UK70s model on), the boost effect is negligible. There is perhaps a slight volume gain. The model might sound more compressed, perhaps, or more distorted, but not much louder. If I push the level on the boost higher, it starts to sound, well, bad for the lack of a better term. More distorted, but not in a good way. I thought that dialing back the gain control on the amph might help, but it doesn't. The volume control on the amph doesn't change the situation either.

It's a pity, since I intended to use the boost as a solo boost with some of those distorted models, but it just won't work that way. Anybody familiar enough with the guts of this amph to know why the boost would work on low gain models but not high gain?

[marnold]

As an extra data point, I tried the pedal tonight with my son's Peavey Blazer 158 (as an aside that Jensen MOD speaker made a WORLD of difference in that amp). The effect of the pedal's boost seemed inversely proportional to what the preamp was set at. Am I just running into a transistor/digital modeling problem or would I run into a similar issue with a tube amph? Tung? Jim P? DVM? Obi-Wan?

[piebaldpython]

Marnold........you are essentially running into the same problem that users of the Fender SCXD have run into. Your AD30VT and the SCXD are DSP units that have their signal "warmed" up a bit with tubes. The "cleaner" the DSP choice is (you mentioned a Blackface) the greater effect a pedal will have on it. The higher the gain model amp (the UK70), the less effect a pedal has.
The DSP signal on the higher gain models has NO where to go. It's at it's upper limit ceiling as a DSP and hence your pedal has no effect.
Now, if you actually played a tube version of the high gain unit, then the pedal would have an effect.
The gurus can explain all of this better than I, but that is the gist of it.

[markb]

Clean boosts often have little effect on high-gain channels, even analogue circuits. All that front end gain compresses the signal and thus flattens the dynamic response so the clean boost has a negligible effect.

[tot_Ou_tard]

As Mark sez, amps that are already breaking up tend to break up and compress more when they are goosed and not get much louder. This happens whether the amp is tube, or modeling the behavior of tubes. In the latter case, it wouldn't be a good model if it didn't.

On a modeling amp the A/D converter necessarily comes before any preamp modeling if you overload that you'll get yucky digital distortion. There should be play before that happens and it shouldn't be model dependent.

The AD30VT also has D/A and A/D surrounding the tube in the power amp section. It goes


guitar -> AD -> preamp and effects modeling -> DA -> tube -> AD -> digital power amp -> speaker.


One could also overload the DA before the tube, but I don't think that I've ever done that, but I don't play with a ton of gain.

A microphonic tube could cause problems with the tube -> AD, but you probably have issues besides the ones you are talking about if that were the case.

Maybe Vood or Robert could chime in as they have more experience using pedals with their AD30VTs.

[marnold]

Would someone who has a Blackheart Little Giant, Epiphone Valve Jr., or the like and a boost pedal (or OD pedal with the gain all the way down and level all the way up) care to run an experiment for me? Dime the amph and then kick in the boost/OD and tell me what happens. I'd be interested to find out if the volume goes up since those are relatively low-gain amphs. Or does it just get more distorted/compressed? Or does the ceiling cave in? Or are you swallowed up in a vortex of awesomeness?

[Robert]

Yeah, those digital amps don't really like a hot signal going in. Now, with a tube amp - different story. The kind of front-end push that sends a good sounding tube amp into pure heaven doesn't really happen with a digital amp, at least not in my experience. Too hot of a signal in will just make the amp sound terrible.

[duhvoodooman]

Yeah, I think the issue here is that pushing a solid state modeling preamp and a tube preamp are two very different things. If the modeling preamp is already at high gain, the boost can push it into that nasty sounding SS distortion. Tubes will just saturate and compress the signal while still remaining musical. Try backing off the gain some on the amp model your using or use one of the lower gain models with a distortion pedal and see if that works better for you.

[tunghaichuan]

I've done just that in the past. The VJ is a lot gainier than the LG, but is not a high gain amp by any stretch of the imagination.

The VJ does produce a lot of distortion on its own when dimed. With a boost kicked in it gets more distorted, more saturated and smoother sounding. The volume goes up only slightly. With the amp dimed and no boost, it is producing almost maximum power.

The Blackheart is inherently more clean sounding, but does basically the same thing. When you kick the boost in it gets more compressed and more saturated. The only difference is that the BH dimed without the boost is not as distorted as the VJ.

The only way to make these amps louder is to mike them through a PA, or use a Red Box or the like and run the line out into a PA. You can hook them up to more efficient cabs, but they don't get that much louder.

tung



Would someone who has a Blackheart Little Giant, Epiphone Valve Jr., or the like and a boost pedal (or OD pedal with the gain all the way down and level all the way up) care to run an experiment for me? Dime the amph and then kick in the boost/OD and tell me what happens. I'd be interested to find out if the volume goes up since those are relatively low-gain amphs. Or does it just get more distorted/compressed? Or does the ceiling cave in? Or are you swallowed up in a vortex of awesomeness?