Touch sensitive!
 

What makes for a extremely touch sensitive guitar amplifier? Is it a matter of a simple circuit? What is negative feedback and what are the trade offs of an especially responsive amp? Any engineers here who have some insights on this?

Thanks

People seem to have different ideas about what "touch sensitive" means.
Very roughly, my idea is to go from clean to slight break-up to crunch by the way I pick.

I'm getting that with a Marshall DSL with the gainy channel dialed back. My Blackstar preamp does it OK too.

So the amp is very sensitive to how the pick touches the string as well as fine gradations of the amount of force of pick against string and breadth of stroke etc. ? Makes sense, thanks. Is that a DSL 40 you’re using? Lots of love for those.

I only have the little DSL1 combo with digital reverb.

I haven't played through all that many different amps, so don't know if mine is anything special in that respect. I often play electric with my fingers too, and that seems to allow even more possibilities for how I touch the strings.

Trainwreck Express and its clones get mentions when people talk about touch sensitive amps.

pretty good definition to me

I'll take the negative feedback question.

Negative feedback (NFB) takes part of the signal being sent to the speaker and returns it to an earlier part of the amp, out of phase. This lowers the gain of the power section just a few decibels.

Side effects of NFB are lower background noise, flatter frequency response, and the amp becomes more resistant to breakup/distortion. When you finally push the amp hard enough, though, the NFB effects go away which causes the amp to break into distortion more abruptly, more of an on/off feeling.

Blackface Fenders have a generous amount of feedback built in, which helps them maximize headroom (like in the Super and Twin Reverb). The tweed Deluxe and Vox AC30 have none, so when they hit overdrive it's a gradual transition. There's a broad range available from just slight warmth to full out roar, and the player's picking and guitar volume controls where in that range he lies.

My opinion is that amps with lower gain are more sensitive to touch. Higher gain amps like Mesas, pretty much any touch of the strings gets you the same response on the lead channel.

I think this video of Joe Gore playing a stratocaster through a Tubedepot Tweed champ clone demonstrates touch sensitivity pretty well:

https://www.youtube.com/watch?v=Nmaby_h5smE

I like that response. I find that once you get too much gain/distortion that it gets too compressed and you don't have the dynamics required for 'touch sensitivity'.

Also, you should consider your guitar's volume control into this. Rolling back the volume a little can take you from distortion to semi-clean. Although not 'touch sensitivity', is can be very sensitive.

Touch sensitive on clean and lower volume with a simple amp like this gives the guitarist fine control of the sound produced - like a acoustic guitar which is highly responsive.

No doubt detailed articulation is possible with single coil pickups played solo. Outside of any gain or distortion this champ clone is close to what I get with the Fender Pro Junior amp which only has a single channel and single tone control.

First rule if you want touch-sensitive: make sure you have decent pickups in the guitar. If the pickups aren't responsive, you're going to lose much of the subtleties of your playing. You might have the exact amp you want, but it will sound like something's missing. Having said that, I'm not much of a pup swapper - I think the stock pups in a decent guitar are usually quite good. I have a couple of cheaper guitars with raunchy, nasty stock pups, but I left them in there - that tone can be fun if you need to bludgeon a song into submission!

Really depends on the skill of the player. One amp may have too much of a change in the transition from clean to dirty for one person where the other person may find it ideal. The other person may like a more gradual change from clean to distorted and call that amp touch sensitive. Neither would be wrong.

Is there any room for a touch sensitive amplifier outside of considerations of distortion? Akin to acoustic guitars, some are more responsive to a light touch, have a greater dynamic range (fine gradations from very soft to loud), without distortion being considered.

As ghostnote mentioned, pickups can have a big effect.

I have mainly played using relatively low output pickups: singlecoils and PAF style humbuckers. I suspect that it is easier to regulate your signal strength with those, than with high output pickups. So, you get the dynamic range from the pickups, and a decent amp will respond accordingly - whether clean or on the edge of distortion.

Sure. Turn up the gain, more responsive. But in terms of for the input effort from the fingers to the output volume most amps are equal with the same amount of gain when played clean. There is a change in the slope of amplification in different parts of a tube signal but not enough to write home about. These are the same tubes used in hifi amplifiers. Want more dynamic range in an amp? get a more powerful amp or more efficient speakers. Since the amp and speaker are analog there is an infinite graduations from soft to loud.

The only way to change the dynamic response is with a compressor or an expander. We do not see much use for expanders with electric guitars, compressors a bit more. But I think that people say they want an amp to give them a different pallet of sounds to play with depending on the difference in level that is sent from the guitar. This usually involves distortion.

Agree. Gain compresses the signal and results in reduced touch sensitivity. With a tube amp, fewer gain stages and a streamlined tone stack results in a more nimble amp with finer control over the output, akin to driving a sports car that isn’t bogged down by unnecessary weight.