v-4/vt-22 sensitivity question

[meexiko]

Hi everybody,
I've just seen in the 1971 Ampeg catalogue (the one that's in the docs section of the site) something that I don't understand very well.
The last page of the catalogue is about V-4 specifications. It's written that the sensitivity switches have 3 positions:

pos. 1: Normal sensitivity with high overload
pos. 2: Medium sensitivity with moderate overload
pos. 3: High sensitivity with easy front end overload

On my Master Volume VT-22 next to these rocker switches it's written -9db/-6db/0db.
So, is it the same thing or is there something different in mine/MV models?

Thanks!

[Hangman]

its the same thing.

Some bozo in marketing probably thought that the "high overload" and "moderate overload" sounded cool. notice, none of them say "low overload".

frankly, I have no idea what they're talking about. The sensitivity switch is a slight gain boost. it basically adds a cathode bypass cap on the first gain stage of the preamp, which boosts the gain of that stage. The original intention was to be able to have a switch that allowed you to plug in your les paul for one song, then switch to your strat, flip one switch and not have to move any of your other controls. I'm not so sure anyone ever actually used it for that, and most people I know use the 0db setting.

Hi everybody,
I've just seen in the 1971 Ampeg catalogue (the one that's in the docs section of the site) something that I don't understand very well.
The last page of the catalogue is about V-4 specifications. It's written that the sensitivity switches have 3 positions:

pos. 1: Normal sensitivity with high overload
pos. 2: Medium sensitivity with moderate overload
pos. 3: High sensitivity with easy front end overload

On my Master Volume VT-22 next to these rocker switches it's written -9db/-6db/0db.
So, is it the same thing or is there something different in mine/MV models?

Thanks!

[meexiko]

Thank you, Hangman. So -9db would be the "normal" input (like in most amps), the other two are the boost options. I always thougth that is the opposite.

[Hangman]

i might not have explained that very well. There is no default setting... Plenty of Amplifiers come with first gain stages that have cathode bypass caps in them and plenty come without.
While the 0 db setting has more gain than the -9db setting, I wouldn't say that either is better or worse, or that one is the normal setting.
Ampeg gave customers the option of custom tailoring their first gain stage to respond to their guitar. If they had a guitar with some weake single coils, they might use it on 0db, if they also had something with some beefy hum buckers they might put it to -6 or -9. But like I said, most people I know just throw it on 0db and roll. The 9db range doesn't seem that important in the scheme of things.
I know that I took advantage of the -9db setting when I lived in an apartment and couldn't play very loud. The volume controls on the v4 are touchy at low volumes and it can be hard to get it right. The switch gave me more flexibility in that case.
I don't think that was what ampeg had in mind when they designed the amp.

I think it is the only amp to encorporate that function that I am aware of, many modern amps have a pad for active pickups, but thisnt usually used in this way.

[meexiko]

Ok, you're right. I was talking about how usually people talks about how to use an amp, stayin' clean until it gets little dirty then push some od/distortion pedal to get the "rock" (like Nirvana etc.).
Today I'm going to get a Rat pedal that I found used and cheap in my city (Trieste, Italy) and next week I'll try it with the VT-22. Anyway I think that I'll end up using the amp distortion 'cause it's so amazing! Or maybe not... ahaha
I was thinking about using also both channels togheter but if I remember correctly I read somewhere (maybe in the old V4 forum) that is not a good choice, am I wrong?
I saw a video on youtube of a guy that uses both channels (one with a rat pedal of some sort) and it sounds very full and crunchy.

[Liquids]

Just wanted to say--consider that the rather similar V4b has no sensitivity switch. For maximum headroom, it's got no cathode bypass cap when stock, which is equivalent to being hard wired in the -9db position.

This allows for 'higher output' instrument level signals--like some active basses provide on transients, or a true "clean boost" pedal might yield--to remain clean at points when the other settings might begin to clip to some degree.

That said, if you're not clipping that first tube stage, the setting probably matters very little unless you are trying to drive the amp into clipping, and/or have the volume set pretty high.

Once you enter crunchy territory with the amp, the interaction between the sensitivity setting and the volume knob can theoretically provide some subtle differences in tonality, as the volume knob also functions to filter some highs a bit when not maxed, as it provides some series resistance to the grid of the next tube which shaves some high end, and if the bright + is engaged, volume knob setting interacts with that tonally, too.

One other thing is, lower sensitivity settings might make the volume pot seem less abrupt in its taper at lower settings.

[Hangman]

Just wanted to say--consider that the rather similar V4b has no sensitivity switch. For maximum headroom, it's got no cathode bypass cap when stock, which is equivalent to being hard wired in the -9db position.

This allows for 'higher output' instrument level signals--like some active basses provide on transients, or a true "clean boost" pedal might yield--to remain clean at points when the other settings might begin to clip to some degree.

That said, if you're not clipping that first tube stage, the setting probably matters very little unless you are trying to drive the amp into clipping, and/or have the volume set pretty high.

Once you enter crunchy territory with the amp, the interaction between the sensitivity setting and the volume knob can theoretically provide some subtle differences in tonality, as the volume knob also functions to filter some highs a bit when not maxed, as it provides some series resistance to the grid of the next tube which shaves some high end, and if the bright + is engaged, volume knob setting interacts with that tonally, too.

One other thing is, lower sensitivity settings might make the volume pot seem less abrupt in its taper at lower settings.

true, the V4B also has a cathody bypass cap that gets put in the second stage when the ultra low is turned on. to help keep the volume consistent.

in the V4B I think the headroom is a more important issue, and I personally believe that the output stage isnt well suited for bass, since it has a lot of negative feedback and distorts very abruptly.

[tdbassman]

in the V4B I think the headroom is a more important issue, and I personally believe that the output stage isnt well suited for bass, since it has a lot of negative feedback and distorts very abruptly.
[/quote]

Steve, are there any V4B output stage mods you can recommend? I love the tone of my PBass (Jazz flats ) on the V4B - its my favorite amp. However, I'm always looking for a better sound. Tom D.

[Hangman]

I have modified one v4b to have a different phase inverter. Basically I used the same setup the SVT uses, which adds another gain stage between the phase splitter and power tube grids...

I used the unused 9pin tube socket on the eq/reverb board for the extra tube.

The end result was a much smoother transition to distortion, it sounded a little more like the SVT, whilst still maintaining its own sound.

This is actually very similar to what Ampeg did with the new v4b.

I can ask my customer to bring the amp back in so I can take some pictures if you want to see.

[tdbassman]

I have modified one v4b to have a different phase inverter. Basically I used the same setup the SVT uses, which adds another gain stage between the phase splitter and power tube grids...


Thanks Steve, I was hoping it might be something a little simpler, like changing out a few resistor and cap values. This might be an interesting project for a blog - "Making the V4B sound more like an SVT."