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circuit difference between ampeg V4 and V4b

3/21/2006 10:34 PM
methodofcontrol circuit difference between ampeg V4 and V4b
any who's ever heard a V4B and V4 back to back can tell you that the difference is more than just the lack/presence of reverb.  
the V4B's i've heard have a massive lowend that the V4's just don't have. and i'm wondering where the difference is in that circuit? is it a matter of filtering? or perhaps the fact that the signal is routed slightly differently owing to the lack of sensitivity switches and reverb tank? or maybe a different output transformer was used. does anyone have this info? i woud like to mod the second input on my V4 to emulate the V4B sound as the amp performs double duty for me. thanks.
3/22/2006 1:56 AM

get the two schematics and compare. They are very similar, but the input stages differ. The PT is the same as is the OT. The B+ voltages are the same. The dropping resistors in the B+ string to the small tubes are slightly different, but the voltage at each node is the same. This would be because the extra tubes in the V4 reverb circuit draw a bit more current through them than the V4B which lacks them.  
The power amp and the 6K11 tone circuits appear to be the same. The first tube is where the differences are., not the least of which is the 0.01uf cap leaving the stages into the tone circuits on the V4 versus the 0.1uf cap on the V4B.
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3/22/2006 6:36 PM
hey enzo, thanks for the tip. so...would i simply need to change that one cap if i wanted the 2nd channel of my V4 to sound like a V4B?
3/22/2006 6:48 PM
"the input stages differ"
Those ampeg values are so unFender. I think the V4B is lower gain to the extent that it's not rock guitar friendly.
3/22/2006 7:42 PM
i dunno man...i layed into my old bass player's V4b w/ a LES PAUL and that thing roared ballsier than any marshall i've ever heard. however...when my friend played bass through it, he simply scooped all the mids and dimed the volume, plugged in and it only had a slight growl on the thunderous tone. actually...the natural overdrive may have sounded better than the regular V4 for guitar. which is weird, because the V4 turns to fuzzy mush around 4-5 on the volume w/ a bass plugged in.
3/23/2006 12:29 AM

That cap should make a big difference in bottom end, but the two front ends are just different. Just tack a .1 in parallel with the .01 - it winds up .11 instead of .1, but who cares. It takes just a moment to do and you will know how much difference it makes. Study the two schematics to see the two front ends. Similar and different all at the same time.
3/26/2006 12:25 AM
i guess i'll just tack a .1 uf in parallel on the existing cap and hear if it's a difference i like.  
as for the 3.3k off of the cathode on the V4B, is that an adjustment that will make a noticabe difference to my V4? seems the V4 has a cathode bypass cap, whereas the V4B does not. how does that effect the tone?  
thanks for the help, i'm getting pretty excited for this project.
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