LM3886/Vox SS Amp Thread(w/ Samples!)

[R.G.]

It's not a Vox Top Boost preamp. It's the preamp from the much-maligned Thomas Vox Super Beatle (and Royal Guardsman, and Buckingham and Viscount) amplifier.

I got laughed at a lot when I would admit that I *like* the sound of the Thomas Vox solid state stuff, at least the big-head ones. The preamp is run so that it does not distort on its own (except for the built-in distortion booster, which is a silicon fuzz face) and does include a limiter before the power amp.

Nasty solid state distortion comes from high gain circuits with high feedback flat-lining sharply or activating their internal protection circuits if you believe the hifi tweakos. The TV amps avoided this by (1) using fairly low gain with low-ish feedback on their power amps (2) putting a limiter in front of the power amp that clips before the power amp does. When these amps clip, you hear the limiter clipping, not the power amp running out of gas. And that lets the limiter keep things better controlled.

I guess I have to be a nut. I own:
1 Super Beatle
1 Royal Guardsman
2 Viscounts
1 Buckingham
1 tube Berkeley
1 solid state Berkeley 2
1 Berkeley 3
1 Cambridge Reverb (Thomas, not Korg)
2 tube Pacemakers
1 Nova
1 Churchill PA head
1 box of miscellaneous parts
A chassis and transformers for an AC30 clone someday.

I'm still looking for a Scorpion. Never did think much of the bass amps, though.

Give the "Thomas Vox Amps" pages at GEO a read.

[RDV]

guys have I missed something? Possibly

Is this a vox top boost preamp schem? No. It's a Vox SS Brilliant channel Preamp circuit from Ampage.

How are you gonna use it? See the first post in this thread.

And why is the limiter there? Because R.G. suggested using it.

If I get it right it should go in this order: vox preamp+limiter+power amp. Yep.

What type of trannies and diodes should I use? I used just some 2N3904 in the preamp. I haven't tried the limiter yet, but may use the same and some Si diodes.

RDV

[RDV]

Sorry if I seemed a bit snotty there Changes, I had a headache when I came home from work and was a bit short with everyone.

I was just looking for a nice preamp for my little LM3886 based practice amp. It might be around a 20 watter at best with the tranny I used.

Everything I've tried(previously) has been disappointing. I just wanted something clean and clear that will work decent with effects at a low volume for playing at my little work desk.

I think I've found it with this little Vox preamp. I really like it with the mid-boost circuit engaged. It's very natural sounding and almost has that steel guitar sort of country sound but without much twang to it. It almost sounds compressed in a good way with quite a bit of sustain to be so squeaky clean. I'll try to record a little sample or two in the next few days.

I didn't use the limiter cause with the 12volt supply I'm using, it doesn't produce enough gain to overload anyways, plus I'm a very lazy sod at heart.

Thanks a ton to Mr. R.G. Keen for his kind assistance.

RDV

[RDV]

Here's some samples recorded by a SM58 mike into a Mackie 1202 Mixer set flat into my soundcard. The distorted one is pretty good I think. This was my first try and will get better I hope.

Mid-Boost(.22cap) with Transistor Obsidian on Low-Gain w/Les Paul

Clean w/no Mid Boost

Switching between the 3 caps in the mid boost.

RDV

[Eric H]

Here's some samples recorded by a SM58 mike into a Mackie 1202 Mixer set flat into my soundcard. The distorted one is pretty good I think.

Sound great from here.

You probably already mentioned it, but what size speaker is that?

-Eric

[RDV]

Sound great from here.
You probably already mentioned it, but what size speaker is that?

I didn't say, but I'm running the LM3886 amp into an old Peavey Stereo Chorus 210 cabinet that was found beside the road by my bass player in a rich neighborhood. It was missing the amp part, but had a couple of Eminence 10"s in there and sounds great.

RDV

[Doug_H]

Sounds good. I like the clean sound. The cap switching sounds good too.

Doug

[vanhansen]

Very nice, Ricky.  That first sample with the Obsidian sounds great.  Has smooth, overdriven Bassman tone to it.

[RDV]

I'm waiting on some caps to come, then I'll be modifying the preamp to take the positive voltage from the power supply from the amp which will be about 25 volts. I figure the clean headroom will be much greater than with the 12 volts it's getting now. I'll probably record it again afterward. I may need the limiter then.

RDV

[Eric H]

I'm waiting on some caps to come, then I'll be modifying the preamp to take the positive voltage from the power supply from the amp which will be about 25 volts. I figure the clean headroom will be much greater than with the 12 volts it's getting now. I'll probably record it again afterward. I may need the limiter then.

RDV

25v sounds good.
Build that limiter  --inquiring minds want to know 

-Eric

[RDV]

Here's a better sounding clean with no mid-boost sample.

Voxy Clean

RDV

[RDV]

One more with that old-time grunge feel with the Obsidian and Mid-Boost.

Spoonvox

RDV

[Doug_H]

Here's a better sounding clean with no mid-boost sample.

Love it! It really sounds great.

Doug

[RDV]

Thanks Doug!

Here's a brave one with a backing track! My son says I'm rushing the beat, everybody's a stinkin' critic!!
Anyways, it's clean with the mid-boost on and I start out on the back PU and then switch to the front of my Epi LP.

Vox Blues in B

RDV

[spudulike]

Ricky - what did you use for the 500mH inductor in the tone section ?

I presume an audio mini-transformer winding would do - but I dont have an inductance meter.  This is different enough to be interesting and the soundclips sound great (nice playing btw).

[RDV]

Ricky - what did you use for the 500mH inductor in the tone section ?
I presume an audio mini-transformer winding would do - but I dont have an inductance meter.  This is different enough to be interesting and the soundclips sound great (nice playing btw).

Thanks for the compliment!
I used a Crybaby inductor I had in my junk drawer, but I think one of those little Radio Shack mini audio transformers might do the trick as well. The effect might be less pronounced, but that might not be a bad thing.

RDV

[Doug_H]

Thanks Doug!

Here's a brave one with a backing track! My son says I'm rushing the beat, everybody's a stinkin' critic!!
Anyways, it's clean with the mid-boost on and I start out on the back PU and then switch to the front of my Epi LP.

Vox Blues in B

RDV

That sounds great. Nice warm clean. I love your playing too, very mature, making every note count.

Sounds like you have a good sounding amp! I'm sure this crowd would love to hear you try the limiter too, since they love anything that distorts.

Doug

[RDV]

Yet another sample as I do get carried away. Obsidian with Les Paul with no delay. In yer face.

Metallivox

RDV

[PenPen]

Heh, metal on a Vox. Thats a new one. Sounds like a very verstile amp. I saved those two schems, I think I'm going to have to put that on my TODO list now.

I have an idea cooking up, using the bare MarshaValve circuit in another post as an input buffer, into this, then the limiter, then into another power stage, maybe the Ruby or something with the 386 for practice. Kicking around the idea of using the Bassman 135 power tube arrangement for a bigger head. But you just convinced me of how good that Vox preamp is, I'm definately using that as a preamp!

[RDV]

Heh, metal on a Vox. Thats a new one. Sounds like a very verstile amp.

Just remember that all the distortion came from the pedal.

RDV