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

[Ge_Whiz]

Got it. Should have read the GEO pages more carefully first - thanks.

[Ge_Whiz]

Slightly off-topic, forgive me - but Ricky, is your Obsidian 'stock' with BS250s? Great sound.

[RDV]

Slightly off-topic, forgive me - but Ricky, is your Obsidian 'stock' with BS250s? Great sound.

No problem. That's the old Transistor version with 2N5089s.

RDV

[octafish]

Thanks Ricky. Cleared that up. So maybe you could use a 4 position double pole rotary switch to switch between off and the different cap values. I have a six position switch that has two "sides" so one side would be the on wired to three poles and then a break. On the other side you would have your three different value caps and your choice of filter caps. You could probably double connect the 100n (.1uF) or whatever your choice is so that it is also connected in the off position.
Hmmm that makes sense to me, or am I missing something?

Just for interests sake I'll be coupling it with this little class A design from RED circuits.
http://www.redcircuits.com/Page80.htm
Looks cool huh?

[RDV]

I'm using a 6PDT which I only have three caps wired to. I have 3 positions of 'off'. It makes a decent 'Jazz' sound in the off position. Maybe I'll do a sample of that.

RDV

[Erik Lion]

Going back to the limiter circuit: http://img.photobucket.com/albums/v165/rickydon/voxtmixlmt.gif
Question for R.G. - and others.
Do I understand it correctly that this is the circuit used in some/all Thomas Vox SS amps to prevent the poweramp from clipping?

I'm considering to try/use it with a bass amp project I'm working on. The preamp is a DIY (schem: http://www.albertkreuzer.com/preamp.htm ) - modded with a passive Baxendall tonestack instead of the active tone controls - into an old HH 130 watt power amp. (I'm aiming for a '60 bass sound).

I've never seen a complete Thomas Vox schematics, but I take it the limiter circuit would go in series with the preamp - just ahead of the power amp, right?
I'm running my preamp on 25V and it would been easy to make a 18V tap - but are there any other problems to consider, or changed to do for making it work?

Erik

[Erik Lion]

One more question. What would be a good choice for the transistors and the diodes in the limiter circuit?

Erik

[Erik Lion]

Anyone - please?

[RDV]

When in doubt, use 2N5087,  2N5088 & 1N4148(1N914).

RDV

[petemoore]

  well..I just say 'excellent'
  Thread,
  Samples,
  Work,
  Preamp
  Sounds/looks great Ricki !!! ...RG...Eric...everybody who posted here.
  Thanks for the learning lessons we can all draw from /!!!
 

[Erik Lion]

Thanks RDV. Have you decided not to do the limiter?

Erik

[RDV]

Have you decided not to do the limiter?

Yeah, cause the preamp as built doesn't have enough gain to make the poweramp clip.

RDV

[B Tremblay]

Ricky, do you like the feel of the Bass and Treble controls?  I breadboarded the preamp (sans limiter) and they seemed fairly subtle.  The Boost switch is a dramatic effect, but I was able to perceive only the slightest difference between the tone controls set at their extremes. However, I may have made an error somewhere.

[RDV]

Brian:

I find them to be somewhat like all Vox-Style tone controls; only one spot where they sound good(depending on the guitar of course).

RDV

[B Tremblay]

Cool, thanks.  I have a couple other questions as well (not necessarily directed at Ricky).

What's the overall gain of the preamp?

It looks like the tonestack has been rescaled (maybe by a factor of 100) from the values I've seen in most classic amp tonestacks.  Is this an effort to pad down the output?  How is impedance affected?

[RDV]

I tested the raw preamp circuit(without tone circuit, just an outcap) and it was reaalllyy loud and quite trebley. The tonestack drags the output way down, though it's a lot louder with the MRB kicked in. If you guys  could do your ROG thing with this circuit and stompbox it that would be way cool.

HTH

RDV,

[petemoore]

  I just recently repaired, smoked, re-fixed, a Dyna Power Amp.
  It has no pre-amp... .

[petemoore]

  RDV, Could you elaborate on:
  'It is a bit louder'
  I've builta  circuit using the schematic [first line] from the title post, it boosts 'mildly', am I expecting too much gain from two transistors or does my circuit not 'jibe'...]error?[, I'm trying to figure that out.
  ya know the 'ol <'but it is right' / but is it right>?

[RDV]

  RDV, Could you elaborate on:
  'It is a bit louder'
  I've builta  circuit using the schematic [first line] from the title post, it boosts 'mildly', am I expecting too much gain from two transistors or does my circuit not 'jibe'...]error?[, I'm trying to figure that out.
  ya know the 'ol <'but it is right' / but is it right>?

It's not very loud with the tone controls as they are with those small values and all and would probably benefit from a gain recovery stage ala BMP.

RDV

[petemoore]

  Nice Build  .
  Great application for my 'spare' inductor, puts out a really nice 'Pure SS Crank' tone on it, I put some Reverb on it and started to really enjoy the 'Zone' it's in.
  Sounds like it would make for very direct sounding presence in a stage mix.