BlackFire Complete Amplifier

[blindsjc]

Hi again friends,
I'm working in a serie of mods in my old project
of complete amplifier. Just to make it clear its a
circuit based in independent subcircuits.

The complete project consists on:
BlackFire (distortion with bypass) -> Tonemender (preamp) -> TDA2050 (Datasheet project amp)

So, the questions:
Can I make it sound better (dont get wrong, its very good by now) changing
the circuit impedances? Theres a correct way to make then work like a better
team than now? Circuit impedance really influence the complete amplifier?

Sorry about poor english. Thnks for all.

Ronaldo

[brett]

Hi
each of these circuits should provide what is needed in terms of impedances.
That is a high input impedance (100kohms or more), and a low output impedance (10 kohms for the effect and pre-amp, 1 ohm for the amp).
I suppose that the greatest potential for a problem will depend on how you organise components around the TDA.  Do yoou have a schematic of that?
good luck

[blindsjc]

Hi Brett,
I dont have a schematic, but I used the circuits in the pcb like independents units,
same design made by gringo to blackfire and tonemender, they just use the same
ground. All connection are made by wires, from input to blackfire, then to dpdt,
then back to tonemender, and after for the TDA. Just Imagine the circuits like islands
in the PCB.

The problem is that sometimes I have a lot of feedback and some noise with the
blackfire (in Brasil we say "microfonia", dont know how you call it, maybe
"microphony") when I wind up the volume.

I think I need just to use shielded wires... LOL ...
Any other advice to make the circuit better is (very) wellcome...

Thanks

[JonFrum]

We use the word microphonics to describe a sound created by a physically vibrating part within the amplifier. If you tap a tube and you hear a "ping" sound, that's microphonics. A vibrating chassis sitting on a speaker cabinet can also cause microphonics.

[blindsjc]

Yes,
Thats the effect, where is your crystal ball?
Really, my amp by now is a circuit pcb unsecurely sitting on a wood box with a
speaker and it may be the cause of "microphonics" (great new word to my
bad english).

Thanks a lot

[Barcode80]

shielded wire and a shielded enclosure are a must for amps, as i understand it.

[brett]

Hi
shielded wire for the early stages is a must, especially with that high-gain Blackfire in there.
Unless you're using ceramic caps, you're probably getting electronic feedback, not physical feedback in the circuit.  Physical feedback tends to happen via the guitar/strings/pickups.

Also physically keeping the input section away from the output sections will help prevent electronic transmission of feedback.  If these things don't help, the next stages are a grounded metal "shield", like a small wall, around the blackfire section, and extra filtering on the power supply (which sometimes "links" different sections).

Other people will have more ideas, too.
PS potentiometers are a potential source of physical feedback, but I've not heard that they're a problem.

[mars_bringer_of_war]

For more ideas about this, go to www.ssguitar.com

[Mark Hammer]

The Blackfire is a VERY high-gain circuit, so it is not surprising that it produces oscillations if the layout is not *perfect*.

[blindsjc]

Guys, thanks for all replies...

brett,
The feedback happens always with my "A" or "La" string.
When the guitar strings are free, after some seconds this string
starts to react to the amplifier. If I stop it, with my finger or
anything else the feedback stops for a while, then starts to
get louder and again.

Thx

[blindsjc]

So, I dont have a schematic
but i link this draw can pass an idea about what I made.
The ground points are all the same, except the transformer ground.
Any comments?




Link: http://blindsjc.v10.com.br/esquema.htm


Thanks

[Meanderthal]

 Sounds like your tone might be resonant right around 440 hertz, causing the A string to feed back. Maybe a tweak of the midrange freq in the tonemender? Different speaker?

Also, if the circuit is microphonic, you might want to tap on the parts with a pencil or something, starting with any Ceramic capacitors, and see if it's any one part causing the problem.

[blindsjc]

Yes, I will try a different speaker for sure,
Mine is really just for test. I just don't understand
what you mean by tap the parts with a pencil. What
I need to search, some reaction like a noise or something
like this when touched by the pencil?

I have ceramic caps and polyester caps. May I change
all for polyester to get a more stable circuit?

Lots of questions...

Thanks

[Meanderthal]

I need to search, some reaction like a noise or something
like this when touched by the pencil?

Yes.

Creamic caps have a bad reputation for being microphonic. Sometimes happens to other parts too.

[blindsjc]

Hi Meanderthal,
I used a pencil for inspect my ceramic caps,
and found a big noise when touch my 0.1uF
just at the blackfire input. The sound is like
a impact in the glass. I will try another cap
type.

Thanks

[brett]

Hi
0.1uF sound like a big ceramic, probably a "mono" or monolythic type.  These have a bad reputation for tolerances, drift and microphonics.  Best avoided except for maybe some rough work in power supplied, etc. 

IMO film caps are the prefered type where available for most guitar audio.  In a few cases people go for the equivalent of film in expensive silver-mica or poly or yellow boxes or orange drops or blue meanies (maybe I'm imagining that one?).  It is uncertain whether they are good, but it is certain that they are very expensive.
Good to hear you found the bug.
cheers

[Meanderthal]

 Even a ceramic cap that's not microphonic would be fine, but poly caps are better...