I am building a guitar reverb pedal from some salvaged parts. From a
dead "Image" guitar amp, I got an itty bitty 5" reverb spring can and a
control pot with an attached circuit board about the size of a cracker
(the kind you eat). This circuit was wired in to the original amp's
circuit as an effects loop. Now the way I want to use it, with a guitar
plugged into the input and the output plugged into the input of an amp,
there was not enough volume, even with the amp cranked. I searched
through my parts/junk boxes and found a few transistors to use to
augment the existing circuit. I now have the thing working with a two
stage amplifier boosting the output of the reverb circuit. I used two
2N4124 transistors connected to the output of the reverb circuit board
with .068 coupling caps (happen to have a lot of those). Other
transistors I could have used are 2N4126 (PNP?), 2N5060 or a host of
others. The power supply is around 11 vdc, wall wart. I haven't
soldered anything yet, will be using a bit of perf board for the new
circuitry. Are these transistors a good choice for this application?

John Kogel

"Porky" wrote in message
ups.com...
I am building a guitar reverb pedal from some salvaged parts. From a
dead "Image" guitar amp, I got an itty bitty 5" reverb spring can and a
control pot with an attached circuit board about the size of a cracker
(the kind you eat). This circuit was wired in to the original amp's
circuit as an effects loop. Now the way I want to use it, with a guitar
plugged into the input and the output plugged into the input of an amp,
there was not enough volume, even with the amp cranked. I searched
through my parts/junk boxes and found a few transistors to use to
augment the existing circuit. I now have the thing working with a two
stage amplifier boosting the output of the reverb circuit. I used two
2N4124 transistors connected to the output of the reverb circuit board
with .068 coupling caps (happen to have a lot of those). Other
transistors I could have used are 2N4126 (PNP?), 2N5060 or a host of
others. The power supply is around 11 vdc, wall wart. I haven't
soldered anything yet, will be using a bit of perf board for the new
circuitry. Are these transistors a good choice for this application?

John Kogel


Does it sound good to you? When it comes to guitar amps that's the important
factor, it may be a horrible amp by looking at the numbers, but if it has
the sound you want then go for it.

Personally I'd use an op-amp rather than making the amp from transistors but
again if it works and you've got it built you may as well go for it.

I guess it sounds ok, with nothing better to ref it to. I've shied away
from op amps for 2 reasons. I don't have a schematic to follow and
don't know the pinouts on any of the chips I've got here. Number 2, you
need either a prefabbed drilled circuit board or a socket to mount them
in. So when you say looking at the numbers, are you referring to these
specific transistors as being horrible amps, cuz that's my question.

JK

In article .com,
Porky wrote:
I've shied away from op amps for 2 reasons. I don't have a schematic to
follow and don't know the pinouts on any of the chips I've got here.

Any hobby electronics book will give you all these. And most op-amps use
the same basic pin out for supply, inputs and output.

Number 2, you need either a prefabbed drilled circuit board or a socket
to mount them in.

They fit direct to veroboard.

--
*Never put off until tomorrow what you can avoid altogether *

Dave Plowman London SW
To e-mail, change noise into sound.

Ok, I will check into that. Why then is an op amp a better choice,
other than fewer connections involved, which is not a major issue. I
like solder.

In article .com,
Porky wrote:
Ok, I will check into that. Why then is an op amp a better choice,
other than fewer connections involved, which is not a major issue. I
like solder.

It's an instant audio solution with a high input impedance and pretty low
out. Easy to set the gain and tailor the response.

--
*Isn't it a bit unnerving that doctors call what they do "practice?"

Dave Plowman London SW
To e-mail, change noise into sound.

"Porky" wrote in message
oups.com...
Ok, I will check into that. Why then is an op amp a better choice,
other than fewer connections involved, which is not a major issue. I
like solder.


Op-amps are just much nicer to work with, it's a one chip solution and very
versatile. There's TONS of info out there on using them, here's a page for
example http://www.northcountryradio.com/PDFs/column003.pdf

Ok, this isn't totallt strange to me it's just been a while. I dug a
little deeper in my boxes of forgotten stuff and found circuit boards
with sockets, part of a practice logic circuit someone was learning on,
and some chips, one of which I recognize as an op amp, it's an LM 741C.
So I'll try it, or maybe one of the others, compare it to the
transistor unit i've already mocked up, and let you know which circuit
goes into the finished pedal.

"James Sweet" bravely wrote to "All" (18 Oct 05 02:26:15)
--- on the heady topic of " Which discrete transistor would you use for a
boost circuit?"

JS From: "James Sweet"
JS circuit? Xref: core-easynews sci.electronics.repair:345548

JS "Porky" wrote in message
JS oups.com...
Ok, I will check into that. Why then is an op amp a better choice,
other than fewer connections involved, which is not a major issue. I
like solder.


JS Op-amps are just much nicer to work with, it's a one chip solution and
JS very versatile. There's TONS of info out there on using them, here's a
JS page for example http://www.northcountryradio.com/PDFs/column003.pdf


OTOH, an opamp IC has about 8 pins to make a connection to while a
transistor only has 3. An opamp is also easier to unwittingly have
oscillate than a transistor. Sometimes a one chip solution is a lot
more of a burden than expected of the novice.

A*s*i*m*o*v

.... Now touch these wires to your tongue!

OTOH, an opamp IC has about 8 pins to make a connection to while a
transistor only has 3. An opamp is also easier to unwittingly have
oscillate than a transistor. Sometimes a one chip solution is a lot
more of a burden than expected of the novice.



Well the idea is that generally you need more than a single transistor for
an amp, but as with anything like this feel free to experiment, there's no
one correct solution by any means.

Yeah how about this problem -- I found an LM1458 op amp i could use,
butt... Vcc is +18 v, I've got 16 v max out of the wallwart, and that
drops off under a load. So now I'll need use a heftier transformer.
I'll give it a try this though, this PM.

In article .com,
Porky wrote:
Yeah how about this problem -- I found an LM1458 op amp i could use,
butt... Vcc is +18 v, I've got 16 v max out of the wallwart, and that
drops off under a load. So now I'll need use a heftier transformer.
I'll give it a try this though, this PM.

That's two 741s in one package. And +/-18 volts is the maximum if needed
to give maximum voltage swing on the output - which I doubt you'll need in
a guitar pedal.

A decent cheap audio op-amp is the NE5534 single, NE5532 twin.

--
*My dog can lick anyone

Dave Plowman London SW
To e-mail, change noise into sound.

"James Sweet" bravely wrote to "All" (18 Oct 05 06:14:25)
--- on the heady topic of " Which discrete transistor would you use for a
boost circuit?"

JS From: "James Sweet"
JS circuit? Xref: core-easynews sci.electronics.repair:345577

JS Well the idea is that generally you need more than a single transistor
JS for an amp, but as with anything like this feel free to experiment,
JS there's no one correct solution by any means.

The thing is the original query was for a bit of a level boost. Also
an advantage of a single transistor is that it might be able to drive
more signal current than an ordinary opamp output. However, note that
an NE5532 can drive line level signals directly into 600 ohms.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.

"Porky" bravely wrote to "All" (17 Oct 05 21:36:43)
--- on the heady topic of " Which discrete transistor would you use for a boost circuit?"

Po From: "Porky"
Po Xref: core-easynews sci.electronics.repair:345569

Po Ok, this isn't totallt strange to me it's just been a while. I dug a
Po little deeper in my boxes of forgotten stuff and found circuit boards
Po with sockets, part of a practice logic circuit someone was learning
Po on, and some chips, one of which I recognize as an op amp, it's an LM
Po 741C. So I'll try it, or maybe one of the others, compare it to the
Po transistor unit i've already mocked up, and let you know which circuit
Po goes into the finished pedal.


An LM741C adds a lot of internal noise and is much too slow for audio.
If there is something like a TL071, LF353, or NE5532 in your storage
boxes, those would be better suited for low level audio.

A*s*i*m*o*v

.... A stereo system is the altar to the god of music.

Thanx Asmo, I'll go to Ratshack for the NE5532 if need be. A single
transistor with standard resistor values for bias and voltage supply
was not enough boost so I ended up using two. So yes, the opamp is a
tidier choice and may reduce the noise levels somewhat, so it's worth
the effort if I use the correct chip. This is what I aim to try. I
assume for power supply I now need a transformer with a bridge
rectifiier or a centre tapped secondary to run the op amp. No
problem......... There's room in the pedal box for a small tranny.

Then there's the third solution, since we're talking tranny swaps
anyway --- I could use a twin triode tube to drive the thing. There's a
cheap way to power the tube with 2 12v or 6v transformers, rest in
peace, Fred Nachbaur. The first one powers the heater. The second one
is wired back-to-back to the first, which gives you an isolated 120
vac, which is then rectified to power the plate. Butt..... that's for
another time. I'm off now in search of transfomers. Thanks, guys.

Porky wrote:
Then there's the third solution, since we're talking tranny swaps
anyway --- I could use a twin triode tube to drive the thing. There's a
cheap way to power the tube with 2 12v or 6v transformers, rest in
peace, Fred Nachbaur.

Indeed....

RIP, Fred.

jak

Sometimes a one chip solution is a lot
more of a burden than expected of the novice.

Amen.

By way of an update for those of you who suggested op amps, thanks.
Next time I'll build a complete op amp reverb driver and recovery
circuit, designed by Roy Mallory. Buttt... for this project, the op amp
boost circuit I tried generates too much noise, and the power supply is
a challenge (major PITA). I will go back to my 2 transistor unit. 3804
or 3805 transistors are said to be low-noise, I will try a pair of them
in place of the flaky ones I started with. Thanks to all for the
inspiration.

John Kogel
on surfin' safari...