Which discrete transistor would you use for a boost circuit?

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

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

They fit direct to veroboard.

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.

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

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 "Re: Which discrete transistor would you use for a boost circuit?"

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

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

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!

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.

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.

"James Sweet" bravely wrote to "All" (18 Oct 05 06:14:25) --- on the heady topic of "Re: 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 "Re: 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.

Indeed....

RIP, Fred.

jak

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...