Can I power this 6V preamp from 12V?

[ELS122]

So I found this preamp circuit on google and it says that it needs a +6 and -6v PSU, Can I power it whit + and -12v cause the amp I’m trying to design needs a hell of a lot of power and a computer PSU is the only powerful enough thing I have. And it has a +12 v and -12v outputs. So can I power it whit that?

And yes I know that you can make a virtual ground from resistors and capacitor and yes it would probably work since the only ground in this circuit is for the input and output. The problem is that my amp probably wouldn’t work whit it then because it would share the 12v rail

So can I somehow make it work?

[Paul Moir]

If you're using a computer power supply, simply use a pair of linear regulators (LM7806 and LM7906) to reduce the voltages from 12 to 6V.  This will help give you some isolation from the noise of the computer power supply, which you are probably going to need lots of.  In particular, the -12V rail tends to be pretty nastily regulated since it's seldom used at all.

[AVGresponding]

Also carefully check the specs on the current output of the -12v rail, it's probably quite small, less than half an amp.

That may not be sufficient to your needs.


EDIT: Taking a close look at your circuit, it doesn't use a ground rail, so you're fine to use a 12vdc supply. Since the main decoupling cap is only 470uF, the whole thing probably uses only a couple of hundred milliamps or so.

Best way to find out is to build it and see!

[Gyro]

No, that is a simple single supply pre-amp with AC coupled input and output.

The supply voltage markings are deceptive, it only requires a single +6V supply. The line marked 6V- is ground, both for the supply and for the input and output.

It was almost certainly intended to be battery powered (possibly explaining the markings as in '6V battery +ve and -ve terminals').


P.S. Can you please edit the thread title in your OP to be less clickbait - Something like Transistor preamplifier supply, that might help others in the future.

[Gyro]

So I built a different circuit that works but when I turn it to max volume it start pulsing DC and burning my tiny test speaker. What could be the problem here? Also the PSU is rated 0.5amps for the -12v rail but it’s a cheap one so I bet it is only like .3amps. And I don’t think it’s clickbait because it IS what I’m asking: would this work. More clickbait title would be; PLZ HELP FAST NEED HELP NOW!!!!!

So you built a different circuit to the one you posted and asked about and now expect us to tell you guess why your tiny test speaker is burning? Maybe its tiny heart is broken? Anyway I think life is probably too short to care.

Maybe clickbait was the wrong word (although yours seems just as bad), but other people seem to manage to think of a sensible topic related titles when they expect help from others! Yours conveys no meaning. 

[mikerj]

So I built a different circuit that works but when I turn it to max volume it start pulsing DC and burning my tiny test speaker. What could be the problem here? Also the PSU is rated 0.5amps for the -12v rail but it’s a cheap one so I bet it is only like .3amps. And I don’t think it’s clickbait because it IS what I’m asking: would this work. More clickbait title would be; PLZ HELP FAST NEED HELP NOW!!!!!

Clickbait titles deliberately leave out certain details to make people curious.  You title leaves out the design which you are asking questions about, imagine if every topic on here was "Please help" or "This doesn't work" or "What's wrong?".  It would make the entire forum worthless.

You haven't even provided the schematic of this different design that you built, do you expect us all to be mind readers?

[soldar]

No, that is a simple single supply pre-amp with AC coupled input and output.

The supply voltage markings are deceptive, it only requires a single +6V supply. The line marked 6V- is ground, both for the supply and for the input and output.

It was almost certainly intended to be battery powered (possibly explaining the markings as in '6V battery +ve and -ve terminals').

Agreed.

P.S. Can you please edit the thread title in your OP to be less clickbait - Something like Transistor preamplifier supply, that might help others in the future.

Agreed. Please use descriptive titles because otherwise the forum becomes unusable, especially because mouse-overing the titles does not give a preview like it does in other forums. Please use descriptive titles.

[Gyro]

Thanks for the help... not! That means that it’s the forum fault. So I need to like imagine what could your brain would process normally as a title and wouldn’t click it in to ‘cocky’ mode!

The help you received on your posted circuit was polite, as was the request to change the title.

And ok that would mean that other forums are better, so I’ll try asking it somewhere else where not as much people are such d** about your creativity

Agreed, I think you'd better ask elsewhere. See if you get a better reception for a badly phrased question about some unidentified circuit - most other forums are nowhere near as polite. You seem to have ruined your chances of help here with your bad manners anyway.

[mariush]

So I built a different circuit that works but when I turn it to max volume it start pulsing DC and burning my tiny test speaker.

If it's a DIFFERENT circuit, then how could the people on this forum tell you what's wrong with it without SEEING the circuit schematic?

Are they supposed to make random guesses?

The -12v on a computer power supply it's often unregulated, because it's only used for serial ports on computers, and that needs less than 50-100mA of power.
You can use linear regulators to bring this -12v down to something reasonable, for example 7905 regulators will bring voltage down to -5v
If you don't have negative regulators on hand, simple diodes like 1n400x would drop the voltage by ~ 0.7v ... so you could have around 6-8 diodes in series to drop 4-6v from -12v

[tooki]

Thanks for the help... not! That means that it’s the forum fault. So I need to like imagine what could your brain would process normally as a title and wouldn’t click it in to ‘cocky’ mode!

A good thread title (like a good email subject line) is a super short summary of the question/message. For example, a good title for this thread might have been "How do I power this audio preamp circuit?" The key is that it should let the reader know what the post is about. "Would this work?" does not do that in any way, because "this" isn't known to the reader yet! It's not clickbait, but it's still a terrible title.

And ok that would mean that other forums are better, so I’ll try asking it somewhere else where not as much people are such d** about your creativity

What creativity? A thread title with no information isn't creative, it's just a waste of others' time.

As for the other circuit, you asked a separate question, while providing none of the information needed to answer it. As the one asking for help, you should be making the effort to make it as painless as possible for people to respond. When you withhold key information, you're wasting others' time. This is one of the fundamental rules of forum etiquette, not just on this forum. (Indeed, it's a good rule of thumb for all questions, regardless of whether online, real life, telephone, etc.)

I highly suggest you read the following guide to asking questions online, written by a prominent computer scientist, Eric Raymond. While it's written with computer questions in mind, the general principles apply to any kind of technical venue. --> http://www.catb.org/~esr/faqs/smart-questions.html

[Simon]

Just use linear voltage regulators to drop 12v to 6V, this will also clean up switching noise from the SMPS. A PC PSU does not provide much -12V paver.

[ogden]

Input and output of this amp have DC blocking capacitors, circuit does not have ground connection whatsoever. It means that indeed it can be powered from single, unipolar +12V supply (leaving -12V rail alone). Connect +6 to +12 and -6 to ground, done.

[tooki]

Before yes! I got great help but you just ‘helped’ me whit the title. And did I need to title this post as ‘would this unidentified circuit I found on google while looking for something else work?’ If so 

Huh? I think someone is a few beers short of a six-pack...

[Rigolon]

The supply voltage markings are deceptive, it only requires a single +6V supply. The line marked 6V- is ground, both for the supply and for the input and output.

I'm not very experienced yet, could you help me understand what made you think that? I don't see a problem with being +6V to -6V rails. It looks like a part of a bigger circuit where they had those voltage levels to use. For me I would think that they wanted a 12V potential difference, but didn't have the 12V or didn't want to use the ground rail for some reason... I don't really know how could you be so certain that it's +6V to GND.

Thanks for the help... not! That means that it’s the forum fault. So I need to like imagine what could your brain would process normally as a title and wouldn’t click it in to ‘cocky’ mode!

Ok... so maybe you felt people were a little aggressive, or so to say. But they do have a point. I guess it should be better to try and filter the information (the comments that help you understand the community and how optimize the way the forum is used)  and ignore the rest (the aggressive behavior). I believe everyone here wants the best for the forum and to help each other.
There are a lot of replies here that just don't add anything.

That being said, I'm not experienced and don't know how Gyro and Soldar got to know that -6V is actually just ground. But I would believe that the schematics are right, so the potential difference there is 12V... As you do want to use a 12V power supply, I would test the circuit with +12V in the +6V line and ground to the -6V line. I would also try what Gyro and Soldar said about just using ground to the -6V line and see if it works out.

Try it out and let us know.

Just to empathize, any modification you make try to upload schematics and pictures, it always help to solve the problem faster.

[soldar]

That being said, I'm not experienced and don't know how Gyro and Soldar got to know that -6V is actually just ground. But I would believe that the schematics are right, so the potential difference there is 12V... As you do want to use a 12V power supply, I would test the circuit with +12V in the +6V line and ground to the -6V line. I would also try what Gyro and Soldar said about just using ground to the -6V line and see if it works out.

Nowhere in the schematic does it say "-6V". That's your clue right there. The schematic does not have two points, one labeled "+6V" and the other "-6V", and even then it could be a single 6V supply.

The way it is drawn, with a thicker line for negative, clearly indicates that is ground.

That schematic is at least 25 years old and I have been reading schematics for decades. I interpret that to be a single 6 V supply. I would bet that was designed for 6V operation and calculating operating currents would confirm it even though it should have a very wide range and probably operates well at 12 V.

It also does not look like the best design. Maybe someone would want to model it in LTSpice and see the response.

[Gyro]

Yes. The schematic doesn't say +6V and -6V. It has two lines, one saying + and the other saying -, with a '6V' near (below and above) the line. That was a big clue in an old hand drawn schematic. As I said previously, it's the way someone back then would have drawn it if it was going to be connected to a battery.

The other clue is looking at the polarity of the electrolytic capacitors on the input and output. Both are oriented expecting the internal circuit nodes to be positive relative to the input and output signals.

EDIT: The final clue is the absence of a marked 0V rail as an input and output reference. Without a 0V rail, there can't be separate +ve and -ve supplies.

[Rigolon]

To Soldar and Gyro,

I see, thank you for teaching me something new. I've misinterpreted the 6V on the lines as +6V and -6V.

[soldar]

This preamp is very similar. It is taken from a book published in 1970 and mentions it uses silicon transistors which were relatively new at the time.

It is not something I would build today except as a learning experience and to analyze it.

Note that it is designed for 24 V but it can be redesigned for lower voltages by just changing the values of a few resistors.

[ELS122]

I have figured out the preamp now there is a problem whit the coupling cap, my amp has a 50k pot on the input put volume and it whit the coupling cap from the circuit created a high pass filter. and if I put a 1uF electrolitic it starts conducting dc for some reason. also when I don't put another  coupling cap at the end of the circuit it also conducts DC for some reason
What could be the problem?
NOTE: I know it's an overdrive circuit but it doubles as a preamp when I turn it down.

[ELS122]

I have figured out the preamp now there is a problem whit the coupling cap, my amp has a 50k pot on the input put volume and it whit the coupling cap from the circuit created a high pass filter. and if I put a 1uF electrolitic it starts conducting dc for some reason. also when I don't put another  coupling cap at the end of the circuit it also conducts DC for some reason
What could be the problem? (Attachment Link)
NOTE: I know it's an overdrive circuit but it doubles as a preamp when I turn it down.

when I put like a 47nF cap for DC coupling at the circuit it doesn't pass DC trough!

[Zero999]

I have figured out the preamp now there is a problem whit the coupling cap, my amp has a 50k pot on the input put volume and it whit the coupling cap from the circuit created a high pass filter. and if I put a 1uF electrolitic it starts conducting dc for some reason. also when I don't put another  coupling cap at the end of the circuit it also conducts DC for some reason
What could be the problem? (Attachment Link)
NOTE: I know it's an overdrive circuit but it doubles as a preamp when I turn it down.

when I put like a 47nF cap for DC coupling at the circuit it doesn't pass DC trough!

That's because it's an AC coupling, not DC coupling capacitor..

If your 1μF was conducting, it was either because it was damaged or connected backwards.