Do all preamps support 18V mod?

[Sandu]

I have a korean preamp and I wanna put it in my gutted Aria, and was thinking of experimenting. I saw that some preamps work with 18 and even 27 volts. I have 2 questions:

Will my korean preamp fry if I run it at 18 volts? I think I know the answer for 27

And are the batteries usually wired in parallel or series? What are the benefits of each, 'cause I saw it can be done either way, with different results.

[eastcoasteddie]

Well, I can't answer the first question about the preamp frying...
But batteries are "usually" wired in series. The series connection is what gives you the 18 or 27 volts (2 or 3 batteries respectively). If you wire them in parallel, you'll only get 9 volts regardless of how many batteries you use, but it will probably give you more battery life where the current draw of each battery is cut by 1/2 or 1/3 (depending on how many batteries you use). I never heard of batteries wired in parallel for preamps, but then again I don't know much about what's out there.

[Ach]

in parallel will give you twice battery life, in seriese - more headroom (you can attack harder and do not affraid the preamp distorts).

i believe most preamps can use 18v, because most of them are classic schematics and using the same op-amps (usually TL72 if i remember).

[seanm]

If the preamp uses opamps, it can *probably* work with 18V. If it uses transistors, you risk unbiasing the transistors.

[Sandu]

I can't tell unfortunately, 'cause it's one of those cast in black epoxy.

[seanm]

You probably won't fry anything at 18V, but if it is a cheap preamp, it probably won't help either.

[DavePlaysBass]

If the preamp is made with circuits not intended to run at 18V, you may fry it. You need to know what's in there or have a MFG rating to be sure.

[WarriorJoe7]

Alot of op amps (ones with IC chips) run optimally above 9V. Some of them at 12V or 15V, so when you run it at 18V it is better than 9V. If you have an op-amp you should look up the specs for it and see what they say. I am not sure so let me ask. If the optimum value is say 12V would 18V run it at the optimum level or does it have to be exactly 12V?

[DavePlaysBass]

Originally Posted by WarriorJoe7

Alot of op amps (ones with IC chips) run optimally above 9V. Some of them at 12V or 15V, so when you run it at 18V it is better than 9V. If you have an op-amp you should look up the specs for it and see what they say. I am not sure so let me ask. If the optimum leve is say 12V would 18V run it at the optimum level or does it have to be exactly 12V?

Opamp datasheets have maximum ratings. Above which things can and usually do fry. Many opamps that have good voltage swing with 9-10V of output when powered from 9-10V may have a maximum rating of 12V or 15V or 16V. If these are present in the design, two series connected batteries would be greater than 18V when new and could cause catastrophic failure. If I had a preamp, I would validate it is rated for 18V operation before wiring up. Unless I was not worried about toasting it. There are also failure modes that could stress your amp's preamp. You would hope the amp MFG has taken this into consideration...

[brake]

Originally Posted by Sandu

I can't tell unfortunately, 'cause it's one of those cast in black epoxy.

then stop dicking around with the musicman

[PilbaraBass]

Originally Posted by DavePlaysBass

Opamp datasheets have maximum ratings. Above which things can and usually do fry. Many opamps that have good voltage swing with 9-10V of output when powered from 9-10V may have a maximum rating of 12V or 15V or 16V. If these are present in the design, two series connected batteries would be greater than 18V when new and could cause catastrophic failure. If I had a preamp, I would validate it is rated for 18V operation before wiring up. Unless I was not worried about toasting it. There are also failure modes that could stress your amp's preamp. You would hope the amp MFG has taken this into consideration...

many op amps like the TL072 are rated +15/-15 (or 30V) so if powered by 18V you won't get catastrophic failure.

Nevertheless, I do agree that validating a preamp is rated fore 18V operation is prudent. One way to do this is by the schematics.

Many common discrete devices like J201 JFET's can also handle 18V quite easily. However, with JFET circuits you often don't gain a whole lot by going 18V.

If a preamp doesn't present any issues (clipping) @ 9V, there's no sense in going 18V, really.

[seanm]

Most opamps, such as the common TL072, want +/-15V and can run up to +/-18V. So you are safe up to 36V. However, at 36V you have to worry that some of the caps may only be rated to 25V.

Again, the problem is more if you have some transistors in there. They have to be biased and part of the bias is the supply voltage.

However, you probably have close to a 9V swing with a 9V supply. That means you need to be putting out close to 4.5V peak to need the extra headroom. That is probably not doable from a passive bass pickup.

[Sandu]

Well then is there a way to find out if it works, other than actually doing it? I can't check the manufacturer's specs, they're lost in the rice fields somewhere far east from my current location. I've had the weird-eyed yellowfolk looking for them, but they came up with nothing.

[musicelectronix]

I can't believe no one had mentioned this.. Opamps or other semiconductors utilized in these type of circuits will tolarate much higher voltages than 18V (based on the data sheet, there might be a limited number that can't, but very limited indeed), BUT your main problem is the voltage rating of the electrolytic capacitors. In my experience, 16V caps (not capacitance, the maximum voltage that particular cap can withstand within %20 range) or even 10V caps are not uncommon in these type of circuits. If you put more voltage on the circuit, you might blow up one or slowly destroy it will it leaks (or all the above).

EDIT: I read the entire thread again and I am begging you people. Please do not give advice on the topics you don't feel confident about, especially when one of the outcomes may cause irreversible harm. It has nothing to do with opamps voltage ratings or there is no rule that says if has opamps it will tolerate, etc. It is about the cap voltage ratings, which OP can easily read himself. just look for the barrel-like standing components, which are most likely blue or gray and with a "-" sign at the other side. You may get away with 16V, but 25V will be safer.

[eastcoasteddie]

Originally Posted by musicelectronix

I can't believe no one had mentioned this.. Opamps or other semiconductors utilized in these type of circuits will tolarate much higher voltages than 18V (based on the data sheet, there might be a limited number that can't, but very limited indeed), BUT your main problem is the voltage rating of the electrolytic capacitors. In my experience, 16V caps (not capacitance, the maximum voltage that particular cap can withstand within %20 range) or even 10V caps are not uncommon in these type of circuits. If you put more voltage on the circuit, you might blow up one or slowly destroy it will it leaks (or all the above).

I can't believe that this is common knowledge..!!!

EDIT: I read the entire thread again and I am begging you people. Please do not give advice on the topics you don't feel confident about, especially when one of the outcomes may cause irreversible harm. It has nothing to do with opamps voltage ratings or there is no rule that says if has opamps it will tolerate, etc. It is about the cap voltage ratings, which OP can easily read himself. just look for the barrel-like standing components, which are most likely blue or gray and with a "-" sign at the other side. You may get away with 16V, but 25V will be safer.

His preamp is encased in black epoxy, he can't see the caps. I have a preamp just like that. The only way to see them is to destroy the preamp. What good will that do?

[WarriorJoe7]

Please read a bit more carefully. It is encased in black epoxy.

I guess I would suggest that the OP tries it only if he doesn't care that he could possibly fry it.

Other than that your basic info is better than ours, but your advice is useless. We have all given to speculation because thats all we can do.

Originally Posted by musicelectronix

I can't believe no one had mentioned this.. Opamps or other semiconductors utilized in these type of circuits will tolarate much higher voltages than 18V (based on the data sheet, there might be a limited number that can't, but very limited indeed), BUT your main problem is the voltage rating of the electrolytic capacitors. In my experience, 16V caps (not capacitance, the maximum voltage that particular cap can withstand within %20 range) or even 10V caps are not uncommon in these type of circuits. If you put more voltage on the circuit, you might blow up one or slowly destroy it will it leaks (or all the above).

EDIT: I read the entire thread again and I am begging you people. Please do not give advice on the topics you don't feel confident about, especially when one of the outcomes may cause irreversible harm. It has nothing to do with opamps voltage ratings or there is no rule that says if has opamps it will tolerate, etc. It is about the cap voltage ratings, which OP can easily read himself. just look for the barrel-like standing components, which are most likely blue or gray and with a "-" sign at the other side. You may get away with 16V, but 25V will be safer.

[DavePlaysBass]

There are 1000s of opamps manufactured today. You cannot make statements such as "opamps will take 18V" as a general statement. There is absolutely no way to know what opamp a designer chooses to use unless you ask him. This is analogous to someone saying "cut the red wire and the bomb will not blow up". That crap is for the movies. Maybe the guy making the bomb decided to use all black wire. People love black and white, quick answers but in the world of eletronic design, there are few. And of course capacitor ratings are the next thing to worry about. And even resistors could be an issue if the designer did something a little risky with miniature components like 402 resistors that do not have much of a power rating.

[WashburnBasser]

I had a similar question, my cheap Washburn preamp was distorting, so I wanted to know if I could wire it for 18 volts. Nobody I called really knew the answer, so I took a plunge and tried it. It didn't fry, but it didn't help the problem either. Anybody know what's going on?

[musicelectronix]

Ok, I stand corrected. I didn't see the black epoxy part. There is no way to verify is this circuit will work on 18V or not. To the op, I wouldn't do it since it doesn't even guarantee better performance.

However, the first component to be checked for voltage rating is always electrolytic capacitors and yes, this is the common knowledge. I can go ahead say, at least 99% of opamps can work up to 24V (This is not a scientific statement, it is my guess.) and almost all of the transistors works with 25V without problems. Resistors are of no significance, because they are rated on power as in W = I x I x R and the current is too low to be issue on a preamp design. Most if not all ceramic caps start from 50V and most film type of caps are around 50V or 100V. Only Electrolytic capacitors may vary from 10V to 400V. One reason for that is, E. caps that carry higher voltages could be really big, so manufacturers try to use the safe rating to save on the space. For example, A 9V application generally built around 16V vaps, because batteries can go up to 11V and unregulated power supplies can go up to 14V-15V based on the current consumption of the circuit.

[DavePlaysBass]

Originally Posted by musicelectronix

I can go ahead say, at least 99% of opamps can work up to 24V (This is not a scientific statement, it is my guess.) and almost all of the transistors works with 25V without problems.

You are mistaken here. These days the trend is to design low power consumption opamps along with what is called rail to rail. Rail to rail means it can swing all the way to the power rails it is running from. These two characteristics almost never result in 18V functionality. No one wants to run off of 18V. The whole world has gone to 5V and 3.3V thanks to the computer revolution. Go to www.ti.com and check out the analog opamp technology if you thing I am BSing you. Here's a typcial datasheet: http://focus.ti.com/lit/ds/symlink/opa704.pdf

Dave, PE, MSEE, Patents, Papers, and a whole lot of time in the lab