Well, before we tear it apart...

Check the speaker.  What does the amp sound like through a different speaker?  ANd play some working amp through its speakers.

ANd let's not assume anything, play into the front of the amp and send the FX send to some other amp.  Does the preamp sound OK?  If the preamp also sounds crappy, we may have a power problem.

Try the CD inputs, how's that sound?

The power amp is just a pair of TDA2050 ICs, one per speaker, simple enough.  Check the power supply, and the 2050s getting BOTH power rails?  The power amp also makes +/-12v for the preamp as well as +5v for the digital stuff.  A collapsed 12v could do this.  I don;t know what the power amp voltages are, probably 20-25v.  A missing one would also kill the 12v for that polarity.

Sorry, I don;t think your theory works.


When you loan this out, do those guys use the same cabinet and speaker cord?  Or do they use their own?   How about the power source?

I think you are confusing power and loudness.  And you certainly seem to be zeroed into power as the only thing between you and loudness.

Going from 10 watts to 20 watts would only be a 3 decibel increase.   And 3db is just about enough you can hear a diference.  Not a lot, in other words.

My point about the car gas pedal and wondering how much output your preamp made was that no matter how powerful the power amp might be, if it doesn't get a full power input, it will never deliver a full power output.

For example, if your preamp puts out 1 volt of signal, and the power amp needs 2 volts of signal for full power, you won;t get it with that preamp.  You follow me?

I am suggesting that you need a larger signal coming out of your preamp.

They only get as hot as the work they are doing.

SIngle supply doesn't matter, the IC only knows how much voltage is between its power pins, so a single 18v supply is the same as two 9v supplies.   SO with 18v, that means from rest, the output can swing about 8v either direction.  That means the signal peaks can be about 8v.  8v peak is about 5.6vRMS.  and that voltage across a 4 ohm load is about 8 watts.

That is 8 watts max, electrically.   But to get 8 watts, you have to fully drive the IC.   Like a 400 horsepower car, it doesn't sit there just making 400 HP, it only does that when the gas pedal is maxed.

I have no idea what level of signal your preamp produces, do you?  But if the preamp only drives the 2050 enough to make half a watt, then that is all the more it will make.

A neon pilot light rinning on 120VAC sees a voltage that swings up to about 170v, then down through zero and up to 170v on the other polarity.  There are two electrodes in the neon bulb, only one actually glows - I don't remember if it is the positive or the negative.   On AC current, the two electrodes take turns at each polarity, so it appears both are glowing, but they really are taking turns 60 times a second.

Nothing says you can't run it on DC and settle for the same electrode doing all the glowing.


A glowing neon bulb is more or less a short across the voltage source, so they put a resistor in series to limit current, not unlike LEDs in that sense.  Those molded plastic ones have a resistor inside them, so you can connect them right to the 120VAC.


One thing concerns me here.  You say you have 167vDC on each end of this light.  VOltage reading taken with respect to WHAT?   If you measure voltage from end to end onthis light and get +167v, then swap your leads, you will get -167v.   The bulb can act kinda like a rectifier.  I wonder if it is fooling your meter?  But frankly I'd just try a new neon light.

perhaps a little more specific?  Just what are you looking for?  Cab plans?  Layout?  Schematic?  And what would it do?

I knew anything over a few watts was SMPS powered, but I was under the impression even those 400 watt - or whatever - models were of a bridged output design.  Not?   I don;t work on car stereo at all.  The guy next door does those.

Are not most car stereo amplifiers already a bridged circuit?  (Neither side of the load is grounded)   And as such are they bridgable in the same sense as pro audio amplifiers?

TDA2030, 2040, 2050, as in 30, 40, and 50 watts.   But those are merely capabilities, the ICs don't MAKE the power, any more than using jumper cables from your car will make a 9 volt battery any stronger.

Power supply will be the limiting factor.

Keep in mind also that you probably will be playing music through it, not steady sine waves.  SO a 30 watt amplifier will not be putting a steady 30 watts on the speaker.  Music has momentary peaks of power - whuch the speaker will handle - but most of it is lower power.

Ohm's Law and stuff, applied, tells me your 6 ohm speaker doeosn;t want to see more than about 9v for 15 watts.  9v RMS of signal, and that means a peak voltage of about 13v.   SO if you ran any of those amp ICs on +/-15v, it would pretty much prevent you from exceeding power to the speaker.

Me personally, I'd design something with a bit more headroom, and use some personal discipline to not crank the thing to the sky.

Having said all that, why have you already settled on the TDA chips?  Nothing wrong with them, but you might consider a smaller amp.  a 5 watt amp is plenty loud, maybe not on stage when competing with a drummer, but your 15 watt would have trouble with that too.

Really?  Two hours, and you are bumping this?

Frankly most amps of any era are not noteworthy, only a few stand out.


Look at Peavey Bandits.  They have been making one form of Bandit or another for many years now, VERY popular amp.  And later models were their "Transtube" circuits, which sound pretty good.

A solid state amp I always liked was the Fender Princeton Stereeo Chorus.

What did you ask Crate in your email?   No manufacturer is going to approve of any changes you might make to their products, no matter how harmless or beneficial they might be.

No, there is no switching power supply in this.  Fender has not hopped on the SMPS bandwagon today, let alone back in the late 1990s.  The giveaway woulpd be the large power transformer, large filter caps and large bridge rectifiers.

What JM said.


Your switching supply comes on and tries to power the system.  SOMETHING is shorted and loading the thing down, so like any good switcher, it shuts itself down.  And then of course immediately tries to start up again.   Sorta like a self-resetting circuit breaker with a shorted load.

A shorted output transitor is most likely, but a shorted rectifier on the switcher itself would also do it.  As could any shorted secondary load.

You can get the schematic and layout for any Peavey product from customer service at the factory.

You can ask the PV parts folks if they still have boards for that model, but it won;t be an empty board if you plan to build your own.

That will test basic capacitor function, but you cannot rely on it.   Older caps might test fine at 10, 20, 40, 80 volts and leak like a screen door at 200v, to say nothing of 450v.

Of course if they don;t work at 9v they won;t probably work at higher voltages either.