uPC1188H upgrade

[nashvillebill]

I've got an older Fender Princeton Chorus amp which uses the uPC1188H chipamp, 10 pin inline amplifier. Although the amp sounds great...it could use more power, it's rated 25watts (x2 since it's stereo out). Not quite capable enough in live gigs, even though I've upgraded the speakers.

I've had a crazy notion to pop in a bigger power supply, maybe up the rail voltage slightly from a nominal +/-27VDC, and put in different chipamps. The LM3886 maybe--but it's a totally different number/pinout. The STK series are 10 pins I think but different pinouts as well. (Which is a shame because I've got a half dozen old stereos that I could pull STK's from)

I've Googled but found nothing so far. Anything feasible to easily replace the uPC1188H? Or am I crazy (wait, don't answer that).

Thanks in advance...

[jrfrond]

It shouldn't be too difficult to build a daughterboard for an LM3886. The parts count is low. With the right supply voltage and current, you could get 60W out of it. They are very common nowadays, especially due to the fact that they are designed to be "stacked" for increased power output capability. They were designed that way. 1 = 60W, 2 = 120W, etc. You just need to up the PSU output accordingly.

[Steve Conner]

I found a little information on the UPC1188 by googling, and it looks like pretty much a standard chipamp. Shouldn't be a problem replacing it with the LM3886. It's very popular with DIY amp builders, and there are boards available to take it from chipamp.com and similar sites.

I've even seen people do without the board and solder all the required components (which is not a lot) straight to the chip's legs.

The only worries would be:

Is there anything else running off those +/-27.5v rails that might blow when you up the voltage? 78/79 series regulators can take up to about 35v.

Have they used current feedback to raise the output impedance? This is very common in SS guitar amps. If they did, and you don't do likewise with the new power stage, then it might sound a bit duller than before. If they didn't, it might be worth trying, it can really bring guitar speakers to life.
http://www.diyaudio.com/forums/chip-...-feedback.html
http://sound.westhost.com/project56.htm


Will you have room for the beefed-up transformer and heatsink?

You might need to replace the filter capacitors with higher voltage ones.

[nashvillebill]

They're powering the +/- 16VDC off the same rails, using a dropping resistor and Zener diode.

And yes they are using current feedback it appears.

And yes space is a problem, I'd have to mount the new transformer outboard.

Looks like I'm reaching the same conclusion that I came to a couple of years ago when I first got this amp: trying to up its power is a lot more trouble than its worth. I guess it's staying like it is. Besides, i've got plenty of other projects to keep me occupied. No reason to muck with an amp that's in pristine condition.

Thanks!

[Enzo]

And since you are going for more loudness, you can double the power and only gain 3db of loudness.

If you really like the sound of this but need a lot louder, why not just run an external power amp? It has a stereo FX send.

For anyone who needs the schematic:

[nashvillebill]

Wow, thanks very much for the complete schematic Enzo, I only had the one page with the one-line. The complete package is very much appreciated!!

My thought was to keep a simple lightweight package I could load in and out in one trip for some of our smaller clubs (notably one where we have to go downstairs into a basement--those stairs back up are a killer when you're carrying gear at 2 in the morning). The amp as it is *barely* keeps up with the volume level we play in smaller clubs--we're classic rock/country/dance stuff, and I play rhythym electric and acoustic guitar...so I don't need "death metal" volume levels. Just a wee bit more oomph so I could carry this amp instead of one of my heavier tube amps (Peavey Classic 50 2x12 combo, Peavey Triumph 60 combo...or the monster Ampeg V4 head/4x12 cab...)

Thanks again for posting a complete package! Very helpful!

[Enzo]

Is there room for you in the PA?

[nashvillebill]

For this particular gig (which we've been doing about once a month for the last three or four years) we use just the house PA, which is pretty small and just barely enough for vocals. If I wanted to go into a PA...I'd have to tote my PA, and since it's far heavier than my bigger guitar amps that's not really practical.

Oh well...I guess that's the drawback to becoming an old fart, the gear seems far heavier than it was when I was a young pup. (I've got a Peavey Classic 400 bass head that's never left the house, it's too heavy for me to carry!) I've put neo speakers in my Classic 50, that helped a lot--but why does Peavey have to make their cabs out of depleted uranium? They must use the heaviest most dense MDF made by mankind.

[Enzo]

Well, you could always get one of those Rogue cabs from Musician's friend, if you want lightweight flimsy stuff.

I often have customers ask me about some piece of gear - Behringer mostly - and what I thought of it. I always tell them that the gear works well enough, but if I were looking for something to take on the road, I'd get a Peavey. The Peavey would be in my view more sturdy and reliable, and would hold up to the rigors of the road.