I know it's not an effect :cry: BUT - I have just got a 30W amp module from an old hi-fi. It has not pre-amp, and I'd like to boost the output power to about 50W. Dose anyone have any schematics that could help me? I was thinking of adding trannies to the amp module (It runs on 2 large "all in one" ICs) but I don't know the best way to wire them uo (all the sutff on the net is for tube amps which scare me!)
Cheers,
H.
I what I use for testin and jammin on for years now.
I havent done anything except replace tubes in the output...K.O.Wood.
It gets much louder than straight in using whatever booster or mixer etc to boost the input.
Unless you want to get inside the [possibly lethal notice] amp and do alot of messing' [I wouldn't] I would just boost the input and load the output [optional...not recommended by manufacturer] with low ohmage speaker.
I would recommend [if you're into spending on something] first using a say Jensen or Celestion [lightweight cone structure] small wattage spkr.
The second thing I would say is find nice tubes. Output first probably...if you can't read the lettering and they're real old lookin etc. but you can't really tell...I used to pull em one at a time and tweek the knobs on the front of the amp to find out which tubes did nothing [probably bad tube there] and which ones did say trebe or bass...by pullin em out one at a time and switching them around you can probly find the weak ones.
Sometimes whatever the amp was hooked to can be a great sounding speaker [Jensen will probably 'beat' it for breakup and Tone] adding to this [these] [watch you're ohmage load] speaker and pushing the input with 'something' can get a load on the tubes and make the amp/speaker sound quite different and higher gain beautiful tube compressed sounds can be had ... caveat ///'usually'.
I test the severity of what it can handle in a 'lab' setting...no drums, PA's etc., so I can hear exactly what's going on [trying to find the limits of Gain/Volume 'safety' for domponents monitering closely for any signs of ['bad']speaker breakup under extended time 'full' on test.
All these tube amps have 'sweet' spots as far as volume and gain, you'll find they can be pushed only so far and then say bass definition starts getting lost or it may sound harsh. The more speakers you use [basically, and diminishing returns at some point] and cabinet size, the more clean bass and cleaner volume you can get. I like alotta speakers but I don't like setting them up and moveing them...
I would not recommend pulling output tubes when the amp is on.
To check these [there's other ways but I like having spares anyway] just replace them and see if you can tell any difference.
Quote from: humbuck(It runs on 2 large "all in one" ICs)
So it is a power I.C. solid state stereo amp? If you can see what type of ic it is, maybe you can find data sheets or application notes.
But I think it is not easy to beef up the power, depends which chip it is. Can you see any markings there?
I have found out it is only 3.5W per channel. It was driving 20W speakers though.
The chip is MPC576H from NEC Semiconductor. I'm wondering if I can do anything with this - I suppose I could make a practice amp out of it.
I could still beef up the power with xtra trannies I suppose. Any Ideas?
H.
The best way to think of a power amplifier is that it's a thin layer of parts that sits on the outside of the power supply that lets some of the power out of the power supply under certain, very specialized conditions.
Said another way, the limitation on power out of a box is not only the power amp chip or transistors, but also the power supply itself. Power IC's and transistors are pretty cheap. Power transformers and filter caps have not had the great leap forward that silicon has, so the power supply is still relatively expensive. That means that manufacturers usually don't put more raw power supply in the box than they need.
That then usually means that there's not two or more times as much power in the box to draw - the power supply won't handle it. This is not an iron clad rule, but it happens a lot. So the chances of getting from 3.5W to 7 watts is reasonable, but getting to 20W without rebuilding the power supply to make that much more power is really small.
Quotewithout rebuilding the power supply
The HiFi unit will be stereo so if you build a mono guitar amp the power supply willl be rated higher than for one channel
The main problem is the existing volage rails won't allow you to get more power. Changing the voltage rails to get more power requires great care on those module firstly because cannot exceed the chip's maximum voltage, the second is you cannot exceed the chips maximum power output (usally caused by a current limitation) & heat dissipation.
On some chips you can double the power by operating the chip into half the load impedance. Other's don't let you get double because at say 4 ohms you have to lower the supply rails and that means you will only get say 20% to 50% more power - here the existing supply can't be used. There's no easy way to say without looking at the details of the datasheet.
You can get double the power into *twice the impedance* using the existing stereo supply by operating two of the modules in a bridge configuration - sometimes this is shown in the data sheet.
Measure the supply rails and get the datasheet for the chip!
Humbuck, seeing as you're in the UK see if you can pick up a copy of 'High Power Audio Amplifier construction' by R A "he who walks on liquid silicon" Penfold.
It only costs £4 and is packed full of really useful practical info, including bridging as Boof mentioned. It doesn't take long to read and is written in plain speak.
Even if it's not relevant to the chip you have, it'll be useful for future projects and you've got nothing to loose at that price!
Publisher is Babani and the code is BP 277
The PSU's main bus/supply rail is: 18v at 400mA which is: 7.2W so that should limit my amp power output to: about 6W power output.
I can't find a data sheet on the net - the chip seems to be a dinosaur.
I have a spare 18V transformer rated 1-0-1A, I supose I could take one output to drive the amp module, and the other to run additional power stages. At this point, I'm wondering if I'd be better off building an amp from scratch.
H.
http://www.electronics-lab.com/projects/audio/013/index.html
Someone put this cheesy Kemo kit schemo online, if Kemo products is available it might be cheap to buy the kit.
It says it needs 24 V at least, but I believe it might work even with 12 V car battery. Great for beach party portable P.A.
Amp parts are cheap and easy, but you need huge heat sinks and huge power supply.
http://www.kolumbus.fi/mikko.esala/12Wamp.pdf
And another with less power, but maybe asks more amps than your 2x18 V transformer
QuoteAt this point, I'm wondering if I'd be better off building an amp from scratch.
Given the chips are old it's probably wise not to invest too much time and effort trying to get small (possibly unnoticeble) improvements out of it. Remember if you try to push the chips and fry them then the show is over.
I don't know what the maximum voltage is for the chips but I wouldn't use much over a 20V unloaded DC rail - the 18VDC is probably aboiut right. The 18V AC 1A transformer would give a 25VDC unloaded rail (perhaps a bit more depending on the transformer design) which is pushing you luck.
I recently found a 5W/ch stereo system and thought about turning it into a small amp. I'm still thinking about it, I don't know if it's worth the trouble. You can get 20W to 50W chips these days quite cheaply and they don't take much to wire up - these power levels are far more useable than 3.5 to 5W! The only thing about building a bigger amp is you have to buy a new transformer and power supply caps.