TDA 2050 Low Volume?

[bigbeck]

I'm new to SS electronics but have built about 15 small tube amps from 5 watts to 40 watts in the past 4 years.

So I built a single supply TDA2050 amp with a ROG "Eighteen" preamp. I used a 15v 1.6 amp wall wart that supplies 17.5 volts with the amp at idle. Overall, I'm quite happy with both the clean and distortion tone. I did expect it to be louder,though. Right now it's not putting out as much volume as my 5 watt tube amps. It's almost loud enough to play with drums - but not quite.

Maybe I botched up the build? I tried lowering the voltage to 14.5 V and the volume went way down and it sounded real bad so I took it back up to 17.5V. Next,I tried using two 12V motorcycle batteries in series, figuring I would get even more volume, but it sounded about the same. Maybe a little more clean headroom.

I used half of a CPU heat sink on the chip and even after10 minutes of loud playing it only heats up a few degrees past body temperature and I can only feel the heat if I put my finger directly on the chip. The heat sink itself,does not heat up. Hmmm... I thought these chips were supposed to run hot? I'm using this amp with a 4 ohm Fender guitar speaker.

My main questions are: Does a single supply only allow the chip to produce half of it's rated power? And why is the chip running so cool? It sure sounds good,though. Oh,one other thing, I mounted the chip in an IC socket so I could try out a TDA2030 and LM1875 too. Maybe that's part of the problem?

Don

[J M Fahey]

Good start, congratulations.
There are a few small problems, which, when summed up start to hurt.
1) Your TDA2050 will be happy with +/-18V (or +36V single supply) driving your 4 ohm guitar speaker.It will be clearly louder than your tube amp.
It's about what most popular practice amps use.(Fender, Peavey, Marshall, etc.)
With that nominal 15V PSU it really is "hungry" and weak, as you would be with 2 daily apples ... and nothing else. It can give you around 2W ... go figure.
2) With both car batteries in series, it will give you about 6W, nothing to write home about.
3) Try to solder ; IC sockets think 50mA is a lot of current.

[Enzo]

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.

[bigbeck]

I have no idea what level of signal your preamp produces, do you?  

No,I don't. But here's a link to the preamp I used. I tried the amp both with and without the preamp and there's quite a big  difference in volume. I would say this preamp almost doubles the volume.  http://www.runoffgroove.com/eighteen.html

I just picked up a 24V 2.7 amp laptop PSU for 8.00. Hopefully,that will help a little. If that doesn't give me enough gas, I guess I'll have to spring for a 24V transformer. That should give me 34V after rectification,right? Will 3 amps be enough or will I be able to get away with 2 amps?

I still can't get over the huge amount of current these tiny chip amps draw compared to tubes.

[joecool85]

I just picked up a 24V 2.7 amp laptop PSU for 8.00. Hopefully,that will help a little. If that doesn't give me enough gas, I guess I'll have to spring for a 24V transformer. That should give me 34V after rectification,right? Will 3 amps be enough or will I be able to get away with 2 amps?

I still can't get over the huge amount of current these tiny chip amps draw compared to tubes.

I would say if the two 12v motorcycle batteries didn't help, the 24v laptop psu won't make a difference either.  That said, to get full power you are going to want +/- 22v.  This would require a (15-16 x 2) 30-32v transformer.

Also, you can up the gain of the TDA2050 by adjusting R2 or R3 on the datasheet schematic.  http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1461.pdf

As for the lack of heat, I'd say that's a sure sign of not supplying enough voltage to the chip.  Give it +/- 22v and it'll get pretty hot.

[bigbeck]

Ok, I found an old Radioshack 12-0-12 2 amp transformer in my garage, hooked it up to a full wave bridge and got 35.8 volts. The chip gets hot now! The transformer gets a little warm after 20 minutes of full volume playing,but not hot. I got some increase in volume so it should be able to keep up with a conservative drummer. We'll see. It's about as loud as a 5 watt tube amp. Of course it doesn't sound as good as a cranked tube amp, but I never expected it to. I'm going to use it mainly for low volume jamming and solo practice. For that,it's perfect.

Thanks guys,for all your help,

Don

[joecool85]

Ok, I found an old Radioshack 12-0-12 2 amp transformer in my garage, hooked it up to a full wave bridge and got 35.8 volts. The chip gets hot now! The transformer gets a little warm after 20 minutes of full volume playing,but not hot. I got some increase in volume so it should be able to keep up with a conservative drummer. We'll see. It's about as loud as a 5 watt tube amp. Of course it doesn't sound as good as a cranked tube amp, but I never expected it to. I'm going to use it mainly for low volume jamming and solo practice. For that,it's perfect.

Thanks guys,for all your help,

Don

Thats great!  I still think you could use a little more voltage to get full potential from it, but you're getting there.  Like I said, you can always increase the gain of the circuit to get some more volume.

[bigbeck]

Joe,

Any suggested values to start with? For R4 I have 510,470 and 330 ohm. The stock resistor is 680 ohm. For R5, I have many choices from 27K to 2.2 meg. The stock resistor there is 22K.

Don

[Brymus]

Hey Bigbeck
I remember you from SEwatt.com
welcome to the board.
Be sure to check out DIYstompboxes too,lots of good people there,Joe Cool included.

[bigbeck]

Hey Bigbeck
I remember you from SEwatt.com
welcome to the board.
Be sure to check out DIYstompboxes too,lots of good people there,Joe Cool included.

Brymus, What's wrong with you? Don't you think there could be other Bigbecks out there? WTF! What is Sewatt?  :lmao: I had to say that as I don't remember ever insulting you over there.

Thanks for the welcome.

Don

[Enzo]

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.

[bigbeck]

Ok Enzo, the guitar puts out about 150 mv ac. The preamp puts out 2.3 V at full gain but that's usually too much distortion for me. At half gain,where I usually play,it's putting out 1.2V. If I bypass the preamp and play directly through the power amp, the volume goes way down, as one would expect.

[bigbeck]

Also, you can up the gain of the TDA2050 by adjusting R2 or R3 on the datasheet schematic.  http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1461.pdf

Well, I changed R4 from 680R to 470R and the gain went up quite a bit. I'm running it back at 18V single supply now. The bottom got bigger too. It sounds quite nice!

I suppose the component values on the data sheet are optimized for a 18V dual supply. Is there another component value that I should experiment with?  It sounds much better than my Peavey Rage. Although that's not a fair comparison because the Rage comes with an 8" speaker that was clearly not designed for a guitar amp.

Also, the component numbering on the 2050 datasheet is different for single supply vs dual supply.

This has really been a fun experiment - so far.

[joecool85]

Yeah, I don't know what values to try as I have done any calculations, I was just pointing out it can be changed.  You probably won't fry anything unless you go with some real extreme values.

[bigbeck]

Well, The amp IS now loud enough to play with drums. It does need to be turned up to about 2 -3:00 to get there,though. Very good clean and semi-dirty tone. I'm really surprised that it sounds this good. I'm also playing it through a 98.7 db SPL speaker,so that helps a lot with the volume.

My 16 year old son doesn't like it too much. Says it just doesn't cut it with the distortion tone. He's spoiled rotten. He's been playing exclusively through tube amps since he was 11.   What did I have for a guitar amp when I was 11? A cheap broken battery powered tape recorder that I hacked into a guitar amp. Sounded so good through that 2.5" speaker! Those were the days!  We were poor,we had to improvise or go without.