I found this schematic for a stereo 22 watt per Chanel amp.
http://www.aaroncake.net/circuits/amp20w.asp
I was wondering if this would work for a guitar amp. Would there be any way to bridge the 2 channels to make it 44 watt mono? Is there any reason this would be bad to use as a guitar amp?
Thanks for your comments.
;D
It would work fine for guitar - however, audio playback amplifiers usually have a response quite different from guitar amplifiers. Their "ideal" frequency response for an amplifier is a completely flat line - no alteration from the origianl source. The ideal guitar amp - well, it depends on your preference - but it typically has a dynamic response. Correct me if I am wrong on this.
Like I said though, it will work, it just maybe wont sound that great to you without some tweaking.
It looks like that TDA1554 is already bridging four channels to get the two 22-watt channels, so you could not bridge them again to get 44 watts mono.
You could run them in parallel mono, however. Split a single source into both inputs, and then have each channel drive its own load. I know some 2x12 guitar cabinets offer you a separate amp channel input to each speaker for stereo rigs (and some 4x12 speakers can work as two separate 2x12s).
Also, as JKowalski noted, this is just a power amp. It would not have any of the character that an actual guitar amplifier would have. That could be corrected by running a BSIAB, ROG Thor or any of the other preamp circuits to be found here in front of it.
-- T. G. --
Thanks for the advice. I was thinking that it probably need a stomp box pre amp to make it sound good. Maybe the Dr. Boogie. Anyway, keep the advice coming. I'll let you know how it turns out!
I have had for years about similar amp, I have used it as utility amp for testing and what ever. My amp uses TDA7370 chip. A week ago I tried a modelling preamp trough it and it was very nice, that modelling cheapo has stereo output and some fx sound nice in stereo, like ping pong delay and some time based fxs. And my cheap modelling box has stereo aux input for some backing trax...
I think my amp works quite nice with modelling stuff because it is quite nice quality hi-fi amp (what ya can get with 12 volts suply) and quite loud too. My power supply is not 5 amps only 2 or 3 amps but it works just nice at moderate bedroom/living room volumes. Indeed I had the voltage set at 10 volts...
http://www.elektor-electronics.co.uk/magazines/2003/july/quad-bridge-car-amp.55320.lynkx (http://www.elektor-electronics.co.uk/magazines/2003/july/quad-bridge-car-amp.55320.lynkx) I think this might be nice design with slightly newer version chip
Thanks for the link. I found another amp on that site that looks interesting.
http://www.elektor-electronics.co.uk/magazines/2006/july/simple-hybrid-amp.58346.lynkx
It has a tube pre amp and a mosfet power amp.
Marshall use the TDA series chips quite a bit in some of there amps. For example one of the best sounding little amps i had, used the the TDA1514A chip this gave 40w output it had 2 of these to give a stereo 40watt per chanel, if you want 40w mono just use one. BTW the schematics for the marshall amps that use these chips are available to look at.
The TDA1514A sounds really good. I found this schematic and layout for it.
http://www.electro-dan.co.uk/electronics/tda1514.html
Yeah that is very similar to the marshall schematic, i think marshall pretty much used the TDA datasheet for the power amp with a few changes. Here is a link to the schematic, the power amp is in the bottom right corner of the schematic on the second page. I think its ok to post this link but if not mods should delete.
http://www.schematicheaven.com/marshallamps/stereochorusrev_2x40w_8240.pdf
Ok, I'm seriously thinking of building the amp based on the TDA1514A chip. This would be the first thing I've built that requires more than a 9V battery or wall wort. The 25+/- power supply is new to me. He says in this link
http://www.electro-dan.co.uk/electronics/tda1514.html
That I will need an 18-0-18 transformer. Where can I find a transformer like this. Can anyone post a link? How is the transformer wired to the circuit in his article?
Thank you for your help!
The link you supplied has a schematic of the PSU already there for you. The secondary of the transformer is like 2 secondary 0- 18v windings in series, so the center wire is tapped off to give the 0v- gnd wire. The two outside wires go to the bridge rectifier. (in the diagram the rectifier is a one piece affair, same can be made from 4 diodes to make a full bridge rectifier.) I hope this makes sense
This is the type of thing your looking for
http://www.rapidonline.com/searchresults.aspx?style=0&kw=88-2622 about £10
http://www.rapidonline.com/searchresults.aspx?style=0&kw=88-3371 about £20
Is that type of transformer used mostly in Europe? The type I see mostly in America is like this one
http://www.radioshack.com/product/index.jsp?productId=2102703&CAWELAID=107594935
Here in England we use both types. The torriods are used in many amps especially where space is important as they can be made smaller than the other type. This makes them very suitable for rack gear. You can use either type.
Thanks Ice :) You've been a big help.
OK guys, I went and built the fist amp I was talking about in this thread. Like you guys said. The frequency response is not good for guitar. I put by dist+ stomp box in front of it and it was a little better, but still not that great. My biggest surprise was that it wasn't as loud as expected. I'm powering it with a 12V DC 5AMP adapter I got from a LCD computer monitor. It's no where near as loud as my 15 Watt Vox Pathfinder. Any theory to why 22 Watts of this amp is quieter than my 15W Vox? Also, any suggestions on getting a better tone out of it?
thanks ;D
Well, first, what are you using for speakers? Speaker efficiency is generally higher in guitar speakers than in, for example, home stereo or car speakers. Another point is that the power chips will want to see line level, so your guitar signal will need boosted quite a bit. Try driving the power chips from the preamp out of another amplifier, or put an EQ pedal in front with bass and treble boosted, and mids cut.
I'm using the 8 ohm speaker in my Vox pathfider combo amp.
I forgot to mention. I used a 47k resistor instead of the 39K . There is only one resistor in the circuit. I don't know if that makes much difference.
So you're using one channel of the power chip into 8 ohms? With 12 volt supply you'll be making about 6 watts.
I am using one chanel bridged (11 + 11). With 12V. How did you get the 6 Watts? Not that I don't beleive you, I just don't understand.
If you are plugging your guitar into the input of the power amp (effect pedal or direct) you are only putting instrument level into power amp which expects a line level, ie there will need to be some preamp circuitry , in most amps this will be the gain treble mid and bass secions of the amp plus other buffers and preamp bits.
Check the link i gave you earlier for the marshall amp that uses these amp chips and you will see how the different circuit sections are built up to form the full amp.
Looking at the datasheet for the chip here: http://www.datasheetcatalog.com/datasheets_pdf/T/D/A/1/TDA1554.shtml
Each half of the bridged amp can swing within about a volt of the power rail and ground, or about 10 volts peak-to peak with 12 volt supply. So the bridged amp can swing 20v p-p between its output pins. To get RMS output voltage, divide by 2.82, equals 7.09 volts RMS. Square that, equals 50.3, divide by your 8 ohm speaker, equals 6.28 watts. It may be a little more than that, depending on just how close to the rails the chip can swing, and on what your actual supply voltage is. Note that the datasheet numbers are taken at 14.4 volts, and at 4 ohm speaker loads. Hope this helps!
Tubebass-
That was an exelent explination, and it makes perfect sense, but since I've very uneducated about this stuff I need some explination of your explination. :)
What do you mean power rail and ground can swing within a volt? How did you determine that?
What does peak to peak mean?
When you say bridged 20V P-P between the output pins, do you mean the actual pins that go to the speaker?
In the RMS voltage formula you described, where did you get the number 2.82?
Thank you for all your help!
What do you mean power rail and ground can swing within a volt? How did you determine that?
If the chip were "perfect", it would be able to swing its output all the way from ground to the 12v rail. However, each output of the chip has a pair of
transistors, one of which pulls the output towards 12v, and the other pulls it towards ground, not both at the same time of course!
If you have a look at the schematic of the chip on the datasheet, you can see those transistors, one between the 12v rail and the output, and the other
between ground and the output.When the signal swings almost to 12v that upper transistor will be turned on fully (saturated), and in that state the transistor
will have a voltage across it of 0.6 volts or so. Same goes for the lower transistor. So the signal can only get within 0.6 volts of either the 12v rail or ground.
Pushing more signal into the chip after this point will only make the output signal clip.
What does peak to peak mean?
Just what it says. It's the difference in voltage between the highest positive peak of the signal, and the lowest negative peak.So if the signal starts at zero volts, increases
to positive 10 volts, then heads downward to minus 10 volts, that's 20 volts peak-to-peak.
When you say bridged 20V P-P between the output pins, do you mean the actual pins that go to the speaker?
Yes.
In the RMS voltage formula you described, where did you get the number 2.82?
Talking about peak-to-peak voltages is all very well if what you're doing is looking at signals on an oscilloscope, but they're
kind of awkward when it comes to calculating power. If you want to figure out how much power is going to your 8 ohm load (speaker)
you need to know the RMS (root mean square) value of your signal. If you have a sine wave going through your amp and measure, say,
10 volts RMS across
your speaker with your digital multimeter set to AC volts, then connect an oscilloscope across the speaker, you will see 28.2 volts
peak-to-peak. The RMS value is equivalent to DC when calculating power. Guys a lot smarter than I am figured out that 2.82 number....
I just use it!
Hope any of this is useful to you!
Thanks ;D I appreciate you taking the time to answer my questions
No problem!