Firstly, welcome to the forum!
I don't think you will find exactly what you want in one piece. You can buy power amp modules that put out the power you want, no problem. But you will also need some sort of pre-amplifier, and you may have to build that yourself, depending on what exactly you have in mind.
Along those lines, it will help a lot if you give us a little more information, so that people have an idea which way to steer you.
Some questions:
- What do you intend to use this amp for? Guitar? Keyboards? Something else? (This drastically affects the design most likely to work for you.)
- What volume level do you expect from the amp? (Quiet practice at home? Coffee-shop acoustic-guitar gigs? Rock jams in the garage with friends? Playing nu-metal for a stadium full of screaming fans?
) - If this is for guitar, what sort of guitar, and what sort of music do you intend to put through the amp? (An amp designed for twin-humbucker guitars playing death-metal is very different than an amp designed for a big hollow archtop guitar playing jazz.)
If we're talking about electric guitar, beware! The reality is that most DIY solid-state electric guitar amps sound awful, and also cost more to build than a cheap off-the-shelf Fender or other commercially-made guitar amp.
-Gnobuddy
thanks for the reply.
this is for a guitar. just something to play around the house and in the yard. I play mostly old school blues on a semi hollow body. I had a fender mustang II with all the digital effects but didn't use much. some distortion/overdrive and a little reverb is good for me.
I enjoy buildng things myself so that is the real object here. researching since I posted this I understand the fx loop a little better. the reverb might jist be a pedal. I want to build a TS clone or Valvecaster in front of the amp. i think I'm going to start with just a chip amp. the 18v tool battery came into it because i have several w/chargers and i think i can get decent volume and clean headroom.
i'm not sure i understand power supply circuits yet or how volume controls are added. i'm just looking for a starting point so i can start building something.
thanks!
this is for a guitar. just something to play around the house and in the yard. I play mostly old school blues on a semi hollow body. I had a fender mustang II with all the digital effects but didn't use much. some distortion/overdrive and a little reverb is good for me.
I enjoy buildng things myself so that is the real object here. researching since I posted this I understand the fx loop a little better. the reverb might jist be a pedal. I want to build a TS clone or Valvecaster in front of the amp. i think I'm going to start with just a chip amp. the 18v tool battery came into it because i have several w/chargers and i think i can get decent volume and clean headroom.
i'm not sure i understand power supply circuits yet or how volume controls are added. i'm just looking for a starting point so i can start building something.
thanks!
Okay, guitar, blues, semi-hollow. Got it!
IMO, solid-state amps have a tendency to make guitars sound worse than they are, and good valve amps have a tendency to make guitars sound better than the actually are.
The good news is that semi-hollow guitars sound pretty good on their own, so yours may sound acceptable even through a solid-state amp.
The bad news is that bluesy sounds are probably the thing that solid-state amps do worst. (They can do an excellent job of Hi-Fi clean, and they can do nasty buzz-saw distortion, but those bluesy slightly distorted tones are quite difficult to coax out of transistors.)
But I think your plan to use a valve preamp (Valvecaster) and run that into a solid-state power amp is a good one. Let the valve do what it does best (generate musically acceptable distortion), let the transistors do what they do best (put out clean audio power in a small, light, efficient, reliable package).
Got it, now I understand better what your intentions are.
There was another recent thread on a related topic (chip amp for guitar use, http://www.diyaudio.com/forums/inst...plifiers-not-crap-guitar-amplification-2.html ).
The person who started that thread was initially quite upset with the chip amp he tried first. But he eventually found happiness with a TPA3116 amp board he bought off Ebay.
The closely related TPA 3118 was also mentioned in the thread - someone else had used one for guitar (with a lithium battery for power, in fact), and was happy with the result.
Lithium iron phosphate (LiFePO4) tool batteries put out 3.3 volts per cell fully charged, so a 5-cell pack delivers about 16.5 volts, and a six-cell pack delivers just under 20 volts.
I'm guessing that "18 volts" is an advertising executive's twist on reality: I bet you have a 5-cell LiFePO4 pack.
(These cells come off the charger, fully charged, at 3.6 volts per cell, which is 18 volts for a 5-cell pack. But if you sit the freshly charged pack down on a table, and come back and measure its voltage an hour or two later, the voltage will have dropped to around 16.5 volts, and that is a much more honest description of the pack's actual voltage.)
You may already know that the battery voltage and speaker impedance (ohms) are the only two things that decide how many watts the amp will put out.
Both the Class-D chip amps I suggested above operate in what is called bridge mode. With a 16.5 volt power supply, you can expect a maximum clean output power of about 12 watts RMS into an 8 ohm speaker. If you use a 4-ohm speaker, you can expect nearly double that power, around 25 watts RMS.
Both chips discussed here are stereo, so you can actually drive two speakers at the same time, if you want. With two 8 ohm speakers, and driving both channels, you could get around 25 watts RMS total power. With two 4 ohm speakers, you can get something close to 50 watts RMS, assuming your batteries can deliver that much power without too much voltage "sag".
Keep in mind that class D amps do not overdrive gracefully, at all. So you want plenty of clean power from the amp, so that it never, ever gets overdriven. All your distortion will come from your preamp (valvecaster, etc). Because of this, I suggest going with one of the setups that delivers at least 25 watts RMS.
If you end up using only one channel of the stereo chip, you will want to ground the input of the second channel, to keep it from picking up interference and going nuts.
So I think this will be a good starting point; get one of those amp modules, get a speaker or two to go with it, figure out how to wire up your battery, fuse, and on-off switch. When all that stuff is working, you can set it aside and focus on the preamp / valvecaster part of the project.
The actual FX loop will probably go between the valvecaster and the chip amp input - that can be a third part of your project, and you can wait till both the preamp and the power amp are already built and working. Then you add the FX loop.
Breaking up a bigger project into smaller, individually solvable pieces like this, is often a key to making the whole thing possible.
-Gnobuddy
With Gnobuddy that you DO NOT want to clip the class D. That means a hard limiter (coupla Zeners in the most brutal and simple form) before the amp.
Given that battery power makes running a real value properly rather difficult I'd suggest you have a look at RunOffGroove where they have a whole range of stomp box preamps (plus sound clips) - something like the Supreaux Deux might be your thing.
Given that battery power makes running a real value properly rather difficult I'd suggest you have a look at RunOffGroove where they have a whole range of stomp box preamps (plus sound clips) - something like the Supreaux Deux might be your thing.
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Dunno about the OP, but I was curious, so I did Google for the schematic, and then took a close look at it.
I believe you when you say you are happy with the sounds you get from this amp. But I'm sure I wouldn't be; the schematic shows this amp has many of the worst characteristics of that generation of solid-state amps. Lots of high-feedback / harsh clipping opamp stages, a few clipping diodes mixed in, and the final touch is a fairly low-powered chip amp with very high negative feedback, guaranteed to clip very harshly if ever overdriven.
There is also no attempt made in the design to generate small amounts of low-order harmonic distortion to improve the clean tones, so from the schematic, I can tell that the clean tones will be thin, cold, and unpleasant (to my ears, at any rate).
Tastes are different from one person to the next, so judge for yourself - here are the only two demos of this amp I could find on You Tube. Note the quality (or lack of quality) of the clean tones, in particular. Ignore the poor playing, as much as possible, and focus only on the sounds:
-Gnobuddy
Particularly as it's intended for 18V Vcc
There's a range of soundclips there too, with multiple guitars at different settings. (Note some reverb has been added in the mix)
Clip #1 is a particular contrast to Gno's H&K examples
(sorry for the autoquote, can't edit the original post anymore)
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It is, indeed! Quite workmanlike guitar tones in that example, with no obvious nasties.
Runoff Groove never seems to have got the attention they should have, considering the quality of their offerings.
One issue is availability of the JFETs used in most of the Runoff Groove designs. Lately I have not seen J201 (JFETs) for sale at any of the big North American electronics distributors, and the 2N5457 seems to be getting thin on the ground as well.
-Gnobuddy
The Valvecaster you mentioned also sounds interesting. I hadn't heard of it until you mentioned it here, but the few You Tube clips I found don't sound too bad.
(I mean that in a good way, as many low-voltage valve circuits sound, erm, rather uninspiring.)
If I had a 12AU7 lying around, I would probably throw together a Valvecaster (or the related, and allegedly better-sounding, Valvemaster) just to see how it sounds in real life.
-Gnobuddy
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