Building a Solid State Amp. Really?

cometazzi

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They are intended and marketed as mainly switches, sure, but that does not mean they have characteristics that make them unsuitable for audio. I have found an old FET databook here, you can find lots of info on different FETs and their manufacturing processes. It seems actually that some FETs marketed as 'general pupose audio' have been given that label because they are not good for anything else. The J11x series has a lower noise level and higher transconductance than many 'audio' FETs.
Of course they are not as good as audiphile devices like the 2sk170, but hey, they cost only 40 cents or so. For lo-fi purposes like guitar preamps they work really well i think.

Ah, interesting. Thanks for the link to the old FET book.
 

printer2

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That Rosie amp sounded pretty good, but with a little bit of fizz on top. I bet a low pass EQ filter could be used to cut off the fizz.
Agree about too much fizz. Seem to recall another vid where I liked his amp better. Was it this one? I don't remember. I had the Fet handbook years ago, wonder if my brother threw it out also. He threw out our version of the Audiocyclopedia, which was a shame.

I have been busy in the Two Preamp thread to do much on this project. Good to see others taking an interest. I doubt I will be making the 'best ever SS amplifier' here. Just want to make a little practice amp that has more than the LM386 in it. If I can come up with a serviceable preamp to put beore any of the chipamp or Class D amplifiers that others can build with generic parts I would be quite pleased. I think I have some of the fets that Roland used in their preamp. Most likely the bulk of the Fets in a through hole package are knockoffs out of China and what you get for performance might be questionable (and with fets having a wide range of characteristics for the same part) I thought of using the circuit (or a variant) shown as it takes care of the operating point without fiddling around too much. Have some ideas on that but Not much time to play around at the moment.
 

TwoBear

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This is a simple amp, I want something small that I can plop down on top of my desk and have it take up the least amount of real estate. Originally I was going to make a pair of small cabinets with a 8" in each with a stereo tube amp for them. I built up the cabinets already but I would have to get rid of a paper tray holding work I need to get to and I am not ready to dump it. I already procrastinate getting to it and if I put it out of site, well it disappears and it is not a problem anymore. Not a good thing. So in the meantime a little amp would do me just fine.

I was going through my parts and have a pair of TDA2005 Chipamp IC's. I had them for a bunch of amp testing, SS watts as compared to tube watts and the like. Just to amuse myself. One day. For now one will be pressed into miniamp service. I have a 5" car speaker, the cabinet will be roughly 7.5" x 6.25" x 5". A laptop brick as a power supply, the chip can run bridged and will make about 12-15W depending on voltage and speaker impedance.

Seems funny something this small took all day to build. Mind you, you can only get so many clamps in play when the clamps are bigger than the box.

mcHPnAT.jpg
Looks like fun, and sounds like you're going to have a lot of headroom... I've built a few of the little Ruby amps, with a Jfet feeding a 386 8pin amp chip, where I think they are supposed to put out about a quarter watt, from a simple 9 or 12 volt supply, it might take up to 15 I don't remember, but they sound incredibly good, and plenty loud for a table top, and even busking outdoors. I remember years and years ago someone saying something to the effect of - speaker technology being so inefficient that if they could reproduce 100% of what they were given you could power an instrument in a coliseum with one Watt!? I doubt if it was James b Lansing, Alvin Altec, Carla Klipsch or Saul Cerwin-Vega that said that, maybe it was Estes Electro-Voice?
 

Gijs

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The "Fizz" in the Rosie amplifier I am sure is not caused by the kind of FETs that are used, but by the way in wich they are used. The power amp section for example, I did a simulation of it (couldn't resist..) and it clips pretty harsh. Tube amp- sound means much softer clipping.
 

printer2

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Looks like fun, and sounds like you're going to have a lot of headroom... I've built a few of the little Ruby amps, with a Jfet feeding a 386 8pin amp chip, where I think they are supposed to put out about a quarter watt, from a simple 9 or 12 volt supply, it might take up to 15 I don't remember, but they sound incredibly good, and plenty loud for a table top, and even busking outdoors. I remember years and years ago someone saying something to the effect of - speaker technology being so inefficient that if they could reproduce 100% of what they were given you could power an instrument in a coliseum with one Watt!? I doubt if it was James b Lansing, Alvin Altec, Carla Klipsch or Saul Cerwin-Vega that said that, maybe it was Estes Electro-Voice?
Most speakers are only 1-5% efficient. Horn loaded it can get up to 50% (from memory, the Audiocyclopedia was my source for some information on horns).
 

zhyla

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Fun project. I've been meaning to do an SS amp one of these days. I want something light, compact, stereo, and I wanted to cram in one of more Spin FV-1 chips (these are used in lots of digital reverbs, delays, etc) to do onboard reverb and tremolo, and possibly a rotary speaker type effect. Maybe also build a couple different preamps and switch between them -- since they're solid state they take up almost no space or power.
 

printer2

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Fun project. I've been meaning to do an SS amp one of these days. I want something light, compact, stereo, and I wanted to cram in one of more Spin FV-1 chips (these are used in lots of digital reverbs, delays, etc) to do onboard reverb and tremolo, and possibly a rotary speaker type effect. Maybe also build a couple different preamps and switch between them -- since they're solid state they take up almost no space or power.
Have the Spin chip also, for some reason I found it hard to get back then, no idea on now. I found a cool reverb using the PT2399 though.

 

archtop_fjk

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I built a pedal sized 10 watt amp from TDA2003's, sounds good clean which is what I wanted it for.
View attachment 946886 View attachment 946885

Unfortunately my drill slipped for the LEDs, close enough for rock n roll ;-)
That’s pretty cool. What power supply are you using? I’ve looked around on eBay and you can get a 33V 1-2amp power supply for cheap. That would be enough for both discrete or chip solid state power amps pushing 8 ohms with 10 - 15W of power.

There are many possibilities for preamps. One idea I’ve had is to create a small amp version of the Vox Conquerer/Defiant (which were used by the Beatles during the Sgt Pepper era). Built in fuzz and mid-boost! :)
 

zhyla

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Have the Spin chip also, for some reason I found it hard to get back then, no idea on now.
I think they’re always in and out of stock on the hobbyist sites. I’ve seen them on AliExpress though always in stock. However, transpacific shipping is a mess right now. There’s probably thousands of those chips parked off LA waiting to be unloaded.
 

hewo

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i actually bought communist china's guitar dongle "H8" muslady factory
Can't beat it either, you know somethings spectacular when u can't put it down, stop playing.
only trouble now is how the heck to i get this to the house reinforce?
it broadcasts bluetooth i saw it on mu cellphone reception.
but that isn't the house's power amp, instead it's my phone android
 

zippofan

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That’s pretty cool. What power supply are you using? I’ve looked around on eBay and you can get a 33V 1-2amp power supply for cheap. That would be enough for both discrete or chip solid state power amps pushing 8 ohms with 10 - 15W of power.

There are many possibilities for preamps. One idea I’ve had is to create a small amp version of the Vox Conquerer/Defiant (which were used by the Beatles during the Sgt Pepper era). Built in fuzz and mid-boost! :)
It's just 9 volts from my Truetone supply, though you can use 12V. The circuit uses three TDA2003's, one as a power multiplier followed by a 15V regulator. I saw the board at TH Custom when I was getting a few others (the Merlin's Glassblower boost is my favorite!) and figured I'd make a pedal sized amp to sit on top of my 1x8" Randall cab, with a Aion Lab Series preamp up front. Fun little setup for when I'm noodling around.
 

Tim E

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I wouldn't sweat too much over the specific JFET you might use. The first JFET circuit I ever made used J174 transistors, which are P channel devices recommended for switching. I used them because they were the only JFETs my surplus place had. Turns out they sound great.

I find JFETs sound great in general, very "natural", sweet sound that overdrive well. The only problem, and really not much of a problem unless you're mass producing them, is that JFETs don't always bias predictably. Trimpots, usually for the drain resistors, will be your friend.

I've been thinking that a limiter circuit before the power amp section might be a good idea. Might help keep the power section from doing the ugly distortion, if it's adjusted to clamp the signal just below the power amp's clipping threshold. Some of these limiter circuits are simple diode clippers tuned to a specific clipping level. Sometimes, they're integrated into the power amp section, such as diodes in a feedback loop set to clip at relatively high levels.

I recommend downloading the Solid State Guitar Amplifier Book by Teemu Kyttala. Find it by a google search. It's a pretty big download, but there's lots of insight to be had there.
 

franblanc

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This is a a schematic of little 15 watt solid state guitar amp. I have a 4 ohm 6" Jensen speaker inside it and it is a comfortable size and weight for home practice. The amp has no manufacturer listed. There is only a tagline that says "Made in Japan." I bought it in 1981. Through my own research I learned that it is a copy of a Panasonic guitar amp. It has three controls. Volume, tone and tremolo (with rate). There are three inputs. I hope it helps you with your build.

solid_state.jpg
 

archtop_fjk

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I wouldn't sweat too much over the specific JFET you might use. The first JFET circuit I ever made used J174 transistors, which are P channel devices recommended for switching. I used them because they were the only JFETs my surplus place had. Turns out they sound great.

I find JFETs sound great in general, very "natural", sweet sound that overdrive well. The only problem, and really not much of a problem unless you're mass producing them, is that JFETs don't always bias predictably. Trimpots, usually for the drain resistors, will be your friend.

I've been thinking that a limiter circuit before the power amp section might be a good idea. Might help keep the power section from doing the ugly distortion, if it's adjusted to clamp the signal just below the power amp's clipping threshold. Some of these limiter circuits are simple diode clippers tuned to a specific clipping level. Sometimes, they're integrated into the power amp section, such as diodes in a feedback loop set to clip at relatively high levels.

I recommend downloading the Solid State Guitar Amplifier Book by Teemu Kyttala. Find it by a google search. It's a pretty big download, but there's lots of insight to be had there.

You can find the SS Guitar Amplifier book at the SS Amplifier forum site:


There’s a wealth of info and discussions about building and repairing solid state guitar amps.

Regarding the role of the power amp (and speaker+cabinet) most suggest that the preamp should provide all of the overdrive and simulated tube tones (if desired) and the power amp will just amplify that signal so that it can replicated through your speaker at a suitable volume. Most chip-based amps do this, for example the Vox Pathfinder, which uses a TDA2030 to cleanly amplify the preamp output. Generally, this arrangement is desirable since chip amps clip in a nasty way and that clipping should be prevented. The Roland BC-30 is one of the only amps I’ve seen that tries to soft clip a chip-based power amp to avoid that clipping and perhaps provide a unique response to large amplitude inputs from the preamp stage. I’ve done some simulations in Spice that suggest it should work and at some point I’ll have a go at fooling around with this on my breadboard.
 




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