Simple solid state amp to build?

[bill0287]

I see lots of traction on the subject of simple tube amps to build (5F1, etc), but are there any decent SS amp schematics out there to try your hand at building an amp like that? I know there are schematics, but I guess I am looking for a recommendation from experience.

[Mike K]

How much power? What kind of attributes?

I'm building a stereo amp around the LM1875. I'm not doing any preamp stuff with solid state, but that's basically your whole power amp package in one chip - just add a few external caps and resistors and a bipolar power supply.

As far as the preamp, the world is your oyster. There are so many different ways to skin that cat. Depends on what you're after, but basically it's a pedal, perhaps running on a a bit higher voltage and without the current draw limitations (battery life).

It would be very easy to use said chip above, and emulate a BF Champ with some simple dip IC. Most SS Fenders do this to some degree. Adding reverb is trivial with the digital blocks.


Personally, I think if you like driven tones, a hybrid between a SS preamp and tube power amp is the way to go. This is essentially like driving a tube amp with a (SS) pedal. Because of modularity, I tend to think it's best just to build a stand-alone tube power amp and then put whatever SS preamp you want in front. There's no need for them to be in the same package other than using the tube amp's power supply, but making a SS preamp without batteries doesn't require a large or high voltage PT, so it's relatively trivial if packaging size isn't an issue - put it in a rack mount enclosure and you can do pretty much whatever.

[bill0287]

How much power? What kind of attributes?

Good question. I should have been more specific. I am thinking like a small 10watt combo (think Marshal MG10). Prefer a 3 band EQ to a tone control. Maybe master volume scenario. No side nonsense like bluetooth or anything, just a down and dirty little combo. FX loop would be nice, but not mandatory. Amp-in-a-pedal might be a good starting point. I wanted to avoid needing high voltage for a tube power section.

[Mike K]

Yeah - I'd just build it in an amp box so you have lots of space to work.

The thing about SS is it doesn't necessarily lend itself to ptp layouts. You might want to buy a power supply and power amp board (like this) and then build the preamp with solder IC sockets or look for a pedal board that will have everything you want.

Given that linked board set, you only need to use one for a mono amp. That LM1875 will generally put out more than 10W, but power is pretty cheap as far as SS goes, and I don't think you'll have too much. I was more asking on the larger end (like if you wanted 200W+).

[Mike K]

Oh - one thing to look into is gyrator circuits. They are a method of simulating speaker dynamics so you get more of a tube amp sound from your SS device. As far as I know, these generally are inserted after the preamp (where you are generating distortion) and before the power amp (which you generally don't overdrive with SS).

The other thing I would look into is Peavey's transtube amps (Bandit 112). They sound awesome. They claim it's the whole amp design that gives the response and tone they have, but I've only studied the preamps thus far. They sound as good or even better than most tube amps I've played.

[Helmholtz]

Oh - one thing to look into is gyrator circuits. They are a method of simulating speaker dynamics so you get more of a tube amp sound from your SS device.

I don't understand what you mean.
A gyrator is typically used to emulate inductance in a filter circuit.
How does that relate to "speaker dynamics"?

[Greg Robinson]

I don't understand what you mean.
A gyrator is typically used to emulate inductance in a filter circuit.
How does that relate to "speaker dynamics"?

At a guess, maybe Mike is thinking of current/mixed-mode feedback? To emulate the current output tube amp increase in power at speaker resonance/presence that typical voltage output solid state power amps lack.

Mike, a gyrator is typically used to simulate an inductor by using a capacitor and active device instead, usually in an effort to make it variable - they're commonly used in equalizer circuits for this reason.

[Helmholtz]

At a guess, maybe Mike is thinking of current/mixed-mode feedback? To emulate the current output tube amp increase in power at speaker resonance/presence that typical voltage output solid state power amps lack.

Load current NFB to increase output impedance is a completely different topic.
I don't see any relation to gyrators.

[Greg Robinson]

Load current NFB to increase output impedance is a completely different topic.
I don't see any relation to gyrators.

There is none, I'm thinking he's probably confused his terms, and speculating what was actually meant based on:

They are a method of simulating speaker dynamics so you get more of a tube amp sound from your SS device.

Which could fit with poweramp current feedback.

[Helmholtz]

Why not let the guy clarify himself?

Someone who gives advice here should know what he's talking about.

Regarding SS amps I highly recommend Teemu's book:
https://www.thatraymond.com/download...ttala_v1.0.pdf

[Mike K]

Wow - so you guys argued over one small detail and had absolutely nothing practical to add. No I meant a gyrator used to simulate an inductor as is used here: https://patents.justia.com/patent/5467400

"The tuned circuit comprises a capacitance and a gyrator circuit simulating an inductance and the reactance comprises a capacitance"



I was specifically not thinking of Marshall's patent, but in order to stop this petty bickering to get to something useful, I pulled the reference. Others have used this as well, and the application I was thinking is for a headphone amplifier, although I'm not entirely positive that the circuit I looked at is correct, but it was touted to be a gyrator. This is why I suggested "looking into it" instead of saying "use this". I'm not sure it's something that will be easy to implement, but the application I saw for the headphone amp looked quite simple, and may be easy to implement. There are also a number of cab simulations that use inductors, which I assume one could implement with a gyrator instead, although I'm not sure they might provide the results that Marshall claim.

[Mike K]

So Bill - Before these guys drift your thread about some insignificant detail about a gyrator which in no way will help you build an amp, just forget I said it. Also, full disclosure, I'm a SS amp noob. I only mentioned the stuff I put here because it's what I came across in my recent research for a small SS build I am working on. I hope it's helpful, that's all I have to add though.

[Helmholtz]

An amp that's connected to a real speaker doesn't need a cab simulation circuit.

[Mike K]

An amp that's connected to a real speaker doesn't need a cab simulation circuit.

According to Marshall's claim, you're wrong:

1. Solid state audio amplifier means for connection with a loudspeaker cabinet or emulation thereof to provide amplification characteristics emulating in frequency response those of a valve audio amplifier driving a loudspeaker cabinet, said loudspeaker cabinet comprising a loudspeaker drive and the enclosure thereof, so that when said solid state audio amplifier means is connected to said loudspeaker drive the frequency response of the audio amplifier means exhibits a low frequency resonant peak in gain representing the fundamental resonance of the loudspeaker cabinet comprising said loudspeaker drive and said enclosure and a monotonic increase in gain at higher frequency associated with the impedance provided by voice coil inductance of the loudspeaker cabinet comprising said loudspeaker drive and said enclosure.

A speaker emulator and tube audio emulator applied to a SS amp do the same thing.

A headphone does not have a "real" speaker. Please tell me what that device is called then.

[Helmholtz]

The long established method to emulate speaker-amp interaction with SS amps is speaker current NFB.
No additional/artificial cab simulation required.
Read teemuk's book.