Protection circuitry and sound quality.

[Chr1]

I am curious as to the various types of amplifier protection circuitry and how they effect sound quality (or not.)

I recently bought a late 80s Spanish power amp (for all of £4.99) from Ebay and the little info I could find online claims that it has an innovative type of protection circuit for higher sound quality. Having listened to it, I have to say that I do think that it sounds better/clearer than a Crown Macro-Tech 1200 that I have (which also has fairly comprehensive protection built in.) I realise that theoretically they should both sound the same, so I am wondering what effect protection circuitry can have on the sound quality of an amplifier?

This is the Spanish amp...

 

[Chr1]

Some more pi

cs...

 

[Chr1]

PS As NAD gives the option to turn their "Soft Clipping" circuitry on or off, presumably they must think that it can be beneficial to remove it from the signal path.

My first proper amp back in 1979 was the 2020 but it is so long ago that I can't remember if I noticed a difference... Got a C372 in storage. Use to use the power section but may have to dig it out to see if I can notice the difference...

 

[Chr1]

Sorry that should read "3020".
doh

 

[MakeMineVinyl]

The way its implemented, at least here, is that all protection sensors are opto-coupled from the audio path. The opto-couplers are fed to a microcontroller which can do things like shutting the amp down or turning off the current sources.

I would assume this is similar to the way its done on most current amplifiers.

That Spanish amplifier looks pretty old, so I would assume any protection is more direct;y analog based, maybe using 555 timers or something similar.

 

[Chr1]

Thanks for the information. Do you think that the reason that I perceive it as having a cleaner sound than the Crown is due to the Crown most likely having a more comprehensive protection circuit in the signal path due to being designed for higher output/PA duties? The Spanish amp looks like it was more likely designed for studio monitoring and therefore not in need of such circuitry.

 

[MakeMineVinyl]

Thanks for the information. Do you think that the reason that I perceive it as having a cleaner sound than the Crown is due to the Crown most likely having a more comprehensive protection circuit in the signal path due to being designed for higher output/PA duties? The Spanish amp looks like it was more likely designed for studio monitoring and therefore not in need of such circuitry.

I wouldn't think that a protection circuit should have any impact on sound quality, no matter how its implemented. That being said, I don't know anything about the Spanish amp beyond the picture you posted. Crown generally makes good amps, so I wouldn't think the protection circuitry would have any impact.

 

[Chr1]

Ideally yes, but presumably for highest fidelity, at least in an anologue amplifier the ideal is still "a straight wire with gain", as I think the old adage goes? ie. Ideally nothing unnecessary in the signal path, quality components only etc...

 

[Chr1]

But perhaps protection circuitry is different ie sensors not actually in the signal path. This is why I ask. My knowledge of electronics is minimal. I wonder if things like the Crowns cooling fan could be the difference. (Not referring to the fan noise itself.)

 

[MakeMineVinyl]

Ideally yes, but presumably for highest fidelity, at least in an anologue amplifier the ideal is still "a straight wire with gain", as I think the old adage goes? ie. Ideally nothing unnecessary in the signal path, quality components only etc...

Protection circuitry usually isn't in the signal path, but rather adjacent to it, so audio wouldn't flow through it.

 

[Chr1]

This makes sense. Thanks.

 

[Doodski]

Ideally yes, but presumably for highest fidelity, at least in an anologue amplifier the ideal is still "a straight wire with gain", as I think the old adage goes? ie. Ideally nothing unnecessary in the signal path, quality components only etc...

This is a schematic of the output circuitry for one channel of a amplifier and the protection circuitry can be seen. The protection circuitry is so isolated from the output current amplification stage that it should not cause any degradation of the audio.

 

[smurfer]

I'm with @MakeMineVinyl on this. Even the crudest of protection circuits I have seen, such as simple 'crowbar' circuits in late 1960s Sansui etc, are effectively out-of-circuit, until sufficient (and unwanted) DC biases that circuit 'on' to trigger a shutdown. You wouldn't hear or even measure any different in output except in exceptional circumstances. This is not to say they it absolutely can not affect the sound, but I would be looking elsewhere first for obvious differences in perceived sound quality.

 

[Chr1]

I guess that what I am trying to figure out is why I prefer the sound of several of my SS amps over that of the Crown. They are well respected in pro audio and given that I like high SPLs, when I scored 4 very cheaply a while back, I thought I may use one at home. I have since sold 2 to a musician friend who loves them. (Definitely keeping one for possible future parties!) Anyway, I do actually like it's sound better than the NAD C372 but it has a slightly veiled lack of clarity in the higher frequencies that the Spanish amp and my two other preferred "hifi" power amps don't have.
Anyhoo, I realise that I may be asking for a bit of a roasting here now, as theoretically all properly implemented SS amps should sound the same! Just my perception. I have got through a lot of amps over the years, so don't think that it is just my imagination.
Anyway, any further insight most welcome!

 

[Doodski]

I do actually like it's sound better than the NAD C372 but it has a slightly veiled lack of clarity in the higher frequencies that the Spanish amp and my two other preferred "hifi" power amps don't have.

Where those double blind tests?

theoretically all properly implemented SS amps should sound the same! Just my perception. I have got through a lot of amps over the years, so don't think that it is just my imagination.

There are some that do sound different. They are rare. Whether they are voiced, have better current drive or just more power at medium to high volumes they do exist and I have owned one too. It was 75w/ch stereo @1kHz.

 

[Chr1]

I will admit that I was not absolutely fastidious in my methodology but I was careful to ensure similar SPL (sound meter) and all of the other components were the same, as was the source material. I guess what I conclude that after good circuit design and implementation, actual component quality most likely then has the biggest effect on sound quality.

Though I have not heard one, I would bet that that I would prefer the sound of a Benchmark AHB2 over the NAD C372... Most likely due to a different design and different components.

 

[Chr1]

Sorry, should have said the power section of the NAD only.

(wasn't a big fan.)

 

[Doodski]

I would bet that that I would prefer the sound of a Benchmark AHB2 over the NAD C372... Most likely due to a different design and different components.

The NAD C372 is a pretty good amp so whatever you are listening to it would need to be pretty different to hear a difference.

 

[Chr1]

I guess, like other components the differences are subtle. But I think that they are there.

 

[Chr1]

All good...interesting and educational. Thanks. Anyway, my conclusion is that I got a hell of a deal on the Ebay Spanish amp and that it is definitely a good backup and that if my neighbours remain stuck in Holland post covid and I want to throw a party the Crown will get things bouncing!