Abomination! or Painting a Mustache on the Mona Lisa meets the Island of Dr. Moreau

[MJL21193]

Originally posted by G.Kleinschmidt



Or if you are feeling really adventurous you can ...

That sounds like a worthwhile thing to do.

Here's how the sim shows it with a "real" power supply. Notice the magnitude of the ripple on the output as opposed to that from the supply.

[GK]

Originally posted by MJL21193



That sounds like a worthwhile thing to do.

Here's how the sim shows it with a "real" power supply. Notice the magnitude of the ripple on the output as opposed to that from the supply.

Well of course the PSRR is high at such a low frequency, genius.

[MJL21193]

Originally posted by G.Kleinschmidt

...genius.

Only my close friends are alllowed to call me by my first name...

[MJL21193]

Originally posted by G.Kleinschmidt



Or if you are feeling really adventurous you can return the amplifiers power supply to ground via 4 or 8 ohm resistive dummy load,

Lets see... that both rails together or one at a time? Let's try one - 72.6VDC rails into 8 ohm load ....equals ~9 amps...or 654 watts...getting quite warm here!
Oh, the 4 ohm, I forgot. that's only 1318 watts into my trusty dummy load.

No problem.

[wg_ski]

Originally posted by MJL21193


That's what is coming out of the supply, BUT although the scope is still at it's lowest setting the probe is set to 10X! Significant ripple, no?
This is what the amp is rejecting and not amplifying.

That's nothing compared to what it has to deal with in operation under load. With music that supply will be jumping all over the place - magnitide shifts, changing ripple amplitudes, subharmonics of low frequencies when driven to clipping. It's a lot harder for the amp to deal with all that trash than a simple periodic waveform. The effects of that will usually be masked by whatever music is playing. But on an adjacent channel on the same supply - you'll "hear" how good/bad your PSRR really is. If the other channel stays dead quiet, then you've got a good design and layout. With most amps, it won't stay dead quiet.

[MJL21193]

Originally posted by wg_ski

- you'll "hear" how good/bad your PSRR really is. If the other channel stays dead quiet, then you've got a good design and layout. With most amps, it won't stay dead quiet.

Ok, now I get it. Yes, I feel embarrassed - slightly. I'll recover .

I did as wg-ski instructed:
I connected another amp to the same supply (OS' Frugal2) and drove it with my signal generator. It was connected to the 8 ohm dummy load. I drove this amp to clipping at different frequencies.
The amp being tested (Abomination) was connected to the scope and a fullrange 8 ohm speaker. Even though the scope did show some ripple, especially at higher frequencies, there wasn't enough to be audible through that speaker. Not depending on my hearing, I asked my 18 year old son to have a listen - nothing. To be sure I switched to a square wave and then and only then could he hear a very faint buzz from the speaker.

Oh well, it must be below the noise floor, and apparently I have a good design AND layout.

[jacco vermeulen]

AND a thick head.

[MJL21193]

Originally posted by jacco vermeulen
AND a thick head.

It's helpful responses like this and from that social dilettante Glen that make this so much fun.

Keep up the good, encouraging work fellas.

[KLe]

Hi MJL
You don't think that it is worth Simming?

[MJL21193]

Originally posted by KLe

Hi MJL
You don't think that it is worth Simming?

Hi KLe,
The sim may show some DC on the output (it does: -3.5V) but that can't be relied on. Real measurements are needed and to justify extra DC offset, it would need to "sound" better, so some critical listening would be in order.

Not my ears though - I strained them listening for sound of bad PSRR (or was that the sound of one hand clapping?)