Class A vs AB -- Do They Really Sound Different?

[Pdxwayne]

Once again, input open or shorted? Input must not be open. You catch fields then.

I am not exactly sure what you meant.

What would be considered open vs shorted?

I have tried with and without any input cable (RCA or xlr) connected to Parasound inputs and it made no difference.

It is obvious with my Paradigm speakers, but none at all with my low cost Pioneer speakers. My Paradigm speakers are not that efficient anyway....

 

[pma]

PSU noise?

Yes, because of very high idle current. However below -90dBV, less than many class AB. PSU related noise is below the 20Hz-20kHz integrated noise which makes 56uV.

 

[pma]

What would be considered open vs shorted?

You must short the input connector of the A21 (it is normally closed by output impedance of the preamp or DAC). Pin 2 and 3 of XLR to pin 1. Or short the RCA input. If you do not do it, input is open, sees the input impedance (resistor noise + EMI coupling). You need to fulfil basics to make valid experiments. Sorry I will leave the PC now , we go to elementary.

 

[Pdxwayne]

You must short the input connector of the A21 (it is normally closed by output impedance of the preamp or DAC). Pin 2 and 3 of XLR to pin 1. Or short the RCA input. If you do not do it, input is open, sees the input impedance (resistor noise + EMI coupling). You need to fulfil basics to make valid experiments. Sorry I will leave the PC now , we go to elementary.

Thanks! I will check that out. Never thought that any kind of short is required....No such instructions I could recall seeing in Parasound user manual.

 

[Ken Tajalli]

Yes, because of very high idle current. However below -90dBV, less than many class AB. PSU related noise is below the 20Hz-20kHz integrated noise which makes 56uV.

high idle current may raise ripple, That! looks like rectifier switching noise.
50Hz is a leak, 100Hz is ripple. higher harmonics of it are high.
not hard to fix.

 

[Pdxwayne]

You must short the input connector of the A21 (it is normally closed by output impedance of the preamp or DAC). Pin 2 and 3 of XLR to pin 1. Or short the RCA input. If you do not do it, input is open, sees the input impedance (resistor noise + EMI coupling). You need to fulfil basics to make valid experiments. Sorry I will leave the PC now , we go to elementary.

I guess this is not really class A vs AB issue?

Apologize to everyone ahead of time for prolonging this side discussion.

Just to be clear, what you want me to do is this:

If I connect via RCA from my preamp to Parasound, I need to connect shorted XLR cables to the XLR inputs.

If I connect via XLR from my preamp to Parasound, I need to connect shorted RCA cables to the RCA inputs.

Am I correct?


Can I do this instead? Would this also close all inputs of my Parasound?
Connect from preamp #1 (stereo preamp that connects to my DAC) via RCA. This is the preamp that plays music.
Connect from preamp #2 (my AV preamp) via XLR. I will use the preamp xlr channels that do not play any music notes.

Thanks!

 

[Ken Tajalli]

Thanks! I will check that out. Never thought that any kind of short is required....No such instructions I could recall seeing in Parasound user manual.

it is not in any user manual. it is however a basic check for trouble shooting.

 

[Pdxwayne]

it is not in any user manual. it is however a basic check for trouble shooting.

Can you answer post #286? Thanks!

 

[Ken Tajalli]

I guess this is not really class A vs AB issue?

Apologize to everyone ahead of time for prolonging this side discussion.

Just to be clear, what you want me to do is this:

If I connect via RCA from my preamp to Parasound, I need to connect shorted XLR cables to the XLR inputs.

If I connect via XLR from my preamp to Parasound, I need to connect shorted RCA cables to the RCA inputs.

Am I correct?


Can I do this instead? Would this also close all inputs of my Parasound?
Connect from preamp #1 (stereo preamp that connects to my DAC) via RCA. This is the preamp that plays music.
Connect from preamp #2 (my AV preamp) via XLR. I will use the preamp xlr channels that does not play any music notes.

Thanks!

need to disconnect your preamp from the poweramp.
use a piece of wire to connect the centre pin of phono input to the outer surround or a part of metal casing.
do the same with XLR inputs as he said too.
turn on the amp, and see if hum persists.

 

[MakeMineVinyl]

Yes, because of very high idle current. However below -90dBV, less than many class AB. PSU related noise is below the 20Hz-20kHz integrated noise which makes 56uV.

Sometimes the orientation of the power transformer is slightly off, and this can cause measurable increases in AC related noise. If the transformer is a toroid, rotating it to find a null can help.

 

[Pdxwayne]

need to disconnect your preamp from the poweramp.
use a piece of wire to connect the centre pin of phono input to the outer surround or a part of metal casing.
do the same with XLR inputs as he said too.
turn on the amp, and see if hum persists.

I see, so this is just to investigate, not a solution suggestion...

 

[Ken Tajalli]

I guess this is not really class A vs AB issue?

Apologize to everyone ahead of time for prolonging this side discussion.

Just to be clear, what you want me to do is this:

If I connect via RCA from my preamp to Parasound, I need to connect shorted XLR cables to the XLR inputs.

If I connect via XLR from my preamp to Parasound, I need to connect shorted RCA cables to the RCA inputs.

Am I correct?


Can I do this instead? Would this also close all inputs of my Parasound?
Connect from preamp #1 (stereo preamp that connects to my DAC) via RCA. This is the preamp that plays music.
Connect from preamp #2 (my AV preamp) via XLR. I will use the preamp xlr channels that do not play any music notes.

Thanks!

disconnect everything from the amp, but electricity and speakers. short the input as instructed.

 

[Ken Tajalli]

I see, so this is just to investigate, not a solution suggestion...

Yes, without diagnosis , we are in the dark.

 

[SIY]

AC power related stuff in there, though still down in the mud.

Likely from radiation from the transformer/rectifier. It was a bit worse in one channel than the other. Point is, though, no repetitive spike in the residual at zero-crossing.

 

[pma]

Likely from radiation from the transformer/rectifier.

... and then PCB design is crucial. Ground returns from bypass capacitors, signal grounds. Induction from charging current peaks. FB take-off point. It may make 20dB difference easily, from a PCB design.

 

[SIY]

... and then PCB design is crucial. Ground returns from bypass capacitors, signal grounds. Induction from charging current peaks. FB take-off point. It may make 20dB difference easily, from a PCB design.

Look at the 60 Hz.

 

[pma]

Look at the 60 Hz.

... and 120Hz

 

[restorer-john]

Guess who sent @amirm a TOTL Marantz PM-90? That's one generation newer than the PM-95, and drops the on-board DAC resulting in better "advertised specs" of 111 dB vs 106 dB SNR and a THD of 0.0015% instead of 0.0080%. It's the last Marantz before HDAM was introduced in the PM-99SE (which resulted in a poorer advertised THD of 0.0050%)?

The PM-90 is basically a PM-88se built on the PM-95's die-cast chassis with a fold down flap instead of visible front panel controls. It was less than half the price of the PM-95 and lacks a huge amount of cost that went into that unit. The PM-95 has (my count in my unit when I restored it) 27 gas-filled relays just for source selection and signal routing. The D/A converter section is the same as the CD12/DA12LE with a hand selected TDA-1541S1- they took the S1 chips and picked the very best ones for the DA-12 and the PM-95 because Bitstream was where Philips was at.

They are similar to look at externally but not remotely close in construction. Just as the PM-94 and PM-95 share no DNA whatsoever (I have them both)- the only thing common is their use of triple paralleled Toshiba 2SJ-115/2SK-405s. Other than that, totally different. Just the optional remote for the PM-95 was $700 (RC-95PM). Mine was never taken out of the box- I use the CD-12/DA12LE remote as it duplicates most of the key functions.

 

[SIY]

... and 120Hz

Yes, exactly what you expect from radiation pickup. If it had been my amp, I'd be rotating the transformer to see if I could get a null. But that's a step too far for a review loaner.

 

[restorer-john]

If it had been my amp, I'd be rotating the transformer to see if I could get a null.

Do you remember cassette decks back in the day had arced and pre-drilled threaded holes in the chassis for rotating/shifting the transformers individually to ensure the lowest levels of hum and buzz from transformers? The good old days.