New Stack of kit is accentuating background noise from my SMV3 = Sad puppy

[elvi]

I'm a man. And I can admit when I need help..

Help!!

I am retiring my vintage receivers (They are working perfectly, but are now worth so much I hate to lose them to daily usage)
I typically rotate a Harman Kardon 800+ and a Sansui QRX-7001.

My signal path with both the SM V1 and the SM V3 are as follows:

My external sources are connected to a 5 position 2 channel RCA switch box

1: CD
2: Phono Preamp
3: Linux Micro PC
3: FIIO Flac Player
4: BluRay

The output of the RCA Switcher connect to the input of the SM. Input level on the V3 is set just below clipping. As it was connected directly to the inputs, once set I did not have to vary the input gain\cut.
SM output is sent to the "AUX" 4 channel input of the 800+ or 7001
Each channel has discrete tone and a 4 gang volume control.

Life was good. Birds sung, brandy flowed freely. My motor was shiny clean .. Elvi was happy man!

New Stack of Kit

I retired the 5 way switcher; the new preamp has 6 dual channels of discrete relay switching

Preamp = Vincent SA-32 (A two channel hybrid\tube pre. Possibly someone knows what this is a copy\clone of)
Preamp has defetable tone, no low or high filter but has motorized volume

Tone\Volume processed audio from preamp out to stereo input of SM

SM3, input level must be constantly adjusted, due to variable level post Preamp

Quad output from SM to two matched Aiyama A07 stereo amp modules. The integrated volume control is set to maximum.

Result?
Very high noise floor\hiss. This is the background procession\amplification stage from the SM.

Brandy glasses broke, birds fouled my motor .. Elvi was troubled..

OK; time to experiment.

Power off the SM effectively placing it in passthrough mode. No hiss

Remove the SM fully from the equation, with no input and both the preamp and amp module volume in minimum cut (Max volume) No hiss

Short the inputs of the SM, Power the SM on, set the volume control on the amp module to min cut (Max volume). Hiss

So; what I have learned.

Even with no input; and the input level on the SM set to maximum cut (Min volume) the processor\preamplification gain hiss from the SM is present. This is not unexpected, stuff has to happen; and that takes energy..

So; the following begs to be answered?

Why was this not detectable with the 800+ and the 7001?


Here is the Scat of the 7001

Input is through "AUX"
Switches on F-2423 are 4 channel enable and tape monitor; tone tweaking and then volume.

OK. now we have our answer. The 800+ \ 7001 amplify the sum of the selected inputs AND the processing background. I cant hear it, as its buried deep in the media.

With the new kit; with no signal into the SM, we are still amplifying any signal from the SM, at 100 %
The SM is the "Last" In the audio chain, and amplified at whatever the Amp modules can muster. at an advertised 300WPer and a GAIN:21.5db I can see why.

Here is what "We" want. (Yes. you want one too.. )

A preamp that will take many inputs, has a "Quad" input before the tone\amp circuits and Quad out to the amps.

So, Is there a modern multichannel Pre that will work?
Love to have relay switched inputs, motorized 4 channel volume and full tonal control.

Comments welcome!!

 

[chucky3042]

Err um not really sure but it is probably a level matching problem. Can you see if the red clipping LED occasionally comes on, if not try to increase levels somehow.

 

[elvi]

Morning Chucky..

My observations, distilled to a few lines.

1. When the SM is treated like any other signal processor and is allowed to see full unattenuated signal from the various audio sources ( CD, BluRay, FIIO FLAC, PC DAC ) I can dial in a level that flashes the input clipping led, and then slip in the "feeler guage" and back off a snootch. Then the 4 channel output is fed into the preamp tone, amplification and volume controls.
This allows the SM processing/ amplification background to be buried deeeeep in the audio signal, and undetectable. This is the better implementation.

2. If I send all source line signals into the preamp, amplify/ tone tinker them and then take the output of the preamp and send that signal into the SM AND have my amps volume controls to full tilt ( what you want, as the preamp is your volume control) the amps pick up the SM background noise between tracks.

This is NOT a defect of the SM. ANY device could slip in a touch of signal at this point.

So, I'm building a Pre from scratch.. will "insert" the SM just like any other signal processor. Think Carver Holographic here...

( WISH me luck.. off to the bottle shop, and the shed to tinker. )

 

[chucky3042]

Morning Chucky..

My observations, distilled to a few lines.

1. When the SM is treated like any other signal processor and is allowed to see full unattenuated signal from the various audio sources ( CD, BluRay, FIIO FLAC, PC DAC ) I can dial in a level that flashes the input clipping led, and then slip in the "feeler guage" and back off a snootch. Then the 4 channel output is fed into the preamp tone, amplification and volume controls.
This allows the SM processing/ amplification background to be buried deeeeep in the audio signal, and undetectable. This is the better implementation.

2. If I send all source line signals into the preamp, amplify/ tone tinker them and then take the output of the preamp and send that signal into the SM AND have my amps volume controls to full tilt ( what you want, as the preamp is your volume control) the amps pick up the SM background noise between tracks.

This is NOT a defect of the SM. ANY device could slip in a touch of signal at this point.

So, I'm building a Pre from scratch.. will "insert" the SM just like any other signal processor. Think Carver Holographic here...

( WISH me luck.. off to the bottle shop, and the shed to tinker. )

Yep agreed. The Carver preamp was always one of my favorites but I must do a shameless promotion here.........When Dave the Bitch finally finishes our de clicking, de noising pre amp it will be exceptional. I might be worth waiting for.

 

[elvi]

My living room stack is a TX 2 tuner, C2 pre and a M 200t amp driving a set of Altec Segovia...
I appreciate Carver kit.

And we are all waiting for the new preamp...
Always room for the new kit ...

 

[barfle]

Wild-assed guess here, but do you know what levels you’re feeding the SM? If they’re phono stage level, the S/N ratio will be reduced to the point that background hiss gets amplified to the point of audibility.

The diagram shows all signals, including phono and line level signals routed through your preamp/switch, but it doesn’t really indicate any phono gain or other input attenuation.

 

[elvi]

No wild Arsed guessing allowed. Lets pull some specs, and see what I bodged together.. You will see where I went wrong.

The Preamp.

SA-32
https://www.vincent-tac.de/en/product-types/preamplifiers/sa-32.html

Not seeing anything but this: Nominal Output Voltage: 2 Volt
Signal-Noise-Ratio: > 90 dB (Fair, but it does have tubes)

I dont know that much about this device, and assuming its unity gain?

Amp Modules.

Aiyama A07

https://www.aiyima.com/products/amp...-0-channel-300wx2-hifi?variant=32922293272651
SNR:110db
GAIN = 21.5db
Currently powering them at 38Vdc, with a published upper limit of 48Vdc. A post on ASR noted the Caps utilized are close to their limit at 48 volts.



So, to reiterate.. the Pre is not contributing a large amount to the noise floor. (Connect the A07 amp directly to the preamp output, set pre volume to min cut (Max volume)
Set the Amp to min cut (Max volume) These is a slight detectable noise floor.

So, if you want to follow along at home:

Take a single RCA cable, or a pair of shorting plugs and short the inputs on the SM.
Connect the SM to an amp.
If it has a volume or gain; set that to max. (Leave the amp off)
Power on the SM, set the input gain to -6 (Minimum)
Power on the amp, engage the speaker select or de-select the mute.

This noise is the processors\gain buffers happily humming along doing their job.

To verify see the difference with the SM powered\powered: the noise floor will drop away to naught when the SM is powered off, and in passthrough mode.


Once again; it is not a defect in the SM. All signal processors\input devices have a noise floor to some part.

As I had my stereo cabinet scattered to the 4 corners of the house, I did a little experiment.

My Quad Teac 8-Track needs updated silicone\eCaps.. and sounds like my electric kettle if I turn the amp modules to maximum.
My Pioneer RT-707 hisses as well.
My Sansui SD-5050 scared my cat..
My TATE II was quite egg fry-yee..

At that point, I got tired carrying heavy R-2-R's, gave up and had a brandy ..

What I learned:

So, yes its better to place the SM inline before the Preamp. THAT was the stacking error I made, placing the SM post Preamp, as the gain from the SM was always at maximum.

Currently, I have the gain pot on the amp modules a 60%, and have to adjust the SM and Pre volume in synch. (To keep the peak LED just on the verge of flashing)
Doing this the noise disappears in the program signal, and is not a bother.

( Apparently, I am cursed with the hearing of a 20 year old.. )

Comments?

( Keep checking back, I just dropped orders for parts.. )