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How much do I need to spend to get a preamp that sounds better than no preamp?

Hello all.
I'm using an Audible Illusions L1 preamp and I think my system sounds better when I remove it from the signal path. Oppo BD105 directly to SMC Audio DNA1 Gold power amp. I have read that there is level of quality you need to hit before there will be an improvement in sound. I can't seem to find what that level is. Any ideas?
Thanks in advance,
Ben
honashagen
georgehifi's avatar
georgehifi
10,312 posts
 
I’ve done a blind A/B with 30 of our audio club members using a 10kohm passive preamp. A source with 2.5v at 100ohms output impedance. We had a power amp with 1.5v input sensitivity for full output, the amp had a special switchable input impedance’s on the fly 10 x from 100kohm down to 10kohm

Nobody could tell the difference from 100kohm all the way down to 33kohm, when we got to 20kohm 5 of the 30 members though they heard something but weren’t sure, then it added up from there the lower we got.
During the whole time we made sure the level was spot on within 1 mV from the amps output using a 1khz sine wave.

Cheers George
almarg's avatar
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almarg
9,670 posts
 
Honashagen, some questions:

1)Are you using balanced or unbalanced connections between the Oppo and the Pass? I suspect balanced would be preferable, as I alluded to earlier.

2)Have you tried both the 4 db and 14 db gain settings of the Pass?

3)Are you setting the Oppo’s volume control at or near max when the Pass is being used, which I would expect to provide better results than having that control at a lower setting?

4)If you are using an unbalanced connection to inputs 1 or 2 of the Pass, is a shorting plug or jumper connected between pins 1 and 3 of the corresponding XLR connectors? (See the second from the last paragraph on page 3 of the manual).

Regards,
-- Al

honashagen OP
137 posts
 

I have tried the balanced and unbalanced. I liked the unbalanced better.

I did not try the higher gain setting on the pass.

I do use the oppo at full gain.

I saw those jumpers but did not know what they were for. I'm sure they were not present in input 1 or 2 which were the ones I was using.

atmasphere's avatar
atmasphere
11,841 posts
 

George excerpted a quote from Nelson Pass's website. It makes it look like Nelson had a certain position on the subject, but if you read what follows, you might see that such is not the case. Here is that further text (I've included the end of the text that George quoted earlier):


And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."


I suppose if I had to floor the accelerator to drive 55 mph, maybe I’d think the life was being sucked out of my driving. Then again, maybe I like 55. Nice and safe, good gas mileage…

Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.

This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain – it only interposes itself to make a low impedance into a high impedance, or vice versa.

If you put a buffer in front of a volume control, the control’s low impedance looks like high impedance. If you put a buffer after a volume control, it makes the output impedance much lower. You can put buffers before and after a volume control if you want.

The thing here is to try to make a buffer that is very neutral. Given the simple task, it’s pretty easy to construct simple buffers with very low distortion and noise and very wide bandwidth, all without negative feedback.

There are lots of different possibilities for buffers, but we are going to pick my favorite:


georgehifi's avatar
georgehifi
10,312 posts
 

Ralph (atmasphere) is trying to counter my quote with other quotes.
But it still doesn’t get around the fact, that a favourite sounding Pass preamp of Nelson’s is the Aleph L.
And this preamp is a totally passive switched resistor attenuator as his statement shows, only becoming "active" after the volume control goes beyond 3 o’clock.
This is a patented "active" circuit, that he introduced is for the use with a couple of his Aleph type ect low very gain power amplifiers, which have very little only <20db or so gain, so then the "active" part of this preamp has to make up for this low poweramp gain, but the sound does take a hit as he says when the active circuit comes in beyond 3 o’clock.
Thankfully most power amps on the market are much more gain and the "active" circuit wouldn’t be used, and the Aleph L will stay totally passive.

Nelson Pass:
 "This preamplifier flows from a commitment to create the best sounding product: a simple circuit with the most natural characteristic.

Unique to this preamp, patent pending, is a volume level control which combines the best qualities of a passive attenuator and active gain circuitry:
At the 3 o’clock volume control position, the Aleph L offers a direct path from input to output.
The only component in the signal path is wire and switch contacts.

At positions below 3 o’clock, the volume control functions as a precision passive attenuator using discrete resistor ladders.

Above 3 o’clock, active gain is added to the output signal in 2 decibel increments, for a maximum of 10 dB.
As a result, you suffer the effects of active circuitry only when additional gain is necessary."
As far as impedance matching goes, over 90% of sources and amps have a fine match with passive attenuators.
It’s only the very few tube output >1kohm dacs and very low input impedance <20kohm power amps that can take a slight sound quality hit.
As for interconnects quality low capacitance which thankfully most are, at 2mt or less in length. And you have what Nelson Pass describes as the best way to get the sources signal to the poweramp/s, with control over the volume.

Cheers George
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