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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
mitch2
4,043 posts
 
As George points out, suitable impedance matching and adequate voltage gain are critical to achieving good results with a passive.  Other considerations, depending on the type of passive, are the potential for changes in impedance with changes in volume, and the effect of cables on impedance and capacitance.  Passives seem to work best in situations where there are short cable runs after the passive.  You can read a lot about this in these forums.  Active buffering helps control impedance so that it stays low and consistent, and to help with consistent current delivery.
One thing you should consider is that while the stock DNA-1 has an input impedance of 100K ohms, if Steve's upgrade of your amplifier included adding transformers the resulting input impedance was likely changed to only 10K ohms, which would significantly affect your compatibility equation for use with a passive.  BTW, the amplifier I used for my passive comparison described below has input impedance of 100K ohms.
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
11,861 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:


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