About to try integrating subs...

[DonH50]

In-room bass response is highly dependent upon the room...

 

[ths61]

Here is a whitepaper that may be of interest to you regarding integrating and setting up subs.

http://www.soundoctor.com/whitepapers/subs.htm

HTH

 

[dafos]

I use 2 Gotham subs with my speakers playing full range. I cross the subs at 43 hz so I am supplementing the bottom end with the subs.

I use the second main out from my preamp and run these left and right through a tube buffer and then to my subs. Tube amps and the Gotham subs have a huge input impedance misbalance. Hence the tube buffer

Hi Steve, didn't know about that tube buffer, may I know what brand and where you got it? Your right about the imbalance as the JL audio's input impedance is only 10k while my ref 250's input impedance is 200k. I have in fact wondered if I'm not taxing my line stage's outputs by driving the low input impedance of the JL audio which, to my thinking, is akin to an amp being tasked to drive low impedance speakers.

 

[microstrip]

Hi Steve, didn't know about that tube buffer, may I know what brand and where you got it? Your right about the imbalance as the JL audio's input impedance is only 10k while my ref 250's input impedance is 200k. I have in fact wondered if I'm not taxing my line stage's outputs by driving the low input impedance of the JL audio which, to my thinking, is akin to an amp being tasked to drive low impedance speakers.

Most probably, but no textbook or specification will give you a definitive answer. My advice - get a dummy load of 10k (it easy to assemble, just get a XLR female plug ad solder a 10kohm resistor between pin 2 and 3) and listen with and without load. If you notice any difference you have to get a buffer.

The situation is different from a speaker load - you will not get current limitation or clipping effects. You will get a high pass filter effect due to the preamplifier capacitors (in the REF40 they are larger than usual - 10 microfarad, so it would not be a problem), but some circuits have higher distortion driving lower input impedance. It is not difficult to measure, but AFAIK no one did it for the REF40.

 

[dafos]

Great tip, thanks!

 

[Steve Williams]

Hi Steve, didn't know about that tube buffer, may I know what brand and where you got it? Your right about the imbalance as the JL audio's input impedance is only 10k while my ref 250's input impedance is 200k. I have in fact wondered if I'm not taxing my line stage's outputs by driving the low input impedance of the JL audio which, to my thinking, is akin to an amp being tasked to drive low impedance speakers.

I use MUSICAL FIDELITY X-10 V3 TUBE BUFFER with its optional power supply. They are both modestly priced at about $350-$400 each

http://www.musicalfidelity.com/uploads/manuals/English/x10v3_eng.pdf

http://www.musicalfidelity.com/uploads/manuals/English/xpsuv3_eng.pdf

These are not made anymore but if you search you can find them. I recommend it with its optional power supply. The tube in it will almost certainly never have to be replaced.
Even though JL Audio told me that a tube buffer wasn't necessary, I was concerned that I had 2 unequal loads running in parallel from my Lamm LL1 Signature preamp

 

[DonH50]

That looks like a nice product, Steve.

Note in this application the unequal load should not matter as the amp inputs typically sense voltage and that is the same at both loads no matter the mismatch (assuming realistic -- negligible -- cable impedances, natch).

However, the net load impedance can degrade the sound if the preamp's output impedance is high, as is often the case with tube preamps.