subwoofer output from my tube preamp

[lexx21]

I am looking for a way to add a low pass output off of my tube preamp. Currently I am planning on using a 6sn7 for my next stand alone preamp but here is what I am wondering ....

If I were to build a low pass filter using the LM741 op amp (I have a bunch on hand) and attach that to the output of the preamp:

1) What would the impact be on the audio going from the preamp to the power amp for frequencies above 70hz? The input resistance to a 741 is 300k (at least from what the datasheet says)

2) Would the output of the preamp smoke the op amp?

3) Would such an idea even be worth pursuing?

The input of the op amp would connect to the output of the pre and go from there into a powered sub. I am thinking that this will allow the level of the bass to increase/decrease with the desired volume level of the preamp.

I currently have a passive sub connected to my 6v6 amp but am really not satisfied with the sound so I am looking to do something better at this point.

Any thoughts or does someone here know of a better way of doing this? ANY help here would be greatly appreciated.

 

[Eli Duttman]

Assuming tubed power amplification for the main speakers, use the speaker level I/Ps on the S/W "plate" amp. Do not "daisy chain" from the tubed power amp to the S/W and on to the main speakers. Simply connect the S/W speaker I/Ps in parallel with the main speakers to the tubed power amp, which allows the main speakers to play as close to full range as they can. Adjust the controls of the S/W to fill in, from below, where the main speakers do not reach.

The arrangement described allows the "plate" amp of the S/W to pick up some of the sonic signature of the tube power amp. As a result, overall integration of the sound is BETTER.

BTW, "super-duper" speaker cable between the S/W and the tube amp is unnecessary. You will find 16 AWG "rope lay" OFC zip cord to be quite sufficient.

 

[scott17]

Check out post #8 in this thread:
http://www.diyaudio.com/forums/solid-state/208473-simple-subwoofer-buffer-summer-circuit.html

I built one, works fine.

 

[lexx21]

Yes, this is going to a tube amplifier. All of my gear is tube at this point.

I had thought of trying something like this:

Low pass filter for subwoofer - Electronic Circuits and Diagram-Electronics Projects and Design

My main concern is the input impedance of the op amp and the effect it would have on the loading of the tube preamp output. I'm not sure if that would really make much of a difference or not.

 

[JonSnell Electronic]

The IC is incorrectly described as a TL062! Use TL072 and change the input resistors R1 + R2 from 39k to 390k. Replace the 47k pot R3 with 470k pot. The rest is fine.
That will give you practically no extra loading on your pre amp.

 

[Sodacose]

Assuming tubed power amplification for the main speakers, use the speaker level I/Ps on the S/W "plate" amp. Do not "daisy chain" from the tubed power amp to the S/W and on to the main speakers. Simply connect the S/W speaker I/Ps in parallel with the main speakers to the tubed power amp, which allows the main speakers to play as close to full range as they can. Adjust the controls of the S/W to fill in, from below, where the main speakers do not reach.

The arrangement described allows the "plate" amp of the S/W to pick up some of the sonic signature of the tube power amp. As a result, overall integration of the sound is BETTER.

BTW, "super-duper" speaker cable between the S/W and the tube amp is unnecessary. You will find 16 AWG "rope lay" OFC zip cord to be quite sufficient.

This is how I connected a sub to my integrated tube amp after much reading and deliberation on how to add a sub-out. Sub is on banana jacks and speakers on regular speaker cable to the same binding posts on the amp. Pleased with the result.