How do you wire a sub to a preamp that doesn't have a sub out?

[Mike Lindsey]

As most of you know, I just picked up a pair of La Scala's that Q-Man is currently refinishing for me. I will be using them for both HT and 2-channel systems with separate amplification. The 2-channel system will consist of tube amp/preamp (to be named later) with my Dual CS-5000 TT w/Shure V15V-MR, AES PH-1 phono stage and Rega Planet CD player.

I was wondering if there was a way to wire in my SVS 20-39CSi subwoofer w/Samson S700 amp to handle the low frequencies. This is accomplished in the HT setup by running an RCA cable from the Sub preout on the Denon to the Samson Channel 1 input. Is it possible to use the SVS/Samson with a tube amp/preamp and if so, how? How would it know where to crossover? My Sub is passive and has no controls on it...

Thanks,

Mike

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My Music Systems

[Audio Flynn]

I recently read you can get one of the Manley tube integrateds ordered with a sub out.

Many years ago maybe I would have checked an industrial audio company like Furman. Someone like them would make an outboard crossover that you could run a tape out to perhaps.

[Malcolm]

What you need is a subwoofer crossover.

You may be able to do what you want with a circuit as simple as two resistors and a capacitor. Oversimplified schematic:

L out --------/\/\/\---+

/

Ground -----------/(---+-------- Sub amp in

/

R out --------/\/\/\---+

With appropriate part values, the circuit sums the left and right outputs while maintaining good isolation of the two channels and rolls off the input to the sub. The capacitor will be of a fairly small value and cheap. Value depends on the input impedance of your sub amp and crossover point. This type of circuit is probably best used with speaker level outputs. Used with line level outputs, it may require an additional stage of amplification if the resistors are large enough to provide good isolation. Maybe somebody can post some typical values.

If you want to get fancy, you can build or buy an active crossover. You might want to check out http://www.marchandelec.com/ for ideas.

[Deang]

Mike,

I was in the same boat after I bought my AE-25 and SVS CS+/Samson. I did a lot of reading and looking before finding something I felt I would be satisfied with.

Please click on the link in my signature below and take a look at the HSU crossover.

Nothing fancy here. Just a little black box with volume control, phase button, and bypass (so you can run full range on your mains without the sub).

However, you open it up and you will find only the best parts used.

Another reason I settled on it is because it uses a 24db/octave crossover for both the low pass AND the high pass.

This very important. Most crossovers in subs use a 6db/octave on the high pass. They are primarily designed to work with monitors and satellites, and every sub I had previously used that damn 6db/octave high pass locked in at 80 or 90Hz.

With the HSU unit, you can actually CHOOSE where you want the high pass set at, and since it is 24db/octave -- the integration with the sub is totally seemless.

With my RF7's I got the 51Hz modules for both the low pass and the high pass. It sounds dynamite.

It's very easy to set up. Just run your two interconnects (L/R) from your pre outs on your preamp to the high pass inputs at the back of the unit. You then take two more interconnects (L/R) and run from the high pass crossover outputs to the amplifier inputs (L/R). This takes care of the mains.

To do the Samson, you take your SVS supplied interconnect and put a 'Y' adapter on the end (this will give you 'left' and 'right' inputs) and plug into the L/R low pass inputs. Two more interconnects go from the low pass outputs on the crossover to the Samson inputs -- and you are done.

Since the full signal is run through the crossover -- it really should be the best you can afford. The HSU unit is killer for $413.00.

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Deanf>s>

Cary AE-25 * S F Line 1 * S9000ES * HSU x-over * SVS CS+ * Klipsch RF7s f>s>

Psalm 122:6f>c>s>

This message has been edited by deang on 06-19-2002 at 10:42 PM

[Mike Lindsey]

Thanks Dean! That definitely may be the answer. I'm gonna shoot you an Email as I have a couple more questions...

Mike

Edit: I just noticed your Email was not available so I guess I'll ask it here.

You say to do the Samson, you take your SVS supplied interconnect and put a 'Y' adapter on the end (this will give you 'left' and 'right' inputs) and plug into the L/R low pass inputs. Two more interconnects go from the low pass outputs on the crossover to the Samson inputs -- and you are done.

Not quite sure what you are telling me here. At present, I run an RCA cable from my Denon Sub preout into the Samson channel 1 input with a 1/4" TRS plug on the end of it. I then run speaker wire from the Samson output (banana plug) into the SVS using a spade connector.

I'm kind of stupid when it comes to stuff like this so if you can explain it to me in a little more detail, I would greatly appreciate it. Maybe you are and I'm still not understanding it.

Also, is it possible to do this using channel 2 on the Samson? I would like to leave channel 1 as it is, since it also incorporates my ICBM for HT and DVD-A use. I know I would need one of those Russound A/B splitters to accomplish this (not sure how bad that would degrade the signal) but was wondering if that was possible as well. These will be 2 totally different systems with Channel 1 being used for Solid State HT/DVD-A and Channel 2 for the 2-Channel tube system.

Thanks again,

Mike

This message has been edited by Mike Lindsey on 06-20-2002 at 07:47 AM

[Deang]

You saidNot quite sure what you are telling me here. At present, I run an RCA cable from my Denon Sub preout into the Samson channel 1 input with a 1/4" TRS plug on the end of it...

Of course you don't understand what I'm saying -- it's because I told you wrong.

The 'Y' cable goes on the RCA end of your SVS cable and will plug in the L/R outputs for you low pass section of the crossover.

It's probably easier if I just show you. Click on the Pic.

As far as your other question goes, I'm not quite sure. I suppose you could get another cable from SVS and come off of your HT system into the other, non-used channel of your Samson -- and just use the volume control on the front of the Samson corresponding to the system you want to use the sub for.

This is a good question for Boa, or TV himself. You could email Tom at SVS -- he would know for sure. It should work though.

Did you see that my Super Amp is for sale?

f>s>

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Deanf>s>

Cary AE-25 * S F Line 1 * S9000ES * HSU x-over * SVS CS+ * Klipsch RF7s f>s>

Psalm 122:6f>c>s>

This message has been edited by deang on 06-20-2002 at 09:31 AM

[Mike Lindsey]

Dean,

That explains it much better. BTW, will probably have to set mine at 62hz but will try it at 51hz and see how it sounds. Just out of curiosity, will this allow more power from the tube amps to power the mids and the highs? Isn't this a good thing?

Mike

Edit: Just saw your edited post. I will talk to boa as he seems like the resident genius when it comes to this sort of thing. Did see your AES was for sale but am leaning towards the Wright 3.5's for the same money. I see there is a pair for sale on Audiogon as we speak. Let me think it over and I will get back to you.

This message has been edited by Mike Lindsey on 06-20-2002 at 10:04 AM

[Deang]

In spite of what others might say -- I think you would find the additional power of the Super Amp beneficial in the long run.

The HSU crossover does NOT have an adjustable crossover per se. It uses little plug in modules that connect directly into the ciruit board. You would order it with your desired crossover, and HSU would install the appropriate modules. Additional modules are $15 a piece and you need them in pairs (high pass and low pass). They are quite easy to change out.

Yes, since you are effectively biamping -- you are alleviating the necessity of your amp to play the low frequencies -- this increases the amps headroom.

The lower the crossover point the better. Let your Scalas do what they were designed to do. You don't want to rob from the LaScala's horn loaded bass. I would go with 51Hz and simply try to extend the bass response.

f>s>

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Deanf>s>

Cary AE-25 * S F Line 1 * S9000ES * HSU x-over * SVS CS+ * Klipsch RF7s f>s>

Psalm 122:6f>c>s>

This message has been edited by deang on 06-20-2002 at 01:31 PM