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Peachtree Audio Nova - No subwoofer connection

I just switched from speakers (Martin Logan Ethos) needing no subwoofer to a pair of monitors (Reference 3A MMC Serie) which have an advertised lower limit of 40-42 Hz. This is fine for most of our listening but there are occasions, like when watching movies, when additional bass would be nice. I have a Polk Audio Micropro 4000 which seems very capable but the Nova has no dedicated connection for a sub. I talked to a Peachtree technician who said the only way to connect a sub is to use a splitter at the RCA pre-out connection dividing the signal between the Peachtree 220 amp and the sub. I tried this before and, of course, the sub works fine but it changes the overall sound in a not good way.....and I'm not good at judging minor changes.

I also use the Behringer Ultracurve 2496 in the system and separating the signal this way bypasses the sub's signal from the equalizer so auto room adjustments won't include the range of frequencies that would be produced by the sub. I suppose that if there was a dedicated sub out connection the result would be no different. Because base frequencies, though, are a big part of adjustments for the purpose of room equalization, this is a problem.

Because the 2496 has an unbalanced 1/4" aux out" it crossed my mind that it could be used for a sub. The manual doesn't seem to address this and I've not found discussions about this on the Internet. I've also not been unable to establish communication with Behringer for their help.

There's a good chance that I'm off base on some of these assumptions about this all works but if anyone has suggestions that might help with this dilemma it would be much appreciated.
128x128broadstone
zd542
5,339 posts
 
"These terminals look like speaker level inputs as would be the inputs on a passive sub and if this were the case that connection would bypass the sub's amplification circuitry; they assured me that this is not the case and all capabilities would remain operational such as volume, phase control, room balancing, filters, etc. I'm confused. Having a speaker level signal delivered to anything other than directly to a driver makes no sense unless their is some attenuation circuitry reducing the signal level. Also, what about the impedance reduction resulting from paralleling the speaker outputs."

I get why you think this might be a bad idea, but its not. Its perfectly OK to use the speaker cable connection the way Polk recommends.
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almarg
9,670 posts
 
ZD, with nearly all systems you would be correct, but not in this case.

Jim (Broadstone), I'll start with what is most important:

DO NOT CONNECT THE SUB TO THE OUTPUTS OF THE PEACHTREE 220 AMPLIFIER, unless Peachtree says it's ok, and they have said that it's not ok. I and Kijanki explained the reasons in this thread.

Although powered subs which provide speaker-level inputs almost always do in fact incorporate attenuation circuitry to reduce the signal level provided to the sub's amplifier, and although such subs almost always provide a very high input impedance to a power amplifier they may be connected to (resulting in negligible loading), the design of your specific amplifier appears to completely rule out the use of that kind of connection. At least without the use of a very specialized adapter incorporating DC blocking capacitors, as explained in the other thread.

Regarding connection of the sub to the preamp, can you tell us the exact model name or number of the Peachtree Nova? If it is this one, for example, it appears to have two individually buffered sets of outputs, each having low output impedance. Connecting one to the power amp (preferably Pre Out 1, which is described as being "discrete class A") and the other to the sub should work fine in that case. Aside, perhaps, for subtle possibilities such as ground loop issues that may arise when interconnecting three components.

Best regards,
-- Al
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broadstone OP
310 posts
 
ZD and Al, I'm always glad when you guys respond to my concerns and I've applied your advice more than a couple of times. This one, though, is a bit scary and I probably could have provided more information for you to consider in the first place.

First, the component I'm using as a preamp is the Peachtree Nova 80WPC integrated amplifier. It has two outputs, one marked "pre out", the other is labeled "line out". I accidentally connected the amp to the line out plugs once and thought I'd blown my speakers with the incredibly loud resulting volume.

Also, Peachtree didn't tell me NOT to use the speaker level signal to the sub; they simply said that the splitter from the pre-out connections was the only way. I tried to discuss the specific issue with Polk sub but they, like me, didn't know enough to feel comfortable giving more advice than that concerning the pre-out splitter.

It strikes me that there are 2 ways to do this; the first is to use the splitter method but, and it could have been my imagination, I thought that this resulted in some sound degradation. The other is to reincorporate the equalizer. Is this a good assumption and is it the sonically the best choice?
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almarg
9,670 posts
 
Jim, I couldn't find an output impedance spec on the pre-outs of the Nova 80W integrated. However the Nova 65SE, 125SE, and 220SE all have the corresponding output impedance specified as "< 50 ohms." Assuming your Nova is similar in that respect, I don't know why it wouldn't be able to drive your power amp (which has a very high input impedance) and the sub at the same time, without perceptible sonic degradation.

I recall from the other thread I linked to that you have a multimeter. What I suggest is that you set it to measure DC volts, and while the amp is powered up but no music is playing measure the DC voltage between each of the output terminals of the amp and the ground sleeve of an RCA input connector on the amp. You can do that while the amp is connected to the speakers and the Nova.

If you measure a high voltage, such as 40 volts, that rules out use of speaker-level connections to the sub, at least without the specialized adapter I referred to. If you read a tiny fraction of a volt, then an approach that should work would be to connect the positive speaker-level inputs of the sub to the positive output terminals of the amp, and to connect the negative speaker-level inputs of the sub to a ground point on the amp. The chassis of the amp MIGHT be a suitable ground point, but a surer bet would be the ground sleeve of an RCA connector, or pin 1 of an XLR connector.

Good luck. Best regards,
-- Al
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almarg
9,670 posts
 
P.S: Subsequent to submitting the previous post, I did find an output impedance spec for the pre-outs of your Nova 80W integrated, that spec being "<30 ohms." So, again, I don't know why it wouldn't be able to drive the sub and the amp without sonic degradation.

Best regards,
-- Al
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