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Adding a Subwoofer to Cyrus Pre Power Combo


Standard Member

I would like to add a Subwoofer to my stereo system which consists of a Cyrus PreXvs and two Smartpower Plus's, which are running as mono amps and driving PMC GB1 speakers.

Is it possible to connect a Subwoofer to the Mono Chain Outputs on each Power Amp using Phono Leads?

If not, then is it possible to connect a Sub using speaker wires and if so how?

Haven't decided what Sub to buy yet but it will be an Active Sub.

I also have a Yamaha RX V1065 which is connected to my Pre Xvs via Pre Outs, and that sends the Low Frequency to the GB1's. It would be easier to connect a Sub to the RX V1065 but then I wouldn't get the benefits in stereo too.

Please help cos it's driving me nuts trying to figure this out.


Standard Member
Well 90 people have viewed this and not one of them has replied. I bought a Velodyne SPL 800 Ultra and all I have to do is connect it either to one or both of my Power Amps using phono leads or subwoofer cables. Pretty easy really. Just leave the Yamaha as it is with the Low Frequency's sent to the front left and right speakers, which in turn send them to the Sub. If it turns out that the salesman has misled me and i blow my system up I'll let you know.

Member 639844

Former Advertiser
There are a few subs out there offering a high level connection, which merely requires connecting speakers wires to the existing speaker connections of your amp, and the sub simply reads the low bass content and reproduces it. Some subs will allow a high level phono connection, but not a lot, so you would have to keep your eyes peeled on that one. A normal full range signal via a low level connection isnt ideal, but can work as long as the sub has a variable low pass filter.

In all cases the sub would need to be integrated with your speakers natural roll off, and some experimentation would be needed to get it perfectly smoothly integrated properly. An SPL meter would also be a useful tool in gain matching the sub to the speakers.


Standard Member
Hi Moonfly

Out of interest if I were to connect via speaker wires how would I do so considering my HiFi uses bi-wires?

Member 639844

Former Advertiser
You would need to connect the high level connection of the subwoofer to the bass driver speaker cables, either at the speaker end of the amp end.

Note: in a high level connection system like this, the speaker channels dont power the sub in any way, the speaker wires form the sub are simply reading the bass content being sent to the speakers bass section.


I just noticed you picked yourself up a Velodyne SPL800. IIRC it does not have a high level speaker wire connection anyway, only phono inputs, so that would be your connection method. You simply need to set the low pass filter to match the low frequency response of your speakers, and set the volume of the sub to match that of your speakers using an spl meter and a test tone.

Lets be certain about what we are dealing with here though, is this how the back of your amp looks with regards to input connections?:

Last edited by a moderator:


Standard Member
Hello again
I haven't received it yet but that looks like what I'm expecting. Are you sure that the Cyrus combo cannot be connected either with speaker level inputs or Line levels? I wondered whether it might be better to connect my Yamaha RX V 1065 using its sub pre out and also connect the Cyrus amps using the speaker level inputs. If it was possible to use the speaker level inputs would I have to connect wires to the same wire inputs on my power amps or could I use inputs that are currently free on the power amps. I suppose it would be easier to stick with my first option of using the Line Ins but am I missing out on anything by not using the Yamahas Sub Out? Aside from this apparently my PMC GB1' can go down to 29 herts so what should I set the subwoofers low pass filter? I'm not very techy so maybe I am not using correct terms but hopefully you'll get what I'm trying to say. Thanks again for your time and efforts.


Standard Member
Well, my shiny new Velodyne has arrived and was easy to connect to my Power Amps using Line Level connections. Used the EQ to set it up for my room then played around with volume levels until I was happy with the sound. Bought one of those SPL meters for £15 from Matlins though not quite sure how to use it for gain matching. I've set the Sub Low Pass Crossover to 60Hz and it definitely has added something to the sound that I was already over the moon with. Got some Crystal Method on at the moment and there are some serious low frequencies that I would not have heard before. Will stick some Blu Rays on later.


Active Member
Something of a thread resurrection here as I have a very similar question and it's not clear from my reading of the above whether my interpretation of what to do is correct?

I have a Yamaha AV receiver (an old DSP A2) which connects to my AV sources. This has an LFE out (mono) as most 5.1+ decoders do. This LFE out is obviously a pre-amplified signal. I need to connect this to my sub in order that I get LFE sound on my AV sources.

My AV amp then outputs via the front pre-amp out terminals to my (new) Cyrus stereo integrated amp. This amp is set to direct (unity gain / fixed level) input for the AV - effectively just acting as a fixed stereo power amp. Importantly, it also allows me to connect direct stereo sources (CD, streamed digital) on other digital input channels for improved stereo performance (as these sources don't touch the poorer quality AV pathway at all).

The question I have is can I connect my pre-amp out from the Cyrus to my sub-in (all of which are pre-amplified levels) to ensure my sub also provides LFE for my stereo sources as well as AV? I'm thinking:

AV LFE out -> RCA splitter (mono to stereo) -> two LFE out RCA jacks (identical signal, half the current, pure LFE signal which has been through a low-pass crossover in the AV amp). The splitter may not be strictly necessary but feels "right" to me for some reason.

Cyrus Preamp Out -> two LFE RCA jacks (L/R signal, full current, full stereo signal with no low pass or other filter applied for stereo sources)

Each left RCA is then connected together with another (but reversed) RCA stereo->mono splitter and the same happens with the right RCAs, ultimately feeding into the sub's L and R pre-amp level inputs.

Would this work and would it provide the right level of input? I don't think - but could well be wrong - halving the current by splitting the mono LFE out across two RCAs would matter as the subwoofer probably just adds them back together again anyway.

For AV sources, there is no real effect (I think) of having a second pair of RCA inputs from the Cyrus amp as the Cyrus is receiving high-pass filtered signals without any LFE anyway?

For stereo sources, the AV amp is off and not outputting anything from the LFE channel, so the sub is just getting the full stereo signal, which is pretty much what it is designed to receive on those terminals if a specific LFE feed is not available.

So I think it should work - any thoughts? Any risks? The inputs for the sub look as follows:


While RCA splitters might not be the best quality option, we're only talking about an LFE channel here.

The other option is not to bother to split the LFE output from the sub into L and R, thereby having one RCA splitter from the sub's R RCA input (also marked "LFE") to each of the AV amp's LFE output and Cyrus amp's R pre-amp out. The sub's L RCA input then simply connects directly to the Cyrus amp's L pre-amp out. Let's call this option 2, which on reflection sounds better.

Option 1 or option 2? Or is each one flawed? Help!
Having a sub in a av and stereo system is pretty difficult.

A) just use single cable from AVR to the sub, that is filtered signal from LFE + re-directed from your 5/7 speakers. Fine no problems there

B) When adding a stereo amp, you need to send audio from that to the sub, so either use high level outputs, or use a splitter. Two outputs into a input isn't recommend as you're shorting the output stage on your amp, basically.

For stereo, it works fine, AVR is off, stereo amp is on, sub is active, receiving full range signal, then using the subs own crossover.

The problem is for cinema, as your stereo amp is on, sending bass from L/R (even though it's filtered) then you have LFE to the sub, and you still have the subwoofer crossover and level set for the stereo setup.

Too much bother, I'd just have the sub on for cinema.

I'm not sure how you would integrate a subwoofer in a combines avr/stereo amp system, you need some kind of electronic switching of somekind to do this, ie over RS232 control

1) Shutting off input from stereo amp in cinema mode
2) Enabling and disabling the subs crossover
3) Setting levels for cinema and stereo mode


Active Member
Thanks for that Stephen... Very helpful.

I've just had another idea - I could only connect it to my stereo amp and tell my AV receiver I have no subwoofer but large speakers? Then it routes all LFE to the fronts, out of the preamp outs with the rest of the front main signal and into my Cyrus. The sub then just selects the frequencies it wants from that single source (the Cryus preamp out).

I think that should work!
But then you have the problem of setting full range mode, so L/R amp in home cinema is set to that, which isn't ideal, and whole point of bass management.

In effect you are then doing LFE + main bass...which isn't good.


Active Member
I have a fairly unique situation with my current speakers though, which is my speakers only go down to about 80Hz which isn't usually ideal, but fairly closely complements the sub performance (i.e. that excels where the speakers fall off). So I can set my subwoofer crossover at around that level (I tweak it slightly so the subwoofer crossover roll-off pretty much matches the speakers).

This means regardless of whether we have an AV source or stereo source, I think I want the stereo amp taking the full signal (including LFE) and then passing it (line level) to the subwoofer which will strip out the bass below 80Hz. The speakers then get speaker level main out from the power amp - including that below 80Hz but they can't do anything with that, so does it matter they're getting it?

Perhaps ideally I'd have an active 3-way stereo crossover and I could then bypass the passive crossovers in the speakers, but then I'd want to do that at line level which means needing a pair of stereo power amps (or four monoblocks) - I don't have that kind of budget at the moment :(

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