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Any life in an old Pro Logic amp?

TB Rich

Active Member
I've been using an old Yamaha DSP-A970 as a 2ch amp now for some time, it still to me sounds great in this function and there was no appreciable difference to the sound doing some back to back testing with an Audiolab 8000 (either an A or S it was) a number of years back now when I was curious as to what a supposed dedicated amp would do for me.

However, I've had the TV connected via RCA to it for some time now and was wondering if there was anyway to get a surround setup going. I've never really wanted surround before because of wires and general look of them in the lounge, however I've seen a set of KEF T101 in white which would do the job nicely, but it begs the question now as to if I can actually get any sort of surround signal to it?!

This amp is an analogue Pro Logic only unit with no 5.1 inputs, so decoding must be done externally. My source is an Xbox One S which currently is set to just send a Stereo mix to the TV over the HDMI, and then as mentioned I have RCA out to the amp. Seems to work very well and no issues with centre dialogue unless the film is obviously mastered poorly (amp is set to phantom but I think with a 2ch source that is moot anyway).

Would setting the Xbox to send a 5.1 signal to the TV and then TV via RCA carry a signal the amp would recognise? I believe Pro Logic always worked on a L+R only basis and the rear was carried via an out of phase signal - frankly I'm at a loss as to if it would work or not?!

The other option is of course to replace, but this would be expensive to replace it with something of an equivalent quality. High end Yamaha perhaps RX-A1080, however to be honest I'd probably go Yamaha A-S1100 for 2ch stereo with HT bypass function, and connect a Marantz NR1509 for the surround processing etc - smallest cheapest option I can see with front channel pre-outs. Really I'm far less concerned about the sound of the surround setup vs 2ch for music.

Any thoughts welcomed.
 

Leelo

Active Member
If you want to consider actually utilising current 5.1 or 7.1 or even Atmos DTS X then you clearly understand that your current receiver is not capable of doing this and requires you replacing it, in terms of cost that’s entirely up to you. It seems to me that if you are happy with using the stereo output of your TV currently then you will be surprised with the jump in quality of broadcast 5.1 etc even on a modest modern AVR you don’t mention if you use any other source for sound apart from the he X Box but presumably you at least have a CD player. Remember to get 5.1 from the Xbox you will need to route the hdmi to the avr not via the tv Personally I would ditch the old kit and try a cheaper AVR first or see if you can find a friendly dealer who will let you loan kit and see what you think about 5.1 first before considering spending lots of money
 

TB Rich

Active Member
For video purposes yes the Xbox is my only source, I use it for Blu-ray and Now TV/Amazon Prime. I don't watch any regular TV/Sky etc, but I think as you say xbox -> AVR -> TV would be the way to do that it with new kit.

I've been doing a lot of reading since my post, and it seems Pro Logic will 'attempt' surround on a stereo signal even if it was not encoded with Dolby Surround. The difference seems to be when the stereo signal is properly encoded for Dolby Surround then there will be better channel separation because the Pro Logic decoder is able to properly identify the out of phase rear mono channel, will have a clearer centre, and it'll use dB weighting to steer the sound more accurately in the rears - even though they are mono in source.

This should mean despite my path of xbox -> (HDMI) TV -> (RCA) old AVR, I should get some rear effects, but I suspect it will only be a normal stereo signal and not a stereo signal with Dolby Surround encoded - so I guess it won't necessarily be very good effects!
I'm quite tempted though to add the KEF T101 to the rear wall and see how it is - then if I want an improvement as you say a modest AVR would likely be a huge improvement.

Not wishing to compromise the 2ch stereo music though (my old built like a house Yamaha no doubt better than any modest AVR of today) I guess I could keep the front speakers connected to it and use a line input from the new AVR - it would just require level matching them. Not ideal but gives me time then to save up for a new 2ch amp with HT bypass. Or, I did come across a place many moons ago that could add 5.1 inputs for the old Yamaha's.

One nice advantage of this approach means I've always got a good 2ch amp backing the stereo and music reproduction, whilst decoupling the AVR function means as and when new tech/standards come out then I'm not replacing £1000+ AVR's to get those features. The Marantz NR1509 seems to do everything I want; it's slim, 5.1, 4k and HDR pass through, plus most important has pre-outs for L&R. Time to dust the moths off the wallet perhaps!
 

Leelo

Active Member
Music forms a large part of my listening and as such I have spent a reasonable amount on the avr and power amps to get the best sound I can and while the idea of a separate pre amp is an option I’ve considered given I’m using my Sony X 800 as my disc spinner and streaming everything through the AVR anyway so using the AVR dacs I don’t see much advantage in this for music I just set the AVR to pure direct to remove as much processing and noise as possible that works well enough for me. While I haven’t heard your old receiver I cannot imagine it’s pre amp section is particularly exotic and whilst it would have decent power amp stage it would be more of a case of different more than better for simple 2 channels for music. What I would say is that the DAC in even in a modest modern AVR will be better than the one in an XBox which is just designed to get the job done in a pretty noisy environment
 

TB Rich

Active Member
I checked and it was an Audiolab 8000S I borrowed to do my A-B testing, I was clutching at straws a little but possibly the Audiolab had a slightly better controlled bass, the Yamaha however going a little deeper and fuller. But, I'm quite sure if I was blind testing I probably would have been none the wiser as to which was connected! So it's of a decent standard I would say.

I'm sure a high end Yamaha like a 1080 would probably be the easiest choice, I'd get quality Surround, probably more than decent enough 2ch in Direct mode, plus the onboard DAC is likely an improvement for my music too (I use a Squeezebox Touch so could optical out from it)...however! My concern is I consider it a bit of a tech-fest of a device that in 3yrs will be out of date - and at £1000 I would not be able to justify replacing for many many years. So decoupling the 2ch amp duties from the AVR makes a lot of sense to me. Something like an A-S1100 or 8300A could do my classic HiFi duties basically until they stop working (which may be never) and a 'cheap' AVR to do the surround channels and provide compatibly with whatever source and destination come out at their respective latest standards. It would not be horrendously expensive to change out every few years or whatever to keep up to date.

Using the pre-amp section in the AVR to take the Squeezebox feed and an actual power amp is an interesting thought though, I'll see what sort of power amps are around and what the costs are, though for some reason this does initially appeal less to me. I think my assumption is the pre-amp section in a proper integrated HiFi amp is likely better suited for HiFi that the pre-amp in an AVR, which as said would be of the more budget end.
 

TB Rich

Active Member
As a quick test I decided to hooked up my 2nd systems speakers to the rear terminals and there was indeed audio coming from them - so there does actually appear to be life in an old Pro Logic only system after all!
Only gave it a quick test on both some actual 2ch stereo music and a DVD via the Xbox (which is impossible to know if the later is reaching the amp as simple 2ch stereo or with any potential Dolby Surround matrixed within), however I could hear that it was very much ambient noises only and not voices emanating from the rears, so it's probably going to work out well enough for now. I would say at the very least I can go ahead and get the T101 rears and stagger their purchase with any potential amp changes down the line.
 

Leelo

Active Member
Oh definitely worth giving it a go why not it’s not costing you anything after all
 

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