Pre outs signal

Posted by: Jasper

Pre outs signal - 02/09/13 09:58 AM

Ever since he heard my Axiom system, the father of my (now ex-, but that's another story) girlfriend was inspired to bring his vintage Marantz/B&W gear into the new millennium. He was soon convinced that he needed something called a receiver to get going, so we found a nice used Marantz sr6004 for him to buy. (For some reason, Marantz has always been popular in the Netherlands and it's often easier to find a good deal on a Marantz than, for instance, a Denon.) We thought it'd be nice for him to still use his old, heavyweight pm16 to power his B&W 802s and I told him he could use the pre outs of the sr6004. What we found, however, is that we had to turn the volume of the pm16 almost all the way up to get decent sound -- or at least much higher than when using the old stereo amp with a cd player. Was this to be expected? Or is the signal from a receiver's pre out supposed to be stronger than that? Could we be overlooking something? Thanks for you insights!
Posted by: alan

Re: Pre outs signal - 02/09/13 10:16 AM

Hello Jasper,

What is the PM16 -- a power amplifier? You speak of turning its volume "all the way up". Does the PM16 have input level controls? If it does, it's commonplace to have those at or close to maximum in order to utilize the gain from the power amplifier.

Normally, the signal level on the Marantz pre-outs is controlled by the volume control of the Marantz. Where are you setting the volume control of the Marantz?

Are you sure you've connected the PM16 to the pre-outs of the Marantz and not mistakenly to the tape outputs, which yield a fixed low-voltage signal that is NOT controlled by the Marantz volume control.

Posted by: Jasper

Re: Pre outs signal - 02/09/13 10:43 AM

Hi Alan,

The PM16 is a stereo amp, this one:

Perhaps it's not surprising, then, that we had to turn the volume way up? We were comparing the level of the front speakers, fed through the pre outs and powered by the PM16, to the level of the center speaker, powered directly by the SR6004, and noticed a huge difference. (That is, until we turned the volume of the PM16 up.)
Posted by: alan

Re: Pre outs signal - 02/09/13 03:04 PM

Ok. So, to be more precise, the PM16 is a stereo integrated amplifier, not a basic power amplifier. The PM16 has its own preamp and power amp sections and its own volume control.

If I understand you correctly, then, the amount you can turn up the SR6004 will be limited by the volume of the center speaker, so that volume setting will also limit the signal from the SR6004's pre-outs for the front left and right speakers. And since the PM16 isn't a pure power amp, you have to increase its volume control enough to get sufficient power output to match the center-channel speaker's volume level.

That all makes sense.
Posted by: Jasper

Re: Pre outs signal - 02/09/13 05:19 PM

Thanks, Alan. I suppose what's puzzling us is the difference in volume between, for instance, the signal of a cd player fed into the PM16 and the signal of the pre outs fed into the PM16 -- and this made me wonder if the signal coming from the SR6004's pre outs is supposed to be relatively weak? (Since, in the most common scenario, you would use a power amplifier to amplify the signal?)

Also, if this is true -- does that mean we're making the PM16 work harder/use up more watts/generate more heat by feeding it the pre outs' signal?

I realize we could take the PM16 out of the chain entirely and the SR6004 would likely drive the fronts, center and surrounds without issue -- but it's such a nice, solid, old-fashioned integrated amp that it seems worth keeping it around even if it's for purely sentimental reasons.
Posted by: jakewash

Re: Pre outs signal - 02/09/13 06:36 PM

The low level outputs from various units, even amongst the same manufacturer can and usually are different, the max output from the 6004 might be 2 volts while the output from the CD player could be 3 volts, this makes for the difference you are finding.

As for your power consumption question, it is using the same amount of power to output the same db levels, as you discovered this just means you have to increase the volume/gain control.
Posted by: JohnK

Re: Pre outs signal - 02/09/13 10:19 PM

Jasper, the volume control on the PM16 is a variable resistor which varies the amount of the incoming voltage(from the 6004 pre-outs in your case)which is let through to be amplified from almost 100% to nearly zero. There's nothing wrong with setting it all the way up, letting in almost all the voltage from the 6004, if adjusting the main speaker trim settings(also variable resistors)on the 6004 can achieve a balanced level between the center and mains. You didn't mention how high the 6004 settings(typically about a +/- 12dB range) to the mains were.

The amount of power used from the PM16 for a given volume level of the main speakers is the same regardless of whether you get there by turning the PM16 volume control high or by turning the main speaker trim settings on the 6004 high.

The "huge" volume difference you described is a bit unusual, although the center speaker might be more sensitive than the mains and/or the amplifier in the 6004 might have a higher fixed gain than that of the PM16.
Posted by: Jasper

Re: Pre outs signal - 02/10/13 05:35 AM

Thanks, John, that helps me get a bit clearer on the subject. I don't remember where we left the settings of the 6004 last time, but we'll have more time to play with it today and we'll run Audyssey and see where it sets the mains relative to the center and surrounds.

The center is the B&W HMT7, if I recall correctly, and it should have a sensitivity of 91dB. I'm not sure of that of the mains, but it's definitely lower than that. So that explains at least part of the difference in volume.

Re: Pre outs signal - 02/10/13 07:54 PM

What inputs are you using on the PM-16?

From a quick google search it doesn't appear to have dedicated power amp inputs (if that's incorrect you have another problem but this info still be useful).

If not and you are connecting the SR6004 pre-amp output to a CD/Tape/Tuner/etc. input you may be causing yourself grief.

Try connecting the tape loop or VCR outputs on the SR6004 to the inputs on the PM16s' tape loop. I have no experience using an AVR like this but I used to have 3 stereos each on a different floor of my house connected this way with no problems.
Posted by: Jasper

Re: Pre outs signal - 02/11/13 06:10 AM

Originally Posted By: FATMANBLOWFISH
From a quick google search it doesn't appear to have dedicated power amp inputs

That's correct. We used one of the regular inputs, turned the volume of the PM16 halfway open and ran Audyssey to bring the mains into balance with the other speakers. Seems to work fine for now. What grief are we risking here?

We could use one of the other outputs of the receiver, but I don't think that would allow us to use the mains as part of a 5.1 configuration. If using the pre outs of the SR6004 risks damaging the PM16 or the main speakers, we might be better off not using the PM16 at all.
Posted by: alan

Re: Pre outs signal - 02/11/13 10:24 AM

Hi Jasper,

You're not risking grief or damage to the electronics or your speakers with your current setup.

It's just that you're running the audio signals through two preamp sections and two volume controls, because the PM16 is not a basic power amplifier and lacks power-amp inputs. It makes for a somewhat convoluted setup, with two volume controls to adjust when there should only be one.

Posted by: jakewash

Re: Pre outs signal - 02/11/13 08:57 PM

Try it with out the PM 16(with out Audyssey but level matched) and then try it with the PM 16(with out Audyssey and level matched) and then have fun trying to decide which way it sounds better if there is any difference. If you don't hear a difference then you might as well make things easy and leave the PM-16 out of it.

Re: Pre outs signal - 02/11/13 10:02 PM

By grief I meant having to adjust (and I would guess constantly re-adjust as sources were changed) both units to try to get the sound you want - not any physical damage to the equipment.
Posted by: JohnK

Re: Pre outs signal - 02/11/13 10:13 PM

Jasper, "grief" wasn't described, but as Alan pointed out, the theoretical objection is that the sound runs through two preamp sections rather than one, adding a small amount of extra distortion. This is unlikely to be audible, and if you like to use the PM16, carry on.

If the main speaker level trim was set in the 6004 to the minimum -12dB available(possibly indicating a lower setting was wanted)during calibration, lower the PM16 volume control a bit so that the calibration number comes out higher.

Edit: Roy, once the level is properly calibrated, the PM16 level control wouldn't have to be changed; any volume changes would be done in the 6004.