2. amps-preamps
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New system/room, upgrade amp or preamp first?

Hi all! This is my first post here but I've been an active A'gon'er for many years.

I recently built myself a listening room in the basement. Nothing too exotic in terms of the actual room construction, but I do have 4 OC703 acoustic panels on the wall for front wall reflections and for first reflections. I had a friend build cabinets and I did the crossovers and assembly of Troels Graven's ScanSpeak 3-way Discovery monitors. Just got them done yesterday, they sound very good but need a while to break-in.

I am currently using Jriver set to DoP, out via USB to a Schiit Loki DAC, then on to a Marantz SR-685 5.1 receiver acting as a preamp, and finally on to a B&K AV5000 5.1 separate amp (5 x 105), obviously only using two of those channels. I have the sub out of the Marantz y'd and connecting to two BIC F12's, used only to fill in the lowend. They aren't the most musical subs obviously but they do a fine job to my ears for 45-50Hz and below. They provide a satisfying weight to the sound without dominating the room.

So, I'm pretty OK with the DAC and source. I'm basically using two repurposed home theater components so those are next on my list to upgrade. The room is small, 13 x 10 (speakers are 82" apart, my chair is 82" back from the center point, about 3' from the back wall). I have kicked around an integrated amp but I do prefer separates if I'm being honest. If I have a $1500 budget for ONE component, what should I be looking at first - addressing the AVR-turned-preamp, or the B&K amplifier? The item not chosen for upgrade at this point will be addressed in another 2-3 months.

It's tough to judge a system with such new speakers but so far, the sound is well-dimensioned for both width and depth, though depth is a bit shallow. Voicing is wonderful, thanks in part to the 4" ScanSpeak midrange (wired out of phase with the woofer and tweet).

My listening tastes are varied but primarily I prefer Rock, Metal, and am starting to get more into blues and jazz. I do some orchestral stuff here and there as well as instrumental concerts (violins and piano). Any and all opinions are welcome, I can clarify whatever is necessary. Thanks!
toddrhodes
toddrhodes OP
49 posts
 
I appreciate the feedback! I had considered going to the BlueBook to check it out, I just may do that. Thanks again!
toddrhodes OP
49 posts
 
I've initiated contact with the seller. I just can't find a bad word about this thing unless it's being compared to units several times its price. It checks all the boxes, BlueBook reveals it is priced well... I believe it shall have a new home soon.

Todd
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almarg
9,670 posts
 
I agree with the many suggestions of preamp first, not on philosophical grounds related to the importance of preamps generally, but because the AVR appears to be the weak link in this case.

I took a look at the possibility of impedance incompatibilities arising with the various replacements that have been suggested, given the 33K input impedance of your power amp and the 75 ohm output impedance of the DAC, and I don't see any likely issues, even with the passive Lightspeed.
04-24-15: Toddrhodes
There is a Bel Canto Pre1 for sale locally that I am very intrigued by; unfortunately I do need a remote based on where the preamp will sit, and this seems to be a very good Pre that allows for both sub hookup and remote control.
I took a look at some rear panel photos of the Pre1, and I don't see that it provides a suitable means of connecting to your sub. Even if that's the case, though, your subs provide speaker level inputs which you could use, connecting them to the amp outputs. That shouldn't be a problem given that it does not appear that the B&K amp's outputs are bridged or balanced. But when you eventually upgrade the amp, you'll want to keep in mind that with that connection arrangement you should avoid choosing a new amp having outputs which they are bridged or balanced. The negative output terminals of bridged or balanced amps have signals on them, rather than being grounded, and connection to those outputs of the high level inputs of a powered sub could short those signals to ground, depending on the design of the particular sub.

Keep in mind, also, that you don't need heavy gauge speaker wire to connect the power amp outputs to the subs, since essentially negligible current will be drawn by the input impedance of the amps in the subs. Anything in the range of 18 to 24 gauge, or even higher, should do fine, assuming that the main speakers are connected to the amp separately, via heavier gauge cables.

Finally, you might consider adding another acoustic panel, in this case to the wall behind the listening position. The three foot distance to that wall will result, to some degree, in a suckout of frequencies in the vicinity of 282/3 = 94 Hz. Perhaps reflections from that wall are also contributing to the slight lack of depth which you mentioned.

Good luck. Regards,
-- Al
toddrhodes OP
49 posts
 
Al - thank you so much for that response, it truly is helpful. The plan all along has been to treat the rear wall, I just haven't gotten to it yet but the concern is heard and will be handled post-haste. I have plenty of material left to make another 4" trap - my other thought was to put up a GIK Monster trap (7" thick IIRC) with a diffuser panel on the front of it to treat that space. A friend of mine also turned me onto a bass trap idea using upholstered 12" pipe insulation from OC to sit in the rear corner of the room. I just need to find a source for the insulation.

Regarding the Pre1, I noticed as well it does not have a pre-out, however I found a few references to people using the tape-out to drive the sub inputs. I unfortunately don't know what this terminology means but it is a buffered output that basically is identical to whatever source input is selected on the front panel. The manual suggests I can use both the XLR outs and RCA outs simultaneously as well, so a simple XLR-RCA adapter could fill that need as well.

Again - thank you for your effort and time in digging up that information, I really do appreciate it!

Todd
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almarg
9,670 posts
 
You're welcome, Todd.

Tape outs are not usually suitable for connection to subs, because they are almost always "ahead" of the volume control in the preamp's signal path. So the volume of the signal sent to the sub would not vary as you vary the setting of the volume control. The alternative of using the sub's volume control and continually having to coordinate its setting with the setting of the preamp's volume control is probably impractical as a long-term solution.

I did notice that the Pre1 provides a pair of jacks labelled "loop," but I'm not sure what they do. And I note that the RCA input of the sub is adjacent to a switch selecting which of two receiver types is providing the signal to that input, a Pro-Logic receiver of a Digital SomethingOrOther (I can't tell what it says) Receiver. I'm wondering if that MIGHT be suggestive of the need to provide the sub's RCA input with an LFE (low frequency effects) type signal, rather than a full-range signal. And, finally, most XLR-to-RCA adapters short the inverted signal on XLR pin 3 to ground (XLR pin 1), and the XLR outputs of some equipment cannot tolerate that without the possibility of misbehavior or even damage. I suspect that modestly priced solid state equipment such as the Pre1 may be particularly likely to have that difficulty. I'll mention, though, that relatively expensive Cardas adapters can be ordered with pin 3 left open, as it should be for actively driven XLR outputs. Or a cable supplier could customize an adapter cable which does the same. (Pin 3 SHOULD be shorted to pin 1, btw, when adapting RCA outputs to XLR inputs).

So while it's possible that line-level connections from the Pre1 to the subs could be successfully implemented, there are a considerable number of uncertainties involved, at least as far as I've been able to determine. But as I indicated earlier I see no problem with speaker-level connections, as long as when you upgrade the amp you avoid those having bridged or balanced outputs.

Regards,
-- Al
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