Bass bloom with SET pre and active monitors - impedance mismatch?

Quick question for ye olde gurus of electronics lore...

I'm using a Bel Canto SEP2/1 (it's a 2 that's had its innards upgraded to 1 spec) single ended triode pre into my ATC actives via 5m XLR leads (with basic but solid XLR-RCA adaptors at the preamp end, as the pre only has RCA outs).

It's a fine preamp, one of the best I've heard. Original retail in the US was $2,500 ($3,500 for the SEP1). But it's got a very noticeable bass bloom in a fairly specific frequency. Couldn't tell you what frequency but it's fairly lowish bass (at a guess maybe 50Hz?) Whatever it is, it makes some rock songs sound quite crap (e.g. U2 'Hold Me Thrill Me Kiss Me Kill Me'). Elsewhere, bass is tight, fast, dynamic, powerful and lovely, if a tad rounded and "soft".

I know nothing about output impedances or input impedances or such other arcane lore, but I noticed in the pre's manual that it said it was recommended for use with power amps with input impedances >20K ohms. The ATCs are 10K ohms. I was wondering if this might cause the bass bloom, as it seems unlikely that such a nice preamp would have such an obvious flaw. It is admittedly not very noticeable in classical and jazz, but still pretty glaring.

Other possibilities that occurred to me - the 5m interconnects to the speakers, or possibly even the XLR-RCA adaptors?

Any thoughts?

Thanks,
Dunc

P.S. - I'm not 100% certain, but I think the problem may be limited to my CD player only (Meridian 203 DAC). Which would point the finger squarely at the CD player. Except I didn't notice it at all with the EAR 864 I tried. Sigh.

 

Hi Duncan,,

any system that makes U2 sound like crap is truthful to the source.

Seriously, the impedance mismatch will cause your hf to roll off a bit early, which may make the bass appear a bit stronger.

But the impedance mismatch cannot acount for bass bloom at a specific frequency. It may be a case of more bass output exciting a room resonance that went unnoticed previously. Check that by moving your speakers to a different location. Or it may be a case of an ill-designed power supply. 50 Hz is the mains frequency, bloom in that region will generally be caused by some psu problem.

The first thing, though, is to check whether it's the pre or the CDP causing your problem.

 

Ya-Boo's Audio Aero DAC/pre made my system sound very boomy to begin with. It sounded like a room issue, but the AA just needed an hour to warm up. Maybe the valves are a bit duff?

 

I was using that Bel Canto with the Tact SDA 2175 power amp, input impedence of 100K ohms.. didn't find it in any way boomy in the bass.

 

Oi

 

Will have to investigate the warm-up possibility. And the CD player (I haven't yet found an LP that displays the same sort of boom as on the CD player, but that doesn't mean it's not there...)

Dunc

 

Dev, Markus does have a point

 

Sorry too Dev, much as I like U2 stuff, their bass production especially on Achtung Baby (which I listenend to last night ) is fairly shocking for a band so successful and with such good material.

Dunc, it might just be that your hearing the "truth" re U2

Jeff

 

Hi Jeff, I didn't reply to Andy's post because I didn't want to derail this thread (too much) and to treat his post with the contempt it deserved. I like the older U2 stuff, nothing after The Joshua Tree (which is also highly compressed but I still like it).

 

Glad I'm not the only one that thinks U2's albums are mastered at the bottom of the Mariana Trench...

 

Some U2 albums sound a bit crap (particularly the last couple), but in most cases they're just made to sound a certain way to complement the songs.

For instance, Pop is mastered very, very well, but it's intentionally a bit rough and raw to match the music. (An outstanding album by the way, and vastly underrated.)

Hold Me Thrill Me Kiss Me Kill Me isn't the best produced rock song I know, but it ain't bad. (And it's not just this song that displays the bass bloom. )

Dunc

 

If possible, I would certainly move the speakers around the room; its surprising what a difference it can make. For example, I have a nasty mid-bass resonance with speakers 1m from the wall - go 6 inches further back, yes back, and its gone.

 

It's because Adam isn't a particularly good bass player, so they always try and hide him

 

I'm well aware of the effect speaker positioning can have (took me a full year to find the right position for my speaks in my old room!) but it seems unlikely that it would be affected differently by different upstream components...?

Dunc

 

You have a high output impedance, even by tube standards, a long wire and a low input impedance. I wouldn't want to predict the precise effects but sub-optimal seems safe.

So try another pre.

Paul

 

Dunky, i think you should send me your pre to test it!
Seriously tho, I would try speaker positioning, I had to move mine about again after getting the Bel Canto power amp, and again when i replaced all cables.

Dev, I wouldn't want to lower myself to an argument over boner and his band, but their recordings suck
(Tho i do like the first album )

 

Okay, interesting (and rather surprising) development - had a cable revelation Tuesday night. Specifically, the interconnect between CD player and preamp seems to have a very obvious, very wide-reaching effect on the sound.

My main reference interconnect, and the one I've been using in all cases to evaluate preamps, is an Ecosse Reference MA-2 'Maestro', a £150 splurge from a few years back. I've generally been very happy with it, and I generally think I notice a slight improvement using it over the other cheapo interconnects I have. My experience of interconnects has until recently been that they kinda-maybe-sorta have a subtle effect on the sound - but it could be all in my mind.

A few months back I needed an interconnect for my turntable, so I bought the £30 Wireworld Luna 5 as it had good reviews and I wasn't interested in spending silly money on an interconnect. It actually had a more obvious effect than I was used to, and was more relaxing and easier to listen to than the Ecosse, but less refined and detailed.

Now Tuesday night I finally decided to try the CD player plugged into the Bel Canto via the Luna rather than the Ecosse. It made a huge difference! Really fundamental and obvious. The sound was so much less "uptight" and easier to listen to, with a bigger, deeper soundstage and more tonal colour. It also had a brighter, splashier, more congested treble, and a woolier, slightly bloated bass. Basically the same things I had heard before, but much more obvious.

So, I was really happy with the big, relaxed, open, colourful sound of the Wireworld, but I craved the extra detail, treble refinement, and bass tightness of the Ecosse. Yesterday on a whim I went down to the local 2nd hand hifi shop and borrowed the only cable he had lying around, a Chord Solid 0.5m RCA-RCA. Took it home and did some comparisons - perfect! Gorgeous! So natural sounding, with a total lack of "hifi" artifice, and wonderful punch and dynamics, great tight bass, extremely detailed (it's the old "I was hearing things in familiar recordings that I'd never heard before" hifi cliche) but not at all fatiguing, and the whole frequency band perfectly aligned with no emphases or suckouts... just wonderful really! The soundstage isn't as big as the Wireworld, vertically at least, but I don't really care as it's otherwise the equal or better of either other cable in every way! I couldn't stop listening to music last night (went to bed way to late...) and delayed rushing out the door to work this morning as long as I could so I could keep listening... Just mesmerizing and gorgeous!

So, I'll take the Chord Solid thankyouverymuch!

Oh, and guess what? I think it's cured the bass bloom problem! No kidding! I won't be sure until I've lived with it a while longer and tried more recordings, but for one thing, U2 'Hold Me Thrill Me Kiss Me Kill Me' sounded fantastic, with no noticeable bass problems, whoop!

I haven't yet tried it with the record player, but I'll give it a go. It seems these things are very system dependent. I remember trying the Wireworld Luna 5 with the Krell KSP-7B preamp I borrowed a few weeks back and it sounded awful while the Ecosse sounded rather good! Actually, thinking back, that was the first time cables made a very obvious difference.

Call me Duncan "Cable Sceptic No Longer" Armstrong...

 

P.S. - I read today that Chord used to make cables for use mainly in Naim systems. I would say that the sound of the Chord cable was exactly what I would expect from a very good Naim component - dynamic, punchy, fun ("toe-tapping" if you will), clean, largely neutral, very clear and detailed but not fatiguing, slightly sweet in the upper frequencies, with each instrument/voice having real presence and easy intelligibility, and with tight, powerful, but not at all bloated, bass. And all that from a [15-year-old] Meridian CD player and a Bel Canto single-ended tube preamp..! I might just have to get myself another Chord Solid for the TT (or perhaps experiment with their more recent cables..?)