Phono Stage Recommendations

[ajgriff]

It would seem that we are actually considering the need, or otherwise, for sub-sonic filters. In which case it would be useful to have more details of the OP's speaker arrangement when playing vinyl and whether not a reflex sub-woofer or equivalent large bass drivers are being used. Sorry I was slow on the uptake.

Alan

[Craig Sawyers]

In another thread https://www.vintage-radio.net/forum/...highlight=quad there has been a discussion of the venerable old Quad 33 preamp.

That has a permanent 20Hz second order filter. Because this was back before ICs it was entirely discrete with a total of 6 transistors per channel (!). One of them was dedicated to said filter. It is -25dB at typical arm/cartridge resonance frequencies.

Now Quad never advertised that this existed - it was just given as read that anything with a input for a record deck needed a low frequency filter.

I'm not remotely suggesting that this design is suitable today, just making the observation.

Craig

[gramophone1]

Hi Craig,

Interestingly the link you provided in one of your previous threads for a rumble filter. You can request to have the device completely built and tested for about £80. I have already emailed the company to request this. I am just waiting for a reply from them.

[ajgriff]

I've never delved into the the digital complexities of AV equipment but isn't it likely that a sophisticated piece of kit like the Yamaha RX-V685 (with phono input) would incorporate some sort of sub-sonic filtering? Perhaps somebody with expertise in this field could advise?

Personally I think there's an important distinction here between audible rumble and sub-sonic excitation which might cause speaker damage. I appreciate that the horse may have bolted but I worry that the OP is chasing rainbows with this one rather than concentrating on some of the more critical aspects of vinyl reproduction.

Alan

[Nickthedentist]

I had a Goldring GL75 as a teenager in the late 1980s. There was no audible rumble but I was never very happy with the sound quality without being able to put my finger on what was wrong.

One day, I took the grilles off my speakers (2-way sealed units with 6.5" bass driver) and was horrified to see the cones flapping back and forth in an alarming way, even in "silent" passages in the music.

[bikerhifinut]

Here's a simple idea.

If its worrying the OP that much, and I suspect we are getting a case of listening to the equipment rather than enjoying the music, then back in the day the simple addition of a switchable low value capacitor in series with the output of a preamp or somewhere along the signal chain made an effective High pass filter. Leak used a 20nF capacitor switched in series with the output of, the point1 stereo as an example.
Cost you a couple of quid tops and personally would be my first course of action. And if that works, job done.
That and stop pulling the speaker grilles off to see why they are still working.
A decent RIAA stage should be rolling off the low bass anyway.

Its that or chuck away your LPs and buy a CD player or other Digital playback device.

Andy.

[Edward Huggins]

It's been disappointing to see the way this long meandering thread has progressed -or in my view -not progressed.

We know that AV receivers are not really optimised for Vinyl, but certainly are designed to give a lot of grunt at c. 80Hz for sound effects.

I feel what we have here a case of attending to a car with a holed exhaust whilst the owner investigates the best sound deadening materials!

[Craig Sawyers]

You are not out of the woods with CD alas.

I have a number of CD's with a significant continuous output at a couple of Hz. I only notice that because I have open baffle speakers (LX521 https://www.linkwitzlab.com/LX521/LX521_4.htm ) and you can physically see the woofers moving. The only explanation I have for this is flutter from the studio airconditioning, and a recording engineer who has the bandwidth wide open.

And regardless of whether or not you can see the cones flap around at low Hz, as I posted above there are real audible bandwidth effects resulting from a large cone movement from non-audio very low frequency signals.

If you want a little light bedtime reading https://www.klippel.de/fileadmin/kli...ymptoms_06.pdf

And where this comes from - everything you ever wanted to know about loudspeakers

https://www.klippel.de/know-how/literature/papers.html

Craig

[gramophone1]

Nope, this is a case of spending money on a good pair of speakers, and I don't want to cause any damage to them. Thank you for all of replies, but I am going to buy a rumble filter, and see if that helps.

[Radio Wrangler]

Plenty of systems operate OK without specific rumble filters in them. Usually the RIAA stage and subsequent stages AC coupling cutoff frequencies give some attenuation. But this will introduce a progressive slope-off in the low bass region. If some designer objected to this and increased the size of coupling capacitors, then rumble would be less attenuated. A proper filter design should remain flatter in the passband and achieve a quicker rate of attenuation.

The rumble from a decent turntable, in good order, should be fine with ordinary ac coupling cutoff points. If you need a rumble filter, then either some more extreme choices have been made in your amplification, or you have a turntable problem. The compliance (springiness) of the stylus suspension in the cartridge, and the effective mass of the arm form a mass-spring resonator. It's normal to pitch the resonant frequency high enough that rumble hasn't got much power, and low enough that it doesn't intrude into the wanted bass region. Turntable trouble would mean either having too much rumble in the first place, or exaggerating a reasonable amount.

Seen from the other end, applying a flat response down to limitlessly low bass frequencies is going to give progressively greater cone excursion. For any finite sized and finite cost speaker, there has to be a limit on low frequency content. Just because you can shove it out to them doesn't mean that they can handle it. So things like open-ported speakers, transmission line jobs and open dipoles become fragile at the extreme low frequency end.

Having a controlled low frequency roll-off is something that rarely gets thought of, but is important.

David

[Craig Sawyers]

It isn't turntable rumble from bearings and drive system (idler, belt or direct) that induces cartridge compliance/effective mass resonance - it is defects in the record medium. Either warps and harmonics of that, or ripples in the record.

There have been various attempts to tame that tendency, either with record clamps (often with a designed slight dish to the turntable surface or mat), or in extreme turntables like the long obsolete Rockport Sirius which used vacuum hold down for the record.

The other approach is to damp the arm/cartridge resonance as I mentioned in a previous post. The technique I omitted is to use eddy current damping near the arm pivot, used in some arms.

What is bewildering is that most phono stages, right up to the heady heights of many k, don't incorporate a low frequency filter. It is a bit like omitting tone controls on preamps - there is a perception that the fewer stages in a domestic audio chain improves sound quality. Not understanding how many stages there are in a mixing console on the way to producing the medium that is being listened to.

Craig

[Edward Huggins]

Hopefully, and especially after all of this iteration, the OP will report back on:-

A: Just how he gets on with interspersing a rumble filter in terms of reducing visible cone excursion.
B: How it affects the overall sound?

[Radio Wrangler]

I was simplifying!

Rumble can cover very low frequencies up into the bass region. Record warps, non-concentricity are down in the low frequency region. The arm-cartridge resonance needs to be well above the frequency region of warps because their amplitude is substantially larger than rumble. The amplitude of rumble should fall with increasing frequency so although arm-cartridge resonance will boost it, there should be less to start with.

As you can see, there are a lot of issues that get swept into the low frequency zone, below the music band. The trouble comes if they creep upwards.

A further complication is that cartridges don't necessarily have the same compliance in horizontal and vertical dimensions, though they can be made close. A bigger complication is that arms don't have the same effective mass in vertical and horizontal directions.

Anyway, the electronics has to cut low frequency stuff. It is better that it does it an a controlled and planned way, but in a lot of equipment, it just happens and didn't get the benefit of any thought.

David

[Craig Sawyers]

It is also complicated by the fact that many cartridge manufacturers quote the dynamic compliance at 100Hz. The value at 10Hz is anyone's guess - other than a guesstimate of root of the frequency ratio.

The only real way to measure it is using a test record, such as the HFN one, which has very low frequency vertical and horizontal tracks at 1Hz intervals. You look for the frequency at which the stylus wobbles the most, or hang an oscilloscope on a phono stage that does not have a rumble filter (or lash-up build one).

Craig

[ajgriff]

Setting aside the technicalities I hope that the OP finds what they're looking for. Like Edward (post #92) I'll be interested to learn more in due course.

Out of interest I tried playing a vinyl LP with fairly prominent bass through my B&W DM14s with the covers off. The amplifier was a Yamaha AX-400 with no rumble or sub-sonic filtering. The DM14s' bass drivers are the same size (150 mm) as those used by Wharfedale in the OP's Evo 4.2s. There was the usual low level audible surface noise and rumble but no sign of what I would consider excessive cone excursion even at highish volumes. Results were similar when playing the CD version of the same album. Not a scientific test and the B&Ws are a sealed box design rather than the reflex arrangement utilised by the Evo 4.2s. Also, I notice that the Evos' quoted frequency response is 54Hz - 22kHz (+/- 3dB) with bass extension to 48Hz (-6dB).

Alan

[Radio Wrangler]

I always have a small chortle when I come across an amplifier where someone has made the whole thing DC coupled from end to end. Begone! nasty coupling capacitors!

A friend came home to find his girlfriend's cat snoozing on his breadboard preamp and some B200 cones on the rug.

David

[ajgriff]

Originally Posted by Radio Wrangler

I always have a small chortle when I come across an amplifier where someone has made the whole thing DC coupled from end to end. Begone! nasty coupling capacitors!

David

Sorry David but I don't quite understand the relevance of that remark in relation to the current discussion. Perhaps I'm missing something.

Alan

[Radio Wrangler]

A record-playing amplifier chain needs some DC block/AC coupling/Highpass filter function somewhere along it, else very low frequency stuff like the LF arm resonance is going to cause very large excursions of ported speakers.

With a recording on CD, it really could be DC coupled all the way from the studio, but it would be silly for speakers to be expected to reproduce the barometric pressure of the place and time of recording.

Choice of the inevitable AC coupling function is enough of a rumble filter for most people, most of the time.

It's one of those functions of an amplifier which is usually overlooked.

David

[ajgriff]

Thanks for clarification David. Initially I misunderstood the point you were trying to convey.

Alan

[bikerhifinut]

Originally Posted by Radio Wrangler

A record-playing amplifier chain needs some DC block/AC coupling/Highpass filter function somewhere along it, else very low frequency stuff like the LF arm resonance is going to cause very large excursions of ported speakers.

With a recording on CD, it really could be DC coupled all the way from the studio, but it would be silly for speakers to be expected to reproduce the barometric pressure of the place and time of recording.

Choice of the inevitable AC coupling function is enough of a rumble filter for most people, most of the time.

It's one of those functions of an amplifier which is usually overlooked.

David

David,
is that kind of like what I was inferring, reference some older gear where the preamp output or even the coupling from an RIAA stage would have a simple switch with a lowish value capacitor as a crude but effective High pass filter?
I have to say my recent foray into RIAA opamp experiments gaveme an insight into the effectiveness of a suitable value for coupling capacitors and also the decoupling capacitor on the lower leg of the feedback network to ground where it was possible to roll off bass response before nasty subsonic LF gotin the way. Crude perhaps but I got a lot of pleasure from the end result (and still do, one of my experiments is still doing the job!)

I've observed the odd cone flap over the decades and i haven't blown a single ported loudpeaker yet and I have been known to play heavy metal at window shaking levels in my time!

Andy.