As I understand it, in the ESP P99 design the idea of summing the two stereo channels to mono was originally considered but later discarded because of possible frequency response anomaly considerations.
My own experience with the P99 filter is that its design is superb and it works perfectly in practice as intended. Regards, Fap. |
In his paper on resonances in turntables,Paoul Ladegaard of the air bearing tonearm fame,theorises that cartridge/tonearm resonance is by far the most important issue to be addressed here.Therefore matching your cartridge to the effective mass of your arm,so that you have a cartridge resonance of 11-12HZ is the most optimal adjustment you can make,coupled of course with good isolation.Ladegaard was sure rumble does not exist and you corrected this parameter. |
Most rumble is from vertical groove modulation. Horizontal modulation, which is a mono signal is much cleaner. A good rumble filter will blend the LF signal to mono, which many people do anyway when they connect a single subwoofer. Also, when records are cut the LF is often blended to mono right on the LP so that less-than-audiophile cartridges can stay in the groove. If the LP has been made this way all the LF you are getting off it in stereo is rumble.
Many LPs have rumble cut into the grooves and no amount of vibration isolation will help. Particularly in older recordings the air conditioning systems of recording halls were a big cause of rumble. It went unnoticed until newer playback systems with extended LF response came into being. |
Of course you guys know that you could also do the filtering between the pre and the amp. I'm beginning to think about trying this sometime for exactly the reason Fap pointed out. If you cut those unwanted frequencies out so that the amp and driver doesn't have to work on trying to reach those lowest regions, it should clean up the bass. Hey, it works on the other drivers up the spectrum. |
I suspect you are not able to 'dampen' the vibrations from the wood block or corion table. Squash balls was the right idea. Spikes are a bad idea. Personally I'd try memory foam next or a different sized wood block and platter - to me they both look too thin and both would necessarily tend to vibrate/flex in the vertical plane over their surface. |
Bob, oh I forgot to mention I've noticed no audio degradation to any aspect of the audio quality with the use of the subsonic filter.
I was worried about that possibility, but it hasn't happened. I'm happy! Also there no no gain through the filter. The filter circuit is set for 'unity' gain. Regards, Fap. |
Hi Bob, yes circuit boards are available for the circuit, but all components need to be sourced by the constructor. All parts are easily available from the usual parts shops.
The filter input is connected to the output of the phono stage. I also use the Elliott Sound Products P06 phono stage which actually has an extended low frequency end. The P99 filter cleans up all unwanted cone movement due to warps etc completely. 18 Hz is where my filter starts operating.
As the amp is no longer trying to reproduce all the unwanted subsonic rubbish, there is more power available for the real music! Regards, Fap. |
When I built it I was told that Corian is dense and fairly inert. It certainly is heavy (and pretty to look at), but I often question the same thing as you. I have toyed with the idea of applying a heavy piece of aluminum or some such to its bottom as an additional damping solution. But I have trouble trying to figure out how to attach it sufficiently and whether I should put some EAR Isodamp or some such between it and the Corian (e.g. constrained layer damping of sorts).
Bob |
Thanks for the link Fap. Is this filter available in a kit form, or just the schematic as provided? Where does it plug in, between the cartridge and phono stage or after the phono?
I assume the whole signal rides through it ... if so then I assume the op-amps affect the entire signal. So I would expect that different op-amps might affect the overall sound in different ways - no?
You mentioned an increase in apparent available power, so maybe it adds a bit of gain also?
What phono stage are you using with it? Did you notice any affect on transparency or soundstaging or the top end?
Thanks,
Bob |
Is the Corian material a great option to use for plinth? I only ask because I have a DIY Corian arm-board on my SOTA and question its immunity from feedback. |
Thanks for your suggestions, but I still think the problem is more inherent to the medium than my setup.
My racks are about 200 lbs each. Each shelf is it's own seismic sink with 50 lbs of sand in them. They are spiked to a cement floor. My TT itself weighs about 30 lbs (plus the motor which is about another 30 lbs). I am also using a Mark Kelly designed motor controller (think SDS), which makes the motor dead quiet. That's not the source of any vibrations either.
See here: http://cgim.audiogon.com/i/vs/i/f/1155818474.jpg
and here: http://cgim.audiogon.com/i/vs/i/f/1155818602.jpg
(note: bubble wrap is replaced by squash balls which proved much better at isolation from the shelf)
The subsonics are definitely not due to speaker interaction, since it happens on the lead in groove right away, before anything is playing. It is visible on the regular speakers too, when the sub is on or off. This is not an isolation problem due to standing waves in the room, but a rumble problem due to low signal vinyl interaction with the cartridge and phono stage.
Therefore: standard subsonic issues with vinyl. I even tried damping the tonearm, with no affect on the subsonics but a lack of air and life to the music - so that's been reversed now.
I spoke with Jim Hagerman about this and he said he purposely did not limit any extension at either end, making the Trumpet very wide bandwidth. He suggested changing out the .22uF inter-stage coupling caps to .1uF as a possible partial solution. I did this with no obvious change (however they are now upgraded to RTX's).
Please keep the ideas coming. At this point I think the answer is going to be electrical (e.g. a rumble filter), but I'm open to trying other suggestions first.
Thanks,
Bob |
Well, I took the subsonic filter option. I built this excellent subsonic filter, and if anything the quality of vinyl playback has improved with additional clarity and increased apparent available power. I highly recommend this subsonic filter.
http://sound.westhost.com/project99.htm Regards, Fap. |
My bass horns roll off pretty fast down in that subsonic region. They are down 6dB at 20Hz and drop pretty fast after that. Once you get down below 16Hz or so I would think that the system would begin to pick up resonances from the arm/cart. Who wants to listen to that? :-) |
How far is your speakers to the TT? Your rack, floor if suspended, is moving. Have you tried moving the sub further away from the shelf supporting the tt?
I had the Trumpet. What you described was one of the main reason why I sold it since I have a suspended floor, and acoustic feedback or rumble seems louder on it compared to other preamps I have including the Cornet 2. To be honest, one of the thing that I really hate on this hobby is rumble/acoustic feedback, another one is hum.
You said your isolation is good, maybe it is not good enough. Please check my TTs on my system page. With plinths more than 60 lbs each not counting the TT on top of them, I thought I have a good isolation by mass loading from feedback or rumble (assuming it is not coming from the tt). Even with the 50 hz cut off filter on my orions ASP, the feedback is still there. My solution was to reconfigure the speaker placement making sure that it is further away from the TT. I moved the speakers 2 feet away from the rack (increasing the separation between the two speakers) and solved the problem.
Goodluck! |
