SDA-2B distortion

gmcman

https://www.youtube.com/watch?v=veToMx-9BqI

I have the 2B's running through a B&K ST-202 and my Pre is a CX-1000. I was listening to some Dire Straits today and noticed some distortion at about the 10 o'clock position on the volume dial on the CX. I have heard some slight distortion at higher levels but cut it back right away...was just testing the waters so to speak..this only happened once and I don't listen to these at those levels anyway.

At the time of the distortion I was using a 1200 MK5 TT and a DL-301 Mk2 cart. Here is a vid of the distortion and i'm curious as what to check. I have played my RT800's much louder than this with no distortion...to the point of pain. These are the original mid-drivers but have performed a TL mod recently....about 300 hours on the caps.

The 2B's sound great, I made sure everything is connected correctly when I replaced the caps...sure as heck hope so. Just seems to be excessive excursion on the woofers for the given volume.

Dennis Gardner

What does this passage sound like at lower volume levels. If it is clean, then it may be a spike in volume in the bass line that can't be handled by your amp.

gmcman

Sounds great at lower levels, i'm just concerned that with the current setup that this even happened. Granted I don't know how these speakers were treated before I purchased them...perhaps one of the drivers could be damaged? I did the push test and when I push the driver in straight there is no scraping sound.

What tests can I perform to ensure the drivers are operating at or near what they should? Could this just be age or perhaps a bad cap in the amp?

Wanted to add that I have played this setup at a decent level and the speakers play clean and loud....I do remember one track where I started to get a slight pop or would this be a clip, but was at or near the 12-1 O'clock position on the dial. I generally don't play them that loud but the volume level wasn't terribly high but based on my sound meter tests it was likely around 95ish db's...and I do remember thinking that there shouldn't be anything along the lines of distortion or clipping at that level.

My RT800's play louder but again they are about 13-15 years less aged.

Dennis Gardner

My post about lower volume was simply to eliminate the source (your vinyl/cartridge) as the offending piece of equipment. If you don't hear that particular bass line resonate at lower levels the same way it does at the higher level, then something in the amplified signal is adding that ugly distortion. It almost makes the bass line sound like an aboriginal didgeridoo. You might try a "pushtest" on the bass radiator to check for leaks. The SDAs are a PR/sealed system and need that seal to keep the drivers from over extension. Pushing and holding in on the radiator should see the mid-bass drivers hold their outward positions for 1-2 seconds before slowly working their way back to the resting point. Sealing leaks helps regain control of the drivers and tighten the bass response. I've seen original mid-bass drivers with weakened suspensions actually jump out of their magnet groove and lock in place fully extended. Those prone to this do distort at the extremity of their excursion, until they finally lockup.

gmcman

When I perform the pushtest, the mids retract right away but take about 3-4 seconds to finally come to a rest, they don't remain extended for any period of time. I was under the impression they need to take about that long to retract but not remain still for any length of time before retracting.

When I release the PR, it takes about 3-4 seconds to finally extend to it's resting position.

Joe08867

Your getting rumble. You need a subsonic filter to eliminate the distortion. It is from your TT not the amp or speakers. They are just amplifying the issue.

gmcman

I'm using the subsonic filter on the pre but that doesn't mean its doing its job. What would you recommend in addition or seperate from my existing filter?

MillerLiteScott

How about it being a resonance being picked up by the stylus due to the bass output of the speakers at that particular frequency causing the distortion? Just a guess. Maybe some better isolation of the turntable or more distance between the speakers and the turntable. I don't think it is rumble, but there are definitely some rumble issues as shown by the pulsing drivers.

gmcman

Haven't been messing with it lately but I want to touch on the distortion issue again. This is a pic of the room as it was when I recorded the distortion. I know I need to move the TT but what would you suggest to isolate it from any noise interference?

I was thinking possibly to surround it with some MLV with an absorbing material attached, want to keep it thin. Even being on the top, the TT is quite stable, and level. I don't want to take too much away from the stand but if I need to make a box around it then so be it. The TT being in the corner likely doesn't help any. I also had the cover closed when it happened.

gmcman

Wanted to follow up the progress and I have since moved the turntable to a stand along the right wall and the distortion or woofer-pumping has ceased. Made all the difference.

Joe08867

Alright I am gonna say it. I Told You So. :cheesygrin:

Glad you got it sorted out.