A year ago I replaced resistors, and caps on My Polk SDA 1Bs., as I removed the cross overs from inside the cabinet, and mounted the
three different sections on the rear baffle mounted on rubber isolators.
I took care to minimize coil cross talk, I developed brain damage rewiring the SDA section.
i have been very happy with the results...until I noticed, my music seemed a bit out of balance left to right.
I checked this morning with a Stereophile test disk (2), and found the channels within a half db of each other, left to right,
and the test with both channels measured 3db higher. That seems correct.
My dc offset on my Sansui au317 is <.2mv, the bias is running at 10.2mv, the only thing questionable that i have found is the emitter resistors measuring .671 and .676 ohm respectively, should be .660 ohm, not much difference for a 45 year old integrated amp.
I am beginning to think that cd recordings are not being well recorded and out of balance and phase...am i chasing my tail?
I want to by pass my balance control. My understanding of this i just need to desolder the two earth lugs (center). I really hate to mess with the switches though.
thanks for advice....
three different sections on the rear baffle mounted on rubber isolators.
I took care to minimize coil cross talk, I developed brain damage rewiring the SDA section.
i have been very happy with the results...until I noticed, my music seemed a bit out of balance left to right.
I checked this morning with a Stereophile test disk (2), and found the channels within a half db of each other, left to right,
and the test with both channels measured 3db higher. That seems correct.
My dc offset on my Sansui au317 is <.2mv, the bias is running at 10.2mv, the only thing questionable that i have found is the emitter resistors measuring .671 and .676 ohm respectively, should be .660 ohm, not much difference for a 45 year old integrated amp.
I am beginning to think that cd recordings are not being well recorded and out of balance and phase...am i chasing my tail?
I want to by pass my balance control. My understanding of this i just need to desolder the two earth lugs (center). I really hate to mess with the switches though.
thanks for advice....
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The balance controls may not be the reason for the half dB (which is not unusual). Why not keep them to fix that?
It's pretty common for drivers to have as much as 1 to 1.5 dB mismatch. The reason is interesting: the cone masses are very tightly controlled, and the number of turns on the voice coil is exact, but charging the magnets is difficult to get exactly equal. Unless the factory pre-matched the drivers (not that common, actually), it's the drivers themselves, with 1 dB mismatch pretty typical.
Another source of channel imbalance is the volume control. Poor tracking, particularly below 9 o'clock, is routine, sometimes as bad as a 3 dB mismatch. The only around that one is a fancy stepped-resistor volume control. So keep your balance control. You'll need it.
Another source of channel imbalance is the volume control. Poor tracking, particularly below 9 o'clock, is routine, sometimes as bad as a 3 dB mismatch. The only around that one is a fancy stepped-resistor volume control. So keep your balance control. You'll need it.
I think it may be the SDA arrangement. Mine is SDA-OB
I listen to SDA most of the time and plenty often I get the imbalance sense. (it is my one ear going, finally?) Perhaps the price you pay to enjoy the effect; some recordings...
My system has no balance control - just volume. The SDA driver (silver) is wired in series and out of phase with the main driver (copper) on the opposite baffle; I could add a DPST switch to disable the effect; maybe pull the cable between yours to see if the imbalance goes away in "normal" mode, if Polk's circuit design supports it.
the driver mismatch might be the problem, I am wondering if my "DATS" woofer tester would show me the problem.
Magnet mismatch makes sense to me.
I am not really kean on messing with the balance control either.I wwill leave it alone.
I may try to test my vol control, it is never paled greater than 9"00, I do "exercose the pots monthly though with no power on.
thanks
Tweak I must.........
Magnet mismatch makes sense to me.
I am not really kean on messing with the balance control either.I wwill leave it alone.
I may try to test my vol control, it is never paled greater than 9"00, I do "exercose the pots monthly though with no power on.
thanks
Tweak I must.........
The problem with the volume control is that it is a log pot, not linear, these are often multi-segment pots, with one of the transitions around 9 o'clock. And guess what, the two sections are not exactly the same, with a small positional difference between them.
In the "Golden Age" equipment of the Sixties, volume pots were either dual-concentric, with a friction clutch, or ganged pots with a separate balance control. Might be time to bring back dual-concentric pots.
In modern high-end gear, there's been a trend towards the ultra high performance Khozmo pots, which offer a convenient dual-mono option, so you can set up a 0.5 dB offset on the remote control! No joke! My Don Sachs preamp has this option, and man, is it slick! No worries about system balancing, set and forget.
In the "Golden Age" equipment of the Sixties, volume pots were either dual-concentric, with a friction clutch, or ganged pots with a separate balance control. Might be time to bring back dual-concentric pots.
In modern high-end gear, there's been a trend towards the ultra high performance Khozmo pots, which offer a convenient dual-mono option, so you can set up a 0.5 dB offset on the remote control! No joke! My Don Sachs preamp has this option, and man, is it slick! No worries about system balancing, set and forget.
Any crossover in these?
If not, you will have tonnes of comb filtering effects which at times will be so strong that the balance will be totally off. This is exaggerated by mounting the driver pair horizontally.
//
Nope. The SDA drivers run full range, sometimes with the SDA driver padded down in relative volume to the main driver.
I know Polk eventually discarded the idea of SDA tweeters in his designs and limited the bandwidth of the SDA cone drivers. I'd need two more channels of DSP / Amp to do that, or go to a parallel connection with passive crossovers. That would put amplifier load down to 2 Ohms for some of the frequency range, which it could supposedly handle.
I've no idea what frequency range I'd want to design the crossovers to, to prevent the combing. Apparently Polk's design evolved so that all the audible frequency range wasnt necessary to provide the effect. I havent had the chance to measure a real modern Polk SDA, to see what bandwidth comes out just the SDA drivers.
I am using the stock 1B cabinet, sealed, wish i had room for OB's.
I built a set of Pioneer b-20's years ago, rear port and rear tweeter,,,i should have kept them
After reading about your Sda Ob's, I am thinking of experimenting...I used the stock x over layout
when rebuilding mine.
I have a bread board ans o-scope i would really like to see how the sda cap (185) and coil works (9.6).
I have Bass bos, old software, does not let me build custom circuits....I played with the Hafker circuit in my car years ago...
Seems to me your center channel souldbe infinite abffle in the wall.....
I built a set of Pioneer b-20's years ago, rear port and rear tweeter,,,i should have kept them
After reading about your Sda Ob's, I am thinking of experimenting...I used the stock x over layout
when rebuilding mine.
I have a bread board ans o-scope i would really like to see how the sda cap (185) and coil works (9.6).
I have Bass bos, old software, does not let me build custom circuits....I played with the Hafker circuit in my car years ago...
Seems to me your center channel souldbe infinite abffle in the wall.....
I'd guess it drops the bass and treble levels at some frequencies - no point in running an out-of-phase driver during mono bass and perhaps the high frequency limit is how they address the combing. I still dont have a practical way to address these issues in my setup -