SDA-SRS 3.1TL - Need Assistance with Feedback Problem
heroesunplugged
Posts: 48
I've had this pair of SDA 3.1 TLs for a while and have used them with various amps, preamps and hooked them up to a couple of home audio receivers. My current setup is a NuForce MCP-18 preamp, being fed by a Technics 5 disc CD changer and an Emotiva SA-250 amplifier. The SDAs have been in rotation but have gone unused for a few months.
A few months back when using a Pioneer SA-7500 integrated, as a preamp (with my Emotiva SA-250 as the amplifier) is the first time I noticed a loud, quick swelling feedback. It was as if I had a microphone in front of the speaker. The feedback sends the SA-250 into protect mode. After a couple of attempts I decided to try them without the SDA cable and that seems to have fixed the issue, but doesn't allow the enjoyment of the SDA effect so I went back to a pair of my Norman Labs for a while.
Tonight I'm using a newer preamp. Its a NuForce MCP-18 now feeding the SA-250 driving the 3.1TLs and I'm experiencing the same issue with feedback as before. The overload protection circuit shuts the amp down. If anybody has any ideas on how to remedy the problem of feedback let me know. The speakers have never been modified in any way. Can a bad cap, now be acting as a resistor, be the cause of the feedback?
Your feedback is appreciated, but the SDAs is not!
Thanks for taking a moment to assist.
Chris
A few months back when using a Pioneer SA-7500 integrated, as a preamp (with my Emotiva SA-250 as the amplifier) is the first time I noticed a loud, quick swelling feedback. It was as if I had a microphone in front of the speaker. The feedback sends the SA-250 into protect mode. After a couple of attempts I decided to try them without the SDA cable and that seems to have fixed the issue, but doesn't allow the enjoyment of the SDA effect so I went back to a pair of my Norman Labs for a while.
Tonight I'm using a newer preamp. Its a NuForce MCP-18 now feeding the SA-250 driving the 3.1TLs and I'm experiencing the same issue with feedback as before. The overload protection circuit shuts the amp down. If anybody has any ideas on how to remedy the problem of feedback let me know. The speakers have never been modified in any way. Can a bad cap, now be acting as a resistor, be the cause of the feedback?
Your feedback is appreciated, but the SDAs is not!
Thanks for taking a moment to assist.
Chris
Comments
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Is it a specific tone, or a general increase in volume?
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I'd guess it is about 800 Hz or so.
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Falls within the midrange frequencies. Maybe as high as 2 kHz.
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No, volume on the pre can be set to 0 or can be off for that matter.
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Have you confirmed the amplifier is common ground? I would try another amp if you have access to one.
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Have you confirmed the amplifier is common ground?
Is there a reason to consider other wise???...curious
http://audiofi.net/2014/12/an-emotiva-limited-edition-sa-250-studio-reference-amp/2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC
erat interfectorem cesar et **** dictatorem dicere a -
I was told that it is by 2 different people at Emotiva before making the purchase. It has worked fine. I just have rotated different speakers into the mix and change things up. When coming back to wanting to try them with different gear after about six months of not using them is when I noticed the problem.
I have wondered if I was misdirected, but the person in sales confirmed with somebody in the technical area that the SA-250 is common ground. My concern was I was buying the 250 to replace an Adcom GFA-5500 that I knew was not common ground after reading the discussions here. The SA-250 is similar in design, in that they use different legs of the transformer for better isolation and less crosstalk. -
Fred could you explain
Mentions each channel has it's own independent ground lift switch...does this indicate isolation?
Look at article "Professional Features"
http://www.ultrahighendreview.com/emotiva-introduces-sa-250-limited-edition-studio-reference-power-amplifier/
@heroesunplugged .....FTGV (Fred) is a audio circuit guru2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC
erat interfectorem cesar et **** dictatorem dicere a -
Yes because the issue only appears when the SDA cable is connected.txcoastal1 wrote: »Have you confirmed the amplifier is common ground?
Is there a reason to consider other wise???...curious
http://audiofi.net/2014/12/an-emotiva-limited-edition-sa-250-studio-reference-amp/
A quick look at the description says the amp is dual differential.If that carries to the output stage then it is not common ground. -
I do have an old vintage Sony TA-3200F I can bring back into the system. I know its common ground.
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That would explain the issue. I specifically told them that I need an amp that is common ground for use with the 3.1TLs. I figured asking twice and getting a second opinion before purchase was a safe bet. I had concerns, but trusted that the manufacturer would know their own product.
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That's a different thing.The ground lift feature is used in situations when you have a system ground loop issue.Think cheater plug without disconnecting the chassis safety ground.txcoastal1 wrote: »Fred could you explain
Mentions each channel has it's own independent ground lift switch...does this indicate isolation?
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Alright. I may call Emotiva tomorrow and ask again. I found the e-mails where the person in sales said they checked with tech support and then I went directly to tech support and was told that the SA-250 or the Gen 3 would be a good match for the SDA speakers. The tech said the SA-250 has a lower noise floor and higher slew rate and thought the 250 would be the better pairing. It is a super clean sounding amp. Best try the Sony amp. Not sure how good the circuit protection is in the Sony, but may find out the hard way.
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Just don't over do it
....Please post back to help others, Good luck2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC
erat interfectorem cesar et **** dictatorem dicere a -
Sure thing txcoastal1. Thanks everybody for the input. I'll check back in and let everybody know how the amp change works out and how the discussion with Emotiva goes too.
Another option is to look at the caps. If they're like the caps used in the Norman labs they may show signs of corrosion. The NLs are from the same time-frame and had yellow caps that were made in Mexico. From my personal experience that's always a bad sign. I've been putting off rebuilding the xovers for a while, but may spur me on to get it done. First need to know if the amp is truly compatible with the SDAs. If not that could change the direction I'm going to go.
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Actually on second thought if they are not already you might check that the ground lift switches are in the off position and see what happens. If its has a differental/balanced output section it won't help but might help with a standard output configuration.txcoastal1 wrote: »
Mentions each channel has it's own independent ground lift switch...does this indicate isolation?
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heroesunplugged wrote: »Sure thing txcoastal1. Thanks everybody for the input. I'll check back in and let everybody know how the amp change works out and how the discussion with Emotiva goes too.
Another option is to look at the caps. If they're like the caps used in the Norman labs they may show signs of corrosion. The NLs are from the same time-frame and had yellow caps that were made in Mexico. From my personal experience that's always a bad sign. I've been putting off rebuilding the xovers for a while, but may spur me on to get it done. First need to know if the amp is truly compatible with the SDAs. If not that could change the direction I'm going to go.
It will not be the yellow mylar caps, nor the electrolytics.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Ok F1Nut not caps.
FTGV switches are in the ground position as suggested.
Sony amp is running fine. So far so good. Doesn't have the clarity, transparency, detail, or finesse combined with brute force of the Emo. It seems to be the SA-250 + SDA combination that isn't getting along. Considering the 3200F is 40+ years old and still plays with some low end oomph and control is very impressive. DC offset is still less than 5 mV per channel.
Contacting Emotiva via email to discuss possible problem/compatibility issue with the SA-250 amp.
Thanks for suggestions and chiming in. -
If you have a DVM you can test for common ground at the negative outputs.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Setting the Ohm Meter to lowest 200 Ohm setting I get 14.2.
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Appears, if I'm correct in my findings, this constitutes a non-common ground amp? When touching the probes together it's reading .4 so my meter isn't completely accurate. But I should get the same .4 at the terminals correct?
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14.2 ohms from negative binding to negative binding post? If so the solution would then be to tie the two negative terminals together with a short piece of speaker wire.
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The .4 is the resistance of the probe leads and will be included in your 14.2 ohm measurement. Your measurement indicates that there is still some resistive isolation but by strapping the negative binding posts together can be made common ground.heroesunplugged wrote: »Appears, if I'm correct in my findings, this constitutes a non-common ground amp? When touching the probes together it's reading .4 so my meter isn't completely accurate. But I should get the same .4 at the terminals correct? -
Well, that's one of the reasons I sold a GFA-5500. I had to tie the leads together and it seemed to collapse the sound stage. I had read that you can do that with the Adcoms, but I'm not sure this amp can be run with the negative leads tied since basically its design is similar to monos with a shared power supply. Everything is divided and have separate banks of capacitors for each channel.
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May be okay, but I'd sure feel better if I can confirm its okay.
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As long as the negative terminals are at ground potential, in other words it does'nt have a bridged /balanced output stage then you can strap the grounds together. That applies to dual mono and even separate mono bloc designs. Assuming done correctly your measurement would indicate that the amp does not have a bridged/balanced output stage so can be strapped.
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Gotcha on the including the .4 in the total.
I gave Emotiva a detailed account of the issue with the SDAs. Want to see if I get a correct answer from tech support based on these findings. I have 2 of these amps and this is disappointing that I received bad info. I like the sound quality, but to use these I have to manipulate them. That's the very thing I wanted to avoid. I didn't want to have to build a dreadnaught or put anything else in the signal path. -
Yes double check with them that the amp does not have bridged out stages and can be safely strapped. That being the case you should get the desired result with the addition of a short piece of wire.
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Does "dual differential" mean bridged/balanced? How can I find out?
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Okay. I'll check with them. Thanks Fred for all of your input. That may be a work around.
Chris
