Odd problem playing LPs

[Larpy]

I installed a new cartridge on my turntable (a Linn LP12) and am hearing intermittent distortion, in both channels and most noticeable on louder passages.  I've checked and rechecked the geometry of the cartridge alignment, checked its VTF, etc, made sure the cartridge leads are tight, and I still have the  problem.

I also checked the voltages of my Eros and they're all in spec.  With one possible exception:  the voltage from the PS board was 262v, when last I checked it (a couple of years ago?) it was 278v.  Not a huge drop, but nothing has changed in the Eros since I last measured its voltages.

I've been thinking it's a defective cartridge, but I noticed today that records sound fine when I first turn on the Eros  but sound distorted the longer I listen.  Could the Eros be the problem once it warms up?  I did notice the other day when I turned off the Eros to test it that its PT was very hot, too hot to touch for longer than a couple of seconds.  Is that normal?


Is this a plausible suspicion?  If so, can I confirm it by turning on the Eros, letting it warm up for 30 minutes and then testing its voltage?

 

[ccmccull]

Couple thoughts, since I happen to be working on restoring an old Dual headshell, and I also own an Eros! First, the transformer on my Eros also gets too hot to touch. I think that's normal. Second, I would check the continuity between the cartridge pins and the RCA jacks from the Lynn. I had to replace the four small leads inside the headshell because of high and intermittent resistance there. I guess they can be forgiven for this after 50 years. Next, I would try a known good source and remove the Lynn from the testing. If you have a signal generator that would be best. 2mV rms into the Eros.

 

[Larpy]

Thanks for the suggestions.  I actually replaced the cartridge leads, thinking they might be the issue, but that wasn't it.  I confirmed continuity between the cartridge pins and the tonearm's RCA output jacks (each pin measured .7Ω).

I don't have a signal generator, but I imagine I could download a 2mV signal and play it through the Eros.  But what would I then measure?  This is new troubleshooting territory for me.

Oh, I should add that it's not a matter of the cartridge overloading the Eros.  The cart's output is .4mV and I use Sowter 1:10 SUTs at the Eros input: that should put the signal into the Eros in the 4-6mV target, which is what the Eros is designed for.

I hadn't listened much recently to the cartridge this new one replaced because it had seen nearly 5 years of service and I knew it was worn.  But I remember the last time I listened to it, it sounded terrible.  That prompted me to buy the new cart and to send the old one off to Soundsmith for retipping.

What's confounding is that this distortion is intermittent.  The only pattern I think I detect involves the Eros:  when it's just been turned on, LPs sound great.  After it's been on for 30 minutes or so, I hear distortion.  My digital sources are fine, no distortion there whatsoever, so it must be something in my analog chain.  I changed out all the tubes in the Eros; no difference.  I changed the interconnect between the Eros and my preamp; no difference.

I diligently clean the stylus after each LP I play, so I'm pretty confident that's not the issue.

So I think I'm down to three possibilities:
1) defective cartridge
2) bad connection inside the tonearm (but both channels are affected, so I'm leaning against this explanation)'
3) something amiss in the Eros.

Unsurprisingly, the retailer (online) from whom I bought the cartridge isn't convinced the cartridge is at fault.

Given the pattern of good sound that deteriorates after 30 minutes or so, my attention has turned to the Eros.  As I said, when I measured the voltages in the Eros, all the regulated voltages were spot on, but the voltage from the board above the transformer was a bit low.  This was after I had unplugged the Eros and it had a chance to cool down.

So I'm wondering if there's a measurement I can do with the Eros that would confirm that it's behind my problem.  And then of course I want to fix it!

 

[Larpy]

I just took some more measurements.  The Eros had been turned off since yesterday.

Before I turned it on, I measured the resistance across the PT's primary (29Ω) and secondary (87Ω).  Then I turned it on and waited a couple of minutes.  Then I measured 120 VAC at the PT's primary and 119VAC at the secondary.

According to the PS board above the transformer, the secondary voltage should be 135VAC.

DC out from the PS board was 273v.  So does that mean the regulator is being asked to work harder than it should?  Would that result in distortion, mostly in the upper bass and midrange, on louder passages on LPs?

I'll leave the Eros turned on and take more measurements after 30 minutes or so.

 

[Larpy]

30 minutes later, the transformer's secondary measures 117VAC.  The DC out from the PS board is down to 267vDC.  There was no load during this time.  The Eros was at idle.

 

[ccmccull]

I took a look at my Eros measurements, attached. 267VDC does seem a bit high. PB will have to weigh in on that. If that's not the issue, my next troubleshooting steps would be to use a different source than the Linn. Ideally a signal generator, but even a phone headphone jack with tone generator app on minimum volume. Set up the Eros in a way that you can reach the underside while running. Try to reproduce the distortion, then start chopsticking the underside joints.

I had exactly this problem with a Fender reproduction guitar amp I built. It worked fine for a 2 years, then started distorting intermittently only when it was hot. It turned out that the nut holding down the grounding tab had loosened slightly over the years, probably from thermal cycling. (The ground tab on that amp was fastened to one of the transformer bolts.) I tightened it up and the issue was fixed! But wow it took me a long time to figure out the problem.

 

[Larpy]

267vDC is the voltage out of the board on top of the transformer; it's not one of the measurements listed at the end of the manual.  It's supposed to be 275vDC.

The measurement that has my attention is the transformer's secondary:  I measure 117-119 vAC when it should be 135.  The heater side measures correctly, but the high voltage side of my transforming doesn't seem to transforming at all.  120vAC > 117-119vAC.

The Eros has two grounding points: one near the IEC jack and another between the input jacks. Both are screwed tight.  Of course, I might have a bad ground connection elsewhere, but since I hear the distortion in both channels, and the Eros wiring is dual channel after the PS, I'm thinking a ground problem would have to be in the PS.  Everything looks OK there though.

 

[ccmccull]

Took some more measurements for you, hope this is helpful. LMK if you want any more measurements points from mine.

Transformer:
Primary 13 vs. 15: 29 ohms, 123 VAC
Secondary 11 vs. 12: 85 ohms, 123 VAC
Secondary 7 vs. 9: 0.3 ohms (my dmm leads are 0.1 ohms), 8.9 VAC

P/S board:
275VDC pins: 285VDC. this came down to 283VDC after 5 min.
6.3VDC pins: 6.3VDC. this came down to 6.2VDC after 5 min

 

[Doc B]

Your voltages look spot on, but you are measuring them after only 5 minutes and telling us that the problem occurs after 30 minutes. So....

 

[Paul Birkeland]

The voltages definitely will change a little bit as the Eros warms up.  We provide voltage measurements that are shortly after turn-on, since that's what's useful in the manual.  The high voltage output of the power supply board above the power transformer needs to be at least 230V for the regulator circuit to work properly, so there's plenty of wiggle room there.

Yes, the power transformer in the Eros runs quite hot, but still has a lot of thermal headroom in terms of when the transformer would run so hot that damage would occur.  PJ did keep it cool enough under normal operation that it's hot to the touch but not hot enough to cause any kind of injury. 

I would be interested in knowing what the DC voltages are after the problem starts happening, as there's likely some kind of shift in operation that could be responsible for the problem you're having.

 

[Larpy]

Well, my hypothesis that the distortion only presents itself after the Eros warms up is wrong.  Today I heard the distortion within seconds on the first LP I played.  The Eros had only been on for a minute or two.  The distortion remained for the entire side of the LP.

I took measurements midway through, and all the DC measurements were right on target, except that the DC coming from the PS board above the transformer was a little low:  265v.  But 10 volts too low is no big deal.

The only anomaly I measured was, as I reported yesterday, the power transformer's secondary was 117vAC.  Both the schematic and the print on the PS board where the secondary wires are soldered to specify 135vAC.

So my question is: could this be the problem?  Would 117vAC from the transformer's secondaries result in correct DC voltages on the voltage regulators but cause distortion during louder passages of music?

And, if so, does this mean I need a new power transformer?

 

[Paul Joppa]

The power transformer puts out a nominal 135 vAC when it is unloaded To test that, just pull the tubes, which will remove most of the current draw. The winding resistances you measured indicate it is up to spec.

The voltages I would focus on are the EF86 plates (A6 and B6) and cathodes (A3 and B3).

Incidentally, the OSHA "safe to touch" temperature is 140 degrees for 5 seconds or less.

 

[Larpy]

Yes, of course.  I should have thought of that--that the secondary's specified voltage is without a load.

Well, I guess my Eros is perfectly healthy and not the culprit of the distortion I'm hearing.  Plate voltages on the EF86s are 100v, and the cathodes are 1.7v.  Right in spec.

Thanks for the help, everyone.

I think I must have gotten a defective cartridge.

 

[2wo]

I don't suppose you can Borrow A turntable  for a quick test?

 

[Larpy]

I live in a part of the country where audiophiles are few and far between (not that they're really falling from the trees anywhere these days).  Although I live in a mid-sized midwestern city, I have to drive an hour to visit the closest hifi shop.  I have a few friends with turntables, but all of them use moving magnet cartridges.  They wouldn't work plugged into my Eros as it's configured.

Of course, it wouldn't be all that much work to temporarily rewire the Eros to bypass the SUTs.  Up until now I was hoping to avoid this.  But maybe now it's time.

 

[Larpy]

I took John’s advice and asked a friend to bring over his Music Hall turntable (fitted with a Shure MX97xe cartridge).  While I waited for him, I rewired my Eros input jacks to bypass the Sowter SUTs. Once my friend arrived, we replaced my Linn LP12/Ekos/HanaML with his Music Hall/Shure and put on side 1 of Radiohead’s Kid A.

I heard the same distortion as I did before(!).

I have some speakers and an old Technics receiver (made back when they had internal MM phono stages) set up in another part of the house, and so we plugged the Music Hall turntable into it and the Radiohead LP we had just played sounded fine through it.  No distortion.

So the problem I’m having has to be with my Eros.

What would cause the Eros to distort in both channels on louder passages (usually bass-heavy) even while all of its voltages are spot on?  It obviously can’t be the Sowter SUTs, since they were not in the circuit.

Last night I did the chopstick test on the PS board above the PT and on nearby ground connections but didn’t hear anything through my headphones.

I'm feeling baffled and defeated.  Any help will be hugely appreciated.

 

[Paul Birkeland]

I would expect the voltages to deviate once the problem has occurred.  Are you 100% sure that the voltages are all Ok when this happens?

 

[Larpy]

Yesterday I had the Eros' chassis inverted while I played an LP.  I heard the distortion and took measurements then and there.

I don't remember if I raised the tonearm or not while I took the measurements.  I'll repeat the exercise and take measurements while the Eros is processing a signal and report back.

 

[Paul Birkeland]

It would also be worth a shot to roll in a different tube set, just to rule that out. 

 

[ccmccull]

Have you ruled out the audio chain after the Eros? What do you have the Eros plugged into?

To test this, when you have the distortion happening, you could unplug the Eros output from its subsequent amp input and plug it into the aux jack of your techniques receiver.

On the grounding question, I'd chopstick all the points along the ground bus near the inputs. Since it's a single ground bus for both channels, a bad solder joint there could affect both channels simultaneously.