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Question concerns the phono stage of a ARC-SP16. To start off, I should mention everything sounds great. I have been converting a few LPs to digital using Audacity. When I looking at the monitoring meter but not actually recording that there is "jittery noise" on the left channel but not on the right. If I touch the 1 uF cap on the plate of V1 (left channel), the jitter goes away but the baseline noise jumps up. The same happens when I touch the 1 uF cap on the right channel sans jitter. Did some tube swaps, etc. without any change.
Attached is the schematic of the phono stage and screenshot of Audacity. Any ideas?
I married the perfect woman - the downside is that everything that goes wrong is my fault.
Edits: 04/25/21Follow Ups:
As the filter capacitors allow some seconds of operation when powering off the unit you should check if the 'jittery noise' persists immediately after turning off the preamplifier.
If it disappears the probable culprit is a bad earth solder joint.
Omnes feriunt, ultima necat.
The thought of a poor solder joint occurred to me and that is how my finger ended tapping on the coupling caps. I didn't find anything but it was pretty cursory. I need to return to the crime scene when I get some free time. And yes, the bouncing meter goes away immediately if the power to the pre is turned off, or the input selector switch is changed away from the phono.
The nice thing is that the noise is virtually inaudible and I would never have noticed if I didn't try converting the LP to digital.
I married the perfect woman - the downside is that everything that goes wrong is my fault.
Edits: 04/27/21
'my finger ended tapping on the coupling caps'
... you'll more accurate, safer results using a chopstick or pencil
just sayin'
with regards,
Just curious if the noise is there with the cover on, and that you only removed the cover to investigate. I run my Counterpoint preamp without the cover. But it has grounded shields around those old Wondercap capacitors.
Cheers!
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
Remove C2.
Why? Is that a known standard mod to this product?
I do not know if a standard mod. But, all phono stages use perhaps as large as .047uF in this position, most .02uF. 1uF is ridiculous and poor design.
I don't doubt that the design isn't great but that I would wager isn't the op's problem in a commercial device from a "reputable" manufacturer like ARC.
Pulling parts that are probably OK isn't usually the way forward especially as both channels react the same but only one has a fault.
It is likely a noisy coupling capacitor. Removing that 1uF is a start.
Your finger will act like an aerial for noise into such a high impedance circuit. Much like when you touch the cartridge pins on the cartridge. That in itself doesn't sound like much of a problem.
As for the other noise, that ould be anything; bad valve, noisy resistor or maybe something in the support circuitry/power supply/heatere supply.
The SP16 is the poster boy for poor design. Why would anyone use a 1uF cap to drive signal across a 1M resistor? My suggestion is to replace it with a good phono pre like Bottlehead and don't look back.
--------------------------
Buy Chinese. Bury freedom.
No argument about the design of the SP-16 including the use of 12AX7s for cathode followers but that begs the question. Why the noise? And why does the extra capacitance of a finger make it worse? And why the jittery noise on one channel only?
BTW, I also have a Music Reference RM-5 but I have gotten use to a remote.
I married the perfect woman - the downside is that everything that goes wrong is my fault.
Edits: 04/25/21
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