DAC making analog life difficult

[guy48065]

I've been listening to streaming & digital sources more and more--but I also want to improve my vinyl playback. Several months ago I replaced my Grado MM with a Monster Alpha 1 MC that has been in a box for years. I switched my PS IV preamp to MC and changed the load resistor. The sound was wonderful except for an unacceptable amount of hum at the higher gain.
So again I'm spending more time listening to digital.
Last night I put on an album and was fussing with grounding & connections and nearly by accident I found that pulling the RCAs from my Topping D30 DAC cut the hum in half. There remained some hum, a quiet rhythmic thumping & a faint low tone. Pulling the DAC power cord eliminated most of that.
So... All I need to do is remove my DAC and I have a sweet-sounding, quiet analog system.

I've never had a line-level component inject noise into a phono stage input. The other line level inputs are quiet.
What have I got going on here?

Ps the DAC, TT & preamp all have ungrounded power. The DAC input is optical.

 

[amirm]

The DAC is not injecting noise but rather, changing the balance of ground currents causing more hum. It is purely accidental. This is why you want to use balanced DAC and amps if you at all can. RCA system is broken by design (was never created for external components).

 

[Blumlein 88]

Beside what Amir posted, you also switched from MM to MC so the gain for MC is much higher. Some of that noise may have been there all along, but now you are applying more gain and it is higher in level at the output.

Since you have RCA, it is possible running some ground wires from one component to another might help. Fixing those situations is something of a black art. It is possible if the phono is picking up some RFI/EMI that a grounded plane between it and other gear would help, but the hum is likely from the source Amir is referring to. Your preamp has a ground lug on the back. If your TT has one try attaching that first. You also might find which component is responsible the most by checking AC voltage between the grounds of each component. By this I mean using the ground part of the RCA and connecting the multimeter set to AC volts one end on each component. Though it sounds like you know it is the DAC.

One final question: what sort of interconnects are you using? Anything unusual like something unshielded or simply twisted?

 

[Galliardist]

What happens if you just switch the DAC off and play a record?

 

[Soniclife]

Try to ensure that the phono cables are kept as far away from as many other components as possible, even just a few inches can sometimes work wonders. As said above this is a black art, sometimes you get lucky, sometimes you can go crazy trying things.

 

[restorer-john]

Where is the DAC physically placed with respect to the Phono stage?

It's perfectly possible the DAC is radiating noise straight into the Phono stage. And by pulling the RCAs from the DAC, you removed one ground loop (RCA shield-amp-power ground- to IEC ground on the Topping DAC). Is it the D30 or D30Pro? The D30's extrernal SMPS will also have a cap to gng. Unplugging it entirely, may have removed another loop. The internal SMPS in the DAC (if it's a dD30pro) will likely have a cap to ground on the primary side which is a gigantic hum injector also.

In short, get the Topping DAC as far away physically and electrically from your 60dB+ MC stage, cables and TT/cart.

 

[guy48065]

It's the original D30. I moved it around as far as the interconnects allowed and it made no difference. I don't believe this is magnetic hum radiating into cables or thru the preamp case.

Switching off the DAC makes most of the hum stop but not the low thumping & tone. I need to try another power source to see if it's unique to the SMPS.

Honestly I don't NEED the DAC in the current setup. I got it when I had a DVD player that had no RCAs, but now I have a different one that does. Kinda kills my plans to embrace more digital sources/devices.

 

[MaxwellsEq]

I was using an MC cartridge before CDs (and hence digital) became available. The gain of Moving Coil preamplifiers has to be very high which makes them susceptible to all sorts of mains-bourne and radio noise. They also show up earth loops much more efficiently than almost anything else. RCA was the only connection available outside professional gear in those days.

So your problem is not really your DAC or digital, but the challenges associated with an MC cartridge and unbalanced working (RCA).

@restorer-john is correct, though, DACs and SMPS are more likely to generate noise than other gear.

The problem with ground loops (almost certainly your problem), is that they are always unique to you and your gear and your home. We can suggest methods, but you have to solve it yourself.

In my experience, the best (but expensive, if you have to replace everything) approach is to move to balanced/differential working end-to-end). Everything else is a bit of a lottery. Sometimes you can get a big benefit by using a single mains extension and plugging everything into it. Also ensure that the cartridge and arm are properly earthed at the phono preamplifier. On the other hand, sometimes (rarely) you need to disconnect the earth wire from the turntable at the preamplifier end!

 

[restorer-john]

Sometimes you can get a big benefit by using a single mains extension and plugging everything into it. Also ensure that the cartridge and arm are properly earthed at the phono preamplifier. On the other hand, sometimes (rarely) you need to disconnect the earth wire from the turntable at the preamplifier end!

This is good advice. A decent extension, power board/strip and everything hanging off that with no earth loops, no connections to anything not on the board/strip and sensible component placement.

Like @MaxwellsEq, I also was in the pure analog era, with tons of gain and everything from the light switch wiring in the wall to the local radio station could cause problems. MC is circa 60dB voltage gain, or x1000 times, plus the RIAA curve characteristics. A tiny amount of induced 50/60/100/120Hz becomes quite loud after phono stage amplification and another 20-30dB in your power stage.

Actually, when you think about it, it's amazing we didn't have way more trouble with hum and noise back in the day with SE connections.

 

[guy48065]

This system has been mostly unchanged since the 80's. It's seen mostly MC ctgs over the years. Never any issues with unexpected hum & noise.
It's a "known quantity" in other words. The DAC is causing the problem. What I'm fishing for here is others who've had the same experience with DACs in general or maybe the D30 in particular.

I added a Squeezebox to this system in 2010 and experienced no problems with this first addition of 1s & 0s. I'm thinking the budget D30 may have skimped on preventing noise radiation. It's possibly also 'gone bad'.

I'm sure it's true that balanced circuitry & connections are more immune (CMRR) to these bugaboos but there's no way I'm replacing it all now.

 

[MaxwellsEq]

An earth loop is always a systemic problem, rarely the fault of one device, it just sometimes seems that it's one device.

The way you described this in post #1 was everything seemed OK-ish until you switched to high gain for an MC cartridge. This almost certainly means that the problem has always been there and is now highlighted, probably because of the extra gain (which is the upper limit of any domestic audio gain setting). Seriously, MCs are really challenging if you don't use a balanced/differential approach.

Or, you might have broken something changing the gain and resistance on the preamplifier. Have you tried setting it all back to MM, BUT with the MC cartridge? The cartridge will still play, but it will be quiet and slightly wrongly loaded so will need a lot of volume.

 

[guy48065]

If so, then it's academic. It's a problem that didn't manifest itself until this DAC was connected. I unplug it & the problem goes away.

I'm not throwing in the towel yet. I can try another PSU, borrow another DAC, try disconnecting other components, etc.

Right now I leave the DAC on all the time, for simplicity. But it's not needed when I'm playing vinyl. Since all the unwanted hum and motorboating doesn't entirely go away by switching off the DAC (probably cuts only the +pwr) I'll also try a PSU with its own power switch. Hopefully disconnecting the power ground from the DAC will make all the noise go away as if it isn't even there.

 

[Blumlein 88]

In my experience, which is not universal of course, motorboating is usually from something radiating into the phono stage. Something I've done, which is too easy not to try, is taping some aluminum foil to a notebook or piece of cardboard. Use clip on jumper leads to connect it to a ground point (like the outer part of an unused RCA plug), and move it around to see if any positions lower the motorboating or make it go away.

 

[guy48065]

I was away for the weekend so I couldn't update this.
All "extra" hum, hiss, weird tone & rhythmic thumping is gone. They disappeared as I pulled the RCAs, then the power connector, and finally unplugged the SMPS wallwart.
I did this with shorting plugs in the phono inputs in order to isolate the preamp.

Now with the input switch on MC, the volume at 100% there is the *slight* hum & hiss this preamp has had for 40 years.
Plugging the TT leads back in (gnd wire attached to preamp) didn't increase the noise level. At normal playback levels sound again emerges from quiet inky blackness.

I'm satisfied for now. My system isn't 100% purist analog. I have a Squeezebox digital music streamer and a Fosi class D amp on the subs, plus a DVD player. None of these add any unusual noise to my basic system.
In time I'll fiddle with the D30 DAC to try to figure out if it's defective, or the wallwart is. I don't need it at this time. It was here just to give a bit better sound than the DVD internal DAC.

 

[guy48065]

I have narrowed the problem to the OEM wallwart. I connected the DAC to a bench power supply and there was zero change in hum & noise vs. DAC out of the system. I then reinstalled the wallwart, plugged into a separate outlet. The low tone & tapping sounds could be heard--but at a very low level. I moved the wallwart back to the same strip the rest of the system is powered from and ALL the excess hum & odd noises returned.

This oem power adapter still puts out 15V but it's not clean and it's radiating wierdness into the AC mains. I plan to replace it with a nice linear 15V supply.
My distrust of SMPS continues to increase.

 

[MattHooper]

View attachment 343306

This system has been mostly unchanged since the 80's. It's seen mostly MC ctgs over the years. Never any issues with unexpected hum & noise.
It's a "known quantity" in other words. The DAC is causing the problem. What I'm fishing for here is others who've had the same experience with DACs in general or maybe the D30 in particular.

I added a Squeezebox to this system in 2010 and experienced no problems with this first addition of 1s & 0s. I'm thinking the budget D30 may have skimped on preventing noise radiation. It's possibly also 'gone bad'.

I'm sure it's true that balanced circuitry & connections are more immune (CMRR) to these bugaboos but there's no way I'm replacing it all now.

r/TvTooHigh



But aside from that, looks like a fun set up! Glad you solve your problem.

 

[Gringoaudio1]

My Topping D10 DAC seemed like the source of my problems but it was the PC where my music comes from (JRiver and Spotify) feeding it a signal overlain with noise. When I tried a cheap USB optical isolator I still had the problem. It was solved only when I tried the Topping USB HS-01 isolator between the PC and the DAC.