Help in troubleshooting Piccolo noise...

tketcham · « **on:** 28 Dec 2007, 05:32 pm »

I'm running out of ideas and need some advise. I've had a continued noise (hiss) problem with the Piccolo and one of the suggestions was to see if it was related to the internal resistance of the low output (0.5mV) moving coil cartridge I'm using.

http://www.audiocircle.com/index.php?topic=42837.0

I finally had a chance to try another low output (0.3mV) mc cartridge and the hiss problem was even worse. I've also tried shorter interconnects (0.5m), moving the Piccolo and phono preamp further away from the turntable, and rearranging cords/cables but nothing seems to make any difference. Maybe I need to disconnect everything and start from a baseline. Any other suggestions?

I really like the flexibility of the Piccolo as a head amp and mc loading device. and love the sound I get with the (solid state) phono preamp I'm using. (The preamp is VERY quiet without the Piccolo but doesn't have a loading option below 100 Ohms.) But the noise problem is beginning to dampen my enthusiasm for this head amp. Surely there must be a solution; I read more and more favorable comments about the Piccolo so it must work well with other systems and I'd like to find what the problem is with mine. I need some help!

Thanks.

Tom

hagtech · « **Reply #1 on:** 28 Dec 2007, 05:52 pm »

What is the gain of your phono stage? And at what level do you hear hiss, compared, to say, groove noise? I can easily hear hiss too if I crank the volume up.

jh

tketcham · « **Reply #2 on:** 28 Dec 2007, 07:30 pm »

Hi, Jim,

I'm running the phono preamp at 50 dB of gain plus 12 dB of gain from the Piccolo for a total of 62 dB. That puts the volume control at about 10:30 for typical listening levels of sub 80 dB SPL peaks, with average SPL peaks of around 75 dB. I occassionally run it up to 11:00 for some music, keeping peaks below 85 dB. The Piccolo is set at 44 Ohms loading resistance and is running off the wallwart. The battery pack has the same hiss levels so I just use the wallwart. The phono preamp alone is dead quiet up to volume settings of 3:00 or more and then it's just audible.

Using a lomc cartridge with 0.5mV of output and coil impedance of 17 Ohms, the hiss is audible from the listening chair starting about 10:00 (faint) to noticeable at 11:00 to very obvious (~36 dB SPL) at 12:00 without playing a record. I begin to notice the hiss when playing quiet/blank passages at 11:00 or so; it's subtle but with a nice clean section of lp groove it's unmistakable as hiss. So I guess it's ok in a relative sense; that is, I don't really notice the hiss until I'm up into the higher volume listening levels. It's not ideal but I can live with it (sounds very good) using this particular cartridge.

What is now concerning me is that I'll be running a lower output (0.3 mV) mc cartridge and the hiss becomes noticeable (subtle but audible) even at more typical listening levels. I still run the phono preamp at 50 dB since the next level of gain is 60 dB and with the minimum 12 dB gain on the Piccolo the volume range on the integrated amp becomes too limiting. Unfortunately I had to send the cartridge back for warranty service so don't have it available to troubleshoot right now. I guess I could wait and pursue this with you when it returns. I was just wanting to see if there was a solution that didn't involve cartridge configuration/design.

Are there tests that I can do on the Piccolo to see if it's performing properly? Wiring, circuitry components? Or are there tests that I can do with my system to see if there's something I'm running that just doesn't mesh very well with the Piccolo?

Rocket · « **Reply #3 on:** 29 Dec 2007, 01:24 am »

Hi,

I had moderately bad hum for 2 years in my system. I tried about 5 phonostages and they all had hum including the cornet. I tried everything that I could think of including moving the equipment and different cables etc.

I had to change my denon dl103 cartridge because it was damaged and I bought a benz micro mc20e2 high output mc and I now no longer have problems with hum.

I know how you feel regarding noise from your system because it nearly drove me mad.

Can you try another cartridge?

Regards

Rod

hagtech · « **Reply #4 on:** 29 Dec 2007, 03:24 am »

The problem isn't any of your cartridges. The hiss from groove noise should be much more audible than hiss from a PICCOLO. Something isn't right here. Is this a factory built unit?

jh

amandarae · « **Reply #5 on:** 30 Dec 2007, 04:39 am »

Quote from: Rocket on 29 Dec 2007, 01:24 am

Hi,

I had moderately bad hum for 2 years in my system. I tried about 5 phonostages and they all had hum including the cornet. I tried everything that I could think of including moving the equipment and different cables etc.

I had to change my denon dl103 cartridge because it was damaged and I bought a benz micro mc20e2 high output mc and I now no longer have problems with hum.

I know how you feel regarding noise from your system because it nearly drove me mad.

Can you try another cartridge?

Regards

Rod

I agree, the DL 103 series is a hum magnet! I have six of them (DL103R retiped by Soundsmith, DL103R, DL103 with wood shells x 2, DL103 stock x 2) and all needs to be mated carefully (SUT, cables, and phonostage) so as not to have a hum in the system. My Koetsu Rosewood, Benz, and Shelter are more forgiving and does not experienced the same phenomenon.

I agree with Jim! There is something that is not right somewhere. I have my piccolo for many months now and I do not have a hiss eversince I fired it up.

Is the hiss present when the stylus is not on the lp? Or when you crank up the volume without lowering the arm down? What about doing the same procedure but with the TT powered down?

Jim ,what should be the ac level at the outputs for both channels at idle? Maybe that is a good start to see if it is the unit or the other equipments producing the noise.

regards,

Abe

hagtech · « **Reply #6 on:** 30 Dec 2007, 06:13 am »

Quote

what should be the ac level at the outputs for both channels at idle?

It is hard to measure without the right equipment. Typically at 26dB gain & 100 ohm setting (no cart), the output is 5.6uVrms.

jh

tketcham · « **Reply #7 on:** 30 Dec 2007, 04:54 pm »

Hi, Jim,

Was out snowshoeing yesterday so didn't reply back. The Piccolo is a factory unit. Purchased the end of June 2007.

For those helping to troubleshoot: I don't have any hum in the system, it's very quiet other than the hiss/rush noise.

Additional information: The hiss is slightly lower (35 dB SPL at 12:00 volume setting) without a cartridge attached.

Thank you for helping me get this figured out.

Tom

hagtech · « **Reply #8 on:** 30 Dec 2007, 07:03 pm »

Hmmm, that's odd. I've never heard hiss get louder by adding a cart. Usually the resistance of the cart is much lower than loading resistance, thus making the parallel combination generate less thermal noise (hiss). Most hiss is caused by resistances in the front end.

jh

tketcham · « **Reply #9 on:** 31 Dec 2007, 04:07 pm »

I did some SPL noise measurements at 1 m from the speakers with the amp volume set at the 12:00 position and the Piccolo set for 12 dB gain at 44 Ohms loading and the hiss levels were:

38.0 dB with the cartridge
37.8 dB with no cartridge

No noticeable difference in hiss whether the turntable is on/off.

So essentially the same. Does this make more sense?

PS: Could the slight difference be the difference in tonearm wiring/interconnects between the two (identical) turntables that I'm using? One has a cartridge attached, one has no cartridge (sent in for warranty service) attached. This is probably a red herring unless the difference between noise levels with and without a cartridge should be noticeably different.

tketcham · « **Reply #10 on:** 8 Jan 2008, 02:05 am »

Well, the Piccolo is on its way back to Jim for some diagnostics. Will let you know what he finds.

hagtech · « **Reply #11 on:** 15 Jan 2008, 08:04 pm »

Son of a gun. There was a problem! How embarrasing - a manufacturing error. Ok, small one, but nonetheless the kind of thing that shouldn't happen. I'm going to fire my quality control inspector.

The problem was very simple: the nut on the underside of the ground lug was loose! I (er, the assembly technician) forgot to tighten the nut to the top cover, which helps to insure solid contact. This connects the cover plate to the circuit board ground. Without a good connection, the cover can float and pick up noise from stray fields like an antenna.

And so it is now fixed. I also did the resistor change to reduce dc on output. Sending back for confirmation.

jh

tketcham · « **Reply #12 on:** 16 Jan 2008, 03:21 pm »

Eureka! Glad it was something so simple. (Most problems usually are; they just aren't always obvious.) And thanks for updating the resistor. Looking forward to having the Piccolo back in the chain. If the noise floor drops as much as everyone's been mentioning, it should sound great. As much as I enjoy the Jolida JD9, the combination of Rogue Audio Stealh and Piccolo is a winning combination.

Tom

analog97 · « **Reply #13 on:** 16 Jan 2008, 05:12 pm »

Quote

I also did the resistor change to reduce dc on output/quote]

Did I miss something? I got one of the first Piccolo's. If there is an improvement, I'd like to do it. Thanks.

tketcham · « **Reply #14 on:** 16 Jan 2008, 08:53 pm »

I believe he's refering to the modification mentioned here:

http://www.audiocircle.com/index.php?topic=48783.0

Here's the text of Jim's fix:
"One way to tweak this in is to add about 10 ohms to R10. Change them both from 221 ohms to roughly 232 ohms. At the moment, I am just putting a spare 10 ohm resistor in series with the 221."

analog97 · « **Reply #15 on:** 17 Jan 2008, 01:37 am »

I'm a tad confused, primarily because I don't understand "DC offset". I have built a very early PICCOLO kit. I am using it with the Cornet2. I re-read those posts you referred to and it mentioned that a tube phono stage/Piccolo combo should not be a problem. The problem would occur with a DC-coupled phono stage (not sure what that means). Thus, do I need to change the resistors? Any help appreciated!!

EchoWars · « **Reply #16 on:** 17 Jan 2008, 10:42 am »

The upshot is this...the Piccolo amp uses +/- DC supplies and no capacitors in the output signal path to filter out any DC which may be present...'DC coupled' or 'DC coupling' meaning, in general, a straight-wire path using no capacitors to block the flow of DC currents. Because Jim designed the Piccolo to be DC coupled at the output, the possibility exists that the output of the Piccolo may not be sitting at 0.000VDC, which is the ideal since we're interested in listening to audio frequencies and DC is kinda boring.

DC coupling is preferred in most cases, but it does mean that more care is needed in the design to ensure that the output is 'centered' with regard to DC. In the case of my own Piccolo, I had about 12mV (0.012V) of DC on one channel, and about 22mV (0.022V) of DC on the other, which I felt was excessive.

Whether this matters or not depends somewhat on what you're feeding the output of the Piccolo to. If the Piccolo is feeding a tube RIAA phono stage, it's no big deal. Similarly, if it is feeding a solid-state phono stage using bipolar transistors for its input stage, this is also not usually a problem, since bipolar transistor input stages nearly always have an input capacitor to de-couple any possible DC that might try to flow to the cartridge.

DC coupled solid-state phono amplifiers which use FET's are another story (and most of my own RIAA phono stages are DC coupled FETs)...these type of FET RIAA phono stages are DC coupled directly to the cartridge, and if you put the Piccolo between the FET input phono stage and the cartridge (which is, of course, how it is intended to be used), then the DC present at the output of the Piccolo is presented directly to the gate of the FET at the input of your phono stage. This can and will affect the DC biasing of the first stage of your phono amplifier, and since the gate to source junction on the FET is essentially a diode, the DC can even forward-bias this diode with destructive results (but the DC present at the output of the Piccolo is a long way from doing anything like that...at least until you power it down*). Still, a fully-DC coupled FET-input phono stage is not such an unusual item, and that 20mV of DC coming from the Piccolo can easily be an issue. If it's possible to get rid if it, then doing so is a desirable thing.

To check the offset, just measure the DC with a DMM (set to read DC millivolts) at the output of the Piccolo (there should be no input to the Piccolo, BTW. I unplug the input cables and use RCA shorting plugs). Jim posted a solution (in the thread referred to above) which will reduce any DC offset at the output of the Piccolo, and I also showed my own solution (which is more of a PITA, but will eliminate any DC altogether).

*(As a side note to using the Piccolo with a DC coupled FET RIAA phono amplifier, I noted in my original thread that the Piccolo isn't terribly well-behaved at power-down time and the output likes to jump to nearly 600mV and sit there till the filter caps bleed off. If you're using the Piccolo with a FET phono stage, flip your input selector to something other than phono when you're ready to power it all down, as that 600mV is nearly enough to do some real damage.)

Dat's da story. Sorry you asked?

analog97 · « **Reply #17 on:** 17 Jan 2008, 03:10 pm »

Quote

Dat's da story. Sorry you asked? Hyper

No, never sorry for asking and thanks a ton for your well-crafted answer. My simple question is this: Since I get that terrible "pop" if I screw up and power down my Piccolo w/o changing the input, will the "fix" as described solve both problems, i.e. the "pop" and potential incompatability with certain phono stages?

hagtech · « **Reply #18 on:** 17 Jan 2008, 05:23 pm »

The turn-off "thump" is not related to the operating dc offset. It will still be there. Best not to turn off the PICCOLO unless you are turning off the phono too.

jh

analog97 · « **Reply #19 on:** 17 Jan 2008, 07:21 pm »

One more time, por favor:

1. I use the PICCOLO with a Cornet2.
2. Should I change the R10 PICCOLO resistors to 232 ohms? Is the change important/audible?