Follow Up: Puffin Phono DSP Preamp

[JP]

Of course, if you’re digitizing records, all you really need is an ADC, like a Scarlett 2i2. RIAA can then be done in the playback program.

Heck of a lot easier to de-click pre-RIAA as well.

 

[jhaider]

Is the overload performance in the analog or digital domain?

I bought the coax output version a few months ago. I like it. I just wish the input cables didn’t stick up.

 

[SIY]

Is the overload performance in the analog or digital domain?

I bought the coax output version a few months ago. I like it. I just wish the input cables didn’t stick up.

Presumably analog, but tbh, it’s not something I tested.

 

[DDF]

Re: overloads, the issue isn't just recorded velocities, but also ticks and pops. Morgan Jones did some measurements to look at actual cartridge outputs, and he saw much bigger peaks from vinyl defects than from any signals. Now, if recovery from overload is essentially instantaneous, then no harm, no foul. But I'd rather have the headroom.

Good point, but I wonder if its a real issue in practice if it doesn't make ticks and pops (already ugly sounding) any more objectionable?

Appreciating there is variance between H/W designs, any pointers to characterization data for typical good phono pre's or A/Ds, to set some sort of a baseline?

Not arguing, generally interested, to understand if it needs following up. I didn't notice anything unusually annoying in the ticks and pops through my A/D, and they were overloading it. The benefit of PC EQ seems worth the risk, but I'm open minded about it.

 

[watchnerd]

Is the overload performance in the analog or digital domain?

I bought the coax output version a few months ago. I like it. I just wish the input cables didn’t stick up.

The upward cables are handy for access, but, man, do they mess up the aesthetics.

 

[BDWoody]

The upward cables are handy for access, but, man, do they mess up the aesthetics.

I should have sent these with it! I had to do something about that...

 

[bughunt62]

Thanks! Hadn't realized that Shannon had added the "magic" feature (along with a bunch of others), so I did the firmware upgrade tonight. Tried it out on a very beat-up Lou Donaldson Blue Note (BLP 1566) and, while it wasn't exactly magically, it did make it somewhat more listenable.

I also have those same Mediabridge connectors, which do help avoid the weird octopus look...

 

[watchnerd]

Thanks! Hadn't realized that Shannon had added the "magic" feature (along with a bunch of others), so I did the firmware upgrade tonight. Tried it out on a very beat-up Lou Donaldson Blue Note (BLP 1566) and, while it wasn't exactly magically, it did make it somewhat more listenable.

I also have those same Mediabridge connectors, which do help avoid the weird octopus look...

They should have called it the Octopus instead of the Puffin.

 

[restorer-john]

First up, the noise spectrum, generated with a Stanton 881 as the source:

So what is the 18.5-19kHz spike? Why doesn't it show on the 5mV input spectrum? The input loading with the cart would be pretty close at low frequencies to the gen but becoming a full blown inductor at HF wouldn't it- what is it picking up? An LED/CFL/SMPS on/above your bench? The cart is in a metal box with short leads I guess and I'm sure you don't have nearly 50 things hanging off your power outlet like I do...

 

[SIY]

So what is the 18.5-19kHz spike? Why doesn't it show on the 5mV input spectrum? The input loading with the cart would be pretty close at low frequencies to the gen but becoming a full blown inductor at HF wouldn't it- what is it picking up? An LED/CFL/SMPS on/above your bench? The cart is in a metal box with short leads I guess and I'm sure you don't have nearly 50 things hanging off your power outlet like I do...

You give me too much credit. The 5mV spectrum is not going to show any pickup because it's connected to the AP via coax and an attenuator. The noise spectrum is with the cartridge dangling, the idea being that it's not going to be in a metal box when used on a turntable. Now here's a puzzlement to me: to check the source of the 19kHz, I set everything back up and reran it to see the effects of turning off lights, fans, and the like. With everything going as normal, the 19kHz lines didn't appear! I tried turning all sorts of things on and off, no effect, it was gone. So I'm only left with speculation- as you surmised, I have all kinds of things plugged into the same power strip, And indeed at that high a frequency, the cartridge is an effective antenna. The physical placement of the Puffin and cartridge for the retest is pretty close to the same spot, say within a couple of centimeters. Any ideas?

I did try grounding the Puffin to the AP, and the cartridge shell to that ground, and the mains pickup improved quite a bit. Still more than I'd like to see, and I have a pretty good idea of the grounding issues that cause this. You would too, if you could look at the innards...

 

[restorer-john]

So I'm only left with speculation- as you surmised, I have all kinds of things plugged into the same power strip, And indeed at that high a frequency, the cartridge is an effective antenna. The physical placement of the Puffin and cartridge for the retest is pretty close to the same spot, say within a couple of centimeters. Any ideas?

The reason I asked is due to the fact I have had similar strange HF spikes when testing gear. Ones I couldn't track down. I figured if anyone knew, you would, especially in the mV realm of RIAA stages and keeping noise out. In other words, my motivation was selfish.

I would blame the key scanning of the micro in the device (sometimes they are active only for a few seconds then shut off the clock) so the spike could perhaps be there and then disappear. Other times I'd blame the display multiplexing. Other times I wondered if some HF content (way up from the uP hardware/DSP) was intermodulating and presenting a difference product down the spectrum that appeared in our audible bandwidth.

But I don't have an AP, so I just blamed my various sound-card front ends. At one point, I even tracked down a spectral component from a GPU card in the adjacent slot in the PC which was dependent on the video content it was sending to the monitor (LCD monitors are another source of HF crap).

Here's a similar one I could not track down. This is a totally analog (not even a gate anywhere) Denon preamplifier. Line-in to Line out. 1V in 1V out. Physical loopback versus through the preamp.

Loopback:

Through the preamp (as you can see it's only adding a bit of mains spuriae):

As you can see, 17 minutes apart and I hadn't moved a thing. I turned off everything (all bench gear except the PC (no wireless mouse or keyboard- they are RF devils too) and monitor, WiFi, router, inverter refrigerator, mobile phone, inverter air-con unit- you name it) including the monitor and couldn't get rid of the spike. A whole pile of ferrite clamps on every power lead, including 5 on the PC's PSU IEC improved it, each one incrementally. And then it disappeared...

Here is another preamplifier, this time a Sony TAE-77esd. It has a full blown micro running all the source selection etc and remote. It shuts the micro down (clock sleep) and yet it has a similar spike. This is direct switched on:

This is direct switched off (huh?) Yes.

Here is a Sony TAE-77esD. It has a D/A converter- otherwise identical to the one above. It gets the same basic spectrum plus an additional spike, I figure is the onboard D/A (although it is well shielded in a copper plated and screened box mounted deep under the chassis):

Direct Switch off:

What am I missing? I have a total of 4 of the above preamps- three non-D/A equipped and one with. They all exhibit the same spike but the analog loopback is clean...

You have a high performance analog generator in the APX, is the spike there when you use either generator? *grasping at straws here*

My other thought was something to do with the delay introduced by the DUT and how that would affect the timing in the "loop". The D/A and A/D are synchronously clocked and perhaps the delay, my sampling rate and FFT size (through the device) is causing these "false" spikes?

 

[scott wurcer]

Thanks for doing this, @SIY. @scott wurcer did you still want to play with it next?

That might be fun, I can run the usual set of test LP's. Drop me an e-mail.

 

[watchnerd]

That might be fun, I can run the usual set of test LP's. Drop me an e-mail.

I'm curious which test LPs you like...

I've got the HFN and another I'm forgetting...

 

[scott wurcer]

I'm curious which test LPs you like...

I've got the HFN and another I'm forgetting...

I have the complete set of CBS Labs STR series, but the best pink noise track is on the CH Precision 45rpm calibration disk. Of course being a 7" disk all the tracks are mostly inner groove. That's IMO an overlooked problem with test LP's, if you want serious precision with a conventional tone arm the radius of the test track matters. The STR series has some sides with tracks repeated at outer, center, and inner grooves AFAIK the only case of this (I might be wrong).

 

[JP]

Some others do that, though not many. I've found most modern test records to be junk.

Scott on the unit ping SY - he can send straight to you rather than forwarding through me.

 

[watchnerd]

I have the complete set of CBS Labs STR series, but the best pink noise track is on the CH Precision 45rpm calibration disk. Of course being a 7" disk all the tracks are mostly inner groove. That's IMO an overlooked problem with test LP's, if you want serious precision with a conventional tone arm the radius of the test track matters. The STR series has some sides with tracks repeated at outer, center, and inner grooves AFAIK the only case of this (I might be wrong).

Where in the word did you find those disks?

 

[scott wurcer]

Where in the word did you find those disks?

Audio Amateur sold them, a bit of money IIRC in 1982 $. Actually I don't have the quadro-phonic calibration one or the FM broadcast (?) one.

 

[JP]

Do you have any of the CBS CTC test records Scott?

 

[Speedskater]

"Audio Amateur" magazine, later became "AudioXpress" sold books, CD's, LP's and stuff thru it's "Old Colony Sound Lab" department.

 

[scott wurcer]

Do you have any of the CBS CTC test records Scott?

No I don't.