Living Room System

Friday, October 21, 2016

Aragon Preamp

Recently I've been using the Aragon preamp merely as a source selector, just using the unbuffered tape outputs, with no AC power being provided to the unit.  However, looking at the schematic, there are 2k output resistors to the tape outputs so it's not 100% transparent.  With my low cap cables that likely makes a negligible difference, but when convenient I'm going to bypass those resistors.

I prefer the Aragon preamp as source selector to the DB Systems selector simply because the Aragon is a big heavy box which doesn't move when you turn the knob.  It also looks very cool, is very heavy, and has wonderful chassis mounted jacks.  I wouldn't say that it sounds any better than the DB Systems selector though.  I thought them about the same, but the 2k resistors would darken it somewhat.

I'd always thought the Aragon 28k preamp to have a slightly "dark" sound through the main outputs also when I was using them--though they seemed to measure as perfectly as anything.  Well now I see that a darkened sound might compliment the Aragon 8008BB power amp, which I'm finding (now) to have a (somewhat excessive) brassy top end.  I'm going to be examining the Aragon and other amplifiers technically this weekend, following a week of A/B/X testing last week.  I did not reliably hear differences according to a simple ABX test, but I still strongly believe the differences I hear anyway.  The basic differences are that the Krell is the best sounding and has sweet and entirely unagressive highs, next the Carver TFM-24 which was designed to sound like a tube amp, next the Parasound HCA-1500A which was slightly brighter than the Krell but very transparent--perhaps the most transparent, and the Aragon which is sounding transparent but harsh at times.  Kudos to John Atkinson, still one of my favorite audio reviewers though I often criticize him, who admitted recently he hadn't heard a difference in an ABX test.

A great test disc is the Tchaikovsky Pathetique on RCA Living Stereo hybrid CD.  Just after 10 minutes into track one, there are some biting violin riffs that can be positively strident with some amplifiers.  It sounds more or less OK on Koss Headphones.

I'm not sure if I like the Aragon preamp circuit at all, but it's apparently the same as in Aurum preamps (in Aurum they use 2 per channel because it's a balanced preamp).  It looks like a miniature power amplifier all bipolar with feedback and adjusted bias.

Here's a discussion on modifying the Aragon Aurum preamp.  It includes a crucial section on how to do the bias adjustment on all Aragon preamps.

I've been thinking of modding mine in a few ways, adding balanced inputs and outputs and making the selector deal with that.  The balanced outputs would be pseudo-balanced with ground as the negative.

That would allow me to hook up balanced device(s) and run balanced to Lavry ADC, rather than doing an unbalanced conversion right at the Lavry input jacks with adapters.  Then I could insert the ABX test box and since it would have balanced inputs and outputs there would be minimal degradation.

It would also allow me to have a polarity reverse switch on the Aragon (or the ABX).

But it would have been better with the balanced already designed in.

I would use the line amplifier only when doing gain adjustments on devices for ABX comparison.  Otherwise I'd just use the unamplified tape selector.

But doing that kind of modification, I almost might just as well get a fresh chassis, and indeed I've been looking at the many interesting clone preamp chassis on ebay.

Thursday, October 20, 2016

Hacking I'd like to do

Here's a start to hacking the Sonos API.

I'd be more interested in hacking my Tact RCS 2.0 digital preamps.  Most of the "hacking Tact" groups are really about audiophile mods and don't sound interesting to me as I simply use digital inputs and outputs.  What I'd like to do is bypass the system so that I can set parametric EQ's without having to select a room correction (I don't actually use the room correction feature).  And more conveniently change system polarity with one button press.  And so on.  Making it more useful to me bit by bit.  Maybe add tone controls, something more like Cello Audio Pallete.  Mark Levinson's latest company has a software Pallete but it requires a computer.

Wednesday, October 19, 2016

PCM 1704 still the best chip

A comparison of several top sigma delta converters and the venerable PCM 1704 puts the 1704 on top.

Nowadays, however, it may be possible to do even better but at even more cost building your own flash converter, from FPGA's or something like that, as MSB does, and I think one of the Swiss high end companies also.

As recently as 2013, Lynn Olson of Positive Feedback was still saying the PCM 1704 was the best--better than the then-champion ESS 9018, the TOTL sigma delta converter still used in many well known recommended components.  And he says specifically what I say, that sigma delta converters sound like something is missing (I would say "lifeless") while the grand flash converter is full of life.

Recently I've had to take my Krell FBP 300 offline for repair and put the Aragon 8008BB back online.  It has a far more agressive high end, and can easily sound strident playing SACD's such as the RCA Living Stereo hybrid disc with Tchaikovsky's Pathetique on my Sony DVP-9000ES.  When I played the CD layer on the Pioneer PD-75, it sounded about the same (another bitstream 1-bit sigma delta converter).  But on the Denon DVD-9000, it was several notches better, much cleaner.  The Aragon is what you'd call a "revealing" amplifier but what it may be revealing is its own high frequency instability being set off by high frequency noise from the 1-bit converters.

Monday, October 17, 2016

The Guyz Behind Mondial

I put my Aragon 8008BB back online on Sunday, after a week of A/B/X testing with a Parasound HCA-1500A and a Carver TFM-24.  I've got an RMA to return my Krell FPB 300 to Krell for repair.  I miss the sweet sounds of my Krell FPB 300 and want it back online soon.  But that's no excuse for downtime.  The good audiophile must make do as well as possible with the best that is on hand.  The show must go on.  I have no patience for audiophile nervosa.

Just last week I discovered an obituary for Paul Rosenberg, the Mondial co-founder who along with Tony Federici were responsible for the great Aragon and Acurus components of the 1990's. This was also my discovery of the audio journalist Ken Kessler.  Paul and Tony sound familiar to me I think I once met them.

Ken affirms by telling the story of the big Mondial amplifiers having been designed by Dan D'Agostino.  I had largely discounted that story as hero worship.  It actually doesn't take a god to design a decent power amplifier, and there is no mention of D'Agostino anywhere in the amp or the Aragon literature that I am aware of.  Many have credited the design to Robbii Wessen, whose name is actually found on the circuit boards.  Ken says Robbii, now a well known industrial designer, was only brought in to make the products look cool.

Coming from the pen of Ken Kessler, who appears to have actually had some good times with Paul and Tony, who probably heard it from them, this may be the true story, or at least "true enough" in the sense that D'Agostino might not deny it--there may have been collaboration involved.  I still find it hard to believe he got deeply into the details, I would more imagine that Dan may have proposed the basic circuit (on a cocktail napkin or something like that) and Robbii and others did the layout and fine tuning.

The Aragon is a nicely made amplifier.  However, from a cold start it sounds more than a little strident.  It appears to need about 60 minutes of warm up to sound best, and even then it may be strongly on the Yang side (like the Guyz themselves?), not unlike a lot of high end audio products.  My actual Krell, however, sounds sweeter.

Friday, October 14, 2016

DSD in blind testing

Here is the abstract of the report on blind tests done on DSD in 2004.  DSD was apparently compared with PCM 176/24, and participants were unable to hear a difference.

Of course this cannot in principle satisfy anyone who takes the "listen for yourself" advice seriously.  That advice is an nothing more than an invitation to be conned by slight of ear.  If somebody bothering to make a "superior" sounding system cannot PROVE it sounds better to at least some people if not everyone, they ought to just quit.  And the only way it can be proven is through repeatable blind test results.

This is especially true if we are not just talking about one person's private sound reproduction system, but a scheme to be generally to be used in recording and distributing music.

Tuesday, October 11, 2016

Squeeze Me Together

I've been enjoying high rez music through my Logitech Transporter SE, recently purchased as NEW! on eBay.  Logitech released these SE units, lacking the famous selector knob with force-feedback, in 2011 at a somewhat reduced price from the original model from 2009.  Many complained that Logitech was selling off the spare parts that might be required to repair the original Transporter model, which had been ingloriously discontinued.  But few complained about missing the selector knob.  Most users used it a few times, but then settled in using either the remote control or the Squeezebox web interface or both.

Squeezebox had been an independent company, for some reason then bought out by Logitech who didn't seem to carry the concept very far.

Actually, IMO, the concept doesn't need to be carried very far.  I'd be happy (at least for a start) with a simple Ethernet to SPDIF device.  I imagine such a thing could be built to high standards and still sell for less than $100.

One thing, you do actually need to decide which files the SPDIF is going to be outputting.  So, essentially, you need some kind of "player" (which selects file, plays it, allows for pause or stop).  However, as I understand it, this functionality exists in the Squeezebox software itself, now Open Squeeze.

Now at least I've got the bill filled, plus lots of extras, with a real Transporter.  It turns out some of those extras are at least temporarily useful.  For some reason my Tact processor isn't accepting 88.2kHz inputs, even over coax or AES/EBU from the Transporter.  It does accept 96kHz inputs.  And, it turns out that 88.2kHz is quite a popular high rez format.  So as I do with all my various disc players, I take the (extremely high validated quality) analog output from the Transporter, and resample it to 96kHz with my Lavry AD10.  And, as that always does, contrary to audiophile purism, it sounds marvelous.

Sadly, at this time I don't run balanced all the way to the Lavry…none of my selector devices permit mixing single ended and balanced inputs.  I now intend a large rebuild of the Aragon 28k to turn it into a mostly-passive selector device which would take both balanced and unbalanced inputs, and send a single unbuffered balanced output to the Lavry, with polarity reverse and other features.

However, in that longer term, I should also fix the Tact, and/or exchange the bedroom and living room Tact devices (because I think 88.2kHz still works in the bedroom unit) so I can have direct digital (though I suspect it would be Very Hard to tell the difference).

Anyway, though I don't need it now, here's a discussion of how to replace the Transporter using a Raspberry PI.

You need:

1) Raspberry Pi 2, Model B
2) Hifiberry DAC+ or Hifiberry Digi+ (spdif output!)
3) 5v, 2.5A power supply micro-USB
4) Case
5) 1gb microSD card
6) Picoreplayer (software)

Apparently Hifiberry and Raspberry snap together.

In the week since I ordered the Transporter, apparently Google and Amazon have figured out what I want better than I could.  Now I'm seeing tons of "network players" that might work nearly as well or perhaps even better than the old Transporter.  I have some fondness for the actual Transporter however because (1) I read about it in Stereophile and was incredible impressed by top notch measurements in 2009, (2) that high performance has also been validated in measurements and usage by Archimago, and (3) it uses an allegedly open source Squeezebox software.  The two downsides are that resolution is limited to 96/24 (well that's the same as my system anyway) and that it doesn't support DSD or DSD128 (which would be handy to have to play-into my system through analog reconversion).  I had been thinking about getting an extra gadget, a Pono, to support DSD but it would require the new preamp to use the best-quality balanced outputs of the Pono.  Also the Pono would let me experience first-hand the moving-average type reconstruction filter Ayre has developed.  And that brings to mind a 4th limitation of the Transporter: it doesn't have optional digital filters.  (Now I can imagine a more "ultimate" network player as being one that supports HQPlayer.  However, most machines capable of supporting HQPlayer are going to be troublesome "real computers" that I'd rather not have to deal with.  HQPlayer is part of the emerging player standard of Computer+USBDAC which I am diametrically opposed to.  Somewhere I think the creator of HQPlayer might describe a DIY network player+DAC.)

Anyway, here are some of the alternative players:

Pioneer Elite N-30 (listed for $250!)
Teac NT-506 (does DSD128 and may have variable filters, high quality clocks and clock input!)
Arcam AirDAC

Monday, October 10, 2016

Great American Sound

One of my best friends worked at G.A.S. for awhile, he introduced me to James Bongiorno in 1975 (I also met him later a few times) and Andy Hefley (who became one of the principals after James left).  All very interesting experiences.  I never bought a G.A.S. product new, I was a student at the time and they seemed too expensive, but later I did buy a second hand Son which developed an RFI problem I never fixed.  Having seen my own GAS unit have troubles, and other troubled units, I often wonder whether reliability was the actual issue which brought them down, not one of many others which have been alleged.  But the split between the founder and the remainder certainly didn't help either.  At the time of my last visit to the GAS company in Chatsworth, only a few miles from where I had attended all my primary and secondary schools, James had already left the company and GAS had installed Wave Soldering machines all over (this led to their debt problem I suspect).  Wave soldering was a very new thing at the time, and can itself lead to unreliable construction if not done correctly--which may not be easy.  OTOH, I suspect they went to Wave Soldering after the regular soldering wasn't going very well either.  Andy was doing the final feedback loop adjustments on his prototype Godzilla, which that evening we played at his beach house...

Given the charismatic James, it's no wonder every G.A.S. product was iconic and worth learning about even if his associations or companies didn't last long.  The first amplifier, Ampzilla, has been said to be one of the most copied transistor amplifier designs.  James seemed equally proud of the Thedra preamplifier, which near the time of his death he said there had never been anything like it before or since and he'd never use anything else (he did also create a new generation Thedra, much different, during the 2000's).

So what's special about this?  Many things have been widely copied, others not.

1) Separate MC and MM phono stages (no transformers!)
2) MC stage has servo loop (uniquely so as far as I know)
3) Line (tone) amp also has servo loop
4) DC coupling enabled by servo loops (no coupling caps!, except in phono)
5) Tone Controls with far-out hinge points (160Hz and 4kHz)
6) Tone and Volume controls use stepped attenuators using sealed metal film construction.
7) Low filter is Bessel type with 5 positions.
8) Very low impedance line outputs

Like many before his time, James insisted that preamps should have tone controls.  His final redesign of the Thaedra had the most flexible controls he had ever done (though still not quite what the Cello Pallete offered).

That's very interesting I think now.  Personally, no gear that I have owned has had easily accessible tone controls (I'm not counting fancy DSP) since 1979, about the time JB left GAS.  Before that time, I had been using a Marantz 2270 receiver which did have tone controls which I never used, and it especially irked me that the "stepped" controls were not stepped at all, they were using ordinary pots with a mechanism which made it seem like the controls were stepped.  Indeed when set to "flat" the Marantz 2270 controls were not exactly flat, as you could easily see on a square wave.  And there was no tone defeat switch.  I couldn't wait to ditch the Marantz once I discovered this.  Actually this kicked off a year of experimentation as I tried different IC op amps to replace the line amp in the Marantz.

If only I had bought a Thedra preamp, it might have been all different.