Halcro DM10- a back breaking Preamp!

[JonMarsh]

Things have been so busy this DM10, purchased by a friend and sent to me to check out, has been sitting in its shipping crate for weeks. Well, there's a lot of other things going on this Saturday (today) but at least it's unpacked and ready to warm up for testing tomorrow.

The DM10 weighs about 50 lb., and with the side pieces similar to their power amps, you'd think they'd be throwing in a 75W/channel or better amplifier along with the preamp... but you'd be wrong.







I used to have a very accurate inverse RIAA box, but that function may be built in to the Audio Precision. But for me, the main event is how well it works on the balanced line inputs and outputs. This I'm quite curious about.

[wkhanna]

anxiously awaiting your test results !

[Steve Manning]

Me likey ........

[JonMarsh]

Been a busy afternoon (with other things) but took some data...

I have to say this, this is almost a sort of boring unit to test...


I put it on the bench and warmed it up for a couple of hours while doing other chores. I've heard some reviewers say that both the preamp and the amp can take up to a day powered up before they sound their best- especially the amp. It has a standby mode, so I'm thinking that's forming the electrolytic power caps with voltage applied? I dunno...


Anyway, just sitting there tickling it with some signals a 1 kHz, both at a relatively moderate output level (800mV RMS) and fairly high level (12VRMS), (all measurements on balanced outputs), things look pretty reasonable...

At 800mV RMS output- depending on the sensitivity of your amplifiers, this will likely be fairly loud for old school amps needing just 1.5VRMS to deliver rated power.



At 12VRMS, you'll be well overdriving even the low gain Benchmark ABH2's, but it's pretty clear performance is limited mainly by noise, which is fixed, and so the numbers just get better the higher the output level.



THD versus output level with the gain set to +16dB at 1kHz:


You might be surprised, but a lot of line stages just aren't this quiet when you're in the 300-500mV output level.


Here's a test I tried to redo to make it more interesting- the 20Hz to 20Kz THD was totally boring, other than the fact that though the channel levels match quite tightly, the noise of the two channels doesn't, and so there is an "imbalance" in the THD reading (that was also there on the 1kHz THD level sweep).

So I extended the range to 10 Hz to 50kHz. Didn't help. Still nothing interesting to comment on... :




So, in summary, it has more distortion than a straight or slightly curved piece of wire... but not much more.

[Steve Manning]

Don't you hate when something actually works as claimed.

[wkhanna]

...... in summary, it has more distortion than a straight or slightly curved piece of wire... but not much more.

now that is a classic line!

it seems your Teutonic freund has done his research well.

could you comment on any other pre-amps that might be in same league?
say for example, how would Ayre, BAT or one of the iconic Conrad-Johnson's stack up?


any testing to be conducted on the phono section?

[JonMarsh]

Actually, my friend is Indian, as is his wife, a pediatric doctor. I've known him since he was working in our Singapore division, the Asia Pacific headquarters.

reminder, this is his system:







As to other preamps, well, the easiest way to dig up some comparative data is good ole Stereophile ,and JA's tests.

Here is data from the VTL TL6.5 Series II Signature preamplifier, which is a fairly leading example of contemporary vacuum tube design, review posted this year. about a $15K MSRP


1kHz THD versus level, balanced connections. Curiously, for being tube, distortion climbs pretty quickly with output level.




THD versus frequency for 100K load and 600Ohm load at 2VRMS out (for the Halcro, measured at 4VRMS out, they're essentially identical).







Balanced Audio Technology REX II tube preamp, ~$25K


Frequency response is noteworthy, as it's not as flat as one might expect:




Balanced 1 kHz THD versus output level- too much noise, considering the performance between 100mV and 2V, which is noise limited. This would be pretty solid performance for the 1970's.






3VRMS into 100K (red and blue) and 600Ohms.






Simaudio Moon Evolution 740P line preamplifier $9500 (solid state)

THD versus level, 1kHz




Distortion versus frequency at 10V, 100K and 600ohms




Good measurements, though in the end Fred Kaplan found it lacking a bit in transparency versus the Pass XP30.



Boulder Amplifiers 2110 line preamp - $54K

Gorgeous construction and mostly very good performance, though at this price point I expect a bit more- such as a flat distortion curve within the audio band.


1kHz THD versus level:





Distortion versus frequency, at 15VRMS (the optimum point based on THD versus level)



Compare this to the Halcro, and note the difference in Y axis scaling:



Is this audibly better? I don't know, but for $54K, I'd be happier with the Halcro's curve. This DM10 was a little under $5K used on Audiogon. Decent value I'd say...

[JonMarsh]

Don't you hate when something actually works as claimed.

I know, that's almost like cheating! :B

[JonMarsh]

now that is a classic line!




any testing to be conducted on the phono section?

Yeah, but I had very little spare time yesterday, and even less this week- busy at work, and getting the Element ready to go to Seattle this weekend to pick up the pair of DM68's.

[wkhanna]

ahh...wait second.....

a pair of DM68's?!?!?!?

did i miss somethnig or do i smell something fishy in Bavaria, or is that the Bay Area?

[JonMarsh]

No, the DM68's are in Seattle, a consignment sale at Definitive Audio.

You'll note my friend already has a pair of DM88's, so he's not in need of them.... :B

[JonMarsh]

Some other comparative data, already posted, but to save you the effort of comparisons:

Although the ultimate output level capability and distortion is of interest, I like to focus on the behavior at 200-800mV output, because this is where you're usually using it with most power amplifier pairings- something like the AHB2 being the exception.

Please note carefully the differences in Vertical axis scale- the DM10 is in effect "zoomed in" as regards detail.

Cambridge 851e



AURALiC Taurus Pre




Halcro DM10

[JonMarsh]

Well, it's 7:49 in the morning, I've checked out of the hotel in Eugene OR, I'm sipping a Carmel Machiatto at the Starbucks I spotted yesterday afternoon, and I'll be hitting the road for the last section going home, should be there by late this afternoon- though who knows, the 240 lb of Halcro in the back of the Element may slow me down a bit climbing some of the passes... :B

Definitive Audio is a nice shop, though a little heavy on Macintosh for my taste, but you know, you've gotta sell what sells... Mac must be pretty popular still with a certain set.

[wkhanna]

safe travels to you, for sure Maestro......

...but i am still in a quandary as to the/your connection with Definitive Audio & if this transport is a one-way arrangement ?

IOW, what is the Final Destination for these behemoth’s?

pardon my curiosity as maybe i missed the essential info from a previous, unread, post?

btw, there should a PM in your mail box from me, too.:W

[JonMarsh]

Just got back home yesterday, did the stretch from Yreka to Danville in one blast, after having a nice lunch at the Black Bear Diner in Yreka, my favorite one in that chain. Fortunately I was going counter commute, so actually made it back in time for dinner and the dog walk... though it was close! (There were some highway construction delays up in the mountains).

The final destination for these is my system, though right now everything is being re-organized, and I'm getting ready to deliver my Ardent's to a local work colleague, likely this weekend.

I have no connection with Definitive Audio, apart from this sale- they had these on consignment. I did a tour of the store, after mentioning my involvement in high end retail decades past. They have a nice store, featured high end brands are Wilson Audio and D'Agostino and dCS, though they sell many other brands, including Focal, and a lot of Macintosh on display. They're also an Audio Research dealer, but only had one of the big amps on static display. Other than dCS, I'd say they're more into vinyl than high end digital, but that my partly reflect their market realities.

[wkhanna]

holy crap!

i had no idea you were getting a set of DM68's for el Casa de le Marsh!

guess there was not enough time to measure before bringing them home?

[JonMarsh]

No, not hardly- though they did come with the original manual and the original outgoing test document, which persists in using Bruce Candy's obtuse "xxx parts per billion" methodology to describe distortion, rather than the more standard % value. I'm still doing some re-organizaiton here at home, have the rest of the week off, but GF has some outpatient surgery on Friday. And delivering those Ardents on Saturday, in all likelihood. But I should be doing the basic measurements on them soon- hopefully this week. Then to make room for other things I'm working on, they'll get carted off to storage for the next few weeks!

Now, just for fun, a little HiFi porn....




Doubt I'll ever see mine this way. As little information as one can find about the design and construction, what I can find is fairly fascinating- I'll try to compile the interesting bits and put them in the post when I can measure them.

[Norm]

Dammit Jon, please mark your audio porn NSFW! The image is not a problem, the noises of excess pleasure coming out of my office while I gazed at the disrobed Halcro amp were a big problem. Likely another note on my annual review.

This thread reminds me there is no justice in high-end audio if Halcro can't stay in business. Too good too soon for too clueless customers. The bottom half of the amp shown above is a Power Factor Corrected power supply. Typical audio reviewer and designers "Whats a Power Factor Corrected power supply?" Answer - that thing the EU mandates you include to sell your product in Europe, dummy. Answer #2 - that thing the obviates the need for band-aid power chords and conditioners because the power supply has advanced past 1940's technology. Answer #3 - that thing that allows a power supply to draw power all through the 50/60 Hz AC wave rather that just briefly at the cycle peaks. Answer #4 - that thing that prevents a device's power supply from dumping noise and distortion back on the AC line.

I remember when Stereophile tested one of the Halcro amps noting it did not have as much dynamic power headroom as some of the other brands. Halcro responded that is because the power supply is smart enough to only draw 15 amps out of the 15 amp rated wall socket. So the amp won't burn down your house. I am sure many of our fellow crazed audiophiles counted that against Halcro.

[Norm]

Apparently I spoke too soon about the demise of Halcro. From "http://halcro.com/history/":
The owners of Magenta Audio, a specialist Australian hifi importer, became aware that Halcro was in-tact but lying dormant in a warehouse just on the other side of the city. Longwood Audio was founded by Magenta’s Dr Peter Foster, Mike Kirkham and Halcro’s former lead engineer Lance Hewitt and a deal negotiated to acquire all the assets of Halcro, including the brand, the considerable patent portfolio, stock and tooling.
And http://halcro.com/new-products-coming-soon/ reports "new products coming soon", in July 2016.

[JonMarsh]

Yeah, I've been following the site for about a year, waiting/hoping for something to show up. As one of my former colleagues in Germany would say, (he's passed away, unfortunately) "slow work takes time".

I do power conversion applications engineering for a German semiconductor company, and have done some design suggestions for the Class D team in the division we bought in El Segundo. It's ironic that many magazines think a poorly regulated power supply with high peak transient power is a good deal, as opposed to an amp that can deliver that peak power continuously. The other side to the arguments is this- without PFC, using a conventional bridge input rectifier, the power factor is 0.55, which means that of the apparent power pulled from the wall socket, only 55% is actually delivered to the amplifier power supply. If one only has a standard 15A service, which is 1725 VA, this means that real power you can safely get out of the outlet is 948VA. the other aspect is line voltage/current distortion, as it tends to flat top the AC waveform.

So, a good PFC front end not only can get more power out of the outlet safely, it doesn't mess up the AC waveform for any other equipment.