Analoges Aktivfilter für die Aurichal (AAA)

Die Aktivfilter für die Aurichal wurden zunächst mittels eines HifiAkademie-DSPs entwickelt. Damit lassen sich die Filtercharakteristika sehr einfach und flexibel per Mausklick einstellen, was mit einer analog aufgebauten Filterschaltung unmöglich ist. Der Nachteil ist, dass ein analog-digital Wandler und dann nochmal ein digital-analog Wandler im Signalweg liegen. Meine Ohren waren diesbezüglich schon bei früheren Projekten etwas skeptisch – aber bei der Qualität der Aurichal war es offensichtlich: die A/D- und D/A-Wandler sind nicht gut für den Klang. Ein sicheres Indiz für den negativen Einfluss der A/D- und D/A-Wandler war die beschränkte «Langzeit-Tauglichkeit». Nach längeren Hörsitzungen kam immer der Wunsch auf, eine Pause einzulegen, obwohl die tonale Abstimmung keinerlei Wünsche offen liess.

abacus

Wie von Anfang an geplant wurden also die DSPs mit einem analogen Aktivfilter ersetzt. Die Firma Abacus Electronics war dabei sehr hilfreich, weil sie quasi eine analoge «Kopie» der DSP-Filter hergestellt haben. Im Messdiagramm unten sieht man, dass die analogen Abacus-Filter quasi identische Filtercharakteristika wie das für die Aurichal optimierte DSP-Filter aufweisen. Chapeau!

Transferfunktionen der Aurichal-Aktivfilter: DSP (schwarze Kurve) vs. Abacus-Analogfilter (links und rechts: rote und blaue Kurven).

Transferfunktionen der Aurichal-Aktivfilter: DSP (schwarze Kurve) vs. Abacus-Analogfilter (links und rechts: rote und blaue Kurven).

Klanglich ist das Analogfilter eine Offenbarung! Die tonale Abstimmung ist identisch wie beim DSP-Filter, aber die Auflösung ist viel besser, der Klang löst sich noch besser von den Lautsprechern, und das Musikhören gestaltet sich mit den Analogfiltern vollkommen ermüdungsfrei!

Linnenberg UDC1 DAC

Note: I also published this review on Computeraudiophile. udc1_inside2I was looking for a DAC to complete my new stereo system. I use an Apple MacBook with Decibel to play digital music via the DAC. The rest of the system consists of DIY preamplifier (Thel VX-D, battery powered class-A MosFet output), two Hifiakadmie PowerAmps, and AOS Studio 24 BE speakers (top-of-the-line ScanSpeak drivers). Some more specific requirements for my new the DAC were:

  • High-Res (192/24) asynchronoous USB or FireWire input
  • Discrete analog stage would be nice
  • No volume control or other gimmicks required
  • Down-to-earth price! It’s just very wrong to pay $5000 for a $15 DAC chip, a bunch of $0.05 opamps and a $2.50 «audiophile» face plate made of the same material as kitchen aluminium foil. I really don’t want to support this sick part of the audio industry.

I looked at many different DAC offerings, and I found a very nice list of different DACs with asynchronous USB and FireWire inputs. One of the least flashy DACs on this list was the new Linnenberg UDC1, which seemed like a perfect fit to my requirements. Also, Udo Linnenberg of Linnenberg Audio claims that he’s not making a living from his audio «business», so maybe the price-to-value ratio of the UDC1 is better than with other DACs. I gave the UDC1 a shot in in December 2011, when price was hot. Udo Linnenberg also offered a full return if I don’t like the UDC1, so I couldn’t really go wrong. The UDC1 has a built-in M2-Tech USB interface, which accepts up to 192kHz/24Bit (or 32Bit, I’m not sure). The USB interface has its own dedicated power supply, so it doesn’t rely on the noisy USB power from the computer. The DAC chip is a good old Burr Brown PCM1794A, which drives a discreete analog stage. The analog signal is output to symmetric XLR jacks only, so there are no RCA. I therefore had to use XLR-to-RCA adapters to use the UDC1 in my system. No big deal, but RCA jacks would’ve been nice. The power supply is completely built into the box. The lack of a wall wart is nice because I hate wall warts cluttering up the power outlets. But I also like wall warts because they can be replaced by something better (e.g. a DIY power supply), which is often a very easy tweak to considerably improve the performance of audio electronics. The USB interface built into the UDC1 requires a special driver software, even for current Macs. This is a little unusual, and I am a bit afraid of what’s going to happen if the drivers stops working with a newer version of Mac OS X and M2-Tech stops supporting the software for the UDC1. It also means that it might be difficult to make the UDC1 work with Linux, because there is (currently) no Linux driver available (shame on M2-Tech!). Another slight annoyance is the power indicator LED, which is waaaay too bright. The UCD1 could almost light our entire living room with its uncomfortably bright blue LED! Udo Linnenberg instructed me how to reduce the LED brightness by replacing a resistor. I’d be comfortable doing this, as I know where to hold a soldering iron. Others might not. I solved the bright LED issue simply by stuffing the UDC1 away behind my audio rack, somewhere in the middle between the computer and the preamplifier. So, how does it sound? I compared the UDC1 to my Apogee Mini FireWire DAC (hot rodded with a hefty DIY power supply, which replaces the original wall wart) in my system as described above. With the UDC1, the sound was more detached from the speakers. The sound was «juicier» and livelier, whereas the Apogee sounded dryer and calmer. The bass was better resolved with the UDC1 and there was more air in between the instruments and vocals. I’d say the overall score of my digital chain with the UDC1 is about the same as the vinyl chain (although they certainly don’t sound the same). Really good! Although I was not able to compare the UDC1 to the usual $5000+ «reference» DACs with $0.05 opamps behind the face plate, I am pretty sure the sound quality is up there. I therefore don’t know if the UDC1 is a giant killer, but it might well be… But can UCD1 be improved? Yes. First of all, the LED brightness needs to be reduced, it’s just ridiculously bright. And then I am a big believer in clean supply power. That’s why I use battery power in my phono and line preamps, and an elaborate outboard power supply with a large C-L-C filter for the Apogee Mini Firewire DAC instead of the cheap wall wart. However, doing this with the UDC1 is not trivial, because the power supply is built into the box and sits on the mainboard. And, although the USB interface works very well, I’d really appreciate the freedom to be able to use it without a proprietary driver that might stop working in the future or does not exist for some operating systems.

Note: I also published this review on Computeraudiophile. udc1_inside2I was looking for a DAC to complete my new stereo system. I use an Apple MacBook with Decibel to play digital music via the DAC. The rest of the system consists of DIY preamplifier (Thel VX-D, battery powered class-A MosFet output), two Hifiakadmie PowerAmps, and AOS Studio 24 BE speakers (top-of-the-line ScanSpeak drivers). Some more specific requirements for my new the DAC were:

  • High-Res (192/24) asynchronoous USB or FireWire input
  • Discrete analog stage would be nice
  • No volume control or other gimmicks required
  • Down-to-earth price! It’s just very wrong to pay $5000 for a $15 DAC chip, a bunch of $0.05 opamps and a $2.50 «audiophile» face plate made of the same material as kitchen aluminium foil. I really don’t want to support this sick part of the audio industry.

I looked at many different DAC offerings, and I found a very nice list of different DACs with asynchronous USB and FireWire inputs. One of the least flashy DACs on this list was the new Linnenberg UDC1, which seemed like a perfect fit to my requirements. Also, Udo Linnenberg of Linnenberg Audio claims that he’s not making a living from his audio «business», so maybe the price-to-value ratio of the UDC1 is better than with other DACs. I gave the UDC1 a shot in in December 2011, when price was hot. Udo Linnenberg also offered a full return if I don’t like the UDC1, so I couldn’t really go wrong. The UDC1 has a built-in M2-Tech USB interface, which accepts up to 192kHz/24Bit (or 32Bit, I’m not sure). The USB interface has its own dedicated power supply, so it doesn’t rely on the noisy USB power from the computer. The DAC chip is a good old Burr Brown PCM1794A, which drives a discreete analog stage. The analog signal is output to symmetric XLR jacks only, so there are no RCA. I therefore had to use XLR-to-RCA adapters to use the UDC1 in my system. No big deal, but RCA jacks would’ve been nice. The power supply is completely built into the box. The lack of a wall wart is nice because I hate wall warts cluttering up the power outlets. But I also like wall warts because they can be replaced by something better (e.g. a DIY power supply), which is often a very easy tweak to considerably improve the performance of audio electronics. The USB interface built into the UDC1 requires a special driver software, even for current Macs. This is a little unusual, and I am a bit afraid of what’s going to happen if the drivers stops working with a newer version of Mac OS X and M2-Tech stops supporting the software for the UDC1. It also means that it might be difficult to make the UDC1 work with Linux, because there is (currently) no Linux driver available (shame on M2-Tech!). Another slight annoyance is the power indicator LED, which is waaaay too bright. The UCD1 could almost light our entire living room with its uncomfortably bright blue LED! Udo Linnenberg instructed me how to reduce the LED brightness by replacing a resistor. I’d be comfortable doing this, as I know where to hold a soldering iron. Others might not. I solved the bright LED issue simply by stuffing the UDC1 away behind my audio rack, somewhere in the middle between the computer and the preamplifier. So, how does it sound? I compared the UDC1 to my Apogee Mini FireWire DAC (hot rodded with a hefty DIY power supply, which replaces the original wall wart) in my system as described above. With the UDC1, the sound was more detached from the speakers. The sound was «juicier» and livelier, whereas the Apogee sounded dryer and calmer. The bass was better resolved with the UDC1 and there was more air in between the instruments and vocals. I’d say the overall score of my digital chain with the UDC1 is about the same as the vinyl chain (although they certainly don’t sound the same). Really good! Although I was not able to compare the UDC1 to the usual $5000+ «reference» DACs with $0.05 opamps behind the face plate, I am pretty sure the sound quality is up there. I therefore don’t know if the UDC1 is a giant killer, but it might well be… But can the UCD1 be improved? Yes. First of all, the LED brightness needs to be reduced, it’s just ridiculously bright. And then I am a big believer in clean supply power. That’s why I use battery power in my phono and line preamps, and an elaborate outboard power supply with a large C-L-C filter for the Apogee Mini Firewire DAC instead of the cheap wall wart. However, doing this with the UDC1 is not trivial, because the power supply is built into the box and sits on the mainboard. And, although the USB interface works very well, I’d really appreciate the freedom to be able to use it without a proprietary driver that might stop working in the future or does not exist for some operating systems.

D/A Wandler DDDAC1794

Diese Beschreibung ist zur Zeit nur auf Englisch verfügbar.

Note: an earlier version of this text was first published as «The DDDAC1794 is no (ordinary) DAC!» on Computeraudiophile.

dddac

Why the heck would anyone buy and build a DDDAC1794? This thing seems very much out of place in the arena USB and FireWire DACs out there, it costs a lot of money, and it requires an intimate relationshop with a soldering iron, too. However, I have been in the DIY world long enough to know that nothing beats a good DIY system.

I had many and very different DACs in the past. My beloved Stokes DIY Tube DAC was restricted to S/PDIF and red-book 44/16 audio. I plunged into computer audio with a not-so-great Headroom USB DAC. Then I hot rodded an Apogee Mini FireWire DAC with a hefty DIY power supply. I use an Audiolab M-DAC in our living-room system (and it tends to break from time to time). My main system had a Linnenberg UDC1. And I’ve listened to the Weiss and many other cost-a-lot stuff. However, while some of those DACs sound pretty good compared to others, they all screw up the music in the same way. And I don’t mean the painful „S“ sounds and similar boorishness from crummy DACs. Even the «good» DACs take away the life, flesh and breath from the music, very much in contrast my trusted vinyl rig (Scheu platter and bearing, Teres motor, and Schröder arm). The Stokes Tube DAC and the Audiolab M-DAC both allow using different built-in digital filters with different characteristics. The different filters usually sound slightly different, and some sound «better» than others, but they never get rid of the artificial sound completely. But, maybe unfortunately, the filters cannot be turned off completely.

When I «stumbled» over Doede Douma’s description of his DDDAC1794 that does away with digital filters I knew I had to try a non-oversampling (NOS) DAC sooner or later. Why not just skip the digital oversampling/filter, if it affects the sound by inventing new sound data that never existed in the first place?

Doedes technical description and documentation is very comprehensive and makes a lot of sense. My only hesitation was that I didn’t want to start yet another DIY project that I’d never finish, because time is limited (there’s a family, work, and too many other hobbies). But Doede sells completely assembled and tested DACs modules, power supplies, and USB interfaces. He even gave me a copy of the files needed to order a very nice custom-made chassis for the DDDAC1794 at Schaeffer AG. And when I asked him about the specifics of the additional bits and pieces needed to build a complete DAC, he simply included these in the package. For example, when I asked about which power switch would fit in the chassis, Doede just put the switch in the package (three switches, to be precise. Just in case I’d break the first and loose the second one). All this allowed me to build the DDDAC1794 in no time. The only gripe was when the Schaeffer chassis was a wee to too small to fit the power-supply heat sinks, but there was an easy fix (just a little side note to illustrate how smooth building the DDDAC1794 was: before I found the DDDAC1794 on the net, I asked the local Bryston distributor if I could borrow one of their DACs to give it a try. They keep promising I could have one once they receive one. In the meantime, I am playing my music using the DDDAC1794).

How does it sound? Spectacular? Phantastic? Superb? Damn good? Fucking great? Yes, all of this. But that’s all secondary with the DDDAC1794. The really important thing is that the DDDAC1794 doesen’t sound like a DAC at all. It’s a bit like a vinyl rig on steroids, but without the pops, clicks, and rumble (and I don’t mean the old record player your dad had when he was a boy, but the freaky good 2013 stuff). The music and all the little details are just there in a very relaxed way. Ry Cooder is having a party in my house, Phil Collins‘ (yes!) drumsticks are flying in front of me, Sophie Hunger has moved to my house (was close anyway), Willy DeVille has risen from the dead, no more doubts about No Doubt, Timber Timbre is timber timbered, Mark Knopfler is in Dire Straits, Marianne Faithfull finally confessed her love for Bruce Springsteen, Jeff’s Wine is as Lilac as it gets, Glen Hansard got a shave, Depeche Mode are Exit(er)ing, Lou Reed made me a Perfect Day, and Giant Sand and Marla Glen just called to be the next acts in my listening room. In short: I hear the music, not a DAC. In contrast to oversampling and digial filters, the NOS concept not only works, but also sounds good!

As a final and very important comment, I’d like to congratulate Doede not only for designing the DDDAC1794, but also for documenting everything in full detail. The deep insight into how the DDDAC1794 works provided a lot of confidence that convinced me to try Doede’s design and to buy his stuff. One can only guess why others don’t do that.

Update 11.3.2013: Doede sent me two Sowter 1298 transformers, which he designed as an alternative to the standard coupling capacitor in the analog out line. Apart from avoiding the coupling capacitor in the signal, the transformers also allow using the inverted output of the DAC chips, thus cancelling out even-order distortion. I immediately noticed the sound improvement with the transformers. The music sounded as if the musicians just got a pay increase! The transformers were expensive, but the money was well spent in my case.

Sheldon Stokes DAC

DAC

Die Elektronik deses D/A Wandlers wurde von Sheldon Stokes entwickelt. Der Wandler arbeitet mit den etwas älteren (aber sehr guten) PCM63K D/A-Konverter-Chips, die direkt an eine Ausgangsstufe mit 6DJ8 / 6922 Röhren gekoppelt sind. Der Wandler steckt in einem massgefertigten Gehäuse aus massivem Buchenholz und Aluplatten. Die Holzteile sind innen am Gehäuse mit Kupferfolie versehen, um Brumm- und Störgeräusche durch Interferenzen der Elektronik mit elektromagnetischen Streufelder zu vermeiden.DAC

The electronics of this DAC were designed by Sheldon Stokes. It uses the old (but good) PCM63K D/A converters, which are directly coupled to an output stage with 6DJ8 / 6922 tubes. The DAC is housed in a custom-made enclosure made of solid beech wood and aluminum plates. The wooden parts are internally shielded with copper foil to avoid hum and noise due to electromagnetic interference.