Scrapheap stories: building my dual-mono ß22

That's your ground loop breaker, used to separate signal ground from safety ground. I use AMB's strategy, a 10R 5W resistor paralleled with a 0.1 µF flameproof capacitor. Bottlehead is a fan of a pair of anti-parallel diodes.

So for me, safety ground comes in at the IEC. That is connected to the casework at multiple points, and also to the electrostatic screen of my transformers. Signal ground comes in and is isolated from the chassis. Both of those separate ground come together at either end of the breaker, and confirm there is 10 R between the two.

 

Softer is easier to work with. And imho it gets less yellow but more golden amber. Think acoustic guitar tops as theyre mostly spruce. I think it will look as lovely aged as it does now.

It may be too late now but there are finishes that protect against UV and will minimize color change, but imho thats the charm of wood.


Amazing project btw.

 

UV treatment:
Thanks for that tip @Souldriver. Didn't think about it, but like to agree with you: hopefully it will age well this way.

Ground loop:
I nailed it down to the official Beyerdynamic cable. It has two cable shields, one per channel, that are connected to the shells of the Tesla drivers on my T1.2. Then on the amp end, the two cable shields are joined to the XLR connector shield. That creates a nice antenna and ground loop.

My aftermarket cable from AliExpress has no cable shield and no ground loop issues.
I wonder why Beyer chose to bond the driver shells?

Good thing about this troubleshooting is that I did manage to improve the wiring a bit. Compare the picture below to previous ones to see that I have changed the routing of the ground return wire. It now immediately goes underneath the amplifier boards, where it twists around the output wire, all the way to the terminal strip with the wire.



Listening impressions:
So it's been a while since my last post, and in all that while it has been my daily amp for > 90%. For sure, pride of DIY and newness factors play into that. But after this while, I think most of that prejudice wore off, and I have a clear enough mind about it.

Source: Yggdrasil+ MIB, playing 16/44 FLAC through Unison USB. Sometimes 24/48 masters, which by the way breathe an interesting amount of space compared to 16/44 CD mixes. Headphones: Beyerdynamic T1.2 and Amiron Home.

I think it's important to name my previously most-used amp, because it gives an idea of what I like and was used to. That was a Eufonika H7mk2 with KPCU caps, Telefunken E88CC preamp tube and Svetlana 6S13N power tube. This review is not about that amp, but shortly: it's an OTL tube amp that's very transparent, has an excellent blackground, and a wide soundstage.

So how does the AMB ß22 do? Yeah, love it. Before focusing on specific areas, overall I would say that this amp is very engaging, slightly dark with resolving bass, and overall excellent authority. Those who've read about the technicalities of this amp might believe it's the king of linearity - yet, unlike to those with opamps with 100+ dB feedback, the AMB ß22 is full of soul.

Edit: ß22 measurements by AMB here. Note: that's for a 3-board active ground with one σ22 PSU. Mine is a 2-board passive ground with two σ22 PSUs.

The authority of the amp is a thing to behold. Listen to "Part Zero" by The Pineapple Thief and hear how this authority extends both ways: showing the bass who's boss, and on the other end having a wonderful attack and decay on the acoustic guitar. It's a harmonious combination of dynamics both micro and macro, that add a lot in the way of the plankton that make the amp as engaging as it is.

I've got the luxury of MIB blackground, and it clearly comes through on the amp. When music suddenly cuts in or out, it does so against a deep blackground - and the authority described above emphasises it. If you like to be surprised in music, it's an amazing feat, but on longer listening sessions I can imagine it could also be distracting. That's the thing of a highlight: it's doesn't hide.

Somewhat of a juxtaposition with its authority, but I don't feel the amp is the fastest. It's plenty of fast for metal and whatnot, no complaints, but in all it's more of a tube-like sound than the crazy slew rate of this solid-state machine would make you think. AMB says it's the MOSFETs that make it "musical".

Soundstage is wide, with good height, less depth. Rather intimate. I already told you I loved my Eufonika - still do - so right up alley.

Bottom line: this is one heckuva amp. But you may have already known that, because it's not exactly new. Just this latest incarnation of mine is, and I'm not sure how many out there are dual-mono. But mine is, and I don't imagine I'll part from it until I die - when I'll pass it on to one of my sons for hopefully another generation of love for music.