Review and Measurements of Benchmark AHB2 Amp

[oivavoi]

I'll try.
System: RME ADI-2 PRO FS, my own MC/line preamp design, VPI classic SE TT with Mijajima Madake cartridge, VPI 3D arm. Modified ML Montis, with the bass path separated from the path to the panels. Raspberry Pi/Volumio, HSU ULS15 Mk ii. 4' long double 12 AWG cable from amps to speakers.
The Rogues have non-stock small signal tubes- selected to make the amps sound right to me, with the input of my spouse, who has a music degree and was trained in voice. An Otari MX50 with various 15IPS tapes was also used.
All of the power amps are mine, except for the Halcro units. The Halcro comparison took place at the home of a friend in Atlanta- he has a DM10/DM68 combo and a pair of stacked quad electrostatics. I brought the RME box and the AHB2s with me. He had an analog only (LP, Tape) system.
The Rogues sounded surprisingly close to the AHB2s- the differences were mainly at the very high end where they were a bit less "bright" and when the music became loud and complex they seemed somewhat congested and the image tended to flatten. The dynamics were also a bit more constrained, they have less of the "make you jump out of your seat in surprise" quality. The noise floor was obviously higher when digital sources were used, but it was not noticeable for tape or LP. The stock tubes sounded less like the AHB2.
The Ncore amps sounded, well, dull, in comparison- softer, less dynamic. It's hard to describe, but it was, apparently, obvious.
I had a friend who unbidden made exactly that observation when I was switching between the amps casually without any prior discussion on the matter. Perhaps the issue is some matching issue with the electrostatics. I tried measuring the frequency response, but I could not find anything unexpected- small signal -3db point at, if I remember correctly, about 50kHz. I can't measure large signal behavior.
I tried both analog and hires digital for sources. The conclusions were the same.
All Amps were initially tested with square waves to ensure stability into the speakers. No oscillation or unexpectedly long settling times were noted.View attachment 39397

Thanks!

That seems like a most excellent setup btw.
Very interesting to read about the ahb2 vs the ncore. I have on some occasions had a similar reaction to class d setups. It’s felt somewhat - well, dull, compared to class ab amps. But that has been sighted listening, so I haven’t put that much stock in my listening impressions. I’ve settled for class ab amps for now, a technology which has been perfected commercially for 50 years.

EdIt: but I’ve also heard some excellent class d speakers/setups, so it might be an amp/speaker interaction thing, or most likely just bias on my side

 

[wynpalmer]

Thanks!

That seems like a most excellent setup btw.
Very interesting to read about the ahb2 vs the ncore. I have on some occasions had a similar reaction to class d setups. It’s felt somewhat - well, dull, compared to class ab amps. But that has been sighted listening, so I haven’t put that much stock in my listening impressions. I’ve settled for class ab amps for now, a technology which has been perfected commercially for 50 years.

EdIt: but I’ve also heard some excellent class d speakers/setups, so it might be an amp/speaker interaction thing, or most likely just bias on my side

If the AHB2s weren't there to act as a reference the Ncore amp would be pronounced as being excellent, and I preferred the Ncore amp to the Rogue because it seemed so clean when the music became "difficult".

 

[RayDunzl]

Can the AHB2 deliver 30 db peaks on a typical 87 db sensitivity speaker, with a baseline listening around 80-85 db?

20dB peaks might be more realistic for a requirement, based on what I measure here when listening...

 

[RichB]

If the AHB2s weren't there to act as a reference the Ncore amp would be pronounced as being excellent, and I preferred the Ncore amp to the Rogue because it seemed so clean when the music became "difficult".

A friend brought over his AHB2 for a quick listen and I was impressed. So much so, that I replaced my AT6002's and AT6006 with 4 of them.
If I ever go Atmos (which is a ridiculous pain in my house), then I would consider a class-D 4 channel amp to save space and heat or a pair of AHB2s.

- Rich

 

[JimB]

No Ray, I wouldn't know where to start. You guys would make fun of me anyway! I have two permanent offsite humidity controlled lockups. One is 6x6x4m and the other is 6x3x4m. The smaller one is completely dedicated to electronics and HiFi with floor to ceiling stacked boxes.

At home, there may be 100-150 component pieces, I guess, maybe 20+ pairs of speakers (mostly small/medium two ways and 4 or 5 pairs of towers) at the moment and a lot of it (my partner is very understanding) in my lounge/listening/play room or in my lab. I've also sent a huge amount of gear to my 86yo audiophile Dad's house over the years on "loan". He has a large home with a massive dedicated music (HiFi) room, a speaker room (I call it), systems-of-the-month on various dining tables and a few turntable based systems in his office. His personal collection is also very large, and more 1970-1985 era, whereas I focus on late 70s and 1987-92/3 Japanese pieces.

I have little interest in traditional HiFi components (digital excluded) produced after the Japanese stock market crash(91/92), either from a collector's perspective or a performance perspective. Also from a technician's perspective, it's discrete, through-hole, traditionally engineered product that gets and keeps my attention, as it performs beautifully, can be repaired and returned to spec easily, and is built to last essentially forever.

Both of us have significant repositories of HiFi, music and electronics magazines, reviews and documentation going right back into the late 60s/early 70s. I've got a lot of original brochures and catalogs covering the few decades when I was either buying or selling retail HiFi. So when a product is mentioned, reviewed or compared, I hope it can be useful to have some original documentation or experience details added to the thread.

Final scene of Raiders of the Lost Ark?

 

[Sal1950]

I believe that is why people often have complaints about the LS50's, for example...

I've found with my HSU stand mounts that at some point they just seem to refuse to go much louder. (92 db-2.83rms-in half space) (rolled off to subs at 80hz) My Adcom's are rated at 125 wpc continuous into 8 ohms at 0.18 THD, 200 into 4. I've pushed them till I've seen the clipping lights softly blinking (1% distortion) without any noticeable audible distortion or strain but they just seemed to stop getting any louder at around -6db of that point. A strange occourance that I've noticed with other systems but I've never actually measured the SPL's during those times.

 

[Sal1950]

A friend brought over his AHB2 for a quick listen and I was impressed. So much so, that I replaced my AT6002's and AT6006 with 4 of them.
If I ever go Atmos (which is a ridiculous pain in my house), then I would consider a class-D 4 channel amp to save space and heat or a pair of AHB2s.

- Rich

That would be a good plan, the needs of the Atmos channels shouldn't be too demanding. I'm powering mine with a pair of 60 WPC Adcoms.

 

[restorer-john]

but they just seemed to stop getting any louder at around -6db of that point. A strange occourance that I've noticed with other systems but I've never actually measured the SPL's during those times.

Thermal compression in the voicecoils. Smaller speakers suffer more.

 

[Sal1950]

Thermal compression in the voicecoils. Smaller speakers suffer more.

Thanks John, that make sense.

 

[DonH56]

Thermal compression in the voicecoils. Smaller speakers suffer more.

Exactly. And another argument for a good subwoofer. And one of the reasons I used a dual voice coil design in my old DIY sub instead of an accelerometer; it allows (allowed) me to sense and compensate that (up to a point).

 

[restorer-john]

I find thermal compression really sets in after the 4th or 5th glass of wine on a listening night. It's a dangerous thing to play with- I've loosened a few voice coil windings in the past and kicked myself afterwards. A 2nd pair of speakers on speakers B. Switch off A, let 'em cool down and listen to B for a bit.

Just for fun, have you ever pulled out a woofer after a long listening session? I remember a pair of big Yamahas I dismantled late at night because there was something I could hear in the cabinet (a bit of glue from a seam) and the woofer frame ribs and magnet were almost too hot to hold. It really puts into perspective where the power goes. Mostly it's hidden in the cabinet so it seems not real.

 

[DonH56]

I find thermal compression really sets in after the 4th or 5th glass of wine on a listening night. It's a dangerous thing to play with- I've loosened a few voice coil windings in the past and kicked myself afterwards. A 2nd pair of speakers on speakers B. Switch off A, let 'em cool down and listen to B for a bit.

College parties gave me a lot of business. Alcohol was great for audio sales and service. Probably still is but I've cut back and am no longer in the biz. (The audio biz, not the alcohol biz! Was never in the latter biz except when Dad had a go at making homemade wine. For a guy with a PhD in microbiology his wine was not always potable.)

Just for fun, have you ever pulled out a woofer after a long listening session? I remember a pair of big Yamahas I dismantled late at night because there was something I could hear in the cabinet (a bit of glue from a seam) and the woofer frame ribs and magnet was almost too hot to hold. It really puts into perspective where the power goes. Mostly it's hidden in the cabinet so it seems not real.

Yup, and not even for fun, sometimes on a live gig I had to swap drivers at intermission. They smell bad, too, and I am pretty sure it wasn't me. Not as bad as transformers; worst case of transformer'itis was a guy who, when he blew one of the two drivers in his (tube) guitar cabinet, decided to take the wires and connect them to the remaining speaker for more power. Shorted the transformer which was melted stinky slag when he brought it in. Phew!

Then there was the time I was running sound for a live gig (outdoor) using Bose C800's (don't ask, got them cheap, and they did OK for voice range stuff -- I added bass cabinets and big horn tweeters for bands). A guy came in late, grabbed a chair and put it all the way up front but off to the side, sat down and the chair leg cut through my speaker cable (I was behind the audience facing the stage). The amp died but managed to send full power rails across the speaker as the output transistors shorted, which in turn sent one of the cones out the front of the speaker. Loud boom and silence. As everyone looked around in stunned silence I went up, grabbed the guy's chair (he stood, knew he was the cause), and stuck it (and him) in the very back. Then rewired things, repurposed a monitor and its amp, and the show went on.

Ah, the good old days...

 

[Wombat]

I find thermal compression really sets in after the 4th or 5th glass of wine on a listening night. It's a dangerous thing to play with- I've loosened a few voice coil windings in the past and kicked myself afterwards. A 2nd pair of speakers on speakers B. Switch off A, let 'em cool down and listen to B for a bit.

Just for fun, have you ever pulled out a woofer after a long listening session? I remember a pair of big Yamahas I dismantled late at night because there was something I could hear in the cabinet (a bit of glue from a seam) and the woofer frame ribs and magnet were almost too hot to hold. It really puts into perspective where the power goes. Mostly it's hidden in the cabinet so it seems not real.

About 1% of the energy put into a loudspeaker driver is converted to sound. This is worse than the efficiency of incandescent light bulbs.

Heat sinks for small speaker enclosures could be a good thing?

 

[DonH56]

Haven't seen heat sinks on a cabinet (except for those on amplifiers on the back) but a number of speakers have fins on the back to help cool the voice coil.

 

[Sal1950]

Thermal compression in the voicecoils. Smaller speakers suffer more.

Exactly. And another argument for a good subwoofer.

About 1% of the energy put into a loudspeaker driver is converted to sound. This is worse than the efficiency of incandescent light bulbs.

Also a good argument for my preference of high efficiency speakers & horns.
Leaving aside some folks distaste for the coloration of some horns, in most situations higher efficiency is a win-win-win for high fidelity playback. In the speaker, reduced driver excursion will reduce it's distortion, all things being equal. Also for each 3db of increased efficiency, power demands of the amplifer is reduced by half, usually resulting in performance gains in all areas of a amp.

 

[cookiefactory]

Received my ABH2 yesterday after placing an order on 11.1. Nice looking unit, hooked it up to some Insignia NSB-2111 bookshelf speakers for initial testing and all seems in order.

 

[restorer-john]

Received my ABH2 yesterday after placing an order on 11.1. Nice looking unit, hooked it up to some Insignia NSB-2111 bookshelf speakers for initial testing and all seems in order.

That's a pretty decent delivery period, 10 days.

I hope you enjoy it.

 

[cookiefactory]

That's a pretty decent delivery period, 10 days.

I hope you enjoy it.

Thanks! So far so good as “Nice looking unit” is really an understatement. I’m really happy with the aesthetics, fit and finish, and basically all the intangibles. Will put it through its paces shortly here

 

[617]

Also a good argument for my preference of high efficiency speakers & horns.
Leaving aside some folks distaste for the coloration of some horns, in most situations higher efficiency is a win-win-win for high fidelity playback. In the speaker, reduced driver excursion will reduce it's distortion, all things being equal. Also for each 3db of increased efficiency, power demands of the amplifer is reduced by half, usually resulting in performance gains in all areas of a amp.

Large woofers reproduce percussion instruments in a convincing way that smaller drivers never do (unless you have a big array of them.) Power compression is real. Modern midwoofers can sound pretty amazing but they will never give you what a big cone can.

I think Earl Geddes theorized that power compression caused by VC heating could be a source of subharmonic distortion, where tones lower than the input are created by the heating and cooling of the motor. Interesting to think about.

The tactility of bass in large drivers is one of those things which conventional measurements don't do a great job of representing; it's not a FR issue or a directivity issue but it's very real. Low distortion in the 30-120hz area is a good place to start but I think it's more than that.

 

[anmpr1]

Thanks! So far so good as “Nice looking unit” is really an understatement. I’m really happy with the aesthetics, fit and finish, and basically all the intangibles. Will put it through its paces shortly here

The amp reminds me of some of the 'mini' or 'micro' components from Japan, during the late '70s. The actual fit and finish is first class. Thick aluminum with etched logo. I mean, it doesn't look cheap at all. It just has a serious no-nonsense look about it. Very solid. It's kind of amazing how much stuff they can pack in to such a small form factor--to include all the connectors and switches on the back.