WolfX700 Measurement of Benchmark AHB2 Power AMP

[flowjm]

I owned a Quad 405 amp that used some sort of feed forward. This was late 1970s. I don't know if it was similar to the THX-Benchmark circuit or something completely different. Quad called their circuit a 'current dumping' amp. Not the most poetic of monikers. The 405 was like the AHB2 in that it was a small form-factor device. About twice the size of the old 303, and a quarter the size of something like a Phase Linear. Of course it wasn't that powerful on an absolute basis.

Quad are still using the current dumping topology, with the latest product to use it being the Artera Stereo, which is made in China I believe.

@WolfX-700 is there any chance that you might be able to get hold of one for measurement purposes?

 

[Willem]

Yes. The Quad 405 was the original design and with 2x100 watt was pretty powerful for its time, and with remarkably low distortion, again for its time. Quad later increased power to 2x140 watt with the 606 which was upgraded halfway in its life time with a toroidal transformer (unofficially this model is often called the 606-2). Subsequent models such as the 707, the 909 and the QSP were more or less identical, and the same is still true for the Artera. Production was moved to China halfway into the life cycle of the 909.
I use a Quad 405-2 in my desktop system and a 606-2 in my main system (both fully refurbished). Both are rock solid and as far as I know transparent. I would indeed love to see some modern measurements.

 

[anmpr1]

Yes. The Quad 405 was the original design and with 2x100 watt was pretty powerful for its time.

The original 405 was current limited by design--power dropped about half into 4 ohm loads. I understand a 405-2 version was released in order to 'solve' this limitation.

The 405 also featured higher input sensitivity than typically found in US and Japanese amps, generally mating better with its companion 33 preamplifier (for which it was intended).

I owned the first gen 405/33 combination and really liked the form factor. For that I'd give it an A+. Ergonomically it was not very suited to American market because of the DIN connectors (requiring RCA adapters), and small fuses that were difficult to find.

 

[Deleted member 9286]

One thing I simply do not understand is, seeing as how this power amp was being shown off nearly half a decade ago. Why not a single contender has shown interest in surpassing it, or if they have, they've failed in some fashion or another. Is the scaling of the typical power usage that power amplifiers are made for, simply something that doesn't scale very well with the massive fidelity disparage between them, and headphone amps? I understand it plays a factor, but is the factor THIS BIG where for essentially half a decade no one has been able to dethrone this Rolex of the amplifier world?

There are lots of amps that haven’t been measured by Amir or anyone else. The AHB2 is clearly very capable but just because it’s the best measuring of a small subset does not mean it is the highest performing amp ever built.

 

[anmpr1]

... AHB2 is clearly very capable but just because it’s the best measuring of a small subset does not mean it is the highest performing amp ever built.

I don't think that anyone is saying that. On the other hand, if you are looking for the lowest distortion in a small form factor, and only require 100 watt/ch, and want something that sells for a relatively modest (or at least reasonable) price, then it is arguably the highest performing 'off the shelf' commercial amplifier on the market, today. I think one could certainly make that argument.

For other special applications (for example, a need for a thousand continuous watts into 1.5 ohms, the need for blue meters, a 20 year warranty, the name of a well-known boutique amplifier designer on the front panel) the Benchmark would not be a very good choice and could easily be crossed off the short list.

 

[Deleted member 9286]

I don't think that anyone is saying that. On the other hand, if you are looking for the lowest distortion in a small form factor, and only require 100 watt/ch, and want something that sells for a relatively modest (or at least reasonable) price, then it is arguably the highest performing 'off the shelf' commercial amplifier on the market, today. I think one could certainly make that argument.

For other special applications (for example, a need for a thousand continuous watts into 1.5 ohms, the need for blue meters, a 20 year warranty, the name of a well-known boutique amplifier designer on the front panel) the Benchmark would not be a very good choice and could easily be crossed off the short list.

I get what you’re saying and don’t really disagree with taking that view. If the performance of a component is high enough for you and meets your thresholds of what you’re looking for, then it makes sense. I was really just making a more general point that lately some seem to be viewing the top rated components here as being analogous with a component being the best component available on the market. There could well be off the shelf, commercial components that perform better, they have just not been measured. Amir has measured a lot of stuff but it’s still only a small percentage of available equipment.

 

[Willem]

Thus far nobody has come forward with a better measuring amplifier, however.

 

[Deleted member 9286]

Thus far nobody has come forward with a better measuring amplifier, however.

They don’t need to, yet....hopefully this site will change that over time as more people care about measurements.

 

[Willem]

Since it would be a commercially attractive claim to make, I assume for now that no such amplifier exists. Whether we actually need anything better (or even as good as this) is a different matter. I doubt it.

 

[Willem]

As for the high input sensitivity of these older Quad amplifiers, that was a European standard that has been abandoned by the market. It has been reduced in more recent versions. In my case, I easily addressed it with 12 dB inline attenuators. My late model 405-2 and my 606-2 both have rca connectors. However, there are some who have argued that the DIN connectors actually make better contact.

 

[Deleted member 9286]

Since it would be a commercially attractive claim to make, I assume for now that no such amplifier exists. Whether we actually need anything better (or even as good as this) is a different matter. I doubt it.

I agree, the AHB2 is no doubt more than enough for most. Not all manufactures would be keen to volunteer for measurements though, not just because they don’t think they measure well. It only takes a simple measurement mistake and sales could completely dry up. They don’t need to do it at the moment so there is little to gain, from a sales perspective.

 

[bilzebubba]

The original 405 was current limited by design--power dropped about half into 4 ohm loads. I understand a 405-2 version was released in order to 'solve' this limitation.

The 405 also featured higher input sensitivity than typically found in US and Japanese amps, generally mating better with its companion 33 preamplifier (for which it was intended).

I owned the first gen 405/33 combination and really liked the form factor. For that I'd give it an A+. Ergonomically it was not very suited to American market because of the DIN connectors (requiring RCA adapters), and small fuses that were difficult to find.

I have this pair, and subjectively it annihilates my new NAD D3045...I just had a friend in another town take it to get re-capped and upgrade the op-amps, and the guy who did it told my friend that the limiting factor was the pre-amp -- that with a better one, the 405-2 would really shine. He has since moved away, so I can't go back to him on what he meant by this, unfortunately! Sounds good to me, would like to see it tested.

 

[Willem]

I agree about the limitations of the Quad 33 pre amp. My first system, way back in the early 1970s consisted of Quad els57s driven with a Quad 33/303 combo. The sound was extraordinary, and I used the system until about ten years ago, when I replaced the speakers with the modern Quad 2805s. By that time we had moved into a large house with a large living room, and that, plus the lower efficiency of the 2805s meant that the 2x45 watt of the Q303 was no longer adequate. So I replaced it with the refurbished Q606-2. That made a noticeable improvement on more dynamic music. About a year ago I decided it was also time to replace the Quad 33 with a modern DAC with volume control. I bought the RME ADI-2 DAC and I have not looked back. It is a clearly better/cleaner preamp and allows the Q606-2 to shine.
On the other hand, only just before this I had some trouble with my 2805s and they needed to go in for repairs. Since I still own the ELS 57/Q33/303 set I pressed that back into service. There was nothing wrong with it. It was still a highly refined and transparent sound, better than most modern systems. But the ADI-2/Q606-2/Q2805 is clearly better in many respects. But I agree with that guy: the Q33 is not nearly as good as the Q405-2 or the Q606-2. Its strength is in what was needed most at the time: sophisticated and flexible gain staging for all the various sources and their different levels one had in the days of vinyl (including cartridges with many different signal levels and capacitance), tape decks and fm tuners. Plus refined tone control and filters.

 

[DSJR]

If you look up an old HiFi news article, the 33 preamp was deliberately hobbled for band limiting so the 303 power amp (cap coupled to the speakers) didn't go ape at very low frequencies, especially if ESL57's were connected which pretty well stopped at 60hz or so. With the Belgian? Dada updates, the 33 freshens up ok, but it ain't neutral as lack of very low bass gives it a definite 'character.' The 303 only really works into easy non-critical loads but a good serviced one can sound charming if its very low limits aren't stretched.

The 405-2 can sound very effective but can run very warm if pushed on rock and jazz music. 606 family is a bargain I think, especially used and they seem durable and all but bomb proof.

 

[Willem]

What strikes me most now that I use the rme adi-2 is not so much the tighter bass compared to the Q33 though it is there but the clean smoothness and clarity of the adi-2. It is quite simply not there. The Q606- was a bargain at 350 eurö completely refurbished by a retired Quad nl service engineer. He had a simple philosophy: replace each and every resistor and capacitor. Parts are cheap and labour is expensive so don't bother testing ageing components. It sounds great.

 

[Tks]

There are lots of amps that haven’t been measured by Amir or anyone else. The AHB2 is clearly very capable but just because it’s the best measuring of a small subset does not mean it is the highest performing amp ever built.

Just wondering as an aside, forget about measurements. Does anyone advertise amps with better specs (even if not validated by third party measurements)?

 

[JohnYang1997]

Just wondering as an aside, forget about measurements. Does anyone advertise amps with better specs (even if not validated by third party measurements)?

I'm making one.

 

[bilzebubba]

I agree about the limitations of the Quad 33 pre amp. [...] About a year ago I decided it was also time to replace the Quad 33 with a modern DAC with volume control. I bought the RME ADI-2 DAC and I have not looked back. It is a clearly better/cleaner preamp and allows the Q606-2 to shine.

I looked at the RME review, spectacular, but what might you recommend if analogue inputs (I have an outtboard phono preamp) are needed? Another poster said that the preamp 'matched' the 405-2 for some reason (BTW mine is a 34 not a 33) ...Cheers

 

[VeerK]

I'm making one.

I’ll buy 4

 

[Tks]

I'm making one.