Benchmark AHB2 - To 'mono' or not to 'mono'

Recently I added a second AHB2 to my system to run it in mono.

I was running MacBook Pro (JRIVER) > Benchmark DAC3 > AHB2 > ATC SCM19v2 (as of yesterday – there are two ahb2, running in mono and providing 380watts into 8ohms). My speakers are ATC SCM19v2 (85db / suggested power from manufacturer is 75-300 watts), so I was hoping to get better performance with more wattage.

 After reading posts from different fellow members on this site and other forums, I was not expecting any big changes in the sound quality. But boy, I was so wrong. I guess different ear hear differently.

 I was very happy with single AHB2 (100watts) pumping music into my speakers, with great sound-staging, tonal balance, accuracy, clarity, bass punch, excellent mid-range etc etc. But sometimes, with some tracks, I did wish for fuller/warmer sound, and was doing google research into some tube preamps to use with my setup for the occasions when I really wanted that extra warmth. That problem is now solved with two units.

With two AHB2 (in mono configuration), the sound quality has changed considerably. Tracks which sounded thin earlier, were fuller with more ‘body’ and warmth. The sound staging is definitely much better now. It has completely changed my listening experience to say the least.

 I am expecting to spend more time with my system over the coming weekend, and will share more soon.

Hopefully, I will like this change.

@@Georgehifi

Thanks for sharing your thoughts on the potential root cause for change in SQ for mono application.

I would like to try ‘vertical passive bi-amping’, as per your suggestion. But since, I will have to spend some more time/effort/$$ to get appropriate speaker cables and other connectors, I guess it will have to wait for some time. Also, it will give me only 200watts per channel, and not 380watts, which I expected to get from the setup. Let me know, what you think.

I waited for the delivery of this second ahb2 for 2.5 months, but now I am truly shocked/surprised/disappointed by the mono performance of this otherwise excellent amplifier, to say the least. There is no return-policy in the country where I am located. So, I am pretty much stuck with this, or I can try selling it. Or, maybe I need to give it a bit more time to ‘settle-in’ (I don’t even know how it will settle-in any more than what it is right now though. I was told there should be no break-in period for his amp).

This new sound reminds me of my short time (except the noise floor) with ‘Cambridge Audio 851W’ (Power Amplifier, 200Watts @8ohms) – costing just 22% of what I spent on two AHB2.

I hope I am doing something wrong with the setup and it will get fixed. I had high hopes from this combo.

@@mijostyn

Thanks for your suggestion. I will try reading-up on ‘Channel D’s Pure Music’, and educate myself on the technology/equipment.


I will spend more time with the system over the weekend and will update again!

Thanks all for your suggestions

Hi @douglas,
Thanks for your comments.
I had been using Benchmark DAC2/3 with single AHB2 for the past one year and couldn't be happier. I am very comfortable with the different input/output configuration and settings on DAC and AMP. The XLR jumpers are at factory setting of 0db, and ahb2 gain is at lowest setting (as per user manual). I never had to change the settings and now with 2 amps in bridge-mono mode, it is the same.(using same set of inter-connects and speaker cables what I was using earlier). I want to stay within manufacturer recommended settings and not do anything which will breach the warranty terms & conditions.

After being disappointed with mono-bridge SQ, I have now tried @georgehifi's suggestion of verticle bi-amping. I still do not have all the splitters/connectors/speaker cable to test that theory to its fullest, but put the amps in stereo mode and using one amp each speaker (bi-wiring at speaker end). I can already see, what @georgehifi was saying, and where I can go with this approach.

With this approach, the sound-stage is just mind blowing, which has +ve impact on overall enjoyment/experience. I am hearing things which I never heard on the familiar tracks and that too on the very low volumes. The overall SQ has improved. Its just more musical (to my ears). 

For me (and my ears) bridge-mono is definitely out. My next steps are to get to verticle-bi-amping setup.

I do want to thank all the experienced and knowledgable people on this forum. Its a great place to learn about this passion. I am amazed by the level of commitment of members on this forum to help other fellow members. A big thanks to you all! 

(May be one day I will try mono again......:))