Review and Measurements of Benchmark AHB2 Amp

[etc6849]

My office setup is rack mounted finally! Two Benchmark AHB2's driving electrostatic headphones, speakers or XLR-4 headphones. The energizer circuit uses Lundahl L9202 transformers and an ultra low noise 580VDC bias circuit. In my initial tests with my Stax X9000 headphones (scope and differential probe attached), the two AHB2's can drive the transformers to 1.9kVpp or 3.8kVpp stator to stator using the Lundahl transformers!

I also gutted a really nice Luxman AS-55 speaker selector and added an XLR4 jack (just in case I ever try the Susvara headphones, but the HD800's sound great wired directly to the AHB2's). The speaker selector has a nice OTAX rotary switch, not sure of any details on it as I couldn't find a spec sheet. I assume it's from their Japanese factory. The switcher is made in Japan.

Of course, the AHB2's work flawlessly with everything.

 

[waynel]

My office setup is rack mounted finally! Two Benchmark AHB2's driving electrostatic headphones, speakers or XLR-4 headphones. The energizer circuit uses Lundahl L9202 transformers and an ultra low noise 580VDC bias circuit. In my initial tests with my Stax X9000 headphones (scope and differential probe attached), the two AHB2's can drive the transformers to 1.9kVpp or 3.8kVpp stator to stator using the Lundahl transformers!

I also gutted a really nice Luxman AS-55 speaker selector and added an XLR4 jack (just in case I ever try the Susvara headphones, but the HD800's sound great wired directly to the AHB2's). The speaker selector has a nice OTAX rotary switch, not sure of any details on it as I couldn't find a spec sheet. I assume it's from their Japanese factory. The switcher is made in Japan.

Of course, the AHB2's work flawlessly with everything.

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So many questions... Let me start with why 2 DACs?

Thanks
Wayne

 

[etc6849]

I use it to drive a BHSE headphone amp on a different table. My RME sound card only has digital inputs/outputs. RME's TotalMix software lets me route signals however I want.

 

[tomelex]

My office setup is rack mounted finally! Two Benchmark AHB2's driving electrostatic headphones, speakers or XLR-4 headphones. The energizer circuit uses Lundahl L9202 transformers and an ultra low noise 580VDC bias circuit. In my initial tests with my Stax X9000 headphones (scope and differential probe attached), the two AHB2's can drive the transformers to 1.9kVpp or 3.8kVpp stator to stator using the Lundahl transformers!

I also gutted a really nice Luxman AS-55 speaker selector and added an XLR4 jack (just in case I ever try the Susvara headphones, but the HD800's sound great wired directly to the AHB2's). The speaker selector has a nice OTAX rotary switch, not sure of any details on it as I couldn't find a spec sheet. I assume it's from their Japanese factory. The switcher is made in Japan.

Of course, the AHB2's work flawlessly with everything.

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beautiful setup and very enjoyable post, thank you!

 

[Pearljam5000]

My office setup is rack mounted finally! Two Benchmark AHB2's driving electrostatic headphones, speakers or XLR-4 headphones. The energizer circuit uses Lundahl L9202 transformers and an ultra low noise 580VDC bias circuit. In my initial tests with my Stax X9000 headphones (scope and differential probe attached), the two AHB2's can drive the transformers to 1.9kVpp or 3.8kVpp stator to stator using the Lundahl transformers!

I also gutted a really nice Luxman AS-55 speaker selector and added an XLR4 jack (just in case I ever try the Susvara headphones, but the HD800's sound great wired directly to the AHB2's). The speaker selector has a nice OTAX rotary switch, not sure of any details on it as I couldn't find a spec sheet. I assume it's from their Japanese factory. The switcher is made in Japan.

Of course, the AHB2's work flawlessly with everything.

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That's hardcore as it gets

 

[rdytro]

Anyone taken the AHB2 apart? How easy is it to remove the front and top panel? Want to get them powder coated.

 

[gfinlays]

Nope, not tried it on any of mine yet, but by the looks of the 6 x TX(15/20?) security screws on top and the 4 x 4 mm 9/64" hex screws on the front, it should be pretty easy. It looks like the rack mount front panel and the standard front panel are a straight swap, so once the four screws are removed it should just pop right off.

Why not drop Benchmark a line and ask them? They're normally very responsive. If you're based in the US, just give them a call. Apparently Benchmark is one of those few businesses where it's easy to speak to someone who knows what they're talking about!

 

[rdytro]

Nope, not tried it on any of mine yet, but by the looks of the 6 x TX(15/20?) security screws on top and the 4 x 4 mm hex screws on the front, it should be pretty easy. It looks like the rack mount front panel and the standard front panel are a straight swap, so once the four screws are removed it should just pop right off.

Why not drop Benchmark a line and ask them? They're normally very responsive. If you're based in the US, just give them a call. Apparently Benchmark is one of those few businesses where it's easy to speak to someone who knows what they're talking about!

They gave the usual concerned company view and strongly recommended against it. But a lot of stuff is super easy to disassemble and the manufacturers act like you're suggesting defusing a bomb with no training.

 

[gfinlays]

They gave the usual concerned company view and strongly recommended against it. But a lot of stuff is super easy to disassemble and the manufacturers act like you're suggesting defusing a bomb with no training.

I'm surprised by their response. The DAC3HGC manual, for example has instructions for changing output gain and enabling digital passthrough to D4 by moving the internal jumpers around, to do which you obviously have to open the case.

I also updated the HPA4 firmware (again, Benchmark gave detailed instructions) which entailed taking off the lid, hooking up a PC to the internals with a micro-usb lead and running the firmware updater.

Only one thing for it......

 

[Sal1950]

Anyone taken the AHB2 apart? How easy is it to remove the front and top panel? Want to get them powder coated.

The top panel should be a piece of cake.
OTOH the front panel and separating the LED & switches circuit board from it could be a bit of a task depending
on your skill level with such things.

 

[gfinlays]

OK, so here goes:

Top panel is held on by 6 x TX15 anti-tamper countersunk screws:

Front panel, 4 x 9/64" hex cap screws (had to rummage around to find a bit - I'm in the UK, so usually only see metric fasteners these days!)

There's a ribbon connector attached to the front panel - not much slack in it, but it's easily prised off.

3 x #1 Phillips screws attach the PCB to the front panel via some standoffs, which are easily removed, spring washers underneath.

All in, takes a few minutes.

Safely re-assembled:

One thing I would say is (no surprise, given Benchmark's attention to engineering) the fitup is incredibly tight and precise. If your powder coat adds anything to the dimensions of the front and top panels, you'll have a devil of a job putting it back together. You couldn't slide a Rizla paper in between the panels or between the cap screws and the front panel.

Benchmark probably designed for perfect fit, then allowed about 0.0001" under for the anodising!

 

[Sal1950]

Benchmark probably designed for perfect fit, then allowed about 0.0001" under for the anodising!

Oh yea, been thru that many times with auto/motorcycle stuff.
It very well might require reaming the holes to get the switch and led's thru again.

That was a lot to go thru to help a fellow member!
Thanks a ton @gfinlays !!!
Sal1950

 

[gfinlays]

It very well might require reaming the holes to get the switch and led's thru again.

Quite possibly, I hadn't thought of that.

That was a lot to go thru to help a fellow member!
Thanks a ton @gfinlays !!!
Sal1950

Hehe, no worries. All in the interests of scientific enquiry!

 

[rdytro]

OK, so here goes:

Top panel is held on by 6 x TX15 anti-tamper countersunk screws:



Front panel, 4 x 9/64" hex cap screws (had to rummage around to find a bit - I'm in the UK, so usually only see metric fasteners these days!)


There's a ribbon connector attached to the front panel - not much slack in it, but it's easily prised off.

3 x #1 Phillips screws attach the PCB to the front panel via some standoffs, which are easily removed, spring washers underneath.



All in, takes a few minutes.

Safely re-assembled:



One thing I would say is (no surprise, given Benchmark's attention to engineering) the fitup is incredibly tight and precise. If your powder coat adds anything to the dimensions of the front and top panels, you'll have a devil of a job putting it back together. You couldn't slide a Rizla paper in between the panels or between the cap screws and the front panel.

Benchmark probably designed for perfect fit, then allowed about 0.0001" under for the anodising!

Looks like a piece of cake. And since I have the same Wera hex keys, I can't really blame my tools if i fail. I can just ask the powder coaters to sand the edges off of the top panel and ream the LED holes - good advice.

 

[Roland68]

Looks like a piece of cake. And since I have the same Wera hex keys, I can't really blame my tools if i fail. I can just ask the powder coaters to sand the edges off of the top panel and ream the LED holes - good advice.

Talk to the powder coater about the problem beforehand.
It is better to protect the holes with blind plugs and cover the edges.
If you have to remove the powder coating afterwards and install the edges under pressure, the powder coating could come loose or lift off.

 

[Sal1950]

Talk to the powder coater about the problem beforehand.

Very good idea, see what they may offer as a solution.
As I mentioned before, I dealt with these type build-up issues for many years with both powdercoat, chrome, and even paint while being involved
with custom car and motorcycle builds. Just something to keep in mind.

 

[Roland68]

Very good idea, see what they may offer as a solution.
As I mentioned before, I dealt with these type build-up issues for many years with both powdercoat, chrome, and even paint while being involved
with custom car and motorcycle builds. Just something to keep in mind.

Unfortunately, I also know this from years of experience with high-quality bicycle frames, various industrial housings and aluminum/steel constructions.
As soon as you have transitions, gap dimensions, threads, precise or precision fits, it becomes more problematic.

@rdytro
In particular, the holes, screw holes and, above all, threads and contact surfaces of the screw heads should not be coated. This could cause them to chip.

 

[John_Siau]

Nope, not tried it on any of mine yet, but by the looks of the 6 x TX(15/20?) security screws on top and the 4 x 4 mm 9/64" hex screws on the front, it should be pretty easy. It looks like the rack mount front panel and the standard front panel are a straight swap, so once the four screws are removed it should just pop right off.

Why not drop Benchmark a line and ask them? They're normally very responsive. If you're based in the US, just give them a call. Apparently Benchmark is one of those few businesses where it's easy to speak to someone who knows what they're talking about!

You are correct, removal is easy, but the unit should not be opened by persons that are not fully-qualified to service electronic equipment. Dangerous high voltages can persist on the internal capacitors for several minutes after the removal of the AC power cord, even if the unit was turned off. Do not remove the shield under the top cover and stay away from the spaces around the edge of the shield. There is a low-voltage circuit board attached to the back of the faceplate. This can be damaged by ESD. It is attached to the amplifier board with a ribbon cable. The top board in the main chassis is the power supply board. This top board is the board that can store high voltages. Stay clear of the top board. We always run a ground-bond test and hi-pot test after servicing the unit.

 

[gfinlays]

You are correct, removal is easy, but the unit should not be opened by persons that are not fully-qualified to service electronic equipment. Dangerous high voltages can persist on the internal capacitors for several minutes after the removal of the AC power cord, even if the unit was turned off. Do not remove the shield under the top cover and stay away from the spaces around the edge of the shield. There is a low-voltage circuit board attached to the back of the faceplate. This can be damaged by ESD. It is attached to the amplifier board with a ribbon cable. The top board in the main chassis is the power supply board. This top board is the board that can store high voltages. Stay clear of the top board. We always run a ground-bond test and hi-pot test after servicing the unit.

Many thanks, John. I stayed well clear of all the places that looked likely to retain hazardous voltages. There are a lot of caps on there and the supply is 240V on this side of the pond. I wore an earthed wrist-strap whilst opening it up - I guessed there would likely be some sensitive components in there given the AHB2's sophisticated protection systems.

I'm in the midst of a 3-way fully active speaker build, so that AHB2 hadn't been powered up again after reassembly. In line with your comment, I took the opportunity to hook it up to my multi-function tester and check the insulation resistance and earth continuity before powering on. All checked out OK and the amp is working fine.