Burmester 911 mk3

[garylkoh]

I know that Burmester is working on fixing all the typos in the owner's manuals and website at the request of Robb (Burmester NA CEO). But these things take time. We are all guilty of it - just a couple of months ago, I discovered that when we first put up the dimensions of one of our speakers on the website, we made a mistake - and this same mistake was propagated for years in owner's manuals and brochures and even quoted to customers.

 

[AudioExplorations]

What does it take to measure the input impedance of an amp?

 

[garylkoh]

What does it take to measure the input impedance of an amp?

It's easy with the right tools and/or software. However, I feel that this should come from Burmester. It would feel wrong for me to do it, for example.

 

[NorthStar]

... How do we get Dieter signed up to WBF???

-----That's the spirit! :b ...Just call him, and tell him. :b

 

[NorthStar]

---By the way, I don't know if some of you remember this, but few months ago (perhaps six or so), there was a professional review of the Magico Q5 loudspeaker (or maybe another brand; my memory is failing me on this one right now).

But anyway, there was a typo in the review (not a big deal really), but nonetheless, after I mentioned it to their staff, they corrected it right away.
I thought that this was a very nice touch.
{It had to do with the driver's exact frequency point of its crossover; to the tweeter if I recall.}

And that was right here at WBF, with the reviewer or someone from their staff present. :b

 

[MarinJim]

Well, I can say first hand with over 1 year in use, my Burmester 911 MK3 connected to my Concert Fidelity tubed preamp sounds glorious and has not had one hiccup. This is with custom interconnects xlr to Burmester, and rca to my Concert Fidelity with no adapters.

 

[microstrip]

Well, I can say first hand with over 1 year in use, my Burmester 911 MK3 connected to my Concert Fidelity tubed preamp sounds glorious and has not had one hiccup. This is with custom interconnects xlr to Burmester, and rca to my Concert Fidelity with no adapters.

It is what bothers me ... The CF seems to use a simple architecture - just a cascode tube and should have an high output impedance and be capacitor coupled - it is should not drive a 2K load properly. But it seems it does ...

 

[AudioExplorations]

If Burmester's published value of 2K balanced is inaccurate it would be a pretty big f*ck-up on their part, I wonder how many prospective 911 customers they have lost who disregarded the amp due to likely impedance bridging issues with existing front end equipment.

I personally have no issue measuring it but it seems a little over my head from a quick google search, procedures are pretty vague. I have a multimeter so if someone wants to enlighten me via PM I would be willing to give it a shot.

 

[microstrip]

If Burmester's published value of 2K balanced is inaccurate it would be a pretty big f*ck-up on their part, I wonder how many prospective 911 customers they have lost who disregarded the amp due to likely impedance bridging issues with existing front end equipment.

I personally have no issue measuring it but it seems a little over my head from a quick google search, procedures are pretty vague. I have a multimeter so if someone wants to enlighten me via PM I would be willing to give it a shot.

Very simple to do. You need two 10 kohm resistors, a XLR male and a XLR female. Using a soldering iron connect 1 to 1 using a bit of wire , 2 to 2 and 3 to 3 using the 10 kohm resistors.

Now get a 1khz signal from a CD test track or a signal generator and play it through the amplifier at some level and measure the output at the speaker terminals. Call it Va. Switch the amplifier off and insert the adapter you built in the XLR cable. Without touching the preamplifier volume, switch the amplifier on, and measure the output at speaker terminals again. Call it Vb. Assuming the output impedance of your source is negligible compared with the 10kohm (the case of the Weiss) and I did not make any mistake than Rin = Vb /(Va-VB) * 20kohm.

 

[AudioExplorations]

Ok, seems easy enough. I will need to find a spare XLR cable and the 10 kOhm resisters which should not be a problem. I assume I need to take the reading with the speaker load disconnected from the amp?

If I am going to do this I want to test the SE input impedance also. Same procedure however just insert the XLR->RCA adapter in the chain?

You said "and I did not make any mistake," can you or someone else confirm this before I start messing around with my amp please? :b

 

[microstrip]

Ok, seems easy enough. I will need to find a spare XLR cable and the 10 kOhm resisters which should not be a problem. I assume I need to take the reading with the speaker load disconnected from the amp?

If I am going to do this I want to test the SE input impedance also. Same procedure however just insert the XLR->RCA adapter in the chain?

You said "and I did not make any mistake," can you or someone else confirm this before I start messing around with my amp please? :b

You can keep the speakers connected - setting a typical voltage around 150 mV RMS at the output for the first reading is enough and does not produce too much noise.
For the RCA input impedance the formula should be Rin = Vb /(Va-Vb) * 10kohm.

 

[AudioExplorations]

You can keep the speakers connected - setting a typical voltage around 150 mV RMS at the output for the first reading is enough and does not produce too much noise.
For the RCA input impedance the formula should be Rin = Vb /(Va-Vb) * 10kohm.

Great thanks. I just picked up a cheap 50cm XLR cable and some 10 kOhm resistors (I assume 1/4W 10k resistors are OK, they had 1W also). Will test it tonight.

 

[MarinJim]

Your new signature

Weiss Medea Plus - Burmester 911 mk3 - TAD CR1
Experimental music blog at: www.audioexplorations.com
Experimental Burmester 911 MK3 ohm tester

 

[AudioExplorations]

Ok, the moment of truth...



Balanced:

Va = 1.441
Vb = 0.134

Rin = 2.051 kOhm

Unbalanced:

Va = 0.633
Vb = 0.058

Rin = 1.009 kOhm

 

[AudioExplorations]

So, balanced is the same as the spec, the unbalanced is 1 kOhm instead of the published 20kOhm. Does this make technical sense or did something go wrong with the measurement (given the balanced seems right I would assume not)?

 

[microstrip]

So, balanced is the same as the spec, the unbalanced is 1 kOhm instead of the published 20kOhm. Does this make technical sense or did something go wrong with the measurement (given the balanced seems right I would assume not)?

AudioExplorations,

Thanks a lot. You got exactly the results we could anticipate. This will also raise my consideration for the ARC REF5 - I could not imagine it would drive a 2Kohm load!

 

[Thf99]

Robert Harley of TAS would be the right person to consult on this subject. He mentioned that in practice, there is very little chance of a mismatch between pre and power amps.

 

[NorthStar]

Robert Harley of TAS would be the right person to consult on this subject. He mentioned that in practice, there is very little chance of a mismatch between pre and power amps.

---- Would be cool to have Robert here as a member for the occasional post and interaction for our benefit. :b
{I'm sure he's a very buzy man.}

 

[MarinJim]

---- Would be cool to have Robert here as a member for the occasional post and interaction for our benefit. :b
{I'm sure he's a very buzy man.}

With some very smart members here, and don't think that is necessary.

 

[NorthStar]

With some very smart members here, and don't think that is necessary.

-----Exactly, it would be good for his own benefit. :b