Building a Hafler XL-10 Excelinear attenuator circuit

[HaflerFreak]

Hello forum,

I have decided that it is a moral imperative that I build a XL-10 circuit to perform the 'null' test and adjust the Excelinear trimmer capacitor in my XL-280(s).

I think this is a reasonably simple project but I have a couple stupid questions that have kept me from building this thing in the past.
(Schematic at bottom)

1. For the 100 Ohm 'Fine' pot, would it be OK to use a board mounted, 20 turn cermet 1/2W?

2. Can I assume that the Test Amp input + is connected to the wiper of above mentioned trimpot?

3. Is the Test Amp input ground (-) simply connected to the incoming speaker ground from the driving amp? This is not shown.

4. Is the wiper just connected to one end of the 'coarse' 250 ohm trimpot?

Any comments from anyone with experience with the 'null' test are greatly appreciated. Comments from those that have actually built/used this attenuation circuit are even more greatly appreciated.

[HaflerFreak]

I have sourced the parts for my XL-10 circuit.
Any last minute design suggestions are quite welcome...

This is everything minus the breadboard and hookups:
Mouser #: 594-5073NW2K200J
Mfr. #: PR01000102201JR500
Desc.: Metal Film Resistors 1watt 2.2Kohms 5%

Mouser #: 71-CMF5515R000FHEK
Mfr. #: CMF5515R000FHEK
Desc.: 1/4W, 1/2W and 1W Precision Metal Film Resistors 1/4watt 15ohms 1% Rated to 1/2watt

Mouser #: 273-27-RC
Mfr. #: 273-27-RC
Desc.: 1/2W 1% Metal Film Resistors 27ohms 1% 50PPM

Mouser #: 594-64W101
Mfr. #: M64W101KB40
Desc.: Multi-Turn Trimmers/Potentiometers 3/8 SQ 100ohms Multi Turn, Cermet

Mouser #: 531-PT10MV-250
Mfr. #: PT10MV10-251A2020
Desc.: Trimmer Potentiometers 250ohms 10mm Rnd Top adj

[kurtbauer]

So how did this turn out? I just scored an XL-280 and want to build one of these guys too. What did you use for the Test Amp?

Cheers!

[HaflerFreak]

Greetings, my apologies for the long delay in replying...

I finished the circuit ages ago and will attach a few pics, unfortunately, have never gotten the chance to play with it. Without going into excessive detail, let's just say that I have a tumultuous life and rarely have the money or time for my DIY projects.

I have actually been considering selling one of my two XL-280s in order to finish my F5 build which is only short a pair of heatsinks.

If I get the chance to set stuff up and try this thing, I will post my results here for sure.

Have a look at the pics:

[kurtbauer]

Hi HF,

Many thanks for the info. I'm just digging in trying to understand the whole thing. This project has to get in line behind several other that include an F4/Burning Amp thingie that is getting close to firing up. Woohoo!

Good luck you with your F5.

K