hafler xl-600

[roger1]

Hello all,
I am interested in an xl-600 to purchase and try as I might I cant find any info on the adjustments for the dc offset or current bias. I had a dh-500 and also at one time a dh-220 I believe it was and there was no problem researching the info and keeping the in top operation but alas there is nothing but an owners manual for the xl-600 on the hafler tech site. Any info would be greatly appreciated with many thanks!

 

[dshoaf]

I'll have to check my audio archives to see what I have on the XL-600. IIRC, they have the adjustments, depending on the board version it has in it. This was also the case with the DH-500/P500 versions, too. If you see 2 pots for adjustments per driver board, you have the adjustments needed for both bias and DC offset.

In any case, be prepared to swap the input differential transistors in the voltage amp stage if there's any DC offset that cannot be adjusted out. Do this only after replacing any electrolytics and tantalum caps on the boards.

I've recapped my XL-600 and discovered that the feedback loop caps are some of the more important ones to replace. This was also the case on the Harman-Kardon Citation 16 I rebuilt some years ago.

Right now the XL-600 is driving a pair of Quad ESL63s quite nicely at all volume levels with a clarity and soundstage that's nice and wide.

Hope that helps.

Cheers,

David

 

[damacman]

That's one interesting amp ... The fine tuning procedure outlined in the manual would never pass the sniff test in the world we live in today!

 

[dshoaf]

Recheck: I got back to my Audio files on the home computer to find that the XL-280 used the same driver boards as the XL-600 - at least the XL-280/600 combo I have does.

The biggest difference is the +/- voltage rails are higher on the '600 and there are more output devices on the '600 for the increase in current flow to the speaker.

I'd suggest you check the PC board nomenclature to see if you have a PC40 board. If so, contact me for the XL-280 Assembly Manual, which has the schematic and parts list included. The file I have is 5MB!

Cheers,

David

 

[roger1]

Thanks David,
I do have the pc 40 boards and I did find the bias pot which I adjusted down to 330ma from 440 ma but the only other pot says phase adj and I belive its for the nulling procedure to align the amp with whatever speakers being used. The offset on both channels hover around 10 mv...not bad but I wouldn't mind bringing them down to 0....Thank you for your help!

 

[dshoaf]

Yep, that's correct. Bias adjust is there but no DC offset. These boards use dual differential FETs for the first stage signal splitter. Adding to that, there are dual constant current source circuits feeding them.

I'd suggest you consider changing C8 and the C17/C18 electrlytics and see if there's any change but I doubt it. C8 is the one that made the most improvement in both the XL-280 and '600. Its in the feedback circuit.

Cheers,

David

 

[roger1]

I will take your advice David....many thanks to you!

 

[roger1]

Hi again David,
I have one last question for you..I think my speaker relay might be sticking and was wondering if one from a dh-500 would work as I have a brand new nos relay. Thanks again!

 

[dshoaf]

I don't know right off the top of my head. I know that the DH-500 relay is a 24v device - easily seen printed on it when the top is off.

I didn't pay attention to the XL-600's relay. Why do you think it needs replacing? You can clean the contacts I suspect if the plastic cover can be removed.

Cheers,

David

 

[bowtie427ss]

Why do you think it needs replacing?

I think OP needs to clarify if he feels it's mechanically "sticking", or if the drive circuit is remaining latched when it shouldn't.

 

[roger1]

I powered on the hafler with the cover off and saw the relay function smoothly so now I have a feeling its functioning well. The reason I thought it might be sticking is sometimes after the sound of the relay activating when powering up and listening to music a few seconds after there is a series of not thumps mind you but 3 or 4 click like sounds coming from the speakers. The amplifier plays very well after with no other unusual sounds and plays well at all volume levels with no overheating or other issues. I was thinking of putting some bypass caps with a resistor on each ps cap to sweeten and drain down the caps when powering down..I would appreciate any help or comments in this area...thanks very much for all the help everyone has given to me!

 

[dshoaf]

.....I was thinking of putting some bypass caps with a resistor on each ps cap to sweeten and drain down the caps when powering down..I would appreciate any help or comments in this area...thanks very much for all the help everyone has given to me!

I don't think this is needed. The relay disconnects the speakers at power off so there's no danger that I see.

Cheers,

David

 

[KlausDK]

I do have the pc 40 boards and I did find the bias pot which I adjusted down to 330mA from 440 mA but the only other pot says phase adj and I belive its for the nulling procedure to align the amp with whatever speakers being used.

I know this is a bit late, so just for the records: Factory recommendation for BIAS setting is 400 mA for the XL-600. Schematic and parts-list can be downloaded from hifiengine.com.

BRgds Klaus