DX-1 XPL-200 Frequency Card Discrepancies

[Robh3606]

Hello Ian

Somethings odd. I built my cards based on Marks information and the measured voltage drives using CLIO were dead on from the posted curves he got from GT. Damn this is frustrating. It sucks being 12,000 miles away.

Rob

[Ian Mackenzie]

Mark.

I would look at your wiring to the loudspeakers and check phase continuity of both amps outputs and the connections at the loudspeakers.

If for example you have one woofer out of phase and but the mid/hi end in phase, it will sound strange in one channel. much like you are describing.

I crossover boards look okay but without actual testing we can't be sure.

Ian

[pasadena]

After having a chat with Ian, my plan of attack will be as follows:

1. The most obvious and easiest will be to check that all wiring has been installed correctly.
2. Doubly check that the power taps are set correctly to 220v.....Maybe I'll wear my glasses.....just kidding
3. Swap out the LF/HF cards with my spare set. This will give me an indication straight away if one of the cards are problematic.
a. Swap out the LF card, leave HF card as is.
b. Re-insert original LF card and swap out HF card.
c. Swap out both cards.
4. Move the Dr. Thomas power amp from HF to LF and the NAD 208THX to HF. Note: The Dr. Thomas power amp is a loan from my wife's uncle so it's an newly deviced introduced into the system....could be a possible problem.
5. Disconnect the DX-1 entirely and drive the 200's using only the NAD or the Dr. Thomas at any one time. The Dr. Thomas is not able to drive the 200's bi-wired, whereas the NAD can.
6. Check the parts on the DX-1 cards and on the DX-1 itself are working correctly.
7. Compare the internals of both DX-1's to see if there are any visual differences.
8. Check the voltage drives.

I'm sure I'll think of other tests, once I've started.

It's like almost 4pm and I still haven't head off to work yet.....I've been trying so hard to take off for work all day but all these things keep popping that side tracks me. Terrible. I'll be heading in for a couple of hours and then if I have time when I get back tonight I'll start some of the test.

Cheers
Pasadena.

[Robh3606]

How's it going???

Rob

[pasadena]

How's it going???

Rob

G'Day Rob,

Haven't done a thing as I haven't had the chance to yet...AARRGGH!!

BUT...I will be starting on it tonight. I told my wife that there's no TV and that I'll be working on the hi-fi, so hopefully I'll have some answers tomorrow!!

Cheers
Pasadena!

[pasadena]

Hi Guys,

Sorry for disappearing for a while but I've been tied up with a court claim that's currently in progress for my accident I had a couple of years ago.

Just received notice today that the other side have delayed appearance so I don't know when we're going in next. Oh what fun......can't wait for this damn thing to blow over.

Anyway, back to the fun stuff.

I managed to record some voltage levels on the outputs of the DX-1 and the attached image shows the results. I used TrueRTA Level 4 and adjusted the oscillator output volatge to 1 volt and recorded values between 25hz up to 10khz.

The only issue tha I can see is that the left channel on the low pass is down by .001 volt from 75hz and up.

I checked all the cabling and everything seemed ok. What I'll do next is insert the other low pass card I have into the current DX-1 and record the voltages again. I'll then swap out the high pass with the spare card and record those values and see what I come up with.

After this, I'll set the XPL's to run on only the NAD 208THX power amp and then using the Dr. Thomas power amp and see if I can hear any differences.

Can you do voltage drive tests on the outputs of the power amps and the receiver as I did with the DX-1?

Will keep ya'll posted!

Cheers
Pasadena.

[pasadena]

The DX-1 has been removed from my setup and shipped to Ian Mackenzie along with the second DX-1 for testing and upgrade.

As per my previous testing, with just the NAD connected to the XPL's the difference in detail is notably less but the bright/harshness is not so evident as when the Dr. Thomas amp hooked up only to the mids/high's.

Whether or not it's the combination of the DX-1 and the Dr Thomas amp that made it so bright I don't know but tonight I'll put the Dr Thomas in place of the NAD. I'm thinking the Dr Thomas was causing the harshness (would be nice if it was so simple) but will find out tonight.

As per Greg T's options to upgrade the DX-1's, I have asked Ian to remove the current LM833's and reaplced with socket IC's for op-amp rolling to try a combination of op-amps to see what gives the best results. Secondly, would be to replace the input and output capacitors from electrolytics to Polypropylene capacitors. Greg said that the Polypropylene caps would be too larg to fit inside the DX-1 case but will get around this by cutting the top plate out, about 10-15mm from the edge and raise it to look like a hood. I'm also thinking about drilling smallish type holes throughout the top plate for better heat dissipation.

Should make for an interesting upgrade.

Cheers
Pasadena

[Ian Mackenzie]

Oh No,

Not another crossover project...muhhhahahaahahahaha

Ian

[pasadena]

Oh No,

Not another crossover project...muhhhahahaahahahaha

Ian

Hahaha, I can picture you as the mad scientist.

[pasadena]

Greg. T replaced all his LM833 op-amps with OP275's (his favourite).

I've read that the LM833's are the cheap variety and old technology. The OP275 though a much better replacememnt for the LM833's, still seems to be lacking in some departments.

Of the op-amps I have researched, so far the AD826 seems to be the one I'm leaning towards.

I'd like everyone elses opinions on op-amps, which one's you've heard and prefer.
come on up... you're opinions All welcome.....

Cheers
Pasadena.

[Ian Mackenzie]

DX-1 XPL-200 Frequency Card Discrepancies

Mark and I discussed the DX1's he sent over to me earlier in the week today on the phone.

The plan is to verify the crossover card parts values, verify the voltage drives and consider upgrading the units where it is felt appropriate and desirable.

I have checked the cards this afternoon against the values advised on a memo from G.T 9-24-90. Everything appears correct.

Mark, FYI the J1XXX parts on the boards that look like diodes or resisters are shorting links. These boards are un-biased.

My measurements indicate there are no discrepancies.

All appears to be in order. Both channel track quite accurately. It should
be noted the crossover is asymmetrical. The crossover point is 270 hz according to my measurements. (I have limited knowledge of the XP 200).

The unit(s) appear to be made and designed to a high standard.

Ian

[Earl K]

Hi Ian ( Mark )

FWIW ; Marks' impressions of all the differences he heard between the two cards remind me of at least two or three things. I'll talk about capacitors and not opamps ( which I've never studied ) .

(1) Burning in of capacitors ; In the last year I've paid much more attention to this phenomena. MPP ( or KP ) caps that haven't yet been burnedin will move the soundstage forward ( I figure mostly due to the resonances that the ear easily fixates on )

(2) Dielectrics ;
- Polypropylene as a dielectric (as a for instance ) always seems to offer up its resonances from the presence range to lower sibilance range . Resonances in the lower region of this FR area will make things seem a bit louder ( Hovland comes to mind , from past descriptors) . Slightly above the "loudness effect" voices and cymbals will seem unnaturally strident or thin. Above that unnatural sibilant sounds will dominate the sound.
- Polystyrenes resonances seem to be located a full octave above those of polypropylenes. Their resonances offer a real high end haze ( or air ) .
They do work nicely together ( in my setups ) as a result of these complimentary characteristics.

(3)Mix Ratios of Dielectrics ;
- IME, Mixing these two dielectrics together in different ratios ( while still not burned in ) will have a bunch of predictable results to the soundstage ( in speaker level crossovers / which is beside the point of this discussion ). "Predictable" only to those who have studied the phenomena . GTs' ratios ( in speaker level crossovers ) do in fact make a lot of sense to my ears / for those people after a certain sort of HF & UHF voicing . I actually prefer a larger 1 to one 1, but I could see that it's not for everyone .

(4)Charge Coupling ™ ;
- DC Biasing removes ( at least to my ears ) just about all of these resonances / which is why I'm such a fan of the topology. It offers such a nice stable foundation for the control and thus creation of these sounds .
- DC Biasing only marginally effects that other contributor to the sound of cap makes & models. That's the difference in "spectral dynamics" that I hear with all caps. They all seem to have unigue signatures derived from how "quickly" they'll pass certain frequency areas. Different makes will have different signatures. Passing one FR area quicker than another will alter the spectral balance of what one hears by altering the emphasis of one set of harmonics to the others.

(An) Ad Hoc Conclusion ;

- I'd certainly do a proper burnin of Marks' (suspect ) set of cards before moving on to any of my other points of reference . Some of the worst resonances can disappear after the caps are burned in and that will alter the soundstage .



PS ;
- FWIW; my Passive Line Level HiPass uses only large value DC-Biased Polystyrenes . I haven't mixed dielectrics at this low a signal level. I haven't studied or looked for any sonic effects that may be a consequence of this sort of dielectric mixing ( maybe I should ) .

[Ian Mackenzie]

Hi Earl,

I will audition then try the off station FM treatment.

Thanks for your thoughts.

Ian

[Ian Mackenzie]

Given Earl's pearls of wisdom I have elected to burn in DX1's with FM white noise for a few days while I prepare some cables.

Later in the week I will hook them up.

Ian

[Ian Mackenzie]

Sunday EST

After organising interconnects and setting up for biamp mode I got it
working.

Both DX-1's work and sound identical.

The short report is this unit does not need modifying.

Mark, your only getting one back!!

My view is it performs to a very high standard and as they say if it ain't
broke don't fix it.

I would still like to consider the charge-coupling of the crossover boards
and do the opamp updates but I think to interfere with it in other areas
would be unwise.


Ian

Attached image of the DX'1( note the glowing red Leds) and the humble HiFi.