Whats Optimum when replacing 802D diaphragms with GPAs?????

[LowOhms]

Hello,

In a high-fideilty, critical listening , reference-type audio system, when ONE GPA diaphragm goes " out ", should I have Bill H. replace BOTH diaphragms, at the same time ?? So they will be " matched" to the best of his ability ??


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Here is the situation. A pair of 802Ds of mine were re-magged and re-diaphragmed by GPA 36 months ago. For a stupid reason, one diaphragm was recently damaged, by me.

A new 16 Ohm diaphragm was ordered last month, and I installed it.

After about 50 hours of break in, the two sides ( initially and now ) sound different from each other, which they never did prior, over the last three years. Drives me bananas, am unhappy.

( Q1 ) : Do I need MORE break-in time ??? 1,000 hours??

In CRITICAL LISTENING situations, is it best to have Bill H, replace both diaphragms at the same time, and maybe even let HIM do the diaphragm installations into the 802 Ds? ( I have trouble cleaning the gaps, have little experience , etc. ) .

One person suggested, if I requested it, Bill could possibly carefully eyeball a number of diaphragms, maybe viewing several parameters, and pick out a matched diaphragm pair ala EYEBALL.

So, instead of buying one diaphragm, or two, I will end up buying THREE, and having 802D shipping costs, back and forth to GPA. That would be OK with me, if they sound similar.

Couple other questions:

( Q2 ) If I sent the 802D bodies back, should I have him measure the gauss in the units, and recharge ( after only three years ) ,if and as, he sees fit???

( Q3 ) Would 8 Ohm diaphragms sound BETTER than 16 Ohm ones, transient-response wise, due to less mass of winding wire on the voice coil?? If so, MAYBE I should switch to 8 ohms on the 802Ds only - and modify my 16 ohm DIY crossover.

Comments anyone??

Sorry to ask so many Questions, but if anyone has experience with this, I'd LIKE to do this as optimally as possible.

I am committed to these ALTEC 515B and 802D drivers, hence-forth, unless I were to swap-them-out for the latest designed GPA 604 point-sources / MLTLs, ( but .....I may miss the horn-loading of the 515B, with 825 enclosures ) !!

( Q4 ) 'Anyone have experience with replacing diaphragms in pairs - so they MATCH, versus one at a time ??


Thanks in advance. So much !!!! This could become an interesting thread .


Low Ohms......Jeff Medwin ... the Forum monster.

[mah]

I have never heard of such a thing. Before focussing on the new diaphragm I would be considering that you previously directly soldered speaker cable to the diaphragm terminations. The heat transfer during this process via the diaphragm foils likely damaged/changed the delicate diaphragms.

I would tend to think the replacement is OK. If you haven't made any mods to the new one and think it is below par, then send it back for checking.

I think you are over-thinking it. The problem may well have been caused by your tinkering.

[LowOhms]

I have never heard of such a thing. Before focussing on the new diaphragm I would be considering that you previously directly soldered speaker cable to the diaphragm terminations. The heat transfer during this process via the diaphragm foils likely damaged/changed the delicate diaphragms.

I would tend to think the replacement is OK. If you haven't made any mods to the new one and think it is below par, then send it back for checking.

I think you are over-thinking it. The problem may well have been caused by your tinkering.

Hi mah,

Thanks for giving it a try.

Actually, the original GPA diaphragms were converted to direct wiring by me, about three years ago, with 14 AWG m22759/11 mil spec wire, after the total GPA rebuild, and I never had any problem with the soldering then.

The damage occurred to the one diaphrgam, about two months ago, as I re-soldering a lighter AWG 18 wire, ( replacing the 14 AWG) from my crossovers, directly to each 802. I use a huge iron,, pre tinned the mil spec wire, and am " in and out " in a JIFFY.

The problem does not occur due to the soldering, I believe, but in this one case, it happened as a result of my " clean up." I damaged the diaphragm because I had a small piece of residual tissue paper, used to cover the diaphragm while I solder, come off as I removed the tissue paper, after soldering. It was nestled on the surround area.

STUPID me, I was NOT used to working on drivers, was NOT THINKING. When I used a long nosed thin pair of pliers, to pick up this tiny sliver of tissue paper, the metal pliers got PULLED into the diaphragm, putting a dent in it. Foolish !!

Bill H suggested I gently push it out, and give a listen. Did that first, and it was terrible to hear.

The new replacement 16 Ohm GPA diaphragm is in place NOW, and successfully soldered with 18 AWG, no damage "thought" to have occurred from the soldering itself. It just isn't quite the same-sounding , and I want them to be alike.


So...mah, the several questions in my original post, remain.

Lets see if anyone has direct experience with this.

I am doing this thread now, just as a preparation, before I discuss it with Bill H. I should also probably telephone my vintage reconer friend, Don Davis aka " Dr. Field Coil " in Texas, and get his take on all of this, to prepare myself to talk to Bill H.

I went from 14 AWG to 18 AWG wire, crossover to the 802Ds, to maintain a better high frequency response from my 802Ds.

The soldering of wires, direct to the drivers, is a nice subjective improvement, on the 515B and the 802Ds, particularly under hard drive. It simply sounds better to me, ( maybe 5-6% BETTER in my own set up ), GOTTA HAVE IT.

Superior transfer function, soldered versus press-to-fit.

One way or another, I'll get to the bottom of this. There was no real problem with what GPA sent me, I believe. Thanks for responding.

Low Ohms.......Jeff

[mah]

Well, seeing that you have tinkered with the new one, you can't return it. Simple, buy in one more and try again.

I don't think Bill can give your finessing much time.

[LowOhms]

Well, seeing that you have tinkered with the new one, you can't return it. Simple, buy in one more and try again.

I don't think Bill can give your finessing much time.

Thanks mah.

I do not think buying a single again is the answer at all, I did that once already, and it didn't work great.

It was not a decent enough match for me. Hence, this thread up here.

I need to find out what others do in critical hi fidelity applications, and TALK to Bill H. I am more than willing to pay Bill for all his time, to select parts for me , carefully, visually IF that is possible and doable.

Lets see if anyone has done this already, I actually know of one person who has / does replace such parts in pairs.

Does one really need more than 50 Hours break in to better determine this, like another 950 hours ????

Thanks,


Jeff Medwin.....Low Ohms

[BillWojo]

Buy a matched set and use the proper connectors. DO NOT solder on the terminals. The amount of power going into them is very small. If it makes you feel better, wipe the terminals down with some Deoxit. The chances of damaging them is much greater than anything you might perceive as better sonics. Snug fitting connectors are capable of handling a lot of amperage.

BillWojo