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mark fader

Frazier Model 7 Restore

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Posted (edited)

that's  kinda  what  I'm  thinking . i  wonder  if  this  is  why  jack  frazier  chose  a  pot  instead  of  a L-pad . maybe  that  is  why  he  was  able  to  get  this  kind  of  sound  out  of  this  kind  of  setup .

 

hypothetically  speaking , if  this  were  the  case  then  replacing  the  pot  with  a L-pad  would  be  changing  the  sound . is  that  too  much  of  a  stretch  to  assume  this  is  what  he  was  doing ? then  why  do  some  models  actually  have  L-pads , or  at  least  appear  to  have  L-pads ? has  anybody  ever  taken  a  measurement / take  one  of  those  apart  and  actually  seen  what  exactly  it  is ? 

 

or  did  he  use  pots  just  because ... and  im  looking  waaaayyyyy  to  much  into  it ?

 

 

 

Edited by mark fader

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is  there  anyway  to  get  ahold  of  todd  crane ? he  should  be  able  to  give  some  incite  on  the  matter ?

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Maybe he chose a pot because it was less expensive than an L-pad, sizing it's values appropriately, designing the crossover to be right for what should be the proper position within a narrow useable range of motion, and called it a day?

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Maybe. I’m not discarding any thoughts right now. And that is most likely what happened. Or maybe they were out of lpads and he used a pot because that’s all he could get at the moment. It would be nice to know the real answer so I would know that replacing the pots with pads is ok. 

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You're overthinking it.  Get the next-lowest resistance pot if not the stock value.  Any difference between what you end up with and stock, make up that difference (near enough) with fixed resistor(s) between the third tap and the pair of common wires.  You'll lose a little adjustment range is all.  If you need to swap that range the other direction, just wire the resistor(s) between the other fixed tab and that lead instead of "floating" the commons.  Very simple and correct enough, evidently, to restore what you've got.

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Posted (edited)

I usually do overthink things. I can’t help it I’m a toolmakers by trade and we work in exact all the time and now it’s just a way of life. There is no “ good enough “ in our trade. It’s either right or wrong. 

 

I don’t have my notes in front of me but I remember only a 2 ohm difference between the pot and pad at the crossover( on the midrange out of the crossover ). Is that enough to make any difference? The terminals at the back of the cabinet ( amp in ) remained the same ( 7.5 ohms ) no matter if a pot or pad was installed. 

 

I never considered a resistor on a pot. The closest pot I can find is 25 ohms or 47 ohms. 

Edited by mark fader

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The 25 + a 4.7 resistor wired like I said.  The resultant overall value is 99% of the original, not counting tolerances which exist in all the old and new.  The main thing functionally different is you'll lose the last 16% of adjustment.  It'll be as if you'd put a positive stop in the original pot to limit travel a bit short on one end.  If that area is where you need the range of adjustment, just put the resistor on the other end instead.

 

There would be a minor difference in terms of knob/indicator location in that you'll still have full range of knob motion covering what would have been only 84% of range so each degree of turn will now cover the same ground as 0.84 degrees did before - a little better resolution than originally.  If the knob is in the middle at original reference and you match up the physical end points, the new reference position will be slightly off-center electrically.  If there's a reference mark on the face plate, determine the resistance from the wiper in that position to whichever end that doesn't have the outboard resistor on the replacement, match that value on the new and install the pot so the knob aligns with the reference mark in that knob position.

 

Just looked at your photos.  Is that screw through the middle of the coil a magnetic screw?  If so and it wasn't so originally, then replace it with something non-magnetic.  It isn't much metal but it could alter the value of the inductor nonetheless if magnetic.  Just do exactly whatever was original in that matter.

 

And you're absolutely sure nobody's been in there replacing parts with new that only resembled the old?  It'd be a shame for you to have been fretting over finding something to match something which wasn't correct!

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5 hours ago, mark fader said:

I don’t have my notes in front of me but I remember only a 2 ohm difference between the pot and pad at the crossover( on the midrange out of the crossover ). Is that enough to make any difference? The terminals at the back of the cabinet ( amp in ) remained the same ( 7.5 ohms ) no matter if a pot or pad was installed. 

 

2 ohms difference would alter both, the crossover frequency, and driver level by a couple dB.

 

Unless your meter is using AC to measure resistance, at a frequency high enough to get through the capacitor, you could short the HF leads coming out of the crossover and still read 7.5 ohms at the input terminals (where you're measuring the woofer and its crossover inductor).  So there's no value to you in that reading, in this particular matter.

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One final notion:  be sure to match any internal inductance (hopefully none) of the old pot with the new.  A change there will be unwanted.

 

Can Honeywell maybe put perfect replacement guts in those pots for you?

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Posted (edited)

i see  what  you  are  getting  at  about  adding  the  resistor  to  the  pot . although  i  don't  understand  it  totally  i  understand  that  it  will  be  a  little  different . at  this  point  i  don't  know  if  i  really  care . to  be  honest , i  just  set  the  pots  a  little  lower  than  full . so  if  i  can  get  in  that  range  then  i  will  be  satisfied . i  never  set  them  below  half . but  now   they  have  new  caps  so  if  that  changes  anything  then  i  will have  to  adapt . i  still  don't  see  me  going  below  half .  

 

the  screw  in  the  coil  is  the  same  screw  i  took  out . it  is  stock . that  being  said , i  don't  know  what  it  is

 

my  dad  bought  the  speakers  new  about  1985 . im  pretty  sure  he  never  did  anything to  them . that  is  why  I'm  98% sure  they  were  stock  when  i  got  them . 

 

you  lost  me  on  the  measuring  part . im  not  really  skilled  at  that  kinda  stuff . all  i did was compare #'s . ( i  had  one  cabinet  with  the  original  pots  and  one  with  new  L-pads )

 

i  haven't  heard  back  from  honeywell  yet . they  may  be  able  to  make  replacements for  me .that  would  be  perfect  if  they  could !!!!

 

at  this  point  it  looks  like  the  pot  with  a  resistor  is  my   best  choice  given  what's  available . i  wonder  if  i  could  even  hear  the  difference  between  the  original  pots , the  l-pads , or  the  new  pots  with  resistor ? maybe  ill  just  set  aside  a  saturday  afternoon  and  try  all  thee  and  see  if  there  is  any  difference  to  my  ears . 

 

will  the  L-pads  hurt  anything ? 

Edited by mark fader

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1 hour ago, mark fader said:

will  the  L-pads  hurt  anything ? 

 

I wouldn’t want one in the eye, but using, or not using , them should do no harm to your speakers or amp.

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I shouldn't think any harm would come with L-pads.  Certainly none from any equipment safety standpoint.  Unless by harm you mean different-from-stock sonics which may or may not result from the change.

 

When you stick your meter on the input terminals and take an ohms reading you're most likely injecting a small DC signal, the meter reads the voltage drop in that signal and reports the ohms required to produce that drop.  DC from the meter will not get through the capacitor(s) in series with a high frequency driver, so anything behind the cap(s) is excluded from that result.

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Based on the simplistic crossover, you might want to just go with real 8 ohm lpads.  It will probably manage keeping the crossover closer to the required impedance so that there is less shift.

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I agree with all of you because I don’t know enough about the specifics to disagree. I’m out of town the next few days so I won’t be able to try any different set ups but once I get back I’ll see what I can do. Once I do I’ll post the results. In the meantime I’ll get some pots and resistors and work on the idea above. 

 

If I hear anything from Honeywell I’ll post it. 

 

Thanks you guys. 

 

Any others are free to chime in. I want to hear it all. 

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7 hours ago, pzannucci said:

Based on the simplistic crossover, you might want to just go with real 8 ohm lpads.  It will probably manage keeping the crossover closer to the required impedance so that there is less shift.

 

The only thing I have against that notion (and I'd usually suggest the same) is that from what I not much know about Fraziers is that off-the-shelf parts were combined in specific ways to good result.  Hence my focus heading to staying stock.  Were it me, I'd try both ways and have them speak to a umik so I could see what I was hearing too.

 

Or maybe just go stock and be done with it.

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Posted (edited)

On the other site ( audiokarma ) there is a guy named snade. Who was in the same situation as me. He had the same pots and couldn’t find a replacement. He went with the l-pads and he claims that he can’t hear any difference. Others on the site who have heard them say the same thing. His reasoning was that other sevens he saw had l-pads. I would love to stay stock , but if I can’t I’m leaning towards the pads because that makes sense to me. I’ll let my ears decide once I try the other set ups out. 

Edited by mark fader

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3 hours ago, glens said:

 

The only thing I have against that notion (and I'd usually suggest the same) is that from what I not much know about Fraziers is that off-the-shelf parts were combined in specific ways to good result.  Hence my focus heading to staying stock.  Were it me, I'd try both ways and have them speak to a umik so I could see what I was hearing too.

 

Or maybe just go stock and be done with it.

I'd generally agree.  I bought a pristine pair of 20 yr old La Scalas, finished from the factory and I didn't like the sound.  I didn't modify them because of the same reason.  Not even an lpad or anything to balance the sound.  Sold them because I thought they needed to stay stock. (I do kick myself for that though :-) )

 

Just looked and didn't realize there were two versions of Sevens.  My Mark Vas were with the piezo and 5lb alnico magnet on the woofer (same as yours). 1975 version.

 

The main thing with Frazier is the efficiency.  The pots aren't going to add anything there.

I rebuilt my Mark Va's into Seven's when I owned them and did seek out the midranges and tweeters if I wanted to build an Eleven since you could buy parts from the Frazier dealers.  Nothing to gain in the efficiency area from the specs on the original drivers. The series crossover also didn't hurt and probably helped ease the use of the pots.  I think a lot of the Frazier's gains were from simplicity and good drivers.  On the tweeters, since they are capacitive (assuming piezo), the pot could probably be replace with a different value that was close and be reasonably good.

If you are stuck, lpads would be the way to go if you want flexibility/ adjustability  and can't find the pots.  Also there are ways to sweeten up the tweeters that is worth looking into.  Then you would likely want to switch to lpads on the tweeters.  I noticed the Seven with the mud version of the woofer on AK and it appears that had lpads.  Think that would have been a little newer.  

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16 hours ago, mark fader said:

the  screw  in  the  coil  is  the  same  screw  i  took  out . it  is  stock . that  being  said , i  don't  know  what  it  is

 

A straight-slotted rather gnarled screw?  (Should be taken in a light-hearted manner.)

 

I was just re-looking at the photos, getting the lay of the land.  I noticed in the shot with the plywood the tweeter leads look for all the world like they're out of phase (or is it more PC to say the polarity is reversed?).  I don't know what all's at the end of the leads heading out.  I'd assume it's a two-way series second-order filter with all the drivers, or their volume controls, wired in to the appropriate side, each running what's left of full range from there.  The crystal tweeters won't do anything on their own below a point a bit higher than the filter.  And I guess the mid driver rolls off the upper end on its own, likely near the point where the tweeter kicks in.

 

I still think I'd match the pot overall with one resistor either end of the pot.

 

And check on that polarity thing.  Is that what you want?  Great, if it's what's called for.  I don't know but would guess same polarity for mid and hi.  But I don't know.  However they factory wired it, I'd bet it weren't by chance.  Unlike me, sitting at a solid 50% on this one :^)

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No!  Wait!  Just gandering at the pic again and the tweeter's right.  It's the mid looks polarity-reversed to me.  Hadn't sufficiently narrowed down the root cause of what caught my eye earlier. 

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You are right. that’s original wiring. My top post has an original pic and a post pick. I don’t know why it’s that way but it was the same on both cabinets. I just copied what was there. I looked and looked at that and although it is out of phase it is how Frazier wired it up. I even confirmed that to another website post with pictures. His were just like mine except his had L-pads not pots. He says the pads are original. If I can find the link I’ll post it. 

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