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mark fader

Frazier Model 7 Restore

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Posted (edited)


long  story  short - my  dad  bought  theses  new  when  i  was  a  kid and  its  what  i  grew  up  on . now  i  have  them  but  after  30  years  or  so  i  just  decided  to  give  them  a  little  tlc . about  2  years  ago  i  refinished  the  outside . i  stained  them  black  and  put  on  a  satin  gloss  finish  and  replace  the  grills  with  a  frame  and  grill  cloth . now  i  decided  to  do  the  inside  about  a  month  ago . 

 

the  goal  was  to  make  them  sound  the  way  they  did  new , or  as  close  as  possible . of  course  i  don't  remember  what  they  sounded  like  new  because  i  was  just  a  kid  and  i  hadn't  developed  an  ear  yet , but  at  least  restore  them  with  new  components . the  caps  were  pretty  straight  forward  but  the  challenge  was  the  pots . i  searched  and  searched  and  emailed  anybody  and  everybody  just  to  find  more  confusion  and  dead  ends . as  of  right  now there  is  no  known  direct  replacement  for  the  pots . so  i  just  kept  searching  the  net  to  see  what  others  have  done  and  what  there  results  were . sill , not  a  whole  lot  of  info . so  here  is  what  i  ended  up  doing  - new  caps . the  ones  i  chose  are  dayton  12uf  caps . i  chose  dayton  because  parts  express  is  only  about  12  miles  from  my  house  and  the caps  were  well  spoken  of  and  they  were  reasonable  cost . i  am  still  concerned  about  the  L-pads  because  some  say  that  they  will  change  the  frequency  and  the  impedance  a  little . others  say  it  won't . i  can't  get  a  real  answer  from  anybody  and  i  don't  know  this  stuff  enough  to  argue  the  point  either  way . i  want  a  direct  replacement  but  since  i  can't  find  one  this  is  what  i  decided  to  try . i  installed  a  parts  express  L-pad  in  the  original  holes . the  L-pad  is  8  ohms  15  watts . i  attached  pics  so  let  me  know  what  you  think .

 

 

 

original Crossover.jpg

new cross over.jpg

new x-over and L pads.jpg

Edited by mark fader

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I wouldn't have worried over the pots. All Fraziers I have that feature them I run them in the middle, null mode anyway and the speakers are awesome.

 

Dave

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so  what  you  are  saying  is  that  the  L-pads  are  fine ? there  is  no  difference  between the  original  pots  and  the  new  L-pads ? 

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Should be the only items in need of refreshment are the capacitors unless perhaps the speakers have seen excessive electrical abuse.  Caps can be expected to change over time all on their own while the other components are quite stable.

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The reason for the pot replacement was because 2 went bad. I have a total of 4 because I have 2 cabinets. All 4 were scratchy so I cleaned them.all 4 got better - 2 cleared up real good but 2 not so much. I took those apart and found the wire was broken on 1 and the other had a bad spot. So I just decided to change all of them. I just think it was age. Nothing last forever. That is my only concern because I’m installing something that wasn’t originally there.

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Try them without the lpads and see what they sound like.

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I will. I figured I would try them with and without. I’m even going to put the 2 original good pots in one cabinet and compare them to each other

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30 minutes ago, mark fader said:

I’m even going to put the 2 original good pots in one cabinet and compare them to each other

 

That's some rational thought!

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I have a pair of original Model 7's in working order if you need to do a hearing comparison.

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That’s a long way for you to drive and they are a bit heavy to carry around. but if you feel the need to come over than I guess it would be ok. 

 

Thanks for the replies but I still don’t have a real answer. Are the lpads going to change the circuit in any way ? I stuck my meter on the terminals and it’s reading 7.5 ohms. Close enough to 8 for me. Turning the lpads made no difference on the meter. I haven’t hooked them up too my receiver yet and I don’t think the lpads will harm anything but I’d like to hear from somebody who understands this more than me explain / tell me they will work or not and some expiation as to why. Just wondering because I want these cabinets to be put together the right way. 

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So I’ll answer my own question. After reading more forum pages the answer is yes lpads will make changes. However , since the speaker , crossover , amp , and lpads have so many variables anyway, it won’t make a noticeable difference. So in my mind I’ve come to the conclusion that lpads will be just fine. After all this very purpose is what they were made for. 

 

Thanks to the forum for all the great info !!

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The lpads will start to have dead spots and at minimum, need contact cleaner and lubricant.

 

For their age, I had the Mark Va's of the same vintage, same crossovers, woofer, piezo, and mid, just 1 tweeter though. (piezos can get a little unhappy too though hard to find the old Motorola types).

4 12uf - dayton is fine.  Much better than the originals

Choke should be fine 

From what I remember, wired in a series type configuration

lpads probably could use replacement or tlc outlined above at minimum.  They seemed to burn though so mine ended up with some dead spots (I used to crank mine anyway).  They will not sound good unless you like screechy highs and too much mid unless run around center or slightly higher on the lpads.

 

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22 hours ago, mark fader said:

Turning the lpads made no difference on the meter.

 

LPads are designed to have the same input and output resistance over their range of rotation. That's what they do, while changing the level of the signal that goes to the particular speaker.

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I agree. That’s why I’m so confused as to why the originals were pots. I just don’t understand. 

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Posted (edited)

good  news . i  just  received some  info  on  the  pots . yes  they  are  in  fact  potentiometers . they  are  a  30  ohm  2  watt  linear  pot . not  L-pads  or  t-pads  or  rheostats  or  anything  else . I  stress  this  because  I've  been  told  all  sorts  of  things .

 

honeywell  bought  out  clarostat  many  years  ago . they  have  documentation  of  the  original  clarostat  stock . the  value  listed  above  came  directly  from  honeywell . 

 

now  the  problem  is  i  can't  find  a  30 ohm 2  watt  linear  pot  anywhere  and   honeywell  doesn't  have  a  direct  replacement . however , they  are  able  to  make  these  pots  from  the  parts  they  have  on  the  shelf . i  don't  know  what  is  involved  in  all  that  but  I'm  getting   more  info  on  that  tomorrow ( hopefully ). anybody  else  need  pots ? if  there  is  enough  need  maybe  i'll  get  an  order  put  together . 

 

so  i  have  to  take  a  step  back . above  i  was  sure  L-pads  were  the  way  to  go  but  after  this  info  i'm  not  so  sure . i  don't  claim  to  be  a  guru  with  this  kind  of  stuff , but  as  i  continue  to  reason  on  all  this , jack  frazier  did  it  this  way  for  some  reason . i  don't  know  his  reason , but  it  had  to  be  based  on  something . if  L-pads  were  the  better  way  to  go  then  wouldn't  he  have  done  that ? but  he  didn't . he  used  pots . so  the  search  continues ... 

 

i  haven't  shut  the  door  on  using  L-pads . but  if  i  can  get  my  hands  on  a  direct  replacement  pot  then  that's  what  ill  do.

Edited by mark fader

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How's it wired in?  Crossover output to the outsides and driver to one side and the middle?  If so, it would make a difference.  If one of the outsides isn't connected to anything then the specific 30 ohm value is unimportant except for the knob or whatever lining up with markings on a label.  Even if it was the first possibility, you could go with something with a lower value and make up the difference with a fixed resistor wired between the one outside terminal and the wires from the crossover and driver.  You just wouldn't have full range of adjustment but everything else would be right.

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all  three  terminals are wired . the  center ( wiper ) goes  to  the  speaker positive . one  of  the  outside  is  connected  to  the  crossover positive  and  the  other  one  of  the  outside  is  connected  to  negative .  btw - dark  brown  is  +  and  light  brown  is  - 

 

attached  are  some  pics . the  pot  wiring  pic  is  the  tweeter  pot  still  in  circuit . the  pot  top  and  pot bottom  pics  are  the  midrange  pot  cut  out  of  the  circuit . i  cut  the  wires and  left  a  little  on  the  ends  of  the  pot . that  is  the  original solder  job . apparently  by  Ed  himself  because  the   cabinet  is  signed " may "  right  by  the  tweeter .

origional pot back.jpg

origional pot top.jpg

pot wiring.jpg

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Pots vs lpads... maybe it was too long ago :-) .  From what I remembered, they used to have the woofer in parallel with the caps and mids in parallel with the coil.  If they didn't worry as much about impedance for crossover frequencies, perhaps you should.  Doesn't look like you have the original electrolytic caps which is good (unless you just replaced them).

 

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I just replaced the caps. The pics at the very top show what I did. I just mounted everything on a board and copied the circuit. The cabinets were completely stock when I opened them. The choke is original. 

 

So you are basically saying to go with the lpads because they try to keep the resistance as constant as possible ? 

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So if i understand correctly the pots allowed the varying of the power to the driver but since it was a pot and not a pad this would reflect a different total load back to the crossover which in turn would vary the crossover frequency and slope at least somewhat. Sort of a "sound shaping" control and not just a level control.

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