View Full Version : Refurbishing H.H. Scott S-71 speakers, Part 1


Gregory
12-09-2006, 06:23 PM
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Refurbishing the H.H. Scott S-71 loudspeakers, Part 1

Am interested in refurbishing the Scott S-71, 12" woofer, dual 1" dome loudspeakers with the help of the forum. One of the midranges went out in ~1988 and a `Pyle driver´ was installed in its place. Also 8-ohm, 100w L-Pads were installed (large rheostats) in the back panel for midrange and tweeter levels (only one tweeter active in each now) on Right and Left speaker.

http://home.comcast.net/~mc_audio/S-71_specs.jpg


Please comment, make recommendations, and generally contribute your expertise. Have done some calculations such as the radiation pattern from two 1" domes spaced x-inches apart, etc. Also have crossover schematic, etc.

Oh.. they were for sale back in the '80s as were NS-1000s and a power amp. Yamaha units are long gone, sorry!! :)


-Gregory

MarkAnderson
12-09-2006, 09:44 PM
eBay will likely be your best source for replacement drivers (unless someone here has what you need). Those Philips tweeters come up with fair regularity and don't command a ton of money. If I had to guess, the midrange is prolly a CTS one and there's a good chance you'll stumble onto one sooner or later. You'll want to consider replacing the x/o caps, too. Based on my limited experience, I'd expect them to sound nice with the correct drivers and some fresh caps.

Aren't those 8 ohm tweeters?

Gregory
12-09-2006, 10:12 PM
eBay will likely be your best source for replacement drivers (unless someone here has what you need). Those Philips tweeters come up with fair regularity and don't command a ton of money. If I had to guess, the midrange is prolly a CTS one and there's a good chance you'll stumble onto one sooner or later. You'll want to consider replacing the x/o caps, too. Based on my limited experience, I'd expect them to sound nice with the correct drivers and some fresh caps.

Aren't those 8 ohm tweeters?
Thanks for the reply. The tweeters all work, however I disabled one on each SPKR since the midranges were relatively weak (one blew.) Not sure if tweeters are 8-ohm. Would like to enable all the tweets' and get some STRONG midranges as replacements.

Here's another pic from the web, however these are not my speakers..
mine have light-colored grills.

http://forums.france-hardware.com/~fh/upload/1/5634_scott1.JPG


Have had these BIG Babies since the '70s and hauled them off to college twice, and all around the country when moving. :)

The original midrange units were housed in gray plastic `sub-enclosures´ and I may want to build a WOOD box in there instead (may have already done that - cannot recall.)


Here are some of the project objectives:

* make new grills including wooden mask.

* procure and install hi-performance midrange drivers.

* re-work, modify, and rebuild the crossover network.

* maybe take out the four 100w L-pad rheostats.



Here are the specs aGaiN...

http://home.comcast.net/~mc_audio/S-71_specs.gif


Do you know of any CROSSOVER guys who would like to have a peek at the circuits? I drive these with McIntosh amps and they've been with me since ~1973. Lots of listening hours. :thmbsp:


-Gregory

MarkAnderson
12-09-2006, 10:30 PM
Can you post the schematic here?

Gregory
12-09-2006, 10:36 PM
Can you post the schematic here?
Yes.. have three of four different pencil sketches of it, and will have to clean it up first. Maybe even redraw with a Windows App to make presentable!!

Noticed on the Scott data sheet above, rev dates 6/72 and 10/73.


-Gregory

Nat
12-11-2006, 04:30 PM
The crossover might be more complex than usual since many of the Scotts were designed to offer a relatively easy load to amps. They called it controlled impedance, and I think it was accomplished using zobels.

Gregory
12-11-2006, 05:50 PM
The crossover might be more complex than usual since many of the Scotts were designed to offer a relatively easy load to amps. They called it controlled impedance, and I think it was accomplished using zobels.
Yes.. it's clearly printed on the original cartons (which are here) in bold black print:

SCOTT

CONTROLLED
IMPEDANCE
LOUDSPEAKER
SYSTEM

S-71

Am still working on re-drawing the schematic from sketches to present.
You are right.. it's relatively complicated. :)

What is (are) zobels? :scratch2:


-Gregory

FalconEddy
12-11-2006, 06:06 PM
What is (are) zobels? :scratch2:


Zobels are filters used to basically stabilize impedance between the crossover and the driver.

It employs an extra cap and resistor in series to accomplish this feat.

The resistor is 1.25X the speaker's impedance, and the cap required is calculated using a frequency impedance doubling technique.

Then the cap and resistor are placed in parallel between the crossover and the driver.

Cool, huh?

. . Falcon

Gregory
12-11-2006, 09:06 PM
Zobels are filters used to basically stabilize impedance between the crossover and the driver.
. . Falcon
Thanks, will search around for that!!


Would like to ask the group..

WHAT would be a GOOD REPLACEMENT MIDRANGE DRIVER for the S-71 speakers?


Now.. another sketch from years ago when the new PRO series came out. Here they're compared to the S-71. The -100 wasn't isoplaner (had drivers on top) and the -70 had midranges mounted too far apart (IMHO) and that would result in lobing or interference patterns in azimuth. So, for thses reasons, I didn't replace the S-71s.

http://home.comcast.net/~g-abbey/Scott_dwgs.gif


Any comments on the above? How about a NEW midrange source?


-Gregory

Gregory
12-11-2006, 11:14 PM
Can you post the schematic here?
Here's the schematic. It is correct to the best I can determine at this time.
One of the speaker cabinets must be `opened up´ to recheck.

http://home.comcast.net/~mc_audio/S-71_crossover.gif


Also.. found some midrange drivers at:
http://www.mcminone.com/category.asp?catalog%5Fname=MCMProducts&category%5Fname=3829617


Comments, changes, or redesigns are MOST welcome. :)


-Gregory

Gregory
12-12-2006, 03:29 PM
Ping Mark Anderson.. did ya' check out the crossover diagram?

Any suggestions for a high-quality, high-efficiency midrange driver replacement?


-Gregory

MarkAnderson
12-12-2006, 06:30 PM
Yup. It's greek to me. :D

Really, I'm quite the novice regarding x/o design. I was hoping some of the more savvy members might have a look and offer some tips. Problem is, the stock x/o may not work well with a different driver, so you may need to redesign the band-pass section of the circuit (but then, maybe this was the point of your post :scratch2: ). That helps, don't it.