• Please note that there are a few updates and clarifications made in the Audiokarma Rules, mostly relating to advertising and the addition of the new "Paying it Forward" & "Giving back" forums in the AudioKarma Audio Marketplace section.

Norman Laboratories Model 8s - Help me bypass faulty tweeter resets!

R

ralphus

New Member
Hello, I'm new here :)

I just brought down an old pair of Norman Laboratories Model 8s from the attic. Wonderful pair of speakers. They have a Belgian Philips tweeter and woofer in each. My only problem is they have an automatic tweeter cutoff "feature" which does not respond well to a lot of the music I listen to... This was never a problem when the speakers were new, but now I have to push (in various directions) the tweeter reset button on the back of the speakers a couple times a day when one tweeter mysteriously decides to stop functioning. I've sprayed Caig Deoxit into the switches several times, and it's helped, but the problem persists... I'd MUCH rather simply bypass the reset function. I don't listen to things at insane volumes, so I don't need this tweet safe-fail to protect my tweeters from my own listening habits.

The reset buttons are a simple long red button like you've seen on many '80s products. Part of the problem, I would guess, is the contact they compress is heavily oxidized, and maybe even vibration from within the speakers caused by the woofers is causing the resets to toggle. I don't care to fix or replace the buttons, I just want to bypass them all together. I'm competent with a solder iron, so this should be no problem. The only issue is, the only access I have to the cross-over circuit is through the tweeter hole at the moment as the woofers have a plastic frame glued to the frame of the speakers, preventing me from dismounting them without removing the glue. I need to know how to bypass the tweeter resets before I decide to massacre my speakers and pull off the glued frame to remove the woofers.

I've read a few Norman Laboratories threads here (in fact, they convinced me to get my pair out of the attic), and I hope some of their proponents are still around here to help me!
 
Register to hide this ad
ralphus said:
Hello, I'm new here :)

I just brought down an old pair of Norman Laboratories Model 8s from the attic. Wonderful pair of speakers. They have a Belgian Philips tweeter and woofer in each. My only problem is they have an automatic tweeter cutoff "feature" which does not respond well to a lot of the music I listen to... This was never a problem when the speakers were new, but now I have to push (in various directions) the tweeter reset button on the back of the speakers a couple times a day when one tweeter mysteriously decides to stop functioning. I've sprayed Caig Deoxit into the switches several times, and it's helped, but the problem persists... I'd MUCH rather simply bypass the reset function. I don't listen to things at insane volumes, so I don't need this tweet safe-fail to protect my tweeters from my own listening habits.

The reset buttons are a simple long red button like you've seen on many '80s products. Part of the problem, I would guess, is the contact they compress is heavily oxidized, and maybe even vibration from within the speakers caused by the woofers is causing the resets to toggle. I don't care to fix or replace the buttons, I just want to bypass them all together. I'm competent with a solder iron, so this should be no problem. The only issue is, the only access I have to the cross-over circuit is through the tweeter hole at the moment as the woofers have a plastic frame glued to the frame of the speakers, preventing me from dismounting them without removing the glue. I need to know how to bypass the tweeter resets before I decide to massacre my speakers and pull off the glued frame to remove the woofers.

I've read a few Norman Laboratories threads here (in fact, they convinced me to get my pair out of the attic), and I hope some of their proponents are still around here to help me!
Click to expand...



I have some Normans with the same problem. I've given up on trying to fix the breaker from the outside.
If I play music with any degree of volume, the speakers start to gradually self attenuate in the highs. They never cut out completely.

I want to keep the breaker in the system to protect the unobtanium tweeters.
I'm not sure what needs to be known to completely replace with a new one.

Welcome to AK, someone will chime in. :yes:


Steve
 
it will prob entail finding where the speaker inputs are and routing them directly to the crossover instead of through the resets. luckily the pair of speakers i had the reset buttons and the crossover were on opposist sides of the box. so all i did was reroute the input wires to the crossover directly.
 
Thanks for the welcome and quick replies :) I'll wait a bit longer, and probably crack 'em open and see if I can figure out how to route around the resets. Perhaps, if it's just a contact problem, I can apply some solder to the switch contact and keep the resets in the circuit... I'd probably have opened them up already by now if I wasn't so reluctant to remove the oddly glued on frames preventing me from removing the woofers... Suppose I'll use a blow dryer to soften the glue and apply some gentle leverage.
 
You might try a shot of deoxit right up the reset shaft and work it in a few dozen times.

edit: Must read and comprehend original post.
 
Last edited:
I just bypassed the reset switches. I've left the bulbs in circuit for now. Weekly Deoxit treatments were getting old and each one seemed less effective. I also switched out the tweeters (one of the originals was damaged and I had no luck finding NOS Philips AD 0162/1063 T8s after months of scouring eBay) with a pair of low-crossing Seas 27TDFCs which perfectly fit the original tweeter hole. I'll have to build a new crossover to account for the impedance difference as the 4.8 re Seas overpower the (unmarked but presumably 8 ohm) woofers, but the end result should sound good, however sacrilegious it may be to purists :P
 
ralphus said:
but the end result should sound good, however sacrilegious it may be to purists :P
Click to expand...

No purist here. The end result is what matters.

I have beefed up my boxes and added extra fastening screws for the woofers.
I put a pound of DS on each woofer and felt on the spokes.

All these mods made a good speaker better in almost every way.
Good luck with whatever you do. :thmbsp:

Steve
 
Parts Express sells the reb button protection devices- should be a near drop in. It would e a good idea to recap those old electrolytic caps and upgrade to some cleaner sounding 1% Datons with a bypass cap on them.

I have rebuilt several NL networks and they are easy to do. These are typically very nice sounding & looking speakers-well worth ones time to rebuild. The lamp bulb is usually all one needs to protect the tweeters- short of voltage spikes.
DC
 
Thanks for the encouragement :)

I was thinking of actually just building all-new 2nd order L-R crossovers for them... I've read the model 8's woofers are 6.5 re, the crossover is at 1500hz, and know the tweeters are 4.8 re, so calculating with this, and adjusting for the woofer inductors' dcr, I was going to pick up the Dayton +/-1% caps and some steel laminate inductors from Mediasound for the following build:

C1 = 12.67 uF (10.0 + 2.7)
C2 = 9.05 uF (6.8 + 2.2)

L1 = 0.88 mH (0.90 mH)
L2 = 1.23 mH (1.25 mH)

It'd be radically different from the original crossover with the LCR design, shared capacitor and light bulb, but I didn't think I would need the lightbulb (or resets for that matter) with newer, less fragile tweeters? I never really pass -38db reference for music and -20db for surround content on my AVR. Any problems with this theoretical design? This'll be my first cross-over redesign, so I'm open to any tweaks.

Edit: What do you guys think about these as tweeter protection?
 
Last edited:
dc270 said:
Parts Express sells the reb button protection devices- should be a near drop in. It would e a good idea to recap those old electrolytic caps and upgrade to some cleaner sounding 1% Datons with a bypass cap on them.

I have rebuilt several NL networks and they are easy to do. These are typically very nice sounding & looking speakers-well worth ones time to rebuild. The lamp bulb is usually all one needs to protect the tweeters- short of voltage spikes.
DC
Click to expand...

Can you post the part number from the Parts Express website? I tried to find it, but no luck.
 
Finished my project :) The parts I listed above were wrong... Realized that the day before they arrived--doh. I'd read the speaker terminals on Model 8s had been tested at 6.5 re, and in my mind I remembered that as the woofers' coil resistance being 6.5. So I ended up ordering the following parts after verifying myself that the woofers are actually 5.7 re, though I wasn't able to test across all frequencies so I suppose it's only an approximate (6 ohm nominal? Odd but not that rare I guess):

4.8 Ohm Tweeter / 5.7 Ohm Woofer--adjusted for L2's dcr--5.82 Ohm, 2nd order L-R with

C1 = 9.31 uF (6.2 + 3.0 + 0.10 Dayton 1%s)
C2 = 9.12 uF (6.2 + 2.7 + 0.22 same)

L1 = 1.21 mH (1.20 Jantzen 18ga air)
L2 = 1.24 mH (1.25 ERSE steel laminate)

They sound amazing :P I didn't even realize my Model 8s had 30ish-year-old electrolytic caps till dc270 mentioned it. I suppose that decay explains why one of my speakers used to calibrate to +2.0 db compared to the other. Looks like my NLs will be in service for many years to come.
 
Eh, kinda late to the party, but how old are these speakers? Any chance the HF caps were off spec and allowing too much mid into the tweeters, so the overloads were actually legit? A blown tweeter is a possible symptom.
 
My parents purchased them around '82 from some store in Little Rock. I had them in my room from around 1990 through 2000 and never had to hit the tweeter reset buttons at all. Never had a single issue... Then they spent 10 years in a shed and later an attic inside garbage bags (not the best protection), brought them down and had to work the resets like mad to get the tweeters going... Then the slightest vibration could turn the tweeters off. The fact that Deoxit helped for a while makes me think the switches were really to blame. I left the switches mounted so they still look stock (from behind and with the grilles on anyway), but I definitely think they were the culprit.

Now that I've replaced the old caps, I don't even think the one Philips tweeter was damaged at all--I'm pretty much a newb, though, so I'm not sure if a decayed cap could result in decreased tweeter output with little to no effect on the woofer in a circuit that shares the same 5 uF cap. When I installed the new tweeters and continued to use the old crossovers (until today), I still had that sizable db offset, so I think one crossover aged less gracefully than the other.
 
dc270 said:
Parts Express sells the reb button protection devices- should be a near drop in. It would e a good idea to recap those old electrolytic caps and upgrade to some cleaner sounding 1% Datons with a bypass cap on them.

I have rebuilt several NL networks and they are easy to do. These are typically very nice sounding & looking speakers-well worth ones time to rebuild. The lamp bulb is usually all one needs to protect the tweeters- short of voltage spikes.
DC
Click to expand...

Hey DC....where are these push button style circuit breakers at PE? I have 4 of them in my Model 9's that I'm either going to bypass or find new ones for.
 
ralphus said:
My parents purchased them around '82 from some store in Little Rock. I had them in my room from around 1990 through 2000 and never had to hit the tweeter reset buttons at all. Never had a single issue... Then they spent 10 years in a shed and later an attic inside garbage bags (not the best protection), brought them down and had to work the resets like mad to get the tweeters going... Then the slightest vibration could turn the tweeters off. The fact that Deoxit helped for a while makes me think the switches were really to blame. I left the switches mounted so they still look stock (from behind and with the grilles on anyway), but I definitely think they were the culprit.

Now that I've replaced the old caps, I don't even think the one Philips tweeter was damaged at all--I'm pretty much a newb, though, so I'm not sure if a decayed cap could result in decreased tweeter output with little to no effect on the woofer in a circuit that shares the same 5 uF cap. When I installed the new tweeters and continued to use the old crossovers (until today), I still had that sizable db offset, so I think one crossover aged less gracefully than the other.
Click to expand...

Decreased tweeter output and uneven response between the two channels are also signs of deteriorating caps. Recapping old speakers often 'opens up' the high end. Does sound like you also have some problems with the breakers though.
 
dc270 said:
I have looked intently & cannot find the old red btton types they once had. All I can find are the newer types...........
DC
Click to expand...

Will they operate at the same spec as the older ones? I just want the protection, just in case.

I would use a fuse if I knew what voltage to use.


Steve
 
You must log in or register to reply here.
Back
Top Bottom