Jamo Classic 8's

WillMeyer

WillMeyer

Active Member
I recently picked a a pair of Jamo Classic 8's.

Nice sounding speakers.

They seem fairly well built and the set I've pickup up are in very nice shape.
They appear to be a 4 driver 3 way.
The crossover is mounted on the side and difficult to see, but my impression is the 2 woofers are wired in parallel.

The crossover looks to have nice quality inductors, but uses NPE capacitors of the following values:
72uF
33uF
10uF
6.8uF

I plan on upgrading the crossover in the near future. The crossover actually appears to be stapled to the side of the case, so when I'm ready, it looks like it should be readily removable. I'll go with Solen polly caps, but I might use a NPE for the 72uF with a poly bypass cap - I'm not sure at this time.

Does anyone have any info on these speakers?
I'd like to find a copy of the manual if possible but an internet search reveals nada.

I'm interested in hearing opinions/experience on these.

Thx
 
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Sorry that I'm not familiar with this model Jamo. Thought I'd mention that an ebay image claiming to be of a "new in box" Classic 8 crossover shows 5 capacitors. A small one is tucked right up against the 72uF cap.

Jamo_Classic-8_xovr.jpg

This might be a different version than your crossover, or perhaps that cap is hidden by the difficult viewing situation of yours.

Also, in this image, the two paralleled wires attached in series to the largest inductor would suggest feeding two paralleled woofers. Which supports the notion that two woofers in a 4 Ohm system are most likely in parallel anyway.

Just thought I'd put that out there. Good luck with your project.
 
I have these too and like them. Doing a similar upgrade this summer. Gonna swap the NPE capacitors out with poly caps, swapping the resistor too.
 
Here is a pic from 10FEB21. It shows one upgraded crossover against a stock unit.

I used a Parts Express base. I made it larger so I position the larger caps and reposition the inductors (its best practice to have them in different orientation so they don't influence each orher). To get the values I needed, in some cases I combined smaller caps. IIRC, the mid is in an isolation chamber so the mid isn't influenced by the woofer. The meant I could not readily remove the wires. So I added a polarized connector to make installation easier and facilitate ease of removal in case I needed to pull it later for further upgrades.

The blue disk in the upper left corner is interesting. Its a thermal safety. The tweeter power goes through the thermal safety bypassing the resistor. However, if power gets excessive, the safety blocks the power, forcing it to take the path of routing it thru the resistor attenuating the power and protecting the tweeter.

These speakers sound awesome. I setup a system in my wife's office. I had her audition several sets of speakers. Between these Jamos and other speakers (Advent Legacy, Advent Heritage, Boston T830, Infinity RS-8s [1990s ver version]), she chose the sound of the Jamos.

Let me know if you need any more info on the upgrade.
 

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WillMeyer said:
Let me know if you need any more info on the upgrade
Click to expand...
Is there a resistive value marked on that thermistor?
I was shocked how good these sounded after a repair. Bought them on the cheap from an estate sale flipper claiming 1 tweeter was out. Couldn't' resist cuz the drivers looked good quality and the cabinets were really heavy. One tweet was out but wasn't bad. Lucky! Found ring terminal corrosion behind the binding post cups for an easy fix. Guessing the dissimilar metals there caused corrosion with current applied. Copper wire,aluminum rings,steel posts.

I used those same Audyn brand caps you used in a Polk upgrade. Sounded 30-40% better IMO afterward. Thanks for the photos. I didn't even consider replacing the board until now. Now I'm thinking why not.
Thanks
 
If that's how your crossover is laid out, I'd re-orient that middle inductor by standing it on edge. Three inductors in a row, that close together, is a recipie for magnetic interaction that could degrade the sound of the speaker. Along with the electrolytic caps, change the 4.7 ohm sand cast resistor for a 10W wirewound.
www.parts-express.com

Jantzen Audio 4.70 Ohm 10 Watt Audio-Grade Superes Resistor

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I'm tempted to nix that thermistor and place a 10watt or so wirewound type in place of the sand cast. I gotta do some study on that tweeter though & thermistors before proceeding. I probably won't listen to those speakers as loud as they're designed to play. As old as they are I don't think they're even broke in TBH. Ya don't need a subwoofer with these things. Curious what that parallel resistor & thermistor set up presents at "normal" operating temps in terms of total resistance. Time to whip out the ohm meter! 4.3 ohms from the posts on the tweeter side via crude test.

This is my 2nd speaker upgrade. My 1st upgrade didn't have thermistors so basically seeking thermistor knowledge...all I know is they vary resistance with heat. Do I really need them in the signal path at low to moderate volumes.
 
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My opinion...
I believe its not a thermistor, more of a thermal circuit breaker that changes it from a zero (theroretical) resistance closed circuit, to an open circuit. Power will bypass the 4.7ohm resistor, taking the path of least resistance and running thru the breaker. Once the breaker is tripped and open, the power is routed then through the 4.7 ohm ceramic resistor. So really, the resistor is in the signal path only when the speaker is overdriven to protect the tweeter. While I usually do upgrade resistors, I chose not to as the 4.7 ohm resistor will only come into play under exreme conditions.

I did a Vandersteen crossover upgrade on a buddy's set. He had the same component in his. I was not familar with the breaker, but I found lots of info on AK on it. The general consensus is that the thermal circuit breaker fails as they get older and it is best pulled from the circuit. Our listening at home is not excessive volume; focussing on quality of the music at moderate volumes. If I was to revisit the crossover, I'd pull out the breaker and resistor all together.
 
homebrew said:
If that's how your crossover is laid out, I'd re-orient that middle inductor by standing it on edge. Three inductors in a row, that close together, is a recipie for magnetic interaction that could degrade the sound of the speaker. Along with the electrolytic caps, change the 4.7 ohm sand cast resistor for a 10W wirewound.
www.parts-express.com

Jantzen Audio 4.70 Ohm 10 Watt Audio-Grade Superes Resistor

Jantzen Audio 4.70 Ohm 10 Watt Audio-Grade Superes ResistorJantzen Audio's Superes premium resistors are ideal for use in high-end passive crossover networks. These resistors give you the sound you expect from audiophile quality resistors without the high cost. The low noise and minimal...
www.parts-express.com
Click to expand...
I'm of the same opinion as homebrew regarding the inductors. On my built up board, I took 2 of the inductors and maintained the orietation but moved them as far apart as practical. The center inductor, I placed upright. I was actually suprised to see the 3 crossovers so close together in the same orientation.
 
Well said, thanks. Was the sound a night & day difference afterward?

If I re-use the the old board, I'll mount the middle inductor vertically. Heck, I'll do that on either board. :beerchug:
 
I'm very pleased with the upgrade. I was suprised they did so well when A/B'ed against other, larger, speakers.

Definately a keeper.
 
Yeah they're a sleeper hit IMO. I know 4 ohm speakers can be complicated to an amp, so I removed the bi-amp bar & put some old Yamaha's separately on the high's & low's and wowza. Realized they're power hungry & worthy of a crossover upgrade.
 
Hello. I was hoping to find advice on the tweeter circuit please. I've decided to remove the PTC975 thermistor/polyswitch/resettable fuse, whatever ya wanna call it. Removing the 4.7 ohm cement mold resistor also. I found a few good replacement options on parts express & other sites. I'm him haw'ing too much over resistor value choice so that's what I'm asking about. The old PTC is rated at 1.8 ohms & 1.1 ohms minimum. Out of circuit it reads around 1.4-1.6 in parallel with the cement mold resistor.
So I can't decide yet... 1 ohm, 1.2 ohm, 1.5 ohm...inductive type or the non inductive top dollar Mills type. 10, 12, 20 Watt? Kinda lost in over think at the moment. New caps & ckt board came in, caps are huge lol.
Thanks for any advice folks.
 
If you are going to replace the PTC with a new one, I'd replace the 4.7 ohm resistor with another 4.7 ohm. The Mills are good but pricey. Daytons aren't bad. Mind you, this will have zero effect on the sound quality under normal operation as the resistor is bypassed except in overload conditions. During overload conditions the resistor will attenuate the tweeter by -1.5 to -2 db.

If I was going to redo mine again, I'd remove both the 4.7ohm resistor and PTC, replacing them with a jumper wire.

Keep in mind that under normal load, the resistor is bypassed - current is flowing through the PCT as it is the path of least resistance. When the PTC is in thermal overloaded, it blocks the flow of current, forcing current thru the resistor instead. As current flows thru resistor, it decreases power to the tweeter to prevent it from damage.
 
BTW, the original resistor is 5 watts, so 5 watts should be fine.
Consider 5w as the minimum, but going to 10 or 12 watts won't hurt and are more common sizes (and therefore more readily available) for audio resistors.
 
Sorry I wasn't clear on the PTC. I'm not replacing it. I'm removing it for good and the 4.7 ohm cement mold. Both gone. If I didn't have a teenager living here I'd just straight wire jumper them. I can try it straight jumpered for a little while and see if the highs are too bright. For some reason I feel the need to mimic what was there with one quality power resistor in the 1.2 - 1.5 ohm range, identical to what the old PTC & bypass resistor induced in the signal path.

EDIT for the curious: PTC= Positive Temperature Coefficient. When the temperature increases, the resistance increases in this part.
 
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I just bought a bunch of new old stock ohmites for the tweeter ckt. 1 ohm 10 watt. Will figure it out.
Another question for the pro's:
There's a 10uF cap in the mid range ckt. And another 10uF cap in the tweeter ckt. Spent $10 on one cap, spent $40 on the other cap. Where would you put the $40 high end cap?
Thanks
 
How do ya pry the 3 coils off the old board without damaging them? Hard glue holding them down. Moving them to a new board.
EDIT 7-10-23:
Been yanking them off the old board with success so far. Was tempted to use a chisel at first. Disregard silly question above, lol
 
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