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Post by mauro on Jul 30, 2017 13:14:55 GMT
Good day all! I recently rebuilt a model 524 amplifier for a Wurlitzer 1700 and I have been told it lacks bass. I have not heard it yet but I'm sure it will need some further tweaking. I was hoping someone could tell which components would affect the bass response and might make sense to tweak. The speaker has been substituted and a few different Cobra cartridges have been tried but the sound remains the same.
The only thing that's different from the schematic is the 2mf cap is now 1mf (same as the other 1mf cap) but im pretty sure thats part of the avc circuit.
Any suggestions always appreciated.
Thanks, Mauro
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Post by robnyc on Jul 30, 2017 15:37:18 GMT
Mauro, most "weak bass" problems are, in fact, excessive upper mid-range screech due to dried out damping of the vane in the cobra cart.
You are at a bit of disadvantage in not having the amp in front of you and being reliant on the customer's impressions.
Try injecting some silicone gel similar to heatsink compound into the cart. Do not fill the cart, just add enough to damp the screech.
If we are talking about the cabinet speaker a replacement can contribute to bass problems due to it having different free-air resonance point. It may be either too stiff as in the case of many musical instrument speakers, or too compliant as if a modern hi-fi woofer is used.
Still, the most frequent problem is the cart damping.
FWIW: I replaced all the cobra setups with magnetic in the machines I owned. The early carousel arms are more of a problem to convert, but still doable and really worth it.
RobNYC
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Post by Ron Rich on Jul 30, 2017 16:48:40 GMT
Mauro,
I agree with Rob--and, since the cart has been changed ( unless ALL were old-dried out carts), I would guess the problem is in the replacement cabinet speakers. Not too much you can do about that, as the cabinet/speaker/amp/and cart., is a total design concept -except, maybe find the correct ones, used, from one of the suppliers listed above in the FAQ's ? Ron Rich
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Post by mauro on Jul 30, 2017 21:59:04 GMT
Rob/Ron,
Thanks for the insites and when I go see/hear the jukebox I will try adding some heatsink compound.
The replacement speaker was an original Wurlitzer 1700 as well, it has been in warm dry storage for many year and is in great shape.
Exactly how and where do you add the gel or compound? Do I have to split the cobra open or just try to get it under the needle cantilever?
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Post by robnyc on Jul 30, 2017 23:49:43 GMT
Mauro, I added it by removing the cart, putting the stylus end into the open end of the silicone tube and squeeze just enough to get about halfway into the cart. Remove extra from the stylus tip and the part of the cantilever outside the cart body. I used to "tune" these carts by removing a slight amount of the added damping if they got too bass heavy.
From an electronic standpoint, these amps used the old dual signal path of full range and adding bass through a choke coil and separate pot on the volume control. Checking the continuity and signal level through the choke as well as the resistance of that section of the dual volume pot might yield some results....But do the damping first.
Rob
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Post by Ron Rich on Jul 31, 2017 0:42:38 GMT
If you have it, Dow-Corning # 5 ( clear stuff Seeburg used for a heat sink-compound)-- works very well ! Ron Rich
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Post by mauro on Sept 17, 2017 15:40:25 GMT
If you have it, Dow-Corning # 5 ( clear stuff Seeburg used for a heat sink-compound)-- works very well ! Ron Rich Just realized I never finished this topic. Used just a bit of silicone heat sink compound at the base of the cantilever and that did the trick. Sounds great now! Thanks guys! |
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