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 Post subject: Haunted speakers...?
PostPosted: 22 Jan 2009, 15:02 
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Joined: 20 Jan 2009, 20:31
Posts: 33
Location: Canandaigua NY
First, the crazy question:

Is it at all possible for a faulty L-pad and/or crossover to return a signal and screw up an amplifier's balance or loudness circuitry?

I have an old pair of Criterion 77 speakers from one of my craigslist dumpster-diving forays. They have some kind of an L-pad with a single knob, ranging from Min to Max, whatever that means. I'm beginning to suspect something, since every old receiver I hook them up to then presents a problem in loudness or balance. I can't positively say the problems weren't already there, since there are slightly different manifestations. But three amps >> three left-channel problems, after hooking these things up?


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 Post subject: Re: Haunted speakers...?
PostPosted: 22 Jan 2009, 22:32 
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Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
I have seen these knobs before, it is a variable resistor, sometimes they control speaker gain, other times it sets the frequency range for one of the speakers, personally I hate them, I don't see the need to use them, but I guess for studio purposes it could be usefull.

Open the speakers up if you can and see what kind of crossover setup is there, it's probably a gain control.

Your not crazy asking the question, I am the one that can ask crazy questions... ;)

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 Post subject: Re: Haunted speakers...?
PostPosted: 22 Jan 2009, 22:52 
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Joined: 20 Jan 2009, 20:31
Posts: 33
Location: Canandaigua NY
The Criterion 77s are sealed. Looks like they are shot together with staples. I've had these for a couple of years and never liked them, so I don't mind doing a little router surgery on the back to open them up. Maybe the cabinets can be used later.

Right now they are standing in while I'm building a bookshelf set with the Fostex FE126E. Never done this before, so I thought I'd warm up with the bass reflex enclosure, then later try my hand with the back-loaded horn.

Still, odd that three old receivers I've used with them develop problems in the left channel. Could be just coincidence...

Sometimes I do better from craigslist. I got a pair of Ohm Model E thrown in free when I bought an old Pioneer receiver. Never heard of them before but they are gems. I'll have them re-coned if I have to, they are that good. If the speakers I'm building sound as good as the Model E I will be very pleased.


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 Post subject: Re: Haunted speakers...?
PostPosted: 23 Jan 2009, 07:54 
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Joined: 06 Jun 2008, 20:12
Posts: 972
Location: Houston, TX
Can you just remove the speaker to get to the insides?
Ri

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 Post subject: Re: Haunted speakers...?
PostPosted: 23 Jan 2009, 14:57 
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Joined: 20 Jan 2009, 20:31
Posts: 33
Location: Canandaigua NY
The grill cloth appears to be wrapped around the motorboard; my guess is, the motorboard is then screwed or stapled in from the inside.
Image
I think I'll go in from the back; I can make out where the staples were sealed over on the backboard, maybe there's hope.

Here's the "HF" control on the back, no discernible difference when adjusted:
Image
And here's the latest $20 receiver to be victimized, a Yamaha RX-530:
Image
This has a "CD Direct" selection, bypassing the loudness and balance circuitry; then the distortion disappears. Also disappears if I use loudness to dampen a bit.


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 Post subject: Re: Haunted speakers...?
PostPosted: 23 Jan 2009, 16:42 
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Joined: 04 Jun 2008, 20:59
Posts: 4235
Location: Arizona, USA
Hi, Haunted, I can relate, however a number of problems can cause this. One, The pot may well be bad. There are two types, Simple variable resistors often about 50 ohms that act as a crude (and cheap) level adjustment for adjusting the tweeter level. Seldom for any other drivers. The second type is a constant impedance "L" pad. It generally has two variable resistors in in the same housing and maintains a constant impedance for both input side and load side. Much better. The problem is more likely though damaged drivers. When you engage the tone controls (esp loudness if so equipped) it emphasizes the lowest and highest frequencies. Often old cone speakers have lost there elasticity in the surround and voice coil mounting and distort badly when they are driven at low frequencies with any sort of boost. The only real solution is recone or replace. For the ones you have probably not cost effective. A hint on the grills, many are held in place with staples through the grill cloth. The alternative as you noted is cutting a hole in the back. Personally I would cut the grill cloth and go in from the front. Replacement grill cloth is available from several sources (Parts Express, MCM, AES and others).

Good listening
Bruce

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 Post subject: Re: Haunted speakers...?
PostPosted: 24 Jan 2009, 19:00 
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Joined: 20 Jan 2009, 20:31
Posts: 33
Location: Canandaigua NY
One way or the other, we're going in! But not 'til I get these FE126E enclosures built.

Then I'll bet the Criterion cabinets will be useful for...even bigger full range drivers.

:mrgreen:


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 Post subject: Re: Haunted speakers...?
PostPosted: 24 Jan 2009, 20:14 
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Joined: 28 May 2008, 21:53
Posts: 4589
Location: Winnipeg, CANADA
What enclosure are you building for the FE126E?

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 Post subject: Re: Haunted speakers...?
PostPosted: 24 Jan 2009, 22:49 
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Joined: 20 Jan 2009, 20:31
Posts: 33
Location: Canandaigua NY
gmilitano wrote:
What enclosure are you building for the FE126E?

The standard bass reflex shown here:
http://www.madisound.com/catalog/PDF/fo ... fe126e.pdf

If that enclosure disappoints, I'll take a crack at the back loaded horn, but for starters, simplicity has much appeal.

From browsing the forums, it seems the FE167E is the favored full range, but with the 126E at SPL 93dB and a response curve not that much inferior to the 167E, price point made the difference.

But I'm very new at this, maybe I missed something critical in comparison?


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 Post subject: Re: Haunted speakers...?
PostPosted: 25 Jan 2009, 11:36 
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Joined: 28 May 2008, 21:53
Posts: 4589
Location: Winnipeg, CANADA
The FE167E is higher Q and therefore better suited to a bass reflex cabinet. But I have seen a couple of FE126E in a bass reflex where good results are reported:

Image

and http://www.troelsgravesen.dk/FE126E.htm

Let us know how those turn out.

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