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Old 18th October 2011, 04:31 PM   #1
azvrt is offline azvrt  Netherlands
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Default bi-amping 3-way ovals

I have the old Altec Lansing ALS-693 three-way ovals.
Each speaker has 4 terminals, 2x positive and 2x negative.
The positives are connected together, and the negatives as well.
I broke these connections so I can separately drive the cones and the double-tweeters.

Before breaking the connection the impedance was 4 ohm (DC resistance 3.x ohm). After breaking the connection the impedance of the cone was still 4 ohm.
However, the impedance of the tweeters measured 'infinite' (1) on the digital multimeter.

I had a look at the tweeter combo's (each speaker has a cone + 2 tweeters)
The tweeters seem to be connected in series with each other, and 2 capacitors in line at different locations. One tweeter has 3 connections instead of the usual 2 (+ and -).
With the multimeter I measured at some different locations and did find 3.x DC resistance at 2 locations for each tweeter combo. I can't remember exactly where I measured.


Anyway, when hooked up to 2 channels of my 4 channel Ref Picasso (the other 2 channels drive my Dynaudio front tweeters), the tweeters play without any problems and the passive crossovers (capacitors) are working perfectly.

HOWEVER, I am hearing a whistle from the Picasso. Not the speakers, but from the amp. Could it be that the tweeter-combo is presenting a 'strange' impedance ? Tomorrow I will disconnect the tweeter wires of the Altecs, see what the amp does. I am pretty sure the whistle was not there before, so I am pretty sure the now bi-amped ovals are causing this.

The cones are driven by an other amp, no problems there.
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Old 18th October 2011, 04:39 PM   #2
marko is offline marko  United Kingdom
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Quote:
However, the impedance of the tweeters measured 'infinite' (1) on the digital multimeter.
this is strange and could be giving the Picasso trouble..
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Old 18th October 2011, 05:15 PM   #3
azvrt is offline azvrt  Netherlands
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When measuring the positive and negative terminals (after breaking the connections) of the tweeter-combo's, they measured 'infinite', contrary to those of the cones, they measured 4 ohms.

Looking at the tweeters, I put the positive lead of the DMM on several locations, before and after the capacitors. I can't remember where I put the negative lead of
the DMM, but probably on the negative terminal. At 2 locations I measured 3.x resistance, which would indicate 4 ohms impedance, which would be good. But again, on the two terminals I measured 'infinite'.

However, if the impedance would indeed be infinitely huge, the tweeters would not be playing, would they ? But they are playing fine, and as loud as the 4 ohm Dynaudio tweeters or even a tiny bit louder. That should not be the case with a huge impedance, right ?

Which part of the amp is whistling ? I remember I read somewhere about whistling power supplies on amps, which was said to be a bad sign regarding the amp's condition. Anyway, I did not let the amp play for a long time as I didn't want to damage it, so hopefully I didn't. I wouldn't want to hurt any of my babies !

Tomorrow (it's late over here) I'll disconnect the Altec tweeters from the Picasso, see whether it still whistles. If it does, there's a problem with the amp, if it doesn't, the tweeters are causing the problem.

I soldered very thin (tweeter) wires to the tweeters, which I thought afterwards might be a bit stupid as contrary to the Dynaudio tweeters, which are at a 4 kHz high pass from the hu, for the Altec tweeters the 2 channels of the amp are fed a 80 Hz high pass from the active crossover, and the tweeters have their own passive high pass. So maybe the amp is trying to pump a 80 Hz high pas signal through these thin wires, could that be a problem ? Certainly it can't be the cause of the whistling, can it ?

What's annoying is that I haven't been able to find someone who owns the original manual of the ovals and is willing to scan it for me.
I have been looking for it for almost a year now, as I wanted to know what to expect and what to do before bi-amping these speakers.

Last edited by azvrt; 18th October 2011 at 05:18 PM.
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Old 18th October 2011, 05:29 PM   #4
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have you tried running the picasso on other drivers to rule out something like a loose torroid winding?
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Old 18th October 2011, 05:35 PM   #5
azvrt is offline azvrt  Netherlands
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Up till now the Picasso was driving 4 totally different drivers and I can't remember ever hearing a whistle.
But you are right, I will disconnect the Altec tweeter wires tomorrow, see what happens. But my guess is (since this is the first time I hear the Picasso whistling) that it's the Altecs causing the problem.
Who knows I am wrong and it's the BLT4 to which the Altecs are connected that is causing the problem. My car is stripped, and before reassembling it I wanted to make sure everything works. The BLT4's housing might be touching something metal, the way it's positioned at the moment. Though in that case, my sub amp should also whistle as it is connected to that same BLT. Plus if there was some kind of grounding issue, my guess is the speakers would produce noise, not the amp itself.

It's late over here in Europe so I'll have a look tomorrow.
Hopefully this won't keep me awake tonight
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Old 18th October 2011, 05:51 PM   #6
azvrt is offline azvrt  Netherlands
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My father is telling me the presence of the 2 capacitors for each tweeter-combo can be the cause of impedance on the + and - terminal reading 'infinite' on the DMM.
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Old 18th October 2011, 11:14 PM   #7
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The DMM doesn't measure impedance. It measures resistance. The capacitors will block the DC that the meter uses to determine the resistance in the circuit which will make the meter read infinity/open.
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Old 19th October 2011, 08:03 AM   #8
azvrt is offline azvrt  Netherlands
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Quote:
Originally Posted by Perry Babin View Post
The DMM doesn't measure impedance. It measures resistance.
I know, I just get the two mixed up

Thanks Perry for confirming the suspicions I had (and what my father was telling me) about the capacitors.

Anyway I'll try some other speakers on the Picasso today, see what happens.
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Old 19th October 2011, 12:23 PM   #9
azvrt is offline azvrt  Netherlands
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I performed many tests, but I'll mention only one since it explains everything.

After disconnecting everything (BLT signal wires, speaker wires) but the power wires, the amplifier still whistles. So basically, there's something wrong with the amp.

HELP
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Old 19th October 2011, 12:59 PM   #10
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If the noise is coming from the amp, it may simply be from loose windings on the transformer. Remove the cover and twist the transformer slightly to see if the noise stops.
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