Basement Audio Setup - Impedance, Ohms, Help!

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rknuppel

Guest
I have a question about how this should be setup. I got a Technics receiver off of ebay the other day and it keeps overloading and shutting off on me. I think my ohms/impedance are all out of wack but it confuses the crap out of me. So i have a generic diagram below and would appreciate any feedback on how this should work better.

I'll explain my setup a bit.
8 OHM - 2 channel 100 Watt per channel - Technics Receiver.
4 50 watt impedence matching volume controls
8 total speakers (4 OHMs a piece)

Speaker A and Speaker B are connected to volume control 1 (which has a L and R input on it so 1 speaker is going into each of those).

Speaker C and Speaker D are connected to volume control 2 (which has a L and R input on it so 1 speaker is going into each of those).

Speaker E and Speaker F are connected to volume control 3 (which has a L and R input on it so 1 speaker is going into each of those).

Speaker G and Speaker H are connected to volume control 4 (which has a L and R input on it so 1 speaker is going into each of those).

All 4 volume controls have 2 18 guage speaker wires running back to my wiring closet. Now my biggest question is: How do I get this all into my amp and the correct impedance/ohm level? If I connect just one volume control in, I can turn the amp volume about half way up (which is super loud) before it shuts off and says OVERLOAD. If I connect another volume control to the amp, i can only go about a quarter of the way on the volume before it trips the amp up.

What am I doing wrong? I'm considering buying the AB8SS soon. Will that help anything? HELP PLEASE. I'm trying to get this all worked out before my drywall goes up this weekend :)
 

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Sniper

Active Member
Seems like you're setting up a multiroom audio system! Right?

Looks like your amp is not up to the task - and 8 4ohm speakers connected to a 2 channel amp is no easy task indeed! What's the Amp model no? I assume the idea is to be able to run all 8 speakers at a go, but the fact that with just one pair connected it's overloading is enogh to indicate that your amp's at fault!
 
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rknuppel

Guest
Thanks for the reply.

Yes, multiroom audio setup. 4 rooms with individual volume controls. Each volume control is connected to 2 4 OHM speakers (not 2 pairs, 1 speaker in the L and 1 speaker in the R).

I'm guessing my problem is happening at the point where my volume controls meet my amp. I want to connect all 4 of these volume controls into this amp yet keep the impedance at 8?

I'm new to all of this so please bare with me if my terminology is incorrect.
 

Sniper

Active Member
by any chance - are you using car speakers??

and anyway - if you connect 2 speakers directly to the amp & it cuts off 1/2 way, that's your indication that your amp & speakers don't like each other!
 

deaf cat

Active Member
Looks like the poor little amp is having big trouble.
Have you a couple of 8Ohm speakers to try?

My thoughts would be that the 4 Ohm speakers are pulling far more current than the poor amp can supply - hence the amp shuts down, as it is being worked too hard. Lucky it knows its working too hard and asks for a rest, rather than just blowing a fuse.
 
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rknuppel

Guest
Yes. In fact they are car speakers. Does that matter?

I thought the goal of Impedance matching volume controls were to bring everything back to the amp at the same impedance?
 
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rknuppel

Guest
deaf cat: thanks for the reply. Yes, at low volumes it seems to stay on.

I'm not sure how to find out how much current the speakers are pulling. I don't really have specs on these speakers. They are old Ford speakers that don't really have a label. Heck, now that I think about it, i'm not even sure how I know they are 4 ohms. I think i'm assuming that due to the fact that they are car speakers.
 

Sniper

Active Member
if they are car speaker there's a 99% chance they're 4ohmmers....

how are you connecting the 4 volume controls to the amp? are they all going to the same L&R speaker posts on the amp?

can we have some datasheet for these volume controls?

seems to me you have to anyway change something - speakers or amp!
 

GW43

Well-known Member
My limited understanding of this tells me that you need some high impedence speakers to make this work. Connecting speakers in parallel as you are doing means that the impedence is calculated by 1/R(total) = 1/R(speaker 1) + 1/R (speaker 2), so that running two 4 ohm speaker pairs in parallel means the amp "sees" a 2 ohm load. Not many amps are going to be happy with this. Connecting 3 pairs (1/R = 1/R1 +1/R2 + 1/R3 etc.) means you have a 1.3 ohm load, and 4 pairs gives a 1 ohms load. Not good! You need to find some 64 ohm speakers to be able to connect 4 pairs in parallel to have the amp see a 8 ohm load.

I don't know if these exist, or if you could put resistors on the speakers to increase their resistance.

Anyone, please feel free to correct what I've said above, as I'm wracking my brains to remember A-Level physics!
 

clockworks

Well-known Member
The data sheet seems to say that you can only connect 2 pairs of 4 ohm speakers to an 8 ohm amp.
 
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rknuppel

Guest
Is that per volume control unit though? And currently i only have 2 4 ohm speakers (not a pair, just one individual to L and 1 to R) connected to each Volume Control. I would think this would be ok for the volume control... But how to get all the volume controls at the right impedance with the amp is where i'm stuck.
 

clockworks

Well-known Member
One pair = one left + one right.

The controls seem to be designed to allow one stereo pair per control, and 2 controls per amp (with 4 ohm speakers, and an 8 ohm amp).
They appear to be very simple devices, just a couple of multi-tap transformers.

You could try connecting the units in series-parallel. Run a pair of wires from the amp's positive terminals to the + terminals on the first control. Run a pair of wires from the - terminals on the control to the + terminals on the second control, then from - terminals back to the amp's negative terminals.

Do the same again for the other 2 controls - amp to control 1 to control 2 to amp.

This should have the effect of making the impedence look similar to one control on it's own. It might have other nasty side-effects (increased inductance/capacitance), so keep the volume turned right down to start with, and switch off if the sound starts to distort.
 
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rknuppel

Guest
I think i understand what you are saying for the first two controls. But for the 2nd two controls, are you saying to use the receivers 2nd channel? Or somehow try to interconnect all of them onto one channel. Somehow I just have to get the impedance at 8 i think.

That was a very informative post. I will try it when I get home and let you know the results. Keep the suggestions coming if anyone has them.

Thanks
 

clockworks

Well-known Member
rknuppel said:
I think i understand what you are saying for the first two controls. But for the 2nd two controls, are you saying to use the receivers 2nd channel? Or somehow try to interconnect all of them onto one channel. Somehow I just have to get the impedance at 8 i think.

That was a very informative post. I will try it when I get home and let you know the results. Keep the suggestions coming if anyone has them.

Thanks

The second 2 controls are fitted in parallel with the first 2, using the same speaker terminals.
You would end up with 2 wires going to each of the 4 speaker terminals.

I'm going on the way resistors work. Two 8ohm resistances in series (like the first 2 controls) would give a total resistance of 16ohms.
Two 16ohm resistances in parallel (like adding the two pairs of controls to the same speaker terminals) will give a total resistance of 8 ohms.

In theory, 4 controls in series-parallel will appear to the amp to be the same as one control on it's own. It doesn't work exactly, because impedances aren't pure resistive loads.
 

Sniper

Active Member
clockworks said:
You could try connecting the units in series-parallel. Run a pair of wires from the amp's positive terminals to the + terminals on the first control. Run a pair of wires from the - terminals on the control to the + terminals on the second control, then from - terminals back to the amp's negative terminals.

i see what you're getting at... in could just work - but, as with anything in series, one volume control will also reduce the current to the other volume control!
 

clockworks

Well-known Member
Sniper said:
i see what you're getting at... in could just work - but, as with anything in series, one volume control will also reduce the current to the other volume control!

In this case, I don't think it will!

The controls appear to have a transformer for each channel, with the signal going through the primary. The secondary appears to be a multi-tap winding, with the "volume control" just selecting which tap to use. If I'm right, the amp will see the primary winding, the position of the volume knob won't make any difference.
I assume that this is how the controls achieve their impedance matching - the load on the secondary will have no real influence on the primary, and hence, the amp.

Of course, I could be wrong. The description of the control (link in earlier post) is a bit lacking in detail.
 

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