Technics SU-CH7 - How can I use a normal speaker with this amplifier? It has 4 connections for each speaker (separated High & Low frequencies)

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circ8tz

Joined Sep 8, 2022
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Amplifier: Technics/Panasonic SU-CH7

This amplifier belongs to an Hi-Fi Audio system (SC-CH7) that originally comes with speakers (speakers with separate highs and lows too, 4 connections in each speaker).
It also needed the Tuner unit (ST-CH7L) in order to turn the amplifier on but I was able to bypass that by using a jumper to connect 2 points inside the amplifier. (there's a post in this forum explaining how to do it).

Now I have a problem, this amplifier has 4 connections for each speaker, having separated High and Low frequencies for each speaker. I don't own the original speakers which seem to have been specially designed for this amplifier.

How can I use a normal speaker on this amplifier without loosing frequencies?

I was trying to understand how it separates the frequencies by looking at it's circuit in the Service Manual but I really don't have the knowledge to interpret and understand it correctly. (image of the circuit attached)
 

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Ian0

Joined Aug 7, 2020
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If your speakers are similar to the originals, mainly if they have a similar treble units, then just remove the crossover, and connect the bass and treble units directly to the amplifier.
First, make sure that the amplifier does have electronic crossovers built in - it probably does, but make sure!
 

crutschow

Joined Mar 14, 2008
33,962
How can I use a normal speaker on this amplifier without loosing frequencies?
It's called a biamp system where the woofer and tweeter have separate amplifiers.
It's generally considered superior to using a single amp with a crossover circuit for the woofer and tweeter.

If you have a speaker with a woofer and and a tweeter, you could try separating the internal speaker connections and connect them separately to the amps.
You would disconnect any crossover circuits inside the speakers to do that.

From the schematic it looks like you need to keep the connections to the two speakers completely isolated (no common connection between the speakers).

There are also some speakers available (such as from Klipsch and Polk) that come with 4 terminals for biamp operation.
 

BobTPH

Joined Jun 5, 2013
8,642
The problem with using this with anything but the original speakers is that the sound would not be balanced unless the crossover frequency used by the amp was appropriate for the new soeakers.
 

Ian0

Joined Aug 7, 2020
9,428
There would be a good amount of tolerance in crossover frequency, provided that it was not too low for the new tweeter.
However, the relative sensitivities between bass and treble may be different
 

MisterBill2

Joined Jan 23, 2018
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I examined the posted circuit schematic and what I see is separate amplifiers for the "High" and "low" outputs. So those connections do need to be kept separate.
BUT the earphone (headset) outputs seem to combine both outputs, and so you can try connecting a single speaker for each channel at the headphones connector.
You can also try connecting the high and low outputs directly to a normal "hifi" speaker system, after disconnecting the internal crossover assembly. That will have the low frequency output to the "woofer" and the high range output to the "tweeter".
That should provide a fair approximation of the original performance of the system.
 

BobTPH

Joined Jun 5, 2013
8,642
You can also try connecting the high and low outputs directly to a normal "hifi" speaker system, after disconnecting the internal crossover assembly
I presume you mean disconnecting crossover inside the the speaker then connecting the high and low outputs to the tweeter and woofer respectively. I initially read this as connecting the two outputs together. Which would not be good.
 

Audioguru again

Joined Oct 21, 2019
6,604
You must NEVER connect different-frequency or different-level amplifier outputs together!
I examined the posted circuit schematic and what I see is separate amplifiers for the "High" and "low" outputs. So those connections do need to be kept separate.
BUT the earphone (headset) outputs seem to combine both outputs, and so you can try connecting a single speaker for each channel at the headphones connector.
You can also try connecting the high and low outputs directly to a normal "hifi" speaker system, after disconnecting the internal crossover assembly. That will have the low frequency output to the "woofer" and the high range output to the "tweeter".
That should provide a fair approximation of the original performance of the system.
The headset output is severely attenuated so that you do not blow off your ears.
 

Thread Starter

circ8tz

Joined Sep 8, 2022
6
I examined the posted circuit schematic and what I see is separate amplifiers for the "High" and "low" outputs. So those connections do need to be kept separate.
BUT the earphone (headset) outputs seem to combine both outputs, and so you can try connecting a single speaker for each channel at the headphones connector.
You can also try connecting the high and low outputs directly to a normal "hifi" speaker system, after disconnecting the internal crossover assembly. That will have the low frequency output to the "woofer" and the high range output to the "tweeter".
That should provide a fair approximation of the original performance of the system.
And the headset output is quite powerful I must say, I'm loving using my headset with it. However, how do I know how many watts it outputs and if it would be enough to power a speaker?
 

Thread Starter

circ8tz

Joined Sep 8, 2022
6
I found this information, is it relevant for the frequencies?
It also shows Headset output level/impedance, Is there anyway to know how many watts the Headphone outputs from this information?

Thanks everyone for all the responses, I really appreciate it!
 

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MrChips

Joined Oct 2, 2009
30,415
Headphone output is never intended to drive loudspeakers.
Headphones require about 100-500mW.

For quiet listening, loudspeakers need more than 500mW of power.
Equally as important, the impedance of headphones and loudspeakers are often very different.
 

Audioguru again

Joined Oct 21, 2019
6,604
The headphones spec has an error. 300mV into 330 ohms is only 2.7 thousandths of a Watt, less than a whisper.
Most headphones are 32 ohms and 0.1W in one is VERY loud. Then 1.8VRMS in a 32 ohms headphone produces 0.101W.
 

MisterBill2

Joined Jan 23, 2018
17,723
Note that the high frequency amp is only 5 watts,while the other amplifier is 25 watts. (post #11) so the adjustment has already been made.
AND I did say: "try connecting the high and low outputs directly to a normal "hifi" speaker system, after disconnecting the internal crossover assembly." back in post #10. So the tweeter gets much less power, no attenuater required.
 

Thread Starter

circ8tz

Joined Sep 8, 2022
6
If your speakers are similar to the originals, mainly if they have a similar treble units, then just remove the crossover, and connect the bass and treble units directly to the amplifier.
First, make sure that the amplifier does have electronic crossovers built in - it probably does, but make sure!
How do I check if the amplifier has built in eletronic crossovers?
Thanks for the help!
 

Thread Starter

circ8tz

Joined Sep 8, 2022
6
How do I check if the amplifier has built in eletronic crossovers?
Thanks for the help!
Also, to remove the speaker's crossover, do I just remove the capacitors inside the speaker and make a new connection directly from the tweeter with just wires?
 

crutschow

Joined Mar 14, 2008
33,962
How do I check if the amplifier has built in eletronic crossovers?
I likely does since it's a cheaper to do the crossover with the low-level audio signal. where small, low-power devices can be used, as opposed to doing it in the speaker's high level signal where large, high-power components are used.
Also the crossover characteristics can be made more ideal at the low-level where there's constant impedances, as compared to speakers which have variable impedances with frequency.
 

crutschow

Joined Mar 14, 2008
33,962
Also, to remove the speaker's crossover, do I just remove the capacitors inside the speaker and make a new connection directly from the tweeter with just wires?
Yes.
You also want to remove the likely inductor or other circuitry that goes to the woofer.

Check the speaker polarity connections, so you can match the amplifier polarities to that.
Note that in some cases the tweeter polarity is connected opposite to the woofer polarity.
 
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