Power Amp with Pre Amp...Speaker Selector Knob Bypassed?

[abieleck]

I have a NAD 7020 and a pair of JBL 110's that I thought could use more power so tied in a NAD C270 power amp (to the speaker A terminals on the C270). I used the 'variable in' on the C270 as there is an input level adjustment knob on the back and I wanted a little more play in my 7020 volume knob. It sounds great with the extra juice, but now the speaker selector knob on the 7020 seems to be getting bypassed. All the other knobs work (volume, balance, bass treble ect) but toggling the speaker knob doesn't do anything.....speakers play regardless. I am looking to set up some smaller speakers for the "B" terminals so would like the ability to switch back and forth between 'A' and 'B'

My question......Anyone know why the 7020 preamp speaker selector knob is getting bypassed? It did function just fine when the speakers were hooked directly up to the 7020. This is my first power/pre amp set up so maybe it's par for the course, but that would seem odd to me. Any thoughts/help would be much appreciated. Thanks!

 

[Akustic]

How did you tie this power amp in to the speaker a terminals of the 7020 ??
Does the c270 have high input terminals .. ??

 

[Akustic]

From the picture I'm looking at the C270 doesn't have a high level input and shouldn't anyway ..
If you connected to the 270 from the pre out of the 7020 .. the signal isn't present on the speaker outputs of the 7020..
You could use the a/b switch on the 270 to switch the speakers .. but you would have to connect both pairs to the 270 ..

 

[abieleck]

How did you tie this power amp in to the speaker a terminals of the 7020 ??
Does the c270 have high input terminals .. ??

Thanks for the reply Akustic. I connected the NAD 7020 from the 'Pre Amp Out' to the Power Amp (C270) 'Variable In' using an RCA. I then connected the speakers directly to the C270's speaker 'A' terminals using speaker wire direct from the JBL's.

There isn't any speaker wire connected directly to the 7020, but I guess I just thought the 7020 speaker select knob would still control what speakers are in use even if they are connected to the C270.

There isn't a speaker A/B select switch/knob on the C270 power amp. Could I run the larger JBL's through the C270 and connect my small bookshelf speakers directly to the 7020...... then use the 7020 without the C70 engaged? Or would the pre out connect preclude that?

Like I said, new to the power amp set up, so don't really want to just start trying different things and mess something up.

 

[coonmanx]

Thanks for the reply Akustic. I connected the NAD 7020 from the 'Pre Amp Out' to the Power Amp (C270) 'Variable In' using an RCA. I then connected the speakers directly to the C270's speaker 'A' terminals using speaker wire direct from the JBL's.

There isn't any speaker wire connected directly to the 7020, but I guess I just thought the 7020 speaker select knob would still control what speakers are in use even if they are connected to the C270.

There isn't a speaker A/B select switch/knob on the C270 power amp. Could I run the larger JBL's through the C270 and connect my small bookshelf speakers directly to the 7020...... then use the 7020 without the C70 engaged? Or would the pre out connect preclude that?

Like I said, new to the power amp set up, so don't really want to just start trying different things and mess something up.

The only way that works would be if you got a Y-cable and looped half of it back to the 7020 with the other one going to the C270. Otherwise you could just get a speaker selector switch and connect it to the C270 and use it that way. So it depends on what you want to do...

 

[rothwellaudio]

There isn't any speaker wire connected directly to the 7020, but I guess I just thought the 7020 speaker select knob would still control what speakers are in use even if they are connected to the C270.

And how would that work? The speaker selector knob selects which speaker terminals on the 7020 are in use, but you have nothing connected to them.

 

[Akustic]

Get the y cable that Coonmax suggested ..
If the 270 is off you will only hear the 7020 ..
Choosing spkr b on the 7020 will turn off the speakers connected to spkr a ..

Not one switch but it will work and y-cables are cheap ..
Speaker switches deteriorate the signal .. better to do it with the RCA's..

 

[whoaru99]

Y cables of this style (2M --> 1M) would be fine to simultaneously accomplish the pre out loop back and feed signal to the separate power amp.

 

[Rdenney]

Speaker selector switches work at the power-amp level, downstream from the preamp output. When you removed the u-shaped plugs between the "Pre Amp Out" and the "Normal In", you abandoned the internal power amp and its associated speaker switches. You are tapping out of your 7020 (which is a "receiver" that includes a tuner, a preamp, and a power amp) between its internal preamp and power amp. Thus, the speaker controls on the 7020 receiver are no longer relevant--they apply only to the power amp that you are no longer using.

Three options for driving two pairs of speakers using an external power amplifier:

1. Use Y cables in the "Pre Amp Out" to route the preamp output of your receiver to two separate amps to drive two separate pairs of speakers. Then, you switch each pair on and off separately by simply turning those amps on if you want that pair of speakers and off if you don't.

2. The 7020 does offer a way to feed the amplifier from a separate preamp, it seems, so you can use one side of that Y cable that is plugged into the preamp outputs to plug back into the "Normal In" inputs, in which case you will also be using the 7020's internal power amplifier only for the second pair of speakers. Then, use the 7020's speaker selector switch to turn the speakers connected to the 7020 on and off, and the power switch on your external amplifier to turn the high-power speakers on and off.

3. There are power amplifiers (though very few) that provide A and B speaker outputs. An example is the Adcom GFA-535. But it's not a common feature at all.

A picture helps we explainers:

(from Classicreceivers.com)

Rick "the key is understanding that speaker selector switches work at the power amplifier outputs, downstream from the preamp outputs that feed a separate amplifier" Denney

 

[abieleck]

And how would that work? The speaker selector knob selects which speaker terminals on the 7020 are in use, but you have nothing connected to them.

Apparently it doesn't I was thinking that the speaker selector knob may be tied in and work along with the rest of the pre amp functions, especially since all of the power amps I have seen that have A/B speaker connections don't have their own selection knob.

2. The 7020 does offer a way to feed the amplifier from a separate preamp, it seems, so you can use one side of that Y cable that is plugged into the preamp outputs to plug back into the "Normal In" inputs, in which case you will also be using the 7020's internal power amplifier only for the second pair of speakers. Then, use the 7020's speaker selector switch to turn the speakers connected to the 7020 on and off, and the power switch on your external amplifier to turn the high-power speakers on and off.

This seems like the best set up for me, Denney. So do I have this correct?........I need two all male 'Y' cables. I will hook up the double ends to the 'Power Amp Out' and 'Normal In' for both the Left and Right channels on the 7020 preamp. The two single male ends head to the corresponding left/right channels on the power amp? That will re-engage the power supply of the 7020 and when the power amp is off, I can play off the 7020 power/speaker hookups (A or B) using the speaker selector switch?

 

[Rdenney]

The stem of the Y plugs into the preamp output on the 7020. One leg then plugs into the Normal In, and the other leg goes to your power amp. Use a f-f “barrel connector” to connect the male plugs on the Y adapter and the interconnects to the power amp. Repeat for the other channel.

The feed to the Normal In will provide an input to the 7020’s internal power amp, and you can use its speaker outputs as usual. Do the speaker selector switches include an ”off” option? If not, just hook up one pair in A and use B to turn them off. The speakers wired to the external power amp are switched on and off using the power switch on the power amp.

Rick “going on what I see in the pic” Denney

 

[abieleck]

The stem of the Y plugs into the preamp output on the 7020. One leg then plugs into the Normal In, and the other leg goes to your power amp. Use a f-f “barrel connector” to connect the male plugs on the Y adapter and the interconnects to the power amp. Repeat for the other channel.

The feed to the Normal In will provide an input to the 7020’s internal power amp, and you can use its speaker outputs as usual. Do the speaker selector switches include an ”off” option? If not, just hook up one pair in A and use B to turn them off. The speakers wired to the external power amp are switched on and off using the power switch on the power amp.

Rick “going on what I see in the pic” Denney

The speaker select knob does have a ‘off’ so that would work nicely. Then just flip on the power amp for the larger speakers

That hook up makes sense, thanks for spelling it out for me. Last question(s), I think.....the function of the female/female barrel connectors from the power amp legs of the Y connector to the power amp itself....use those just because the Y connectors won’t reach the power amp? Can use same standard RCA’s as I was before to connect the two female barrel connectors to the power amp? No harm mixing and matching different RCA’s I assume.

 

[Rdenney]

No, that's fine. Any decent RCA cable can be connected to any other decent RCA cable. I have used female-female barrel connectors many times to connect two RCA cables together. But, yes, the reason you need it is because the Y adapter won't reach all the way to the amp.

The world of high-end interconnects is a dark and dangerous place, and if there is a difference, it takes equipment well beyond what either one of us owns to reveal it. Just use any decent RCA cable, including whatever you were already using to go to the amp.

Rick "who keeps RCA gender-benders lying around for just these sorts of needs" Denney

 

[whoaru99]

... So do I have this correct?........I need two all male 'Y' cables. I will hook up the double ends to the 'Power Amp Out' and 'Normal In' for both the Left and Right channels on the 7020 preamp. The two single male ends head to the corresponding left/right channels on the power amp? That will re-engage the power supply of the 7020 and when the power amp is off, I can play off the 7020 power/speaker hookups (A or B) using the speaker selector switch?

There are a number of ways to skin the cat.

But, yes, Y cables of the 2M > 1M nature shown in post #8 are the easiest/cleanest approach.

The short legs provide the pre amp out to normal in jumpers, and the long legs to the external amp. No need for additional couplers/adapters that way.

Then, yes, the external amp will work, as will the A/B switch on the receiver for speakers connected to the receiver.

 

[Rdenney]

The Y adaptor in Post 8 are how long? And what brand? I don’t even see the whole product in the picture—I’m missing something. In my own setup, a typical Y adaptor that is a few inches or maybe a foot long on each leg wouldn’t get within two feet of the power amp. Without specifics, I was assuming the leg length for that run would need to be extended.

Rick “rather be too long than too short” Denney

 

[whoaru99]

Those particular ones come in 3ft or 6ft length. They are Monoprice Onyx Series. But, not endorsing any particular brand. Choose brand as each sees fit and I presume one understands their length requirements.

The picture is provided simply as an example of the general style/type of Y cable being 2 male to 1 male.

 

[spark1]

Apparently it doesn't I was thinking that the speaker selector knob may be tied in and work along with the rest of the pre amp functions, especially since all of the power amps I have seen that have A/B speaker connections don't have their own selection knob.

Interesting. Every power amp with A/B connections Ive ever seen has the ability to switch them on and off.

 

[Rdenney]

Interesting. Every power amp with A/B connections Ive ever seen has the ability to switch them on and off.

Yes, I was also confused by the C270’s two speaker connections and no switch. My Adcom’s two speaker connections are switched.

Rick “wondering at the use case” Denney

 

[Rdenney]

Those particular ones come in 3ft or 6ft length. They are Monoprice Onyx Series. But, not endorsing any particular brand. Choose brand as each sees fit and I presume one understands their length requirements.

The picture is provided simply as an example of the general style/type of Y cable being 2 male to 1 male.

I didn’t realize they were of usable length by themselves. Good to know.

Rick “might grab a couple just to have them around” Denney

 

[abieleck]

Those particular ones come in 3ft or 6ft length. They are Monoprice Onyx Series. But, not endorsing any particular brand. Choose brand as each sees fit and I presume one understands their length requirements.

The picture is provided simply as an example of the general style/type of Y cable being 2 male to 1 male.

Thanks for sending these connectors along, going to put a couple on order and look forward to setting them up.

Thanks all for clearing this up for me, info is much appreciated.