Connecting sub to older amp

[tyler711]

Hey everyone. I'm setting up a temporary system (24 hrs) with an old amp and some new speakers. The amp is an old, high end sony HT system, 100 watt per channel, 5 speaker output, A+B output, 4 or 8 ohm output, NO sub output.

I have a set of 100 watt speakers to hook up, those are new and work great. But I also want to hook up my sub, it is powered and has low level and high level inputs. I first tried hooking it up low-level to a MONITOR output on the amp, which worked, but made the sub ignore volume changes on the receiver (obviously).

I tried hooking it up to the amplified "B output" on the amp, which works except the amp has a sensor that only allows it to power both A and B speakers if there are speakers actually connected. The sub does not draw enough power to trigger this (almost enough, the other speakers play barely).

So what would be the best way to wire this up? Connect in parallel over the A speakers? I also have some smaller speakers that I can put on B to trigger the speaker sensor circuit, but then I'd have to wire in parallel over those?

Sorry about the novel, just trying to let you know what I'm trying to do.

Ty

 

[j_garcia]

Ignore the wattage spec of the speakers, it is almost irrelevant. What are the specs for these speakers? Does the sub have a high-pass speaker level output? If you have mains that go pretty low, you probably won't want to put the sub inline with the mains. If you have smaller bookshelf speakers that don't extend very low, then I'd connect them to the speaker level outputs and set the mains to large.

If you run the sub and mains in parallel off the A speaker output, you will have to set them to large which will send a full range signal to both the mains and sub, and that may not work well fpr the mains, depending on their frequency response.

 

[tyler711]

I'm not worried about sound quality as much as just the best way to hook this up. The speakers are cheap $100 a set sony's, bookshelf with tweeter, mid, and 8inch sub. They sound great at up to full volume on this amp.

This amp does not have large speaker/small speaker settings like my newer one does.

The sub has a "frequency" dial, that cuts off anything above x Hz. High pass filter I guess that is? There are no outputs on the sub, just RCA line-level in and speaker-type high level inputs.

Would it be bad to just connect the sub to the same terminals as the main speakers on the amp? Or could this hurt somethine - the sub is powered, so it does not draw much speaker power (I would assume).

 

[tyler711]

bump? bump?

 

[j_garcia]

The sub has a "frequency" dial, that cuts off anything above x Hz. High pass filter I guess that is? There are no outputs on the sub, just RCA line-level in and speaker-type high level inputs.

The dial adjusts what frequencies the sub gets. If there are no outputs, then you would just connect it to the main outs and adjsut the dial until it blends in with the main speakers.

Would it be bad to just connect the sub to the same terminals as the main speakers on the amp? Or could this hurt somethine - the sub is powered, so it does not draw much speaker power (I would assume).

Won't know until you try it. It may alter the impedance seen by the amp even though it isn't drawing much current, which may drive the amp harder. Based on what you said, I'd try that setup and see how it goes. As long as you are certain those are speaker inputs and not outputs, you should be OK.

 

[tyler711]

Yep, I'm sure those are inputs on the sub, marked "HIGH LEVEL INPUT". I just don't want to hurt the amp. Would it be better to double-connect the sub with a smaller set of speakers on the amp's other outputs?

 

[Pyrrho]

I'm not worried about sound quality as much as just the best way to hook this up. The speakers are cheap $100 a set sony's, bookshelf with tweeter, mid, and 8inch sub. They sound great at up to full volume on this amp.

This amp does not have large speaker/small speaker settings like my newer one does.

The sub has a "frequency" dial, that cuts off anything above x Hz. High pass filter I guess that is? There are no outputs on the sub, just RCA line-level in and speaker-type high level inputs.

Would it be bad to just connect the sub to the same terminals as the main speakers on the amp? Or could this hurt somethine - the sub is powered, so it does not draw much speaker power (I would assume).

It should be fine to connect both the subwoofer and the speakers to the same outputs of the receiver.

The reason it should work well is simple: The powered subwoofer, as it uses a line level input, reduces the speaker level signal with resistors, such that it draws very little current from your amplifier. It probably is presenting your receiver with a load in the neighborhood of 50,000 ohms. Hooking 50,000 ohms in parallel with your normal 8-ohm speakers (or 4-ohm, 6-ohm, 16-ohm or any other common impedance speaker) will make practically no difference to your receiver (though, strictly speaking, it does reduce the impedance ever so slightly).

 

[tyler711]

It should be fine to connect both the subwoofer and the speakers to the same outputs of the receiver.

The reason it should work well is simple: The powered subwoofer, as it uses a line level input, reduces the speaker level signal with resistors, such that it draws very little current from your amplifier. It probably is presenting your receiver with a load in the neighborhood of 50,000 ohms. Hooking 50,000 ohms in parallel with your normal 8-ohm speakers (or 4-ohm, 6-ohm, 16-ohm or any other common impedance speaker) will make practically no difference to your receiver (though, strictly speaking, it does reduce the impedance ever so slightly).

Thanks, that's what I wanted to hear. It made sense in my mind, but just wanted someone who knows more than me to agree.

 

[Pyrrho]

Thanks, that's what I wanted to hear. It made sense in my mind, but just wanted someone who knows more than me to agree.

You are welcome.

From rereading your first post, it seems likely that that Sony hooks up the A and B speakers in series rather than parallel:

I tried hooking it up to the amplified "B output" on the amp, which works except the amp has a sensor that only allows it to power both A and B speakers if there are speakers actually connected. The sub does not draw enough power to trigger this (almost enough, the other speakers play barely).

If the receiver hooks up the A and B speakers in series, then that would explain why the main speakers only played barely, as you would effectively be putting a very large resister in series with the speakers. You may wish to check the owner's manual, which might be available to look at on Sony's web site if you don't have the original.

 

[tyler711]

About the A and B outputs on the Sony: they seem to be independent. My problem was that this amp includes a circuit that makes the A+B setting only play if there are in fact speakers connected to both the A AND B outputs. I assume it does this by sensing the load of the speakers. My dad says this is to avoid damage if you accidentally leave it on A+B without B speakers attached.

So when you put speakers on just A, and turn it to A+B, it plays no sound. If you connect two sets of speakers, A+B mode plays both. So I had normal speakers on A and the sub on B. This made audio barely play over the A speakers and the sub.

I think that the sub uses such little power (it is amplified) that it was just barely kicking over this safety circuit.

 

[Pyrrho]

About the A and B outputs on the Sony: they seem to be independent. My problem was that this amp includes a circuit that makes the A+B setting only play if there are in fact speakers connected to both the A AND B outputs. I assume it does this by sensing the load of the speakers. My dad says this is to avoid damage if you accidentally leave it on A+B without B speakers attached.

So when you put speakers on just A, and turn it to A+B, it plays no sound. If you connect two sets of speakers, A+B mode plays both. So I had normal speakers on A and the sub on B. This made audio barely play over the A speakers and the sub.

I think that the sub uses such little power (it is amplified) that it was just barely kicking over this safety circuit.

If the receiver has the A and B speaker connections wired in series, if you don't have a speaker hooked up to one of them, and you select A+B, you will hear nothing, because the circuit will be open (it would be the same as not bothering to connect one of the two wires going to a speaker). Some receivers are designed this way to prevent damage from hooking up too low of an impedance to the output amplifier. Most receivers hook up the A and B speakers in parallel, which presents a lower impedance load to the amplifier than either speaker. If, for example, you were to hook up two 4-ohm speakers to a receiver that hooks them up in parallel, the amplifier would be presented with a 2-ohm load, but if you hooked them up to a receiver that has them in series, the amplifier would be presented with an 8-ohm load. As lower impedances are more difficult for amplifiers than higher impedances, having them in series protects the amplifier.

 

[tyler711]

Thanks you guys. I noticed the amp has a 4ohm/8ohm switch on the back as well. But I'm just gonna hook up the sub in parallel with the main or B (smaller) speakers.

 

[tyler711]

This setup is for a party, so it's all about volume (but I refuse to use anything that I don't already have in the house). Everything sounds good, but I think it can be better.

The sony amp is a STR-d1015, which after some research, seems to have been pretty good back in its heyday.

But in my cheesy HT I have a Philips FR-996. Now the music is coming from my computer, so it is really about medium-quality.

With the philips I would have the benefit of a coax digital input, a dedicated sub output, and newer technology. I know that wattage is not a good comparison, but the sony is 220 where the philips is 500. I could not find the per-channel rating of the Sony.

Would I experience any better sound quality using the Philips amp? I am going to try it tomorrow and see how it sounds. The sony sounds pretty good, but I can tell that the speakers are just on the edge of total distortion.

tyler