Stereo producing strange bass-tone "heartbeat" when connected to new speakers.

[Dragunov-21]

Hope I'm posting in the right section (as it looks pretty dead).

I have an old Yamaha AST-C10 stereo. I recently bought a pair of Wharfedale 9.1s, and hooked them up.

When I turn the stereo on, the speakers emit a couple of fast heartbeat-like bass tones, then emit them slowly while oscillating the woofer from one extreme of travel to the other at about 1Hz.

The original speakers (Yamaha AST-SC10) work fine, and the 9,1s have the required minimum impedance. (EDIT: Though the nominal impedance is listed as 6 ohms, the speakers themselves only measure 3.8 on a multimeter. Could this be related to the speakers being capable of being bi-wired?)

Is anyone able to point me in the right direction in diagnosing this?

Any help much appreciated.

 

[highfigh]

Hope I'm posting in the right section (as it looks pretty dead).

I have an old Yamaha AST-C10 stereo. I recently bought a pair of Wharfedale 9.1s, and hooked them up.

When I turn the stereo on, the speakers emit a couple of fast heartbeat-like bass tones, then emit them slowly while oscillating the woofer from one extreme of travel to the other at about 1Hz.

The original speakers (Yamaha AST-SC10) work fine, and the 9,1s have the required minimum impedance. (EDIT: Though the nominal impedance is listed as 6 ohms, the speakers themselves only measure 3.8 on a multimeter. Could this be related to the speakers being capable of being bi-wired?)

Is anyone able to point me in the right direction in diagnosing this?

Any help much appreciated.

Your amp may have some issues. Make sure it can handle low impedance loads before turning it on again. If not, these speakers won't be a good choice, but 3.8 Ohms also seems a bit low- have they been modified?

 

[markw]

Your amp may have some issues. Make sure it can handle low impedance loads before turning it on again. If not, these speakers won't be a good choice, but 3.8 Ohms also seems a bit low- have they been modified?

That 3.8 ohms is the speakers DC resistance which can be obtained from a simple meter reading. This is not the same as impedance.

impedance, also rated in ohms, is a different animal entirely. It takes into account crossover and driver interaction at different frequencies to come up with a "computed" number which, confusingly enough, is stated in ohms as well.

That 3.8 ohm resistance is not unusual for a speaker trated at 6 ohms impedance.

Not much is available on line on that amp. I'm thinking that the amp/speakers are part of an integrated system where the two are made to operate as one. Kinda like trying to use non-bose components to replace the original items in a bose "integrated" system.

 

[just-some-guy]

i would take the jumper out and they em. idk what that would do. but it may tell you something.

and i would for sure try them on another receiver. that will tell you something.

and i would take the drivers out to see if anything is amiss inside.

 

[Seth=L]

The speakers that come with that system don't operate at full range, and my guess is that those speakers were receiving that same signal (some type of noise from the amp) but you just didn't realize they were making any noise or moving because of physical limitations of the drivers.

 

[TLS Guy]

Hope I'm posting in the right section (as it looks pretty dead).

I have an old Yamaha AST-C10 stereo. I recently bought a pair of Wharfedale 9.1s, and hooked them up.

When I turn the stereo on, the speakers emit a couple of fast heartbeat-like bass tones, then emit them slowly while oscillating the woofer from one extreme of travel to the other at about 1Hz.

The original speakers (Yamaha AST-SC10) work fine, and the 9,1s have the required minimum impedance. (EDIT: Though the nominal impedance is listed as 6 ohms, the speakers themselves only measure 3.8 on a multimeter. Could this be related to the speakers being capable of being bi-wired?)

Is anyone able to point me in the right direction in diagnosing this?

Any help much appreciated.

Your old Yamaha unit is unstable into that load. Not uncommon for old speakers and cheap older gear. If you continue to operate it like that you may well damage the speakers.

You need more modern or good classy vintage amplification, for those speakers.

 

[Dragunov-21]

Thanks for the replies, guys.

I thought these speakers would be ok as they're rated at 6Ω (cheers for the clarification on impedance) and the AST-C10 requires says that the minimum required for connected is 6Ω.

That said, I guess it's an impedance issue after all, as when I connect the standard speakers in series with the new ones it works fine (but obviously sounds crappy). I can't understand why that's the case when it states 6Ω is ok.

Here's hoping I haven't managed to damage them >_>

In that case, anyone care to recommend a reasonable entry-level integrated CD/Amp source of some kind for someone tight on cash?

There are a few decent-looking ones at a second-hand store I was at the other day, but honestly I've got no idea what to look for as I'm new to the whole non-portable audio game.

 

[TLS Guy]

Thanks for the replies, guys.

I thought these speakers would be ok as they're rated at 6Ω (cheers for the clarification on impedance) and the AST-C10 requires says that the minimum required for connected is 6Ω.

That said, I guess it's an impedance issue after all, as when I connect the standard speakers in series with the new ones it works fine (but obviously sounds crappy). I can't understand why that's the case when it states 6Ω is ok.

Here's hoping I haven't managed to damage them >_>

In that case, anyone care to recommend a reasonable entry-level integrated CD/Amp source of some kind for someone tight on cash?

There are a few decent-looking ones at a second-hand store I was at the other day, but honestly I've got no idea what to look for as I'm new to the whole non-portable audio game.

You have run into an issue that confounds neophytes.

First the nominal impedance of a speaker specified by the manufacturer is virtually meaningless. The impedance is a curve varying with frequency. In addition an amp output is not DC but swinging above and below zero and therefore has to be regarded as AC. Now in AC circuits voltage and current do not flow in synch, and so speakers have a phase angle between them.

If the phase angle is positive then capacitative/reactive elements are dominant. If the phase angle is negative then inductive elements are dominant.

Large negative phase angles indicate larger current draws from the amp than would be calculated from the impedance curve by ohms law. That is why some (a lot) of speakers are a beast to drive.

Here is the impedance curve of your speakers.

Now the impedance varies all the way from 3.9 ohms to 16 ohms.

Of even more importance is that the phase angle in the deep bass is strongly positive (reactive) and it is this that is setting off the low frequency instability of your low priced amp.

Basically you are trying to drive decent Hi-Fi speakers with a boom box!

As you have found out, that will not work.

I don't know where you live, but there is a very nice complete Quad 33/FM3/303 set on eBay now. I bet bidders will get in the game, they always do. Although this unit is older, it is super reliable and will give years of excellent service most likely. If not there are plenty of individuals that service these. You won't have oscillation problems, as all Peter Walker's designs are guaranteed stable into all loads. The unit ships to Canada and the US. If you are in the UK Quad gear is easy to come by.

You can pick up a good CD player for next to nothing.

 

[just-some-guy]

while i don't know. i wouldn't doubt the amp in that little plastic box is clipping "trying" to drive real speakers.

 

[TLS Guy]

while i don't know. i wouldn't doubt the amp in that little plastic box is clipping "trying" to drive real speakers.

The problem is not clipping, but oscillation. Many amp designs are driven to oscillation by reactive loads. In this case it is the phase curve that is the crux of the matter in hand and not the impedance curve.

 

[Dragunov-21]

Ahk, that makes a lot more sense, cheers for the explanation.

I'm in Australia, so my options may be a little more limited and far-between.

Are 2nd-hand Sony/Yamaha amps <$400 new worth a look as a start? At the moment money for luxuries is pretty tight, and that's not gonna change anytime soon.

Obviously I don't want to waste money, but on the other hand, I can deal with something a bit more modest/limiting than I would have chosen had I realised I'd have to buy one at the outset.

 

[TLS Guy]

Ahk, that makes a lot more sense, cheers for the explanation.

I'm in Australia, so my options may be a little more limited and far-between.

Are 2nd-hand Sony/Yamaha amps <$400 new worth a look as a start? At the moment money for luxuries is pretty tight, and that's not gonna change anytime soon.

Obviously I don't want to waste money, but on the other hand, I can deal with something a bit more modest/limiting than I would have chosen had I realised I'd have to buy one at the outset.

Get something decent.

It's your lucky day.

http://cgi.ebay.com.au/Quad-33-Complete-revision-upgrade-service-/130275977175?pt=AU_Electronics_Audio_Amplifiers&hash=item1e550da7d7

http://cgi.ebay.com.au/Quad-303-complete-revision-upgrade-service-/130275975345?pt=AU_Electronics_Audio_Amplifiers&hash=item1e550da0b1

They look like nice units and you won't go wrong.

 

[highfigh]

Get something decent.

It's your lucky day.

http://cgi.ebay.com.au/Quad-33-Complete-revision-upgrade-service-/130275977175?pt=AU_Electronics_Audio_Amplifiers&hash=item1e550da7d7

http://cgi.ebay.com.au/Quad-303-complete-revision-upgrade-service-/130275975345?pt=AU_Electronics_Audio_Amplifiers&hash=item1e550da0b1

They look like nice units and you won't go wrong.

Unfortunately, the link for the 303 includes this- "This is a service for revising/upgrading your existing 303, NOT an amplifier for sale."

 

[TLS Guy]

Unfortunately, the link for the 303 includes this- "This is a service for revising/upgrading your existing 303, NOT an amplifier for sale."

Sorry, I missed that. However there are people in Australia who will fix it. Otherwise more will come up. There are lots in Australia.

 

[Dragunov-21]

I'll have to see what I can do about an amp...

As far as a source goes, are cd-players pretty much cd-players? Can I use RCA outputs from my DVD player until I get a dedicated source and have it sound reasonable?

 

[TLS Guy]

I'll have to see what I can do about an amp...

As far as a source goes, are cd-players pretty much cd-players? Can I use RCA outputs from my DVD player until I get a dedicated source and have it sound reasonable?

If you have a DVD player, you do not need a CD player as well. It will sound fine.

 

[TLS Guy]

I have had time to spend longer on the Australian eBay site. You have a lot of choices, well within your budget.

Try and buy classy older units. Avoid low end jink with CD player/amp/tuner.

There are a huge number of good older receivers from Marantz, Pioneer, TEAC etc.

There are some nice integrated units like this one, which would do you very well.

You should be able to get of trouble very inexpensively.

Here is a nice 33/303 that has one owner.

 

[Dragunov-21]

Cheers TLS. A couple of things.

- Your ebay-fu is a heck of a lot better than mine; I wasn't able to find either of those yesterday (mind you, I should have just trawled the audio/amps/power amps rather than using keywords)

- The 33/303 is local pick-up only, but I've inquired, thanks.

- I'll try to snipe the Rotel if it stays within my budget, and search for a few others, thanks again.

- I got a year-old Onkyo TX-SR574 last night for 150 bucks from a local classified ad. On the one hand it's impatient newb-itis, but on the other hand I've got a few mates waiting to get a home theatre reciever who I can onsell it to once I find the right stereo amp. In the mean time, it works great and will give me something to compare the "classier" amp to when I find it.