Speakers A+B of stereo amp is only a trick? - Page 1
Forum section: electronics / repair

author: max.wwwang
author_rank: Frequent Contributor
timestamp: September 27, 2020, 05:55:52 am
content: Recently repaired a SONY TA-FB740 Music amp. My attention was brought to the circuitry for the widely seen Speakers A/B arrangement. With this, as far as I understand, you can connect to your speakers using bi-wiring, if your speakers also support.Previously I thought this must be done by two sets of amp module in the unit. But in this case, it seems like it's only splitting one amp into 2 sets of bind posts!Any thoughts?

author: james_s
author_rank: Super Contributor
timestamp: September 27, 2020, 05:59:02 am
content: You are misunderstanding what this feature is for. The purpose is to connect two separate sets of speakers to the same amplifier. For example maybe you have one set of speakers in the livingroom and second set of speakers outside on the patio. The A/B function lets you select which speakers the amplifier is driving, usually it will allow you to enable both at once provided the impedance is not too low.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: September 27, 2020, 06:20:33 am
content: Quote from: james_s on September 27, 2020, 05:59:02 amOk. That makes sense and seems I only misunderstood this feature.So, for a set of speakers with two sets of input (Hi/Low frequency), connecting them to this amp with bi-wiring is no different from single-wiring (with Hi/low bridged as is the default configuration) except, perhaps, lower impedance of the wires (because of using two pairs rather than one pair for each of L or R channel)?

author: shakalnokturn
author_rank: Super Contributor
timestamp: September 27, 2020, 04:20:39 pm
content: True there's not much benefit here other than lowering wire impedance if you think that's worth the trouble.As a side note on minding the total speaker impedance:Most amplifiers parallel speakers when on A&B position but I have come across a couple of exceptions that would put them in series.

author: SpecialK
author_rank: Regular Contributor
timestamp: September 27, 2020, 05:41:47 pm
content: My understanding:A/B speakers just select which set of speakers are connected to a stereo amp's single L & R outputsBi-wired speakers are to be driven by two stereo amplifiers. Ideally you can trim each amplifier to control how much power to tweeter vs woofer. You'd need a special pre-amp with two sets of outputs I suppose.I was always weird to me that car amplifiers had 4 channels and you could fade front/rear but home gear would drive four speakers without being able to fade. I alway thought I should have a speaker in each corner.

author: james_s
author_rank: Super Contributor
timestamp: September 27, 2020, 06:17:27 pm
content: Quote from: SpecialK on September 27, 2020, 05:41:47 pmIn a car you have passengers in the front and in the back and the volume requirement varies considerably depending on the car and operating conditions. In home hi-fi there was for a while quadraphonic setups that used four speakers with one in each corner but it never achieved much popularity. The two sets of speakers thing is rarely used, but I have seen it done occasionally to have a set of speakers in another room, or more often outside on a patio or in the garden. Fading could be useful in situations where you want to run both sets of speakers at once, however that would add a lot of cost for a rarely used feature that is easily implemented by having a second amplifier.

author: fordem
author_rank: Regular Contributor
timestamp: September 27, 2020, 08:28:55 pm
content: Perhaps the term bi-wired is misleading and should be avoided.I'm accustomed to bi-amped & tri-amped - bi amped would have two separate power amps for high & low frequencies, tri amped would three power amps, typically high, mid and sub woofer.The signal from the preamplifier is fed to a low level crossover and the cross-over outputs fed to the power amps and separate speaker systems - this type of installation would normally be considered "high end audiophile" and rarely found in consumer/grade residential systems where the cross over comes after the power amps.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: September 28, 2020, 12:00:05 am
content: Quote from: fordem on September 27, 2020, 08:28:55 pmI agree (I dare say in the hifi area there might me a good deal misinformation or misconceptions) although I'm not very sure if there are models with similar A/B sets of binding posts and indeed they are driven by separate amp modules.I now had a bit feeling of disillusionment about the idea of bi-wiring, especially because when I recently got some gear set up I diligently applied this in the hope of getting even a tiny bit of improvement of the outcome (my mindset was why not, with all the existing gear and without too much extra cost). I probably wouldn't have done so if I had known I was only tricked.

author: bdunham7
author_rank: Super Contributor
timestamp: September 28, 2020, 12:33:44 am
content: Quote from: max.wwwang on September 28, 2020, 12:00:05 amThere are. Some modern multichannel AVRs will have the option of using two pairs of channels as A/B or as 'passive bi-amping' for speakers that have internal crossovers in sections that can be connected to separately. Often all of the amplifier modules are fed from the same power supply, so the value of such a setup is questionable.