Basic, Decent Stereo Audio for Netflix/DVDs

[Zig13]

Looking to replace my dying Aiwa XR-EM20 (90/00s HiFi minisystem) in it's function as layman-good PC speakers for my partner's PC when we watch Netflix/DVDs. Neither of us are audiophiles and we're not interested in surround-sound.
We've been perfectly happy with the sound quality of the XR-EM20 but it cuts out and the LCD display is stuck/dim.
Looking to spend sub-£100 on some kind of amplifier and ideally keep existing 6 Ohm speakers to be replaced/upgraded later. Don't really care about tape/CD/radio but would be nice to be able to add them on later.
Focus is on longevity/stability over sound quality.

Inspired by Techmoan's series on a Beginner Budget Hifi Build, I've been looking at 80s/90s Recievers and Cassievers on eBay. A KENWOOD AX-31 Cassiever at £50 has caught my eye but I've also seen a Technics SA-K2L as a even cheaper option at £20 although it has one fewer input. The problem is with such pre-internet products you can't exactly look at reviews :/ .

The plan would be to pair such an amplifier with an affordable DAC with 3 optical inputs connected to it's Aux. That way the amp/speakers can be connected to my partner's PC (and 30-inch Apple Cinema HD display) for DVDs/Netflix but also a Chromecast Audio and my PC for my music collection.
A priority would therefore be a lack of hum as the amp would be kept on 24/7 connected to the chromecast audio.

What do you think? Am I crazy? Is there a better way of achieving the same effect? Am I being a bit too stingy? What's the advantage of the expensive, branded DACs over the numerous cheap ones? Is it a really bad idea to use 6 Ohm speakers with an 8-16 Ohm rated amp - even in the short term?

Thanks!

 

[lucid]

The speaker impedance question depends on how loud you need the system to go, and in the quality of the amplifier, and whether the speakers themselves are an 'easy' or 'difficult' 6 Ohm load.

When a speaker is described as 6 or 8 Ohm, or any other impedance rating, what they're talking about is a nominal impedance, which you can think of in a similar way as an average. With speakers, the impedance goes up or down depending on the frequency of the sound and it is affected by something called Phase Angle. In a nutshell, if you were to feed an 8 Ohm speaker with a tone sweep from 20Hz to 20,000Hz, and measure the impedance in a continuous trace, you'd see the resulting Ohms figure vary from as little as 2-3 Ohms to as much as 20 Ohms or more. Fortunately, music tends to have a combination of tones, so some of the low Ohms load is balanced out by higher Ohms figures elsewhere. Hence, the averaged impedance if you will.

When the nominal impedance is lower, say 6 Ohms, then it means that the speakers can dip quite low or not go so high in impedance at certain frequencies. This has an implication for the amount of power being drawn from the amp. Lower impedance means more current is drawn, and current flow means heat. Put too much current through a wire and it'll glow then melt. Do the same with an output transistor and it will fry itself. This is what happens when an amp blows up.

The amount of current flow is dictated in part by the speaker impedance and how loud the system is being driven. That means you could have a fairly modest amp partnered with some 4 Ohm speakers, but never run it any louder than low level for quiet background music, and be perfectly safe. Someone else could have a more powerful amp with 8 Ohm speakers, but cane the daylights out of it and blow it up pretty quickly.

The bottom line is that 6 Ohm speakers could be run quite happily with an amp that can deliver a lot of current and still be safe to run at higher volumes. Amps that deliver a lot of current tend to be British Hi-Fi brands with toroidal (donut-shaped) transformers, or some of the better Japanese brands. These are the products where the spec sheet quotes a fairly modest wattage figure for 8 Ohms, but if you check the amp's maximum power consumption you'll find that it's quite high. There's a good example of this on Ebay right now. It's a Cambridge Audio A500 (Ebay item no# 264094808488). Depending on whether it's a v1 or v2 then the power rating is 50W- or 65W per channel. From the listing's pictures you can read the back panel power consumption as 400W. What they've done is measured the speaker power very conservatively (high ohms rating, both channels driven with full range audio, and sustained power, with a very low distortion figure) so there's a lot of power in reserve. That's what you want for lower Ohm speakers and good longevity.

Compare and contrast with a Technics SUV620 also on Ebay right now. This is rated at 2 x 70W/ch, but the power consumption figure on the rear panel is just 190W, so there's a lot less power in reserve to cope with more difficult loads.

 

[Zig13]

That's a very clear, detailed explanation thank you very much! I feel like I have learned things

The speaker impedance question depends on how loud you need the system to go

Neither my partner not I like things loud. When watching a film we have it just loud enough for dialogue to be clearly audible. Not that it really means much, but we usually settle on a volume of 21/29 on the Aiwa and it's rated at only 65W!

There's a good example of this on Ebay right now. It's a Cambridge Audio A500 (Ebay item no# 264094808488). Depending on whether it's a v1 or v2 then the power rating is 50W- or 65W per channel. From the listing's pictures you can read the back panel power consumption as 400W.

That's a real deal! Unfortunately it's collection-only which probably explains the lack of interest.

The Kenwood I saw is rated at 90W
The Technics I saw is rated at 120W

What are the British Hi-Fi brands to look out for? Obviously Cambridge Audio but who else?

 

[lucid]

Of the two you listed, the Kenwood is the better option. That said though, neither is a great choice to be honest.

When I look at these combo units, it takes me back to the start of my electronics career, all the way back to the late '80s. These were common in the entry-level home stereo systems in either full width of midi-system sized gear. Putting two or three components in a single box meant shared power supplies, fewer circuit boards - or even just a single one in some cases - fewer parts, fewer boxes to pack etc etc. It was all about cost saving.

I know that compared to your Aiwa, they'll both be a step up in power, but I think you can buy better for similar money to the Kenwood.

This is going to be used for controlling sound from the TV among other things, so I'm going to presume that having a remote control would be a sensible addition. Would that be accurate? For this reason then, and because of your budget, I think you're going to have to forgo the true British Hi-Fi amp route unless you drop very lucky on one of the ARCAM amps. Instead, focus on Cambridge Audio (A-series and Azure, but not Topaz), and the Japanese Hi-Fi brands of Marantz, Yamaha and Denon. Look at the for sale pictures. If you can spot amps where the main speaker outputs are rated 6~8 Ohm or better still 4~8 Ohm then you should be safe. If not, then search online for a user manual for anything that catches your eye. There are web sites that list manuals or spec sheets for amplifiers going back to the early '80s. Check the specs. You're looking for something where the speaker wattage is measured with both channels driven, RMS, @ 20Hz~20KHz, and with a low THD %...0.05 or better still, 0.01%. Oh, and stick to full width Hi-Fi products 420~440mm wide. Stay away from anything midi or mini sized unless you know exactly what to look for when checking out the specs.

Slightly more left-field choices are TEAC and Harman Kardon. This last in particular is an American brand with a good track record of building decent 2 channel Hi-Fi amps. It's just not a widely known brand in the UK, but they have been present here for at least 25 years. TEAC is another Japanese brand, but one with less consistency in its product line-ups. It has had some really outstanding gear, and then some rather run-of-the-mill equipment; so again, a bit of research in to any prospective models wouldn't go amiss.

Casting the net wider still, I'd strongly recommend some of the late '90s AV receivers from Yamaha. The DSP-AX620 was particularly good as a stereo amplifier as much as it was a really good 5.1 AV receiver. Other models to have a look at are the DSP-AX640 and 795, and the DSP-A5. All have multiple Optical inputs (2 or 3 typically), and they're equipped with very good DACs, so there's no need to buy any external switching boxes. Each can be configured to work in plain stereo, and so they'll take multichannel sound from a TV or TV recorder box (Freeview, Freesat, Sky, Virgin etc) and convert it down to simple stereo.