Speaker - terminal connected to the AC line?
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From: David Nebenzahl on 25 May 2010 21:49 On 5/25/2010 4:39 PM Paul G. spake thus: > That's funny.... when I was visiting my daughter in Ottawa, I > spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed > a Techics (!) "new class A" amp, and a Technics CD player, and > stuffed them in the trunk of the car for the 1200 mile return trip. Hey, my current amp is one a'them Technics "new class A"s, a SU-V6X. What's yours? Got mine really cheap years ago at a Starvation Army store. -- The fashion in killing has an insouciant, flirty style this spring, with the flaunting of well-defined muscle, wrapped in flags. - Comment from an article on Antiwar.com (http://antiwar.com)
From: Paul G. on 25 May 2010 23:29 On Tue, 25 May 2010 18:49:19 -0700, David Nebenzahl <nobody(a)but.us.chickens> wrote: >On 5/25/2010 4:39 PM Paul G. spake thus: > >> That's funny.... when I was visiting my daughter in Ottawa, I >> spotted a bunch of stereo stuff piled up for garbage pickup. I grabbed >> a Techics (!) "new class A" amp, and a Technics CD player, and >> stuffed them in the trunk of the car for the 1200 mile return trip. > >Hey, my current amp is one a'them Technics "new class A"s, a SU-V6X. >What's yours? Got mine really cheap years ago at a Starvation Army store. Mine's a SU-V7B. I imagine there's not a lot of difference... I used the schematics for SU-V98 to change some of the circuitry. That was the only close schematic I could find on the internet. It wasn't quite the same, but the reference designators (like R520, C123) were good enough to locate things. The original fan was irritatingly loud... I can't imagine how anyone could put up with it. It uses a hybrid module to drive the output, and I imagine only much earlier models would use discrete transistors. I found it to be a surprisingly powerful amp for class A, but their "new Clas A" just slides the biasing up and down so that at low power it's still class A but biased low enough to stay cool. There is an art to doing that, and keeping the system well behaved and linear. I imagine there could be problems if the amp is biased for quiet music, and a sudden loud passage comes along that requires fast changing the operating point. There are probably a good number of patents that relate to that bias circuitry. I've had no complaints about it, except for having to replace the on-off switch (a low power switch that controls a relay which switches the AC line). Because of the weird shape of the switch, and it being alternate action, I had to jury-rig a small toggle switch with an extension on its handle. I used ductape to channel the air flow over the heatsink, to improve the cooling. Running full output, the heatsink doesn't get overly hot, and the exhaust air is quite warm. The fan I used was a 12v small quiet fan, similiar to those used on smaller CPU's. Typical for much electronics, it's the mechanical stuff that seems to fail first, or isn't properly designed to last. Paul G.
From: Franc Zabkar on 26 May 2010 00:25 On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh" <newsgroups1(a)idontwantjunqueemail.walshcomptech.com> put finger to keyboard and composed: >I have a Technics SA-929 stereo receiver that is in good working order. >However, when I was inside it replacing a burnt out light bulb and repairing >the protection relay, I noticed that there is a wire coming from the >printboard that holds both the AC power input and accessory outlet >connections going to the "speaker -" connector for the "B" speaker >terminals. > >There is a resistor inline with the wire coming from the AC wiring board. That gives me an idea for testing subwoofers ... Connect each speaker terminal to the active and neutral of a mains supply. The frequency is not critical -- either 50Hz or 60Hz is fine. A sinusoidal 240VAC source would be preferred, but 120VAC will do, too. If you damage your speaker, don't be discouraged. In fact you may need to test quite a few units before you have weeded out all the inferior ones, especially those used in car audio. - Franc Zabkar -- Please remove one 'i' from my address when replying by email.
From: David Nebenzahl on 26 May 2010 02:58 On 5/25/2010 9:25 PM Franc Zabkar spake thus: > On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh" > <newsgroups1(a)idontwantjunqueemail.walshcomptech.com> put finger to > keyboard and composed: > >> I have a Technics SA-929 stereo receiver that is in good working >> order. However, when I was inside it replacing a burnt out light >> bulb and repairing the protection relay, I noticed that there is a >> wire coming from the printboard that holds both the AC power input >> and accessory outlet connections going to the "speaker -" connector >> for the "B" speaker terminals. >> >> There is a resistor inline with the wire coming from the AC wiring >> board. > > That gives me an idea for testing subwoofers ... > > Connect each speaker terminal to the active and neutral of a mains > supply. The frequency is not critical -- either 50Hz or 60Hz is fine. > A sinusoidal 240VAC source would be preferred, but 120VAC will do, > too. > > If you damage your speaker, don't be discouraged. In fact you may need > to test quite a few units before you have weeded out all the inferior > ones, especially those used in car audio. Thank you. I love that! Maybe I can convince my homies around here to implement this new testing methodology. We could set up a free testing station on the main drag around here. -- The fashion in killing has an insouciant, flirty style this spring, with the flaunting of well-defined muscle, wrapped in flags. - Comment from an article on Antiwar.com (http://antiwar.com)
From: Meat Plow on 26 May 2010 06:56
On Wed, 26 May 2010 14:25:51 +1000, Franc Zabkar wrote: > On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh" > <newsgroups1(a)idontwantjunqueemail.walshcomptech.com> put finger to > keyboard and composed: > >>I have a Technics SA-929 stereo receiver that is in good working order. >>However, when I was inside it replacing a burnt out light bulb and >>repairing the protection relay, I noticed that there is a wire coming >>from the printboard that holds both the AC power input and accessory >>outlet connections going to the "speaker -" connector for the "B" >>speaker terminals. >> >>There is a resistor inline with the wire coming from the AC wiring >>board. > > That gives me an idea for testing subwoofers ... > > Connect each speaker terminal to the active and neutral of a mains > supply. The frequency is not critical -- either 50Hz or 60Hz is fine. A > sinusoidal 240VAC source would be preferred, but 120VAC will do, too. > > If you damage your speaker, don't be discouraged. In fact you may need > to test quite a few units before you have weeded out all the inferior > ones, especially those used in car audio. > > - Franc Zabkar Cerwin Vega used to demonstrate one of their professional low frequency audio drivers by plugging it into 120VAC line. |