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12vdc linear regulared desktop wart?
12vdc linear regulared desktop wart?
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Old 16th September 2019, 06:27 PM   #11
cgallery is offline cgallery  United States
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Quote:
Originally Posted by kodabmx View Post
It depends on the age. They will certainly be lighter than linear (smaller transformer), but I see no reason why you couldn't use an SMPS and filter the output of that instead. I use SMPS to power RIAA tube phono amplifiers and there is no noise issue. If it needs to be linear, why not build one?

A 12V transformer, a couple of capacitors, and a 7812K should do the job... Still, filtering the SMPS seems easier.

What depends on the age?


I thought older/larger/heavier meant there was a transformer, which means it is linear?


Is that not the case?


In other words, switching supplies wouldn't employ a large/heavy transformer?
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Old 16th September 2019, 06:37 PM   #12
Bill_P is offline Bill_P  United States
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Quote:
Originally Posted by cgallery View Post
If only I could find a version that had a cord instead of plugging directly into a receptacle.
Use an extension cord then.

There are some rough rules of thumb for small AC adapters, under 15 Watts or so.

1. If the power input is 120V 60 Hz only, it is probably linear. Switchers these days cover 100V - 240V and 50 - 60 Hz.

2. Linears are large, heavy and inefficient compared to switchers which should be 70% efficient or better.

3. If a linear AC adapter is not specified as regulated, it probably isn't.

Both adapters you found appear to be linear but the 273-1653A is probably not regulated.

It isn't clear why a switcher is not suitable to run a turntable motor. Not all of them are very noisy - have you tried one and found it to be unusable?
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Old 16th September 2019, 07:42 PM   #13
cgallery is offline cgallery  United States
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Quote:
Originally Posted by Bill_P View Post
Use an extension cord then.

There are some rough rules of thumb for small AC adapters, under 15 Watts or so.

1. If the power input is 120V 60 Hz only, it is probably linear. Switchers these days cover 100V - 240V and 50 - 60 Hz.

2. Linears are large, heavy and inefficient compared to switchers which should be 70% efficient or better.

3. If a linear AC adapter is not specified as regulated, it probably isn't.

Both adapters you found appear to be linear but the 273-1653A is probably not regulated.

It isn't clear why a switcher is not suitable to run a turntable motor. Not all of them are very noisy - have you tried one and found it to be unusable?
Thank you (and everyone) for your help.

When using a small switching supply (12vdc, 1.5a), I get some audible noise picked-up in the signal. Sounds sort of like 7k or 10k and is faint but not faint enough. As I adjust the gain up on my phono stage, the noise is amplified with it. When I unplug the power supply, the noise instantly goes away.

So I picked up a couple of 12vdc linear wall warts (each 12vdc 1a) for $2 each at a thrift store. I'm pretty sure these are unregulated, but I don't know how to tell. Googling part #'s didn't help. One is a Teac, the other a Cambridge Soundworks. I don't get the noise with either of these. But sometimes, the table won't start with these unless I give it a little nudge. Once started, it runs fine and is about as torque-y as with the switched supply.

My theory is that the lack of regulation is causing a problem with the linear supplies. I don't think the problem is the smaller 1a (versus 1.5a) rating, as the running table is pulling 2w (according to my Kill-A-Watt meter). Slowing the table with my thumb causes the power consumption to increase to as high as about 6w. I suppose I could be right on the line, that when the platter isn't moving that the power supply is just shy of what is needed to start it. BTW, the specs for the Technics SL-6 turntable indicate a power consumption of 11-watts, but there are some boards and an additional motor or two (for tonearm control) that I'm not using.

The noise might be a problem with my cheap phono stage. OTOH, I figured the best way forward would be to simply find an inexpensive linear regulated supply.

FWIW, this motor is a magnetically driven servo-type thing, where there are permanent magnets (a ring) mounted to the bottom of the platter and a PCB that fires some electro magnets correctly. I'm actually very surprised that when the linear power supplies don't start it (about one out of four or five times), that nudging the platter gets it going.

Last edited by cgallery; 16th September 2019 at 07:49 PM.
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Old 16th September 2019, 09:24 PM   #14
kodabmx is offline kodabmx  Canada
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12vdc linear regulared desktop wart?
Since you bought them for 2$ each at the thrift store, and the are both 12V 1A, connect them both in parallel and see if that starts the platter...
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