No more 60 Hz hum in a PL2000 preamp.

Gepetto

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Well, the upgraded transformer is a failure. Turned on the system this morning and heard a slight hum. Cranked up the volume, and yes, it's definitely there.
I have a early 70's class A bipolar amp upstairs that has always been very susceptible to hum issues in anything connected to it.
Brought the preamp upstairs and connected it to the bipolar. Yup, really pronounced hum. Went through every troubleshooting procedure I could think of, no joy.
Pulled the large transformer, reinstalled the origonal. No more hum with the units seperated, very slight hum with the units stacked. Typical of the approximately 50 years I've had the amp. The amp has two big transformers and induces slight hum in anything stacked on it.
I really liked the way the preamp performed with the big transformer, but won't tolerate hum in the main system. Guess I'll look at mounting it off board. Really don't want to, but that's the only way it will work. Need to research enclosures and connectors.
No big deal in the large scheme of things. Learned a lot trying to make it work.
Try this George

AN-0212 - 25VA 12V Transformer - AnTek Products Corp (antekinc.com)
 

George S.

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It's back in the system running on the original transformer. It's very quiet with no hum. But it's lost the punch and bass definition it had with the Hammond transformer.
The difference is really noticable. These preamps definitely need a larger transformer.
Going to finish listening to side 2 of the album. Then download the datasheet for the Antek, and make some paper cutouts to make sure it'll fit.
12 deg F. outside, turned on the 8 Lava Lamps to heat up the room some. It'll probably take about 4 hours for the big one to get going.
 

George S.

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They'll fit easily. Ordered 2. I've never worked with a toroidal transformer before, but the datasheet looks like the wiring is a non-issue. Looks like I join the primary connections and join a single green and blue secondary to create the center tap.
 

BlueCrab

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The nice thing about toroidal transformers are their lower "hum field". You might also consider mumetal shielding around it. Cured a problem I was having although steel will work too. It's a function of the strength of the field.
 

J!m

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I'm cheap so I just remove the offender from the area...

The phono preamp has been successfully built MANY times with the switch mode PS right next to the amp boards, but I moved mine out anyway.

In that case the "filter board" was specifically designed and tailored to filter that specific power supply. The filter board I mounted in the main cabinet, but the A/C line filter and SMPS were outboard, with low voltage DC going up to the main cabinet only, into the filter board (tucked in a corner inside a steel box) and then onward to the power switch and amp boards.
 

George S.

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Jim BC, I do have a good size sheet of mumetal left over from a past project, but that cover is the bomb. Going to open up a preamp and find a cover that fits. My mumetal has adhesive on it, so I can always stick it on the cover if needed. Thanks! I will have to revisit the rules for bonding mumetal to ground if it's needed.
 

George S.

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I'm cheap so I just remove the offender from the area...

The phono preamp has been successfully built MANY times with the switch mode PS right next to the amp boards, but I moved mine out anyway.

In that case the "filter board" was specifically designed and tailored to filter that specific power supply. The filter board I mounted in the main cabinet, but the A/C line filter and SMPS were outboard, with low voltage DC going up to the main cabinet only, into the filter board (tucked in a corner inside a steel box) and then onward to the power switch and amp boards.
Jim, yup, understood. As last resort I'll put the transformer in it's own enclosure. That would simplify matters, but I'm going to try to keep it self contained if possible.
 

George S.

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Well, the cover for the AN-0212 transformer is a CA-002. Not listed on the website, but it is in their eBay store. Too big, won't fit the available room in the chassis. None the less, I have two of those 25VA on the way.
The next smaller size is the AN-0112, a 10VA unit. This one takes a CA-001 cover which will fit the available space.
So, also ordered the smaller units and covers.
We'll see how this sorts out once the stuff arrives and I can get to it.
Lee once said "We need a great sounding PL preamp".
That's the goal.
 

George S.

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Maybe put the Aragon guts inside the PL box?

Or a WOPL preamp? Joe?
I started to clone a Acurus L10 for the PL2000 chassis. Even have enough NOS Toshiba transistors for several builds. But quality switches that fit the chassis and faceplate are a issue. I'll get back to it once I retire and can keep from getting sidetracked.
Given all the different preamps built, there's probably no way to make a preamp retrofit board profitable.
Easier just to buy a Acurus or whatever and call it done.
 

laatsch55

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Well, the cover for the AN-0212 transformer is a CA-002. Not listed on the website, but it is in their eBay store. Too big, won't fit the available room in the chassis. None the less, I have two of those 25VA on the way.
The next smaller size is the AN-0112, a 10VA unit. This one takes a CA-001 cover which will fit the available space.
So, also ordered the smaller units and covers.
We'll see how this sorts out once the stuff arrives and I can get to it.
Lee once said "We need a great sounding PL preamp".
That's the goal.
Amen George!!
 

Gepetto

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Hopefully it fixes your issue George. You may also learn some new tidbits about leakage flux
 

George S.

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Hopefully it fixes your issue George. You may also learn some new tidbits about leakage flux
Yes. And if I do have to remote mount it, I'll have options. After hearing it with the upgraded transformer, it's depressing to listen to it now. It made such a huge difference.
 
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