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October 29, 2020, 08:59:37 AM

Author Topic: Problem Seduction pre-amp_radio station in background  (Read 3122 times)

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Offline Doc B.

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Re: Problem Seduction pre-amp_radio station in background
« Reply #15 on: January 30, 2018, 09:44:20 AM »
The plot thickens, as you already have the shield box on there. Tighten up the chassis safety ground screw next to the IEC input to be sure that's not creating any extra resistance. Is the Seduction plugged right into the wall socket, or is it plugged into some form of power strip or conditioner? Also, has your Stereo 70 been converted to a three wire (safety grounded) power cord?
« Last Edit: January 30, 2018, 09:46:18 AM by Doc B. »
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Offline fullheadofnothing

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Re: Problem Seduction pre-amp_radio station in background
« Reply #16 on: January 30, 2018, 09:48:10 AM »
I see tons of places you could put it: 
Rotate it 90° and put it behind the table.
Rotate to whatever angle works in its current position.
Add a wall shelf above.
Move the CD player up, put the Seduction in the cubby that holds the CD player now.
Swap locations b/t the tt and power amp so your system goes right-to-left instead of left-to-right.

Those are the obvious ones from the pictures shown.

What you want to do is plug in just the Seduction and move it around and see if you can minimize the pickup, then rearrange the system to suit the placement.

Also worth noting that I was picking up radio for a while in my system. When I isolated it, it turned out that I had a bad solder joint on the ground of my stepup transformer. It's possible that the problem is revealing itself now not because the system has been moved, but because in moving it, you jostled a dodgy solder connection.
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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #17 on: January 30, 2018, 10:09:57 AM »
The plot thickens, as you already have the shield box on there. Tighten up the chassis safety ground screw next to the IEC input to be sure that's not creating any extra resistance. Is the Seduction plugged right into the wall socket, or is it plugged into some form of power strip or conditioner? Also, has your Stereo 70 been converted to a three wire (safety grounded) power cord?

It's plugged directly into a dedicated line wall outlet.  Dynaco has been converted.  All components have their own dedicated wall outlet line run back to the electric panel. 

Offline Doc B.

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Re: Problem Seduction pre-amp_radio station in background
« Reply #18 on: January 30, 2018, 10:23:50 AM »
There may be certain 6922 tubes that are less prone to RFI pickup than others. Unfortunately I don't have any experience to share about that. Something I would probably try if it were my system is wrapping the tubes around the cylindrical part (not over the top) with adhesive backed copper tape, then soldering a drain wire to the tape that attached to one of the tube socket screws. Aluminum tape like you can get in the HVAC section of Home Depot might work too, but of course you wouldn't be able to solder the wire to the alu. Just tape the drain wire to the foil with another piece of the aluminum tape. Try to keep it neat so you can still fit the shield can on. Removing the spring from the shield might help gain some clearance. The spring is not absolutely necessary.

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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #19 on: January 30, 2018, 10:29:21 AM »
I tried tightening the screw but nothing changed.  It was already pretty tight.  One odd thing I noticed while doing this is that if I put my hand held in a vertical position between the Dynaco and the Foreplay the sound from the radio was significantly diminished.  Could that be a clue to anything? 

Offline Doc B.

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Re: Problem Seduction pre-amp_radio station in background
« Reply #20 on: January 30, 2018, 10:43:14 AM »
It confirms that it's RFI and that your hand is screening it a little. That is why it was suggested that moving things around a little might make a difference. The RFI can have nodes and antinodes in a room, where it is stronger or weaker. You could also try attaching all three chassis together with wire, i.e., run a wire from Seduction to Foreplay like you have already, and run another wire from ST70 to Foreplay, attached to the same point on the Foreplay chassis as the wire from the Seduction is attached.
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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #21 on: January 30, 2018, 10:44:52 AM »
Another thing I noticed just fiddling around is that if I put my hands / fingers on the Foreplay metal chassis the radio sound is diminished.  Likewise if I hold the RCA output cables in my hand that go from the Seduction to the Foreplay.
« Last Edit: January 30, 2018, 10:51:37 AM by choff »

Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #22 on: January 30, 2018, 11:12:30 AM »
I'll try the wiring between chassis as you suggest.  Hopefully that works.  Problem with moving the set-up around is that it would require longer RCA cables which obviously could be costly for me. 

Online Paul Joppa

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Re: Problem Seduction pre-amp_radio station in background
« Reply #23 on: January 30, 2018, 11:42:22 AM »
...
The ground connection that you added should have been in the preamp, but IIRC the original Foreplay preamps didn't have signal ground tied to chassis.  I believe the recommendation was to jumper terminal 13 to terminal 14 to make this connection (which is now standard on all of our preamps).
I'm re-iterating this because I've not seen any indication it's been checked. By tying the chassis to the signal ground, you allow the chassis plate to act more efficiently as a ground plane shield.
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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #24 on: January 30, 2018, 02:17:23 PM »
I'm re-iterating this because I've not seen any indication it's been checked. By tying the chassis to the signal ground, you allow the chassis plate to act more efficiently as a ground plane shield.

Thank you for the reminder.  I'm pretty sure I did make that jumper connection.  Can you tell from these photos?

Offline faskenite

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Re: Problem Seduction pre-amp_radio station in background
« Reply #25 on: January 30, 2018, 02:41:04 PM »
Can we see a pic of the underside of the Seduction?

I want to see more pics of that record collection!

Offline Paul Birkeland

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Re: Problem Seduction pre-amp_radio station in background
« Reply #26 on: January 30, 2018, 05:41:41 PM »
Man, the magnet wire is difficult to photograph and see well.

On the five lug strip up front, the middle lug is the chassis connection. There's a light next to it with many wire connections, some of which go to the striped sides of each filter capacitor. Those are the terminals that should be connected (I don't believe they are based on your recent information).
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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #27 on: January 31, 2018, 03:22:19 AM »
Man, the magnet wire is difficult to photograph and see well.

On the five lug strip up front, the middle lug is the chassis connection. There's a light next to it with many wire connections, some of which go to the striped sides of each filter capacitor. Those are the terminals that should be connected (I don't believe they are based on your recent information).

Thanks. I checked again. Perhaps these photos will show it better? 13 and 14 (middle and terminal to left in photo) are definitely connected with a single piece of copper wire.

Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #28 on: January 31, 2018, 11:26:28 AM »
So I hooked some copper wire from some 10-2 romex to the ground on the Seduction, thru the undeside of the Foreplay chassis to hold it tight to the plate because I had nothing to attach to and then to the Dynaco.  Not pretty, but this did decrease the radio sound significantly. In fact it almost eliminated it entirely except at the top two settings on the pots with no music playing I could still hear the radio a bit. 

Any further thoughts?  Suggestions on maybe making this a permanent solution?  Thanks so much for everyone's help.   

Online Paul Joppa

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Re: Problem Seduction pre-amp_radio station in background
« Reply #29 on: January 31, 2018, 01:41:28 PM »
I know I'm being a dog with a bone here, but the T13-T14 solder joints look a little iffy, and I remember those older Foreplays used a ground wire with really tough insulation that was very hard to solder to. It was a frequent problem on the old Forum. You might try to measure the resistance from chassis plate to T14 (the terminal itself, not the wires soldered to it).
Paul Joppa