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September 23, 2020, 10:12:17 PM

Author Topic: Problem Seduction pre-amp_radio station in background  (Read 3068 times)

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Offline ALL212

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Re: Problem Seduction pre-amp_radio station in background
« Reply #30 on: January 31, 2018, 02:00:58 PM »
For a permanent solution without major mods - use a ground post similar to that on the Eros or Reduction insuring it was grounded at each device.  Then run whatever cable you like the looks of from device to device using spade lugs or similar as terminations.  That way you can move these around without a solder gun involved.
Aaron Luebke

Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #31 on: February 02, 2018, 04:04:30 AM »
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).

I was finally able to check on this after getting a fresh 9V for my voltimeter.  Anyhow, I believe both 13 and 14 check out at 0 ohms.  With the negative lead touching the chassis and the positive on the terminals, the voltimeter beeps and shows zero initially and then slowly climbs to around 0.5 on each terminal check.  I think the beep indicates that it is zero ohms, as the initial reading indicates? 

I should also note that when switching to the Seduction from the cd selection on the Foreplay, there has always been a lot of what I will call "air" at high volume without any music playing compared to the black silent background when set to cd playback.  Not sure if this is typical or has something to do with the radio signal I am now receiving? 

Really hope I can get this resolved somehow.  Thanks for the continued feedback. Much appreciated.

Offline Doc B.

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Re: Problem Seduction pre-amp_radio station in background
« Reply #32 on: February 02, 2018, 04:27:55 AM »
High volume as in higher than you would actually listen? The sound you hear is called tube rush. The amount varies from tube to tube, but in general it only becomes audible at settings higher than one would ever use. That, however, depends a lot on the nominal output of the cartridge you are using. If it is low the signal to noise ratio gets worse. Do you know what the nominal output of your cartridge is?
Dan "Doc B." Schmalle
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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #33 on: February 02, 2018, 05:36:08 AM »
Cart is a Clearaudio Concept V2 and output is 3.3mV 

The air is noticeable at around 10 and becomes very apparent at and above 12 o'clock on the Foreplay volume pots.  Most records get played at around 12-2 o'clock on the Foreplay.  Some quieter records I have had to go all the way to the last volume setting on the Foreplay.  Not really all that noticeable when playing music, but I always wondered why it was so much louder than the dead silent background of the cd player, which is the same at any volume setting.
« Last Edit: February 02, 2018, 05:50:04 AM by choff »

Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #34 on: February 02, 2018, 07:06:17 AM »
Just to follow up on this some more and my last post.  I spent some more time with the amp trying to see what was and wasn't working with the copper wire, etc. 

My conclusion is the wire between all three units helps but not dramatically.  What really reduces the radio sound is when I am touching any of the components or wires or have my hand between the Foreplay and the Dynaco. 

Also, the "air" I described is really only noticeable on the two or three highest settings on the Foreplay.  Just much more obvious now that I hear the local radio station (always the same one) playing classic rock.  The station is pretty good, but not what I want to listen to when playing a particular record. 

So the bottom line is I don't really think the wire is a solution to my problem.  It helps, but I can still hear the radio at normal listening levels starting around 11 o'clock on the Foreplay.  Very frustrating.  Any further help would be greatly appreciated.
« Last Edit: February 02, 2018, 07:41:58 AM by choff »

Offline Paul Birkeland

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Re: Problem Seduction pre-amp_radio station in background
« Reply #35 on: February 02, 2018, 07:16:27 AM »
Does your Dynaco have a 3 wire power cord?
Paul "PB" Birkeland

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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #36 on: February 02, 2018, 07:32:28 AM »
Does your Dynaco have a 3 wire power cord?

Yes

Offline Doc B.

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Re: Problem Seduction pre-amp_radio station in background
« Reply #37 on: February 02, 2018, 07:50:16 AM »
That's at the low end of the recommended nominal output for a cartridge into the Seduction with a C4S upgrade. Without the upgrade the gain of the Seduction is 3 or so dB less and the power supply isolation is about 50dB less. Thus the signal to noise ratio will be less optimal than it would be with a more standard 5mV cartridge. This is all with respect to the tube rush.

The RFI problem, if it is is not present in one room and bad in another, is probably going to be tough to tame without spending time checking every ground connection and potential ground loop.  Touching the gear and making the noise go away means that you are grounding the equipment better than the existing grounds are. So they need some improvement. There are many ways the interference could be getting into the Seduction - through the cartridge, through the cables, through the power line, etc. So you just have to try a lot of different things to determine of you have a loose ground somewhere. It could be that the mains ground in the outlet you are using is not optimal.

Are the shields of your cables attached to the plug shell at only one end? If the shield is attached at both ends that can create a ground loop.

Dan "Doc B." Schmalle
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Offline Paul Birkeland

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Re: Problem Seduction pre-amp_radio station in background
« Reply #38 on: February 02, 2018, 07:51:07 AM »
What really reduces the radio sound is when I am touching any of the components or wires or have my hand between the Foreplay and the Dynaco. 
This is grounding.

If the wire between the ground post on the Seduction and the chassis of the Foreplay made any difference at all, then the jumper we have mentioned previously is not well soldered and needs to be reheated.  This jumper serves the same purpose.

I would connect one end of your DVM to the ground post of the Seduction, then measure the DC resistance to the Foreplay chassis plate and the DC resistance to a screw on the Dynaco chassis.  What do you get?

What is the ground wire on the power cord going to the ST-70 connected to? 

I'd also recommend buying one of those inexpensive outlet testers with the three bulbs to check your outlet.  This could be a grounding issue at the outlet. 
Paul "PB" Birkeland

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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #39 on: February 02, 2018, 09:13:24 AM »
All the questions about the 3-wire power cord jogged my memory that I may never have attached the ground wire back in the day when I made that upgrade. 

Popped the top and sure enough (see attached photos) the green wire with the beige sleeve is not attached to anything. I believe should be the ground wire? Can't remember why, but whoever I was consulting with on the work at the time said it wasn't necessary.   The white wire goes to the power switch and the black wire to the fuse.

Could this be the source of the trouble? 
« Last Edit: February 02, 2018, 09:16:00 AM by choff »

Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #40 on: February 02, 2018, 09:44:17 AM »
Also, I just measured the ground on Seduction to Foreplay chassis and it came up as 0.00 mV. 

Note : This was measured without the Dynaco connected to the system (not sure if this would have any effect on the reading?).  I can hook the Dynaco back up for a similar reading between the Foreplay, but was holding off to see if there was anything more i should do with the Dynaco while I have it taken apart?


Offline Paul Birkeland

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Re: Problem Seduction pre-amp_radio station in background
« Reply #41 on: February 02, 2018, 10:15:58 AM »
That green wire absolutely has to go to the chassis. That is the big reason to add the three wire power cord in the first place.

The reading between chassis plates is a resistance measurement, though if the problem is really bad you may be able to measure voltage.

I would bet that if you provided a proper ground at the outlet and grounded the St70 chassis that you'd be in good shape in terms of noise.
Paul "PB" Birkeland

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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #42 on: February 02, 2018, 10:26:56 AM »
That green wire absolutely has to go to the chassis. That is the big reason to add the three wire power cord in the first place.

The reading between chassis plates is a resistance measurement, though if the problem is really bad you may be able to measure voltage.

I would bet that if you provided a proper ground at the outlet and grounded the St70 chassis that you'd be in good shape in terms of noise.


Sorry, messed that up. Checked again using ohm setting for resistance on the meter and it does the same thing when I measured terminal 13 and 14......beeps showing 0.0 and then oscillates between 0.3 and 0.6. Does that check out?

I did think it was really odd at the time that I wouldn't be using the ground wire.  Any suggestions on how best to properly attach this green wire to the chassis?   
« Last Edit: February 02, 2018, 10:29:17 AM by choff »

Offline Doc B.

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Re: Problem Seduction pre-amp_radio station in background
« Reply #43 on: February 02, 2018, 10:42:55 AM »
This is a classic example of "they don't make them like they used to".  You have discovered that there is a very good reason they don't make them like they used to! There is a two terminal strip  to the left of the power transformer and more or less behind the power switch. One terminal has a yellow-looking high voltage wire from an output transformer connected to it. The other terminal has nothing connected to it and is bolted to the chassis. That would be a place you could try attaching the green power safety ground wire, as it looks like it should reach. UL approved connection requires a dedicated screw, solder tab and lockwashers, which is what we do in our kits. But attaching the ground wire to that empty terminal will yield the same result.

Another way we don't make them like they used to is we isolate all the iron from the chassis with insulated washers and run a drain wire from each transformer or choke body (metal) to the same safety ground point. This reduces eddy currents in the chassis that can create hum and buzz and still keeps the amp safe in case of a short from a transformer winding to the lams and end bells. That's a  lot more work to retrofit than properly attaching the safety ground wire to the chassis.

I can't tell for sure, but it also looks like old filter cap is completely disconnected? If so, that is probably fine.  Otherwise there might be some concerns about ground loops there, too.
Dan "Doc B." Schmalle
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Offline choff

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Re: Problem Seduction pre-amp_radio station in background
« Reply #44 on: February 02, 2018, 11:00:18 AM »
This is a classic example of "they don't make them like they used to".  You have discovered that there is a very good reason they don't make them like they used to! There is a two terminal strip  to the left of the power transformer and more or less behind the power switch. One terminal has a yellow-looking high voltage wire from an output transformer connected to it. The other terminal has nothing connected to it and is bolted to the chassis. That would be a place you could try attaching the green power safety ground wire, as it looks like it should reach. UL approved connection requires a dedicated screw, solder tab and lockwashers, which is what we do in our kits. But attaching the ground wire to that empty terminal will yield the same result.

Another way we don't make them like they used to is we isolate all the iron from the chassis with insulated washers and run a drain wire from each transformer or choke body (metal) to the same safety ground point. This reduces eddy currents in the chassis that can create hum and buzz and still keeps the amp safe in case of a short from a transformer winding to the lams and end bells. That's a  lot more work to retrofit than properly attaching the safety ground wire to the chassis.

I can't tell for sure, but it also looks like old filter cap is completely disconnected? If so, that is probably fine.  Otherwise there might be some concerns about ground loops there, too.

Very interesting info. I think I have some isolation feet I purchased a while ago for those transformers and never got around to doing that install.  Sounds like I might want to find the time one of these days. 

I was eying up that empty terminal as well as a possible good spot.  Assume this is the one you are referring as shown in this photo?  I have plenty of slack in the green wire to reach that point. If so, I'll get to work on that and report back once I have everything back up and running.  I can't thank you all enough for the guidance.  Fingers crossed that does the trick......