Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Seduction => Topic started by: choff on January 29, 2018, 02:43:06 PM
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Hello,
I recently moved my listening room to another location in my house. Unfortunately, I now have a local radio station playing (fairly loudly) in the background during playback of records with my Seduction amp run thru a Foreplay to a Dynaco 70. I have no idea what to do to correct this issue? Tried searching forum but couldn't find any relevant topics. Would really appreciate any feedback or suggestions. Thank you.
Carl
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If you unplug the cables on the input side of your Seduction, does the noise go away?
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No, the radio station noise remains. It only goes away when I remove the output cables going to the Foreplay.
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Can you try temporarily connecting the chassis plates of the Seduction and Foreplay together with a piece of wire.
It might also help to see the build underneath the Seduction, but if you're getting the radio station in both channels, it's doubtful that there's something unusual in the build.
What may end up being helpful is adding 100-330pF of capacitance across each 47K resistor across the input jacks, or pursue additional shielding of the base (you are using the tube shields I presume).
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I am indeed getting the radio signal in both channels. I am using the tube shields. This Seduction amp has worked flawlessly for me since I built it about 8 years ago. How would I connect the chassis with a wire? How would I shield the base? Can you explain a little further how I would perform this task.....100-330pF of capacitance across each 47K resistor across the input jacks. I am pretty good at following instructions but don't know or understand all the inner workings of these amps. Thanks for your feedback and assistance!!
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To do the wire experiment, use a piece of wire and touch it on the ground post of the Seduction and the chassis of the Foreplay.
The Seduction was originally designed so that a Hammond metal box could be mounted over the circuit (you have to file out parts of the box where the wires come and go). So few folks needed this that it barely came up, but it's an option.
On each input RCA jack, there's a 47K resistor from the center post to the ground buss. To add the capacitors, solder one end of each cap to the end of the 47K resistor going into the center post of each input RCA jack, then solder the other end to the ground plane (or the other end of each 47K resistor that connects to the ground plane).
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Thanks for the reply. I tried the wire and it reduced the amount of the sound, but did not eliminate it. Probably cut it in half to 3/4. It seemed to work best if i layed the bare wire across the face of the chassis rather than just touching at a point.
Any further thoughts on how to proceed? Is there anything that might be causing this as far as the house wiring, or is that not associated with this type of problem. Thanks again....much appreciated.
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A box covering the underchassis circuitry is the solution we proposed for this problem originally (17 years ago), so it probably makes sense to try that next. IIRC a Hammond 1590J was what we suggested, but I don't recall if that accommodates the C4S board or just fits the basic circuit.
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Also at some point the screw holes for the Hammond box were removed from the chassis since no one ever seemed to actually need them. A picture would help here.
Is there any space in the setup to try different positioning/orientations...?
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Here are a few pics
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It looks like you have the holes for the Hammond box (though perhaps with some added screws?).
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).
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Hope these pics help clarify things. Unfortunately, I am pretty locked into the layout of the system without much flexabilty to make changes, unless you see something I can easily tweak to improve the situation. I do have CS4 in the Seduction.
I will also note that the new location is a room in an addition on top of my house. It is lightweight framing with alluminum cladding on the exterior, whereas the original room was lower and masonry exterior wall construction. I imagine this higher more transparent location is allowing the radio signal to get to the amp more easily?
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Can we see a pic of the underside of the Seduction?
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For some reason it won't let me upload the image? I'll keep trying, but it looks like I already have the Hammond.
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fingers crossed this finally works
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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?
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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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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.
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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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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?
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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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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.
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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.
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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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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?
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Can we see a pic of the underside of the Seduction?
I want to see more pics of that record collection!
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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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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.
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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.
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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).
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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.
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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.
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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?
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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.
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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.
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Does your Dynaco have a 3 wire power cord?
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Does your Dynaco have a 3 wire power cord?
Yes
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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.
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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.
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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?
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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?
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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.
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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?
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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.
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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......
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Yes, that is the terminal. Make sure the nut and screw are good and tight. Your amp will be much safer with that connection even if it doesn't completely solve your noise problems. But it may very well help.
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Awesome....will do and let you know. Thanks Doc!!
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Well.....no luck. Made the green wire ground connection and with high hopes fired everything back up. Radio signal remains unchanged. :(
I also measured the resistance between the Foreplay and the Dynaco. This was exactly the same as between Seduction and Foreplay as well as terminals 13 and 14 on the Foreplay. Meter beeps with 0.00 reading and then climbs to 0.5 and settles on that number.
Lastly, I hooked the Dynaco up to another outlet on a different circuit using a heavy duty extension cord thinking this may determine if the dedicated outlet had a grounding problem as some had thought possible. Fired it all back up and everything remained unchanged, including the voltimeter readings.
I'm obviously disappointed the fix was not obtained, but still determined to do what I can if there are any next steps you all can suggest? Appreciate the continued support and guidance with this problem.
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Update : on a whim I took the rca cables running from Seduction to Foreplay out and put them back in, reversing the orientation of both lead ends. This nearly eliminated the radio signal!! No idea why? The more I mess around with those cables the more it seems like they might be the source of the problem. Perhaps picking up the radio signal like an antenna? Going to try and borrow some more cables from a friend to continue experimenting.
Note : looked up the radio station I am receiving and it is broadcast from a tower on a huge skyscraper about a 1/4 mile from my house. I can see the building from my back window. I'm clearly getting blasted by it's signal and not surprising that this is causing issues.
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That is why I was asking if the interconnects had the shield connected at only one end. You have moved that end of the shield to the most optimal ground point.
Sometimes it may feel like we are barraging a person who asks for tech support with questions. It can helpful to go back in a thread and check to see if there are questions about the configuration that we asked which may have been missed. They might lead to more things to try to solve the problem. Tech support by the forum can be a cumbersome process, but it puts more than one brain on the problem.
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Thanks Doc. I have to admit I didn't really understand what you were referring to when you suggested that earlier in the thread. I should have just asked for clarification, but probably didn't want to show my ignorance.
Anyhow, I would be nowhere had I not had this forum and you all to provide guidance to resolve the issue. Plus I was able to make my Dynaco safer in the process!! Listening to a record now and all is well. This hobby sure can be frustrating, but is whole heck of a lot of fun when you get to the positive end result. Can't wait to have time to eventually upgrade and build another Bottlehead product in the future.
Thank you again...cheers!!