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RF preventing me from using my home studio
Old 6th January 2021 | Show parent
  #31
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GusMachado's Avatar
 
🎧 5 years
Quote:
Originally Posted by analogguru ➑️
Your "slope demodulation" can only occur when there is enough RF-signal to be "demodulated". I doubt that there enters enough signal at a frequency of 100 MHz - not with today's equipment, nada.

You don't know the country the guy is living, the guy can't even post a (helpful) picture of the "big antennas on his roof" and "GusMachado" sounds spanish so it can be a caribean island, therefore any speculation what is been transmitted on which frequency is worthless.

The guy doesn't even know if it is 107,9 MHz or not, so it is not clear what he heard - can also be some ghost voices.

BTW, I am a licensed radio amateur since more than 40 years.

Soo.... are you ready to bet against my claim that the FM-radio station on 107,9 MHz in a distance of 2,5 km is NOT causing the problems that the guy has ?
I don't know a lot about radio frequencies, that's right. I'm musician more than a sound engineer.
As much as it sounds spanish, Machado is a portuguese name. I'm Brazilian, and I'm at SΓ£o Paulo. If that helps. And what I heard is actually the Tropical FM, from 107,9 Mhz. Because I actually heard to the radio host telling the name of the radio and the frequency.
Old 6th January 2021 | Show parent
  #32
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GusMachado's Avatar
 
🎧 5 years
Quote:
Originally Posted by analogguru ➑️
Did you see ? In exact 2,68 km distance south-south-east from "Tropical FM" is another broadcast station: "FM Radio 105".

Maybe this is the new home of GusMachado ?
https://www.google.at/maps/place/Fm+...9!4d-46.683019
This is my building, if it helps. The antennas above are actually, cellphone antennas.
https://www.google.com.br/maps/place...4!4d-46.708042
Old 6th January 2021 | Show parent
  #33
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David Rick's Avatar
 
🎧 15 years
Quote:
Originally Posted by GusMachado ➑️
Sadly, I don't think those guys deliver outside the US.
Here in Brazil, I found those
I tried them, but I cannot fell much difference, if any.

Maybe they're not the right one.
I can't really tell which material they're made from. It might be the right stuff, but not the right solution. Ferrites can help with RFI injected on the shield because the shield resistance is very low, but they won't help if the RF is getting on the signal wire because that looks into the 1 Megohm impedance of your preamp's input jack and the ferrite impedance is only about 100 ohms.

Quote:
I also found this one.

It's a little bit expensive, but if it solves my problem I would buy it. Do you think this is the right one?
You don't want that. We have one of those sample kits (we get 'em for free) and they're full of stuff to quiet down microprocessors and the like.

Question Gus: Have you opened the electronics cutout in your guitar to see if it's properly shielded? If not, lining it with copper foil tape might help. Be careful though -- that stuff has wicked-sharp edges, like playing with razer blades.

David
Old 6th January 2021 | Show parent
  #34
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David Rick's Avatar
 
🎧 15 years
Quote:
Originally Posted by GusMachado ➑️
...what I heard is actually the Tropical FM, from 107,9 Mhz. Because I actually heard to the radio host telling the name of the radio and the frequency.
OK. Call the station's business-side number and make an appointment to speak with their chief engineer. Explain your situation, maybe email a link to this thread for background. Such people can sometimes be very helpful if they understand you're trying to resolve the problem at your end rather than complaining to the regulatory authorities. It's not unheard of for them to actually come for a visit and try to improve things. And like @ jaddie says above, RF problems are a lot easier to diagnose when you're actually on site.

David L. Rick
Old 6th January 2021 | Show parent
  #35
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jaddie's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Rick ➑️
OK. Call the station's business-side number and make an appointment to speak with their chief engineer.
Ah yes, the days when stations actually had a full time engineer on site. Still worth calling to try. If it's anything there like it is in the US, most of us are looking after more than one station, and being spread thinner all the time. And getting a message through might be tough.

In the old days (two+ engineers per station!) we'd take the listener call, grab some caps, chokes and ferrites and stop over to try to get things working. Everything from school PA systems to private homes. Boy I have some stories about that! Sometimes the interference complaint was solved with a free t-shirt.

Anyway, I think those days are long gone, but a chat with the chief is a good place to start, if you can find him.
Old 6th January 2021 | Show parent
  #36
Gear Head
 
GusMachado's Avatar
 
🎧 5 years
Quote:
Originally Posted by David Rick ➑️
I can't really tell which material they're made from. It might be the right stuff, but not the right solution. Ferrites can help with RFI injected on the shield because the shield resistance is very low, but they won't help if the RF is getting on the signal wire because that looks into the 1 Megohm impedance of your preamp's input jack and the ferrite impedance is only about 100 ohms.



You don't want that. We have one of those sample kits (we get 'em for free) and they're full of stuff to quiet down microprocessors and the like.

Question Gus: Have you opened the electronics cutout in your guitar to see if it's properly shielded? If not, lining it with copper foil tape might help. Be careful though -- that stuff has wicked-sharp edges, like playing with razer blades.

David
Hey David, haha. Yes, i have my experiences and blade cuts with copper foil tape hahha!
I am a luthier enthusiast and I have shielded all of my guitars... Remember that, even without the guitar, if I just move the cable around the room, I get RF.
Old 6th January 2021 | Show parent
  #37
Gear Head
 
GusMachado's Avatar
 
🎧 5 years
Quote:
Originally Posted by David Rick ➑️
I can't really tell which material they're made from. It might be the right stuff, but not the right solution. Ferrites can help with RFI injected on the shield because the shield resistance is very low, but they won't help if the RF is getting on the signal wire because that looks into the 1 Megohm impedance of your preamp's input jack and the ferrite impedance is only about 100 ohms.
David
Sorry, man. Im trying to keep it up with all that info, but now you got me lost.
I don't know much about impedance. Can you explain it?
Old 6th January 2021
  #38
Gear Head
 
GusMachado's Avatar
 
🎧 5 years
Oh, another thing that may help. LEt's put aside all my signal chain for a moment.
I have Yamaha DD20, which is a drum machine with in-built speakers. If I just plug into the power outlet and turn the volume on, I' still getting RF.
Old 6th January 2021 | Show parent
  #39
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David Rick's Avatar
 
🎧 15 years
Quote:
Originally Posted by GusMachado ➑️
I am a luthier enthusiast and I have shielded all of my guitars... Remember that, even without the guitar, if I just move the cable around the room, I get RF.
OK, good. If you modify guitars than you probably know how to solder. The next step is to add a simple RF filter at the input of your preamp. If you don't want to open it up, you can actually build this into the cable.

Get a small 100k resistor (1/16, 1/10, or 1/8 W) and a small ceramic capacitor of 15 or 22 pF. Disassemble the 1/4 inch plug at the the amp end of the cable. (Mark this end for future reference.) Unsolder the center conductor and solder the resistor in series between it and the plug's tip lug. Next solder the capacitor between the tip lug and the shield contact. Screw the cable back together, being careful not to short anything. This will add a single-pole low-pass filter at around 100 kHz, yielding about 60 dB attenuation of the FM interference signal.

Interference coupled into an open-circuit cable is not uncommon, even in my studio. With the far end open, it's basically an antenna, as I said before. But you should see a big improvement with this filter circuit added.

I don't have an easy fix for your drum machine. If it's got problems without any cables attached, then it needs internal modifications to make it more robust. That's rather advanced stuff.

David L. Rick
Old 6th January 2021 | Show parent
  #40
Gear Head
 
GusMachado's Avatar
 
🎧 5 years
Thank you so much, David. Can I build a XLR - XLR cable with this? because i need it for my condenser mic.
Old 8th January 2021 | Show parent
  #41
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nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by GusMachado ➑️
Thank you so much, David. Can I build a XLR - XLR cable with this? because i need it for my condenser mic.
I would doubt this will help much..May make things worse..
First the audio circuit will not pass a 100MHz signal..
Old 8th January 2021 | Show parent
  #42
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GusMachado's Avatar
 
🎧 5 years
That would make me not record some frequencies on my instruments as well right? So what should I dry, according to you?
Old 8th January 2021 | Show parent
  #43
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David Rick's Avatar
 
🎧 15 years
Quote:
Originally Posted by GusMachado ➑️
Thank you so much, David. Can I build a XLR - XLR cable with this? because i need it for my condenser mic.
This circuit won't work for XLR cables, but they are balanced to begin with, so the problem is usually just whether the shield is properly-grounded or not. If pin 1 goes to the metal case and the metal case is properly grounded, there's usually no problem. But your preamp doesn't do this right.
Old 8th January 2021 | Show parent
  #44
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David Rick's Avatar
 
🎧 15 years
Quote:
Originally Posted by nosebleedaudio ➑️
I would doubt this will help much..May make things worse..
First the audio circuit will not pass a 100MHz signal..
It's not passing it, it's demodulating it. This is a countermeasure that's simple enough for Gus to try on his own. I know other tricks (I've been doing this a long time), but most are not simple enough for an end-user to do. Therefore, let's wait to see what transpires with this approach.
Old 8th January 2021
  #45
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JohnRoberts's Avatar
 
🎧 10 years
Lots of advice already, some good.

For a simple (but not cheap) possible solution, have you tried using an audio transformer in series with your audio cable?

Typical audio transformers will behave like a bandpass filter, not passing DC or RF.

JR
Old 4 weeks ago | Show parent
  #46
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Aaron Rash's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Rick ➑️
OK, good. If you modify guitars than you probably know how to solder. The next step is to add a simple RF filter at the input of your preamp. If you don't want to open it up, you can actually build this into the cable.

Get a small 100k resistor (1/16, 1/10, or 1/8 W) and a small ceramic capacitor of 15 or 22 pF. Disassemble the 1/4 inch plug at the the amp end of the cable. (Mark this end for future reference.) Unsolder the center conductor and solder the resistor in series between it and the plug's tip lug. Next solder the capacitor between the tip lug and the shield contact. Screw the cable back together, being careful not to short anything. This will add a single-pole low-pass filter at around 100 kHz, yielding about 60 dB attenuation of the FM interference signal.

Interference coupled into an open-circuit cable is not uncommon, even in my studio. With the far end open, it's basically an antenna, as I said before. But you should see a big improvement with this filter circuit added.

I don't have an easy fix for your drum machine. If it's got problems without any cables attached, then it needs internal modifications to make it more robust. That's rather advanced stuff.

David L. Rick
Hi David,

I'm having a similar problem with a speaker amplifier in my studio. The RCA cables are acting as antennas I believe and I'm picking up a radio station. The only inputs on the amp are the RCA unbalanced inputs. Would building this filter into my RCA cables help do you think? I'm just tired of hearing this radio station and want to get rid of the RFI!

Aaron
Old 4 weeks ago
  #47
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David Rick's Avatar
 
🎧 15 years
Aaron,

Please describe precisely the equipment at both ends of the cable, what kind of connector is at each end, and how it is powered. What is the cable length?

David L. Rick
Old 4 weeks ago | Show parent
  #48
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Aaron Rash's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Rick ➑️
Aaron,

Please describe precisely the equipment at both ends of the cable, what kind of connector is at each end, and how it is powered. What is the cable length?

David L. Rick
I'm running out of a Universal Audio Apollo interface into a Adcom GFA 545 II amp that's powering my NS-10 monitors. The inputs on the Adcom are unbalanced RCA inputs. The output on the Apollo going into the adcom is 1/4. So I just built some TS to RCA cables.

The Adcom has a floating ground I believe... there is no 3 prong on the power cable, it's just a basic 2 prong ac cable. I was thinking about grounding the shield to the Adcom chassis but since the ground is floating I don't want to mess anything up.

However, I am getting a solid ground on the cable shield from the Apollo interface. So the cable shield is grounded on a single end.

Not sure what I'm doing wrong here, but I've tried many different things and can't get rid of this terrible RF!

I will try to identify what frequency radio station it is I'm picking up... It's hard to tell because it has a lot of static and distortion in the signal.

I also forgot to mention my cables are about 3 foot long.

Also just to confirm. If I leave the cable unplugged on the Apollo, I still get the RF signal from the cables connected to nothing. When I disconnect the cable on the end of the Adcom, the RF disappears... So it's 100% the cables but I don't know how to keep the RF out.
Old 4 weeks ago
  #49
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David Rick's Avatar
 
🎧 15 years
What is the exact model of the Apollo interface? What kind of bulk cable stock did you use when building the cables?
Old 4 weeks ago | Show parent
  #50
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Aaron Rash's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Rick ➑️
What is the exact model of the Apollo interface? What kind of bulk cable stock did you use when building the cables?

It's a Apollo Twin USB. For the cable I used some mic cable I had laying around. The shield on it is very thick x braided stuff.

Over the past few hours I've tried some instrument cable and some other brands of mic cable. Still no difference. Radio is coming right on through.


I must be in a pretty contaminated area... However, nothing else in my studio is suffering from this. My mics work fine with no RFI issues. On the other hand, everything else is balanced. I imagine if I had a electric guitar I would probably be picking up the same thing that the amp is picking up.
Old 4 weeks ago | Show parent
  #51
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Aaron Rash's Avatar
 
🎧 10 years
I've identified the station I'm picking up is KIRO Radio 97.3 FM here in Seattle.

The tower/transmitter is about 2 miles from my location.

Last edited by Aaron Rash; 4 weeks ago at 07:27 AM..
Old 4 weeks ago | Show parent
  #52
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nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by Aaron Rash ➑️
The Adcom has a floating ground I believe... there is no 3 prong on the power cable, it's just a basic 2 prong ac cable. I was thinking about grounding the shield to the Adcom chassis but since the ground is floating I don't want to mess anything up.


.
I would try and ground the Adcom to a Known grounded piece with a wire from chassis to chassis..And see if the RF goes away.
YOU wON'T MESS anything up..
I have installed MANY grounded AC cables on gear over the years, it only becomes safer, provided you have a GOOD AC grounded outlet..
Old 4 weeks ago
  #53
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David Rick's Avatar
 
🎧 15 years
Stupid power amp tricks

All right, Aaron, I understand what's going on here. It's a combination of several things, some of which (like your proximity to a radio transmitter) are merely unfortunate and one of which (the design of your Adcom power amp) is genuinely dumb. How dumb? Well, I hereby award it my first-annual Neil Muncy memorial worst-practice award for RF susceptibility. If there were a trophy associated with this award, it would be a copper-plated statuette of Neil Muncy wagging his finger at the recipient. (I leave it your imagination which finger.)

I reached my conclusions after studying online photos of the Adcom 545ii internals, a 545 service manual, a 555 service manual and a 555ii service manual. Based on this research, I'm pretty confident that I understand what's going on in the 545ii. I also looked at the manual for your UA Apollo Twin interface.

Because it uses a two-wire line cord, the chassis on your particular ADCOM 545ii is not actually connected to earth ground. There's an "E" version with a 3-pin IEC power jack that does actually ground the chassis, but that's not the version you have. If you want to try grounding the chassis to earth, you can do it pretty easily by connecting a spade lug to either of the (-) speaker outputs. It's an easy experiment to try and perhaps it will help, but I have my doubts.

The most important piece of information is that, even if the Adcom's chassis were grounded, its RCA inputs are not connected to chassis. They are isolated and the Adcom differential input transistor pair is looking at the difference between tip and shield. The shield side is "soft-coupled" to circuit common through a parallel RC network (100R || 1 uF). This is done on the circuit board, so any fault current has to flow across its ground plane, the precise situation Muncy warned against in his classis 1994 AES paper on the "Pin 1 problem".

The shield side of this coupling network is driven by NJM4558 op amp that is acting as a servo control to null out any DC component at the speaker outputs. This circuit is the main "improvement" distinguishing the 545/555 "ii" versions from the original versions.

You heard me correctly: Adcom is attempting to drive the cable shield instead of grounding it! I know what you're going to ask me: "How can they drive the shield effectively if it's grounded at the far end?" Answer: "Give me a long enough lever and a Japanese op amp, and I can move the earth!" Well, not really. The amplifier card is isolated from ground by the power transformer, so what happens is the servo attempts to wiggle the whole thing relative to the shield potential by dumping current through that RC network. On a good day, it succeeds, but only at low frequencies. If there's RF interference on the shield, the op amp can't do a thing about it because a NJM 4558 has a unity-gain bandwidth of only 3 MHz and the FM radio interference is about 100 MHz. The Adcom engineers apparently hoped any RF crap would simply get shunted through the 1 uF capacitor to chassis but, if chassis is floating, where's it going to go?

You may wonder why the 100 MHz junk isn't getting shunted off the shield at the drive end. Well, your UA Apollo interface doesn't have a chassis connection either! It's powered by an isolated line lump with a floating two-wire output. So the only actual earth connection comes from your USB computer connection or from the shields on other audio cables. These have pretty high inductance at 100 MHz. Of course you could ground the interface chassis yourself with a flat braid to your studio's technical ground. It might help, but there's no guarantee. You could also consider grounding the RCA cable shield itself, since the fact that its floating at RF frequencies is why it's not acting as an effective shield. I'd be inclined to try this at the interface end and put a ferrite core over the cable at the amplifier end to encourage RF energy to go the other direction.

What you should probably not do is earth both the UA box or RCA cable and the Adcom chassis simultaneously because the Adcom service manual warns bench techs of possible damage from doing so.

The mitigation ideas mentioned above are just suggestions that may or may not work. If you want a solution that certainly will work, buy a couple of good quality line-level audio transformers and mount them inside the Adcom chassis. Connect the Adcom chassis to your studio's technical ground with a thick braid. Wire the audio transformer primaries to the RCA connectors and jumper the RCA shield terminals to chassis with nice short leads. Then connect the amplifier cards to the floating secondary windings of these input transformers. Now the cable shield is properly earthed and the amplifier cards can still do their DC servo thing.

Good luck, Aaron.

David L. Rick
Old 4 weeks ago | Show parent
  #54
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Aaron Rash's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Rick ➑️
All right, Aaron, I understand what's going on here. It's a combination of several things, some of which (like your proximity to a radio transmitter) are merely unfortunate and one of which (the design of your Adcom power amp) is genuinely dumb. How dumb? Well, I hereby award it my first-annual Neil Muncy memorial worst-practice award for RF susceptibility. If there were a trophy associated with this award, it would be a copper-plated statuette of Neil Muncy wagging his finger at the recipient. (I leave it your imagination which finger.)

I reached my conclusions after studying online photos of the Adcom 545ii internals, a 545 service manual, a 555 service manual and a 555ii service manual. Based on this research, I'm pretty confident that I understand what's going on in the 545ii. I also looked at the manual for your UA Apollo Twin interface.

Because it uses a two-wire line cord, the chassis on your particular ADCOM 545ii is not actually connected to earth ground. There's an "E" version with a 3-pin IEC power jack that does actually ground the chassis, but that's not the version you have. If you want to try grounding the chassis to earth, you can do it pretty easily by connecting a spade lug to either of the (-) speaker outputs. It's an easy experiment to try and perhaps it will help, but I have my doubts.

The most important piece of information is that, even if the Adcom's chassis were grounded, its RCA inputs are not connected to chassis. They are isolated and the Adcom differential input transistor pair is looking at the difference between tip and shield. The shield side is "soft-coupled" to circuit common through a parallel RC network (100R || 1 uF). This is done on the circuit board, so any fault current has to flow across its ground plane, the precise situation Muncy warned against in his classis 1994 AES paper on the "Pin 1 problem".

The shield side of this coupling network is driven by NJM4558 op amp that is acting as a servo control to null out any DC component at the speaker outputs. This circuit is the main "improvement" distinguishing the 545/555 "ii" versions from the original versions.

You heard me correctly: Adcom is attempting to drive the cable shield instead of grounding it! I know what you're going to ask me: "How can they drive the shield effectively if it's grounded at the far end?" Answer: "Give me a long enough lever and a Japanese op amp, and I can move the earth!" Well, not really. The amplifier card is isolated from ground by the power transformer, so what happens is the servo attempts to wiggle the whole thing relative to the shield potential by dumping current through that RC network. On a good day, it succeeds, but only at low frequencies. If there's RF interference on the shield, the op amp can't do a thing about it because a NJM 4558 has a unity-gain bandwidth of only 3 MHz and the FM radio interference is about 100 MHz. The Adcom engineers apparently hoped any RF crap would simply get shunted through the 1 uF capacitor to chassis but, if chassis is floating, where's it going to go?

You may wonder why the 100 MHz junk isn't getting shunted off the shield at the drive end. Well, your UA Apollo interface doesn't have a chassis connection either! It's powered by an isolated line lump with a floating two-wire output. So the only actual earth connection comes from your USB computer connection or from the shields on other audio cables. These have pretty high inductance at 100 MHz. Of course you could ground the interface chassis yourself with a flat braid to your studio's technical ground. It might help, but there's no guarantee. You could also consider grounding the RCA cable shield itself, since the fact that its floating at RF frequencies is why it's not acting as an effective shield. I'd be inclined to try this at the interface end and put a ferrite core over the cable at the amplifier end to encourage RF energy to go the other direction.

What you should probably not do is earth both the UA box or RCA cable and the Adcom chassis simultaneously because the Adcom service manual warns bench techs of possible damage from doing so.

The mitigation ideas mentioned above are just suggestions that may or may not work. If you want a solution that certainly will work, buy a couple of good quality line-level audio transformers and mount them inside the Adcom chassis. Connect the Adcom chassis to your studio's technical ground with a thick braid. Wire the audio transformer primaries to the RCA connectors and jumper the RCA shield terminals to chassis with nice short leads. Then connect the amplifier cards to the floating secondary windings of these input transformers. Now the cable shield is properly earthed and the amplifier cards can still do their DC servo thing.

Good luck, Aaron.

David L. Rick
Hi David,

Fist of all, thank you so much for actually taking the time to look at my situation and all the useful information. Just amazing to have this kind of support here. I can't thank you enough!!

Okay so... a few things. I was able to get the noise to go away if I coil the cables up and set the interface on the Adcom so there's only a few inches of cable length. The noise is gone, but it's not practical since I would have to get up and walk all the way over to the unit on the floor any time I need to adjust volume. The interface needs to be on the desk. I included a photo of what worked. Also, you can see in the picture, I made a cable twisting 2 wires to see if it would reject RF any better than the shielded cable. It was about the same, not much difference at all.


So I need a way to be able to get my interface about 4 foot from this thing without it turning into a radio station.

I understand the transformer approach but I would rather not color the sound in any way since I'm using the amp for mixing.

Also, you were right about the 100R resistance between the RCA ground and chassis ground. Oddly enough... after the unit is on and playing music for about 10 minutes that value drops to about 50R. Check out the photo. Im not sure if this is a sign I should replace the caps. I have a little experience with soldering so doing some mods/recapping is no big deal.

Also, yesterday I tried using a 2 conductor wire + shield and wired the hot and ground side of the RCA cable to the TS cable and left the shield disconnected on the Apollo end of the cable and then I just tied the shield to actual ground through the wall outlet and it actually gave me more noise for some reason.

You are right about the Apollo getting ground from the USB cabled. I just measured it directly to the wall ground outlet and I'm getting about 30ohms.

What would be the best thing to try first?


Again thank you!
Old 4 weeks ago | Show parent
  #55
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Aaron Rash's Avatar
 
🎧 10 years
Heres the photos
Attached Thumbnails
RF preventing me from using my home studio-img_3713.jpg   RF preventing me from using my home studio-img_3712.jpg  
Old 4 weeks ago | Show parent
  #56
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Aaron Rash's Avatar
 
🎧 10 years
I also forgot to ask, what type of beads would be a good fit for the frequency range I'm picking up?
Old 4 weeks ago
  #57
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David Rick's Avatar
 
🎧 15 years
In a coax cable, the shield also carries the return current from the center conductor. If you disconnect the shield at one end, that current has to return through the chassis ground. That results in a giant loop area and will usually pick up a lot of line hum.

Beads made with type 28 ferrite material are best for rejecting the FM frequency band. Choose something that fits over your cable and has a high impedance at 100 MHz. Here's an example:

Laird 28B0592-000
Old 4 weeks ago | Show parent
  #58
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Aaron Rash's Avatar
 
🎧 10 years
Quote:
Originally Posted by David Rick ➑️
In a coax cable, the shield also carries the return current from the center conductor. If you disconnect the shield at one end, that current has to return through the chassis ground. That results in a giant loop area and will usually pick up a lot of line hum.

Beads made with type 28 ferrite material are best for rejecting the FM frequency band. Choose something that fits over your cable and has a high impedance at 100 MHz. Here's an example:

Laird 28B0592-000
Awesome,


Thanks David... I'll give those a try.

Also, I was wrong about the resistance between the RCA hot and shield pins dropping from 100R to to 50R from the amp warming up. It's actually coming from having both monitor plugs in on the output of the Apollo. If I unplug either one of them the resistance goes back up to 100R. Not exactly sure why this is happening or if it matters.


I want to try grounding the chassis of the Adcom, but wouldn't this be going against what Adcom says? Since the shield end of the cable is connected to ground on the Apollo side wouldn't grounding the Chassis also ground the shield on the Adcom side? At this point I might be overthinking it. I need to look at the schematics for the RCA shield side in the Adcom.
Old 4 weeks ago | Show parent
  #59
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Aaron Rash's Avatar
 
🎧 10 years
I tried grounding the chassis and measured the resistance between ground and the 100R the Adcom wants to see. Its shorting to ground, which is what the service manual warns against so I didn't even turn the unit on. I won't be able to ground the chassis of the Adcom.

I measured again on the Apollo and I just didn't have a good test point on the Apollo chassis but its getting a solid 0 ohm connection to ground. Thats where I assume the Adcom is taking the shortcut around the 100R resistor if I were to actually ground the Adcom chassis.

Which lead me to my original question. Would building a filter into the RCA cables help at all?

I'm pretty much out of ideas besides that.
Old 4 weeks ago | Show parent
  #60
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Radardoug's Avatar
 
🎧 10 years
Aaron, if you buy a couple of good quality Jensens, you will not hear any audio difference. Or you could sell your piece of crap amplifier and buy something that will work, with proper input circuits and a ground on the chassis. Dont try and flog a dead horse.
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