R-C's
CG,
Going back to the RC on the speaker end of the cable, I have tried this with .01uf and 10 ohms and it does work. It improves things across the board.
A product called Walker HD links is the same thing and the cost is around $350 USD. The more I do to reduce RFI in my SS equipment the more tube like it sounds.
Something else to think about is that some folks say that speakers act like antennas to the AM radio band. I know that the voice coil is sheilded, but AM radio antennas are a coil wound around a ferrite rod, and speakers are a coil around a magnet.
I am going to connect a driver to my Tektronix 7L12 spectrum analyzer and see what I get.. Also how about the air wound coils in the crossover acting as antennas?
CG,
Going back to the RC on the speaker end of the cable, I have tried this with .01uf and 10 ohms and it does work. It improves things across the board.
A product called Walker HD links is the same thing and the cost is around $350 USD. The more I do to reduce RFI in my SS equipment the more tube like it sounds.
Something else to think about is that some folks say that speakers act like antennas to the AM radio band. I know that the voice coil is sheilded, but AM radio antennas are a coil wound around a ferrite rod, and speakers are a coil around a magnet.
I am going to connect a driver to my Tektronix 7L12 spectrum analyzer and see what I get.. Also how about the air wound coils in the crossover acting as antennas?
scott wurcer said:
Been away from DIY home too long, I meant schedule K copper pipe as a shield.
There are some international standards for EMI robustness around, getting xDSL to work in the same box as 802.11 can be difficult since the xDSL signal is sensitive to the same IMD issues. There are some recommended tests mentioned too.
Re: R-C's
Those AM antennas have to be resonant in the AM band in order to have any significant efficiency. Once upon a time when tuning caps were used in radios, there was usually a separate section just to tune the antenna to resonance. It sure would be bad luck if your speaker cross-over coil just happened to resonate at the frequency of the local AM station. In any case, I'd think that the pseudo-Zobels you placed at your speakers would kill the efficiency, but who knows?
The good news is that those types of loop antennas are pretty direction and have deep nulls. That doesn't help with speaker placement, but it may be useful as an analytical tool.
I guess one solution if you have that problem might be to couple another coil to the field of the cross-over coil, and load it heavily. That might kill or at least dampen any RF resonance without screwing up the audio.
I've read about those Walker parts. From what I can tell, they're just what you built. There's some other guy who sells a less fancy version with good quality parts for much less.
This is a different problem than the common mode resonance of the cable working on the amplifier output.
Rick Miller said:
Those AM antennas have to be resonant in the AM band in order to have any significant efficiency. Once upon a time when tuning caps were used in radios, there was usually a separate section just to tune the antenna to resonance. It sure would be bad luck if your speaker cross-over coil just happened to resonate at the frequency of the local AM station. In any case, I'd think that the pseudo-Zobels you placed at your speakers would kill the efficiency, but who knows?
The good news is that those types of loop antennas are pretty direction and have deep nulls. That doesn't help with speaker placement, but it may be useful as an analytical tool.
I guess one solution if you have that problem might be to couple another coil to the field of the cross-over coil, and load it heavily. That might kill or at least dampen any RF resonance without screwing up the audio.
I've read about those Walker parts. From what I can tell, they're just what you built. There's some other guy who sells a less fancy version with good quality parts for much less.
This is a different problem than the common mode resonance of the cable working on the amplifier output.
John, were you concerned about RF entering the Blowtorch thru the output? If you were, how would you recommend reducing the RF? I believe that the Blowtorch does not have a global negative feedback loop so in that case it would not be subject to RF from the output coming back to the input. Perhaps this is another advantage of a non feedback design. Being all Fet places it at a great advantage to start with as Fets are far less affected by RF that bipolars.
It’s a great design John!
It’s a great design John!
PMA, when insulated connectors are used I have seen a small value (.01-.001uf) non inductive cap between the shield of the connector and the metal chassis. Have you used this technique, and if so how successful is it in reducing RF and does this cap have any audible impact on the sound of the equipment?
Hi Rick, to be honest, some of the solutions suggested by both you and PMA remind me of 'throwing the baby out to change the bath water'. If you have that much RFI, something is wrong with where you live. However, if you were located at a broadcast station, I can see where this might come up. Do you have problems like this, Rick, at Comcast?
What concerns me is that super RF proofing, using ceramic caps, shielded wire on the inside of the shielded box, etc. , will change the quality of the sound we are trying to preserve. Bear's silver wire has no shield, and 'we don't need no stinkin' shielded wire inside our box'.
What concerns me is that super RF proofing, using ceramic caps, shielded wire on the inside of the shielded box, etc. , will change the quality of the sound we are trying to preserve. Bear's silver wire has no shield, and 'we don't need no stinkin' shielded wire inside our box'.
john curl said:
What concerns me is that super RF proofing, using ceramic caps, shielded wire on the inside of the shielded box, etc. , will change the quality of the sound we are trying to preserve. Bear's silver wire has no shield, and 'we don't need no stinkin' shielded wire inside our box'.
Hi John, I don’t feel that I live in a high RF environment but everything that I have done to reduce RFI has improved things. Now I’m sure that there is a point of diminishing returns and impacting the sound as you point out. I am interested in RF entering the output of an amplifier and causing reduced sound quality. I feel that most people don’t think about RF coming into an amplifier from its connection to the outside world.
In the RF world radio repeaters co-located on the same tower can suffer from intermod where the output of one repeater will be received by another and enter its output and mix in its output stage with its frequency and be transmitted out as a intermod product. Could this happen with RF and audio in our output stages?
Rick, the best that we have found is high speed, high frequency linear open loop, low or no global feedback designs. Then, a little RF in the loop is not too bad. Kind of like designing a video amplifier.
IF it is an entirely open loop design, like the Ayre, it is relatively easy, because the high speed low open loop Z output stage, absorbs the RF coming in, just like an attenuator. If you use global feedback, then a very linear, high speed design is necessary. This is one place where a 'lead' cap in the feedback might be questionable. Think about it, everyone.
IF it is an entirely open loop design, like the Ayre, it is relatively easy, because the high speed low open loop Z output stage, absorbs the RF coming in, just like an attenuator. If you use global feedback, then a very linear, high speed design is necessary. This is one place where a 'lead' cap in the feedback might be questionable. Think about it, everyone.
Hi John,
Most people live in areas where there is a fair amount of RFI. Just think of all those cell phones for example. Switching power supplies, florescent lamps (in a neighbor's house for example). This is a concern for almost everyone in today's world.
RFI can cause any design to become non-linear. They can overdrive some stages well above your hearing, but you will hear the effects on your audio signal. Even with some systems with no active music input, you may be able to hear the effects if you listen close to your speaker. It varies.
Where my business was, there was a location in our area where a strong AM station was operating, and still is to this day. The RFI was so strong that many CD players would not operate, they couldn't track at all. Phono preamps were constantly distorted due to this, and some power amplifiers were sent to amp heaven. So, the effects of RFI can certainly be destructive, depending on the field strength. A couple recording studios I did work in were also strongly affected. The Metalworks in Mississauga had to create a Faraday cage around Studio A. It was wrapped in sheet copper, not expanded metal or perforated metal. A solid sheet of copper that was grounded and connected to the room ground. Technical grounds do not help in these situations.
I think too, you have to consider both the material and value of inductors and capacitors used to bypass RF in the audio range. A ferrite bead, as commonly used (not really large at all) has very little effect at audio frequencies. It's also not going to be saturated unless you have very real big RFI problems. Also, the use of NP0 / C0G ceramics at small values will not present a problem to your audio signals. You can always use Teflon® or mica capacitors without too much fear. If you are really concerned, use a Johnson (or equivalent) screw adjustable capacitor and run your lead through that instead. It will have external metalization already, solder to that. I'm talking about something like this, or this and similar products. You can see that you can run a relatively large conductor through these with minimal effort.
Once you look at the idea and consider the values of components under consideration, I'm pretty sure you will not think you are 'throwing the baby out to change the bath water'. Off the cuff, that view is pretty closed. Always remember John, "Condemnation without Examination is Prejudice". I think that applies here. The ideas presented here are valuable ones from where I sit. Many of your customers may not have the advantage afforded by living in an RFI free zone, not in this day of cell phones and (horror) Wi-Fi signals. Even AM radio presents a very real threat to musical enjoyment.
-Chris
Edit:
Most people live in areas where there is a fair amount of RFI. Just think of all those cell phones for example. Switching power supplies, florescent lamps (in a neighbor's house for example). This is a concern for almost everyone in today's world.
RFI can cause any design to become non-linear. They can overdrive some stages well above your hearing, but you will hear the effects on your audio signal. Even with some systems with no active music input, you may be able to hear the effects if you listen close to your speaker. It varies.
Where my business was, there was a location in our area where a strong AM station was operating, and still is to this day. The RFI was so strong that many CD players would not operate, they couldn't track at all. Phono preamps were constantly distorted due to this, and some power amplifiers were sent to amp heaven. So, the effects of RFI can certainly be destructive, depending on the field strength. A couple recording studios I did work in were also strongly affected. The Metalworks in Mississauga had to create a Faraday cage around Studio A. It was wrapped in sheet copper, not expanded metal or perforated metal. A solid sheet of copper that was grounded and connected to the room ground. Technical grounds do not help in these situations.
I think too, you have to consider both the material and value of inductors and capacitors used to bypass RF in the audio range. A ferrite bead, as commonly used (not really large at all) has very little effect at audio frequencies. It's also not going to be saturated unless you have very real big RFI problems. Also, the use of NP0 / C0G ceramics at small values will not present a problem to your audio signals. You can always use Teflon® or mica capacitors without too much fear. If you are really concerned, use a Johnson (or equivalent) screw adjustable capacitor and run your lead through that instead. It will have external metalization already, solder to that. I'm talking about something like this, or this and similar products. You can see that you can run a relatively large conductor through these with minimal effort.
Once you look at the idea and consider the values of components under consideration, I'm pretty sure you will not think you are 'throwing the baby out to change the bath water'. Off the cuff, that view is pretty closed. Always remember John, "Condemnation without Examination is Prejudice". I think that applies here. The ideas presented here are valuable ones from where I sit. Many of your customers may not have the advantage afforded by living in an RFI free zone, not in this day of cell phones and (horror) Wi-Fi signals. Even AM radio presents a very real threat to musical enjoyment.
-Chris
Edit:
The idea is correct, but you are assuming that the output is low impedance at RF frequencies. That is where your idea may fall down.
Hi John,
With all due respect sir, just because you design stuff does not mean you have a full depth of knowledge in every subject. It is possible you are mistaken or over-reacting. Beating your chest will not change that fact.
I was merely pointing out facts that I know to be true, backed up with both experience and other professional guidance. I even took the trouble to point you to acceptable solutions to what you seem to think are problems.
Now, consider what others have told you, I'm only supporting what others have said here, and use the gray, gooey stuff between your ears to think about this. Look a the information, not the messenger.
Regards sir, Chris
With all due respect sir, just because you design stuff does not mean you have a full depth of knowledge in every subject. It is possible you are mistaken or over-reacting. Beating your chest will not change that fact.
I was merely pointing out facts that I know to be true, backed up with both experience and other professional guidance. I even took the trouble to point you to acceptable solutions to what you seem to think are problems.
Now, consider what others have told you, I'm only supporting what others have said here, and use the gray, gooey stuff between your ears to think about this. Look a the information, not the messenger.
Regards sir, Chris
Alright everyone, this is the situation with the BLOWTORCH and I might remind people that this thread is a continuation of the original Blowtorch Preamplifier thread. This is important, because my name is associated with the BLOWTORCH as I designed the electronics for it.
Now with 40 units out there, have we EVER had a complaint or comment about RFI problems? The answer is NO! Now why? First, because the case is so thick and almost air tight, it is almost RF proof, except for the input cables and the power supply connecting cord between the two chassis.
Also, the open loop design tends to pass or naturally roll off RF even if it does get in the input lines. The power supply lines are separately buffered with individual mosfet buffers with appropriate RF quality bypass caps on both input and output of the buffers. We are not unaware of RF, but the circuitry is not especially sensitive to it. IF we had used bipolar inputs, perhaps we would have more problems, but fets are more RFI immune.
Why we built the Blowtorch with such a thick case was to provide a shield from RFI. Even that thick of an aluminum case does NOT protect much from 50-60 Hz hum pickup. Only steel or mumetal will do that effectively. However, it is true that we did not COMPLETELY RFI proof the design although I am pretty sure it would pass any normal RFI immunity test.
Being over-concerned about RFI is like being over-concerned about idiot proof safety protection.
I might remind everyone that I once worked at UL Labs. for about 1 year as a test tech, I know something as well about electrical safety, but I would get some people raving at me, if heard my opinions about their over-zealous statements.
For example, I don't think that people should put their power amps on a shelf over their salt water swimming pool, only to have it pulled off by their pet monkey into the pool and perhaps hurting somebody. However, in this litigious society, the designer would be blamed anyway, so let's obey the rules, everybody.
Now with 40 units out there, have we EVER had a complaint or comment about RFI problems? The answer is NO! Now why? First, because the case is so thick and almost air tight, it is almost RF proof, except for the input cables and the power supply connecting cord between the two chassis.
Also, the open loop design tends to pass or naturally roll off RF even if it does get in the input lines. The power supply lines are separately buffered with individual mosfet buffers with appropriate RF quality bypass caps on both input and output of the buffers. We are not unaware of RF, but the circuitry is not especially sensitive to it. IF we had used bipolar inputs, perhaps we would have more problems, but fets are more RFI immune.
Why we built the Blowtorch with such a thick case was to provide a shield from RFI. Even that thick of an aluminum case does NOT protect much from 50-60 Hz hum pickup. Only steel or mumetal will do that effectively. However, it is true that we did not COMPLETELY RFI proof the design although I am pretty sure it would pass any normal RFI immunity test.
Being over-concerned about RFI is like being over-concerned about idiot proof safety protection.
I might remind everyone that I once worked at UL Labs. for about 1 year as a test tech, I know something as well about electrical safety, but I would get some people raving at me, if heard my opinions about their over-zealous statements.
For example, I don't think that people should put their power amps on a shelf over their salt water swimming pool, only to have it pulled off by their pet monkey into the pool and perhaps hurting somebody. However, in this litigious society, the designer would be blamed anyway, so let's obey the rules, everybody.
I'm thinking about ten times the highest audio frequency, how about an f3 of 200Khz?
Also;
Thinking about it, once RF enters the output one thing that can get rid of it is when it passes thru the output devices to the rails the bypass caps would short it out. Also is it true that the higher the output stages idle current the better for RF being lowered there and not passing towards the front end of the line stage?
Thanks for your input John.
Also;
Thinking about it, once RF enters the output one thing that can get rid of it is when it passes thru the output devices to the rails the bypass caps would short it out. Also is it true that the higher the output stages idle current the better for RF being lowered there and not passing towards the front end of the line stage?
Thanks for your input John.
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