I built an EAR 834p clone a couple of years ago using a bare board from eBay and a power supply designed by one of the guys associated with the Lenco Heaven forum. It's all quality parts. I have issues with it attempting to pick up 93.7FM and I'm struggling to figure out a solution. I live up on a hill with line of sight to the 93.7 tower which is also on a hill. It's like a 100,000watt monster so I'm getting blasted. I was using interconnects with minimal shielding which clearly was adding to the problem so as a test I changed the interconnect from my Well Tempered Amadeus to Blue Jeans LC-1 since they are pretty heavily shielded and that helped. Here's what I don't understand...I'm also getting an antenna effect from the interconnects from the EAR clone TO my Sugden integrated amp. I know this is the case b/c I can move the cables around and change the radio reception issue. I can understand having the issue on the tonearm (input) side given the low nature of the source signal, the significant gain in the phono stage, etc. What I don't understand is why am I also getting a radio effect on the line level output of the phono stage but I'm not experiencing the same issue on any other source. My Qutest DAC, Sansui FM tuner, etc are all fine and using the same minimal shield interconnects. I've ordered some more LC-1s to try on the line level output side to see if that's enough to knock it out.
I don't think I have any obvious issues in the grounding or layout of the phono stage? Any thoughts on what else to try/test? It's driving me crazy.
I don't think I have any obvious issues in the grounding or layout of the phono stage? Any thoughts on what else to try/test? It's driving me crazy.
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Try ferrite beads in all input and output lines or better try to find VK200 cores, they are designed for VHF chokes. Add ceramic or SMD capacitor of proper voltage ratings in any wire input and output. Make shiels with copper paper around tubes and ground them using strips of the same material, no round wires (stripes have less inductance than round wires). Add ferrite cores for common mode in all cables (like those bulks in PC monitors) and use cables whose long aren't multiple or submultiple of lambda/4 metres (lambda is the wave long in vacuum and is 300/f[MHz] in metres). I'm ham radio from 1987.
Add COG/NPO 0.01uF ceramic disc capacitors, from the input RCA ground lugs, directly to the chassis,
with very short leads. Also from the output jack ground lugs to the chassis.
In the most difficult situations, reduce the turntable and output RCA cables to about half their lengths.
This detunes the cable RF resonance. Or using cables with a twisted pair and a foil shield may help.
with very short leads. Also from the output jack ground lugs to the chassis.
In the most difficult situations, reduce the turntable and output RCA cables to about half their lengths.
This detunes the cable RF resonance. Or using cables with a twisted pair and a foil shield may help.
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You could try adding a 2k2 & 2n2 cap LPF on the input, that'll roll off everything above 32khz without effecting the frequency response of your preamp hopefully. For clarity that's the 2k2 from RCA IP to V1 grid, with a 2200p or 2n2 from grid to ground. This can easily be done on the RCA IP most times with some small components.
Andy.
Andy.
Output impedance of a cathode follower is inductive at HF, so it resonates with the cable capacitance. My guess is you need a 100R build-out resistor, and a small grid stopper on the input too.
Thanks for this, I'll do some reading on the subject. I've built several things from kits so my assembly skills are pretty solid, but my electrical knowledge (outside of the basics) are a work in progress.
It's hard to tell from the original picture, but there is a safety earth connection in place already from the mains inlet to a dedicated screw on the silver chassis mounting plate. It's the green wire going down and to the right off the mains inlet. The green wire going left is the ground to the power supply (where everything else star grounds). Here's another angle where you can see it clearly.
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Oh I can see clearly now!
Yesterday while doing a search I came across a rod coleman aid to using bead chokes.He pointed to and referenced a particular type.They need to be right on the grid pins.You could glue it.
Maybe use the input wiring scheme that's on that valvewizard article.
Btw I have owned that EAR834P Phono Box....many years ago.The edition that used an autoformer mc step-up.Worked well with my Denon 304 cartridge.
Yesterday while doing a search I came across a rod coleman aid to using bead chokes.He pointed to and referenced a particular type.They need to be right on the grid pins.You could glue it.
Maybe use the input wiring scheme that's on that valvewizard article.
Btw I have owned that EAR834P Phono Box....many years ago.The edition that used an autoformer mc step-up.Worked well with my Denon 304 cartridge.
While I wasn't getting radio, I was getting hum and oscillation on one of my builds a while back. I now use RG174 for the I/O wiring.
I did have a phono build that picked up 99.9MHz FM radio that I was using 12SN7 Westinghouse black plate tubes from Japan. Swapping them for Canadian GE sorted it in that case.
I did have a phono build that picked up 99.9MHz FM radio that I was using 12SN7 Westinghouse black plate tubes from Japan. Swapping them for Canadian GE sorted it in that case.
Good to know on the RG174. I was considering whether I should have used something shielded on the I/O wiring. I'm going to try some 0.01uF ceramic disc caps on the inputs first since it's easy and see what that accomplishes.
I have built one of these and it's dead quiet and I am very close to the local FM, though not your close. Couple Qs, you didn't build the Chinese kit/board regulated supply? It's a alternate/3rd party one? That's a big unknown right? What do you know about it?
Also, what is the copper shield foil for? Is the case not metal already? Mine is in aluminum and it's fine as-is. That foil tape is usually for things in plastic or wood with no electrical shielding properties. If it is in metal already, that's just a non-needed expense.
Some film caps either with/or replacing the electrolytics on the phono board will help a lot. Soundwise. Judging from the sizes on the actual signal pass and RIAA stuff, I think those could get some love too with better parts. But then I go, if that concerned with shielding, why is the in/out cable braided vs shielded? And looks like violating the single ground path of both of those very important signal carriers. Maybe but doubtful.
Do you have access to an high end oscilloscope? You could trace the radio then if it could handle the bandwidth. A hobbyist scope won't cut it. My gut though is something is not built correctly to the schematic. But then I go... are those wires run underneath and outside of the case or between the holed floor and case? I think you may in your attempt to shield everything, have built the natural air spaced caps that make radio receivers. All that metal and space means lots of low value capacitance. I have 35+ years in tube audio, but never played in radio land really so can't comment, but that is what comes to mind from looking at this.
Some other phone amps I have repaired and built, do indeed have low value caps across the in and out jacks specifically to filter high frequency noise at the enter/exit of the phone pre. I don't see those here.
Also, what is the copper shield foil for? Is the case not metal already? Mine is in aluminum and it's fine as-is. That foil tape is usually for things in plastic or wood with no electrical shielding properties. If it is in metal already, that's just a non-needed expense.
Some film caps either with/or replacing the electrolytics on the phono board will help a lot. Soundwise. Judging from the sizes on the actual signal pass and RIAA stuff, I think those could get some love too with better parts. But then I go, if that concerned with shielding, why is the in/out cable braided vs shielded? And looks like violating the single ground path of both of those very important signal carriers. Maybe but doubtful.
Do you have access to an high end oscilloscope? You could trace the radio then if it could handle the bandwidth. A hobbyist scope won't cut it. My gut though is something is not built correctly to the schematic. But then I go... are those wires run underneath and outside of the case or between the holed floor and case? I think you may in your attempt to shield everything, have built the natural air spaced caps that make radio receivers. All that metal and space means lots of low value capacitance. I have 35+ years in tube audio, but never played in radio land really so can't comment, but that is what comes to mind from looking at this.
Some other phone amps I have repaired and built, do indeed have low value caps across the in and out jacks specifically to filter high frequency noise at the enter/exit of the phone pre. I don't see those here.
Slope detection I think...
"Slope detection is the very simplest form of frequency modulation, FM demodulation. An FM slope detector consists of a tuned circuit where the centre frequency is tuned to a frequency slightly offset from the carrier of the signal. In this way the frequency modulated signal sits on the slope of the response curve, giving rise to the name of FM slope detector.
As the frequency of the signals varies up and down in frequency according to its modulation, so the signal moves up and down the slope of the tuned circuit response curve. This causes the amplitude of the signal to vary in line with the frequency variations. In fact at this point the signal has both frequency and amplitude variations.
FM slope detection concept
It can be seen from the diagram that changes in the slope of the filter, reflect into the linearity of the demodulation process. The linearity is very dependent not only on the filter slope as it falls away, but also the tuning of the receiver - it is necessary to tune the receiver off frequency and to a pint where the filter characteristic is relatively linear.
The final stage in the process is to demodulate the amplitude modulation and this can be achieved using a simple diode circuit. One of the most obvious disadvantages of this simple approach is the fact that both amplitude and frequency variations in the incoming signal appear at the output. However the amplitude variations can be removed by placing a limiter before the detector.
A variety of FM slope detector circuits may be used, but the one below shows one possible circuit with the applicable waveforms. The input signal is a frequency modulated signal. It is applied to the tuned transformer (T1, C1, C2 combination) which is offset from the centre carrier frequency. This converts the incoming signal from just FM to one that has amplitude modulation superimposed upon the signal.
FM slope detector circuit showing the signal waveforms
This amplitude signal is applied to a simple diode detector circuit, D1. Here the diode provides the rectification, while C3 removes any unwanted high frequency components, and R1 provides a load."
"Slope detection is the very simplest form of frequency modulation, FM demodulation. An FM slope detector consists of a tuned circuit where the centre frequency is tuned to a frequency slightly offset from the carrier of the signal. In this way the frequency modulated signal sits on the slope of the response curve, giving rise to the name of FM slope detector.
As the frequency of the signals varies up and down in frequency according to its modulation, so the signal moves up and down the slope of the tuned circuit response curve. This causes the amplitude of the signal to vary in line with the frequency variations. In fact at this point the signal has both frequency and amplitude variations.
It can be seen from the diagram that changes in the slope of the filter, reflect into the linearity of the demodulation process. The linearity is very dependent not only on the filter slope as it falls away, but also the tuning of the receiver - it is necessary to tune the receiver off frequency and to a pint where the filter characteristic is relatively linear.
The final stage in the process is to demodulate the amplitude modulation and this can be achieved using a simple diode circuit. One of the most obvious disadvantages of this simple approach is the fact that both amplitude and frequency variations in the incoming signal appear at the output. However the amplitude variations can be removed by placing a limiter before the detector.
A variety of FM slope detector circuits may be used, but the one below shows one possible circuit with the applicable waveforms. The input signal is a frequency modulated signal. It is applied to the tuned transformer (T1, C1, C2 combination) which is offset from the centre carrier frequency. This converts the incoming signal from just FM to one that has amplitude modulation superimposed upon the signal.
This amplitude signal is applied to a simple diode detector circuit, D1. Here the diode provides the rectification, while C3 removes any unwanted high frequency components, and R1 provides a load."
The copper shield was something I had and was an experiment to see if it helped...it didn't. In hindsight, it was clearly redundant given the case is metal and grounded. This was the first real project I did that wasn't a full kit from somewhere so my limited experience resulted in what you see now. I've been considering redoing the in/out cable with something shielded. I do have a good scope that I inherited from a friend but I don't really have any experience using it so I'll have to do some research.
There is a metal case floor under the holed mounting floor. None of the cables run under the holed floor. I know in that first picture it may look like those black/red power wires run under the floor but they don't. If you look at my second pic you'll see they just run along the front wall to the power supply. Re: the power supply, it came from here: https://www.alpha2delta.co.uk/PSU1/ The designer turned it into the commercial product you see linked...originally it was just a board he made available for these Chinese EAR boards. https://www.lencoheaven.net/forum/index.php?topic=27259.45.
Can you elaborate on 'violating the single ground path'? I'm pretty confident in my soldering (having built a number of other kits) but grounding on this was always an area where I was a little unclear on best practice. In particular, it's not clear to me where the signal ground terminates (and maybe that's the problem).
Thanks for all of the help here guys...it's a learning experience and I really appreciate it.
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Thank you for the follow up. The idea for lowest noise is a single point of ground. Some call it star... whatever floats your boat. But with that idea, your in and out leads can't be grounded at both ends and have a single, smallest path to ground. So usually in low noise apps, only one side is the closest to ground. I don't think that is your problem, but it is something to consider.
