You didn't see a list of equipment possibly because I am slightly ashamed of having a Radio Shack phono preamp. Actually it's not a bad little preamp for the $25 or so it cost. The model is 42-2111, and from googling a bit the 42-2111 is well regarded, as budget $25 preamps go.
I gave the circuit board a visual inspection tonight. There appeared to be rework at the same spot on each channel, with a particularly egregious solder joint on the right side. I touched it up and put the unit back together, though I could not tell any difference in the sound.
One thing I noted is that WHRI comes in only on the right channel, not the left. Something has to be rectifying the RF, and I suspect a bad solder joint. I was thinking of touching up all the connections but whatever solder was used has a very high melting point. I can crank my iron up high enough to melt it but I don't want to ruin anything.
The output of the Radio Shack is going into a Threshold FET ten/hl, which you might consider a vintage piece since I've had it in almost constant use for going on a quarter of a century. It's probably the only piece of Neslon Pass equipment I'll ever own, so I am in no hurry to replace it.
I used to have a Kenwwod preamp with phono stage, but I sold it. Before that I had a Dynakit, which I still have, and before that a Scott Kit, which was the first piece of audio gear I built.
As much as I might like to replace the phono preamp, I have a thread going in the Equipment & Tools section about the drill press I just ordered. I'm not going to be getting much of anything, including food, in the near future.
I could always try the Dynakit, though I would not expect it to be better than the Radio Shack, except maybe not receiving WHRI.
I did a quick experiment: since the left channel of the phono preamp works better than the right, I disconnected the right channel and connected the right channel of the cartridge directly to the Threshold, with the left channel still going through the Radio Shack.
Not bad at all! Maybe the best phono preamp is no phono preamp.
Edit: After listening a bit realized I forgot about RIAA.
Not bad at all! Maybe the best phono preamp is no phono preamp.
Edit: After listening a bit realized I forgot about RIAA.
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I see you haven't found any 20 pf disk caps yet. My RS doesn't have grab bag parts anymore, in fact they don't have any parts anymore. What a waste of space. I've found RS lead tin rosin core solder to be okay, but that was 20 years ago. I've found RS soldering irons to be terrible. I found a dead Weller WP25 by the ATM and cleaned the connections to the heater, much better. A chisel tip is worth the $6 to order it, if you are not doing IC's.
Turning a sow's ear into silk is what we do here, some of us. My RA88 disco mixer was $15 at the flea market. Played records just okay, maybe 45 db S/N, but got me through while I chased the channel imbalance in my Dynakit PAS2. Was a 50 year old paper cap with the wax case burned through, hidden on the bottom, but hiding it doesn't keep moisture out. After that I took after the hiss and hum on my disco mixer RIAA device, to see if I could make it as good as the PAS2. Almost- took about a dozen revisions, and about $20 in new parts. Not etching PCB's, and not driling square holes or slots in sheet metal with a hacksaw, is worth piddling with a Failure in design like the RA88a. I've parked the PAS2 back in the attic, saving 100 watts and the 50 year old tubes. (most caps & resistors are new, now). When you are not employed you have time to Do It Yourself.
Oh, dead PCAT power supplies from the charity resale shop are useful supplies of random parts. I got my last PC, with a serial mouse, for $4. Also, if you have a computer, you have probably replaced the power supply once or twice, I have a stack of 5 dead PCAT supplies. Useful pile of parts, when I blew 32 parts in the Peavey 1.3k by something stupid, I had them all. Also old TV's found on the curb.
Turning a sow's ear into silk is what we do here, some of us. My RA88 disco mixer was $15 at the flea market. Played records just okay, maybe 45 db S/N, but got me through while I chased the channel imbalance in my Dynakit PAS2. Was a 50 year old paper cap with the wax case burned through, hidden on the bottom, but hiding it doesn't keep moisture out. After that I took after the hiss and hum on my disco mixer RIAA device, to see if I could make it as good as the PAS2. Almost- took about a dozen revisions, and about $20 in new parts. Not etching PCB's, and not driling square holes or slots in sheet metal with a hacksaw, is worth piddling with a Failure in design like the RA88a. I've parked the PAS2 back in the attic, saving 100 watts and the 50 year old tubes. (most caps & resistors are new, now). When you are not employed you have time to Do It Yourself.
Oh, dead PCAT power supplies from the charity resale shop are useful supplies of random parts. I got my last PC, with a serial mouse, for $4. Also, if you have a computer, you have probably replaced the power supply once or twice, I have a stack of 5 dead PCAT supplies. Useful pile of parts, when I blew 32 parts in the Peavey 1.3k by something stupid, I had them all. Also old TV's found on the curb.
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Lavcat, noise and affordable Pass designs
Lavcat, great preamp. Absolutely an excellent piece, but may require capacitor / resistor replacement (almost all pieces at 25 years old or so should be.).What cartridge do you use? What turntable (I didn't see mention of that).
You might consider making a simple DIY passive RIAA preamp. Very few components. A DIY microphone amp should give you enough gain if your preamp doesn't through a regular input. Or rebuild the Radioshack piece, but with new components. The Threshold deserves to be fed by a better RIAA stage. Pass DIY has the Pearl phono stage...
I've had noise issues with my TT, but it was a tonearm wire/ tonearm wiring issue. Electrical noise can be frustrating to diagnose. I think you are on the right track.
Regarding replacing "almost all" components, I made those suggestions assuming the basics have already been covered, and that there existed problems with the rest of the system.
Vintage amplifiers and receivers, and a note to any about Pass designs, not all are expensive today: if you do have a a few spare $$$s get yourself a Nakamichi "SR" reciever. It uses a Pass designed (and Threshold licensed) "Stasis" circuit. When I sold audio about 20 years ago I did a comparison between (then new) the NAD 7240PE, a HK PM645, a Nakamichi SR3, and a Bryston 2BLP/.5B combination. All used whatever phono stage they had internally, and all were in the same power output class ranges (50ish watts/ch). Guess what? The Bryston pair was tops (but was more than 3Xs the cost of the next most expensive piece), followed by the Nak, the HK, and then the NAD. The only sonic area that the Bryston pair had over the Nak was the apparent bass. Not sure what the Naks go for now, but I gotta believe some must be available below $100. I bought one a few years ago for under $50. I'm keeping this one forever. I upgraded the speaker outputs from bad binding posts to good ones. The HK was pretty "etched in sound, but had the capability to push lots of current. The NAD was let down by a weak linestage.
Lavcat, great preamp. Absolutely an excellent piece, but may require capacitor / resistor replacement (almost all pieces at 25 years old or so should be.).What cartridge do you use? What turntable (I didn't see mention of that).
You might consider making a simple DIY passive RIAA preamp. Very few components. A DIY microphone amp should give you enough gain if your preamp doesn't through a regular input. Or rebuild the Radioshack piece, but with new components. The Threshold deserves to be fed by a better RIAA stage. Pass DIY has the Pearl phono stage...
I've had noise issues with my TT, but it was a tonearm wire/ tonearm wiring issue. Electrical noise can be frustrating to diagnose. I think you are on the right track.
Regarding replacing "almost all" components, I made those suggestions assuming the basics have already been covered, and that there existed problems with the rest of the system.
Vintage amplifiers and receivers, and a note to any about Pass designs, not all are expensive today: if you do have a a few spare $$$s get yourself a Nakamichi "SR" reciever. It uses a Pass designed (and Threshold licensed) "Stasis" circuit. When I sold audio about 20 years ago I did a comparison between (then new) the NAD 7240PE, a HK PM645, a Nakamichi SR3, and a Bryston 2BLP/.5B combination. All used whatever phono stage they had internally, and all were in the same power output class ranges (50ish watts/ch). Guess what? The Bryston pair was tops (but was more than 3Xs the cost of the next most expensive piece), followed by the Nak, the HK, and then the NAD. The only sonic area that the Bryston pair had over the Nak was the apparent bass. Not sure what the Naks go for now, but I gotta believe some must be available below $100. I bought one a few years ago for under $50. I'm keeping this one forever. I upgraded the speaker outputs from bad binding posts to good ones. The HK was pretty "etched in sound, but had the capability to push lots of current. The NAD was let down by a weak linestage.
A 'passive RIAA preamp' would need to be accompanied by a rather high dynamic range flat preamp with a gain of around 60dB or, better, two 30dB flat preamps. It might be simpler to just use a phono preamp, DIY or not, designed to do the job in one box!Nanook said:
There are ways of stopping RF from getting in to a circuit. Google RFI or EMC. Basically you want a high RF impedance in series and/or a low RF impedance to ground. Of course, it might simply be a poor ground connection somewhere. No need to change the entire system (salesman's solution?); just find and fix the problem.
DF96: salesman's solution...
.. that's not what I was getting at. I'm not selling anything, nor am I trying revert to "buy something" as the only out. As I have understood Lavcat's problem:
Someplace in there I suggested rebuilding the RS phono stage if that's what you want to do. For the same $$$s, one could build a good battery operated RIAA kit. The idea of a passive RIAA "stage" is that it is "quick n' dirty". Of course one can always got to the AD apps or similar (or build passive RIAA with whatever amp you choose).
My comments regarding the Nakamichi and others were in response to Lavcat's comment about never being able to afford another Pass design (I assume in the future).
digits: I used to blame the kids for "cranking" my stereo, but as all the kids are moved out, I now I know it's been the dishwasher all along
all: This is becoming the kind of banter that had ruined audioasylum. I'll bow out before that happens.
.. that's not what I was getting at. I'm not selling anything, nor am I trying revert to "buy something" as the only out. As I have understood Lavcat's problem:
- a dishwasher has affected the phono stage that is in use causing RF
- a Threshold (Nelson Pass design) linestage (Fet10 h/l)is in the system and is coveted
- that the problem has been narrowed down to the RS phono-stage (1 side)
- the problem persists
- New components in the RS phono stage can't be a bad thing
Someplace in there I suggested rebuilding the RS phono stage if that's what you want to do. For the same $$$s, one could build a good battery operated RIAA kit. The idea of a passive RIAA "stage" is that it is "quick n' dirty". Of course one can always got to the AD apps or similar (or build passive RIAA with whatever amp you choose).
My comments regarding the Nakamichi and others were in response to Lavcat's comment about never being able to afford another Pass design (I assume in the future).
digits: I used to blame the kids for "cranking" my stereo, but as all the kids are moved out, I now I know it's been the dishwasher all along
all: This is becoming the kind of banter that had ruined audioasylum. I'll bow out before that happens.
It's RF. Fast switching or something else is creating a broadband RF burst, which is either conducted or radiated or both into your system. Any semiconductor P-N junction can rectify RF. But so can other things. Sound quality can be affected in obvious ways, but also in subtle ways, which you will be glad to be rid of.
Everything is an input, for RF, including the system's output, DC power inputs (if any), signal inputs, and every length of wire or PCB trace.
In your case, it should turn out to be a very good clue that it only affects one channel. Have you checked the cable shield connections of your phono cables (both input and output cables)? If you have any other cables lying around, you might want to try swapping them in, to see how it might affect picking up the radio station when the phono input is engaged. Also, have you tried it with a different power amplifier (or whatever is downstream from the preamp)?
Does the phono preamp have low-pass RF filtering on its signal inputs? (Is there a schematic available?) If so, does the filter on the affected channel look OK? Maybe the cap to ground is not connected well?
If there are no low-pass RF filters for the inputs, I would definitely add a filter to each channel's input, especially since you said you can receive radio stations. The sound quality could improve significantly if the RF is blocked or sigificantly attenuated.
There is good information about RF filtering and shielding in section 7 of the following free book: ADI - Analog Dialogue | Op Amp Applications Handbook .
If there is a resistor already in series with the signal input conductor, you might be able to just add a small film capacitor to ground just before the input to the active circuit. (And you should first try just temporarily connecting a capacitor, there, one channel at a time, while you are hearing the radio station through the phono preamp, to see if it goes away. But I would still recommend adding a filter to each of the two channels.)
Otherwise, you should add a series resistor and then a cap to ground, for each input channel. (Or, for inverting amp inputs or others that don't respond well to a cap to ground from their input, simply use two Rs and put the cap to ground from between them, but you might have to use double the R value to get the same cutoff frequency, especially for an inverting amp input with negative feedback loop.)
The cutoff (-3dB, i.e. half power) frequency for a low-pass RC filter is
f = 1 / (2 x 3.14 x R x C) where f is in Hz, C is Farads, R is Ohms.
Usually you would probably pick f and C and calculate R, then fudge a little to a standard R value.
R = 1 / (2 x 3.14 x f x C)
But if you already have a series R, use that value and pick f then calculate C:
C = 1 / (2 x 3.14 x R x f)
So if you already had a series R of 330 Ohms and wanted a cutoff frequency of 220 kHz, which is probably a good one to try, you would calculate C = .002 uF. You could use .0022 uF (2.2 nF or 2200 pF), which would give f = 219.2 kHz.
It's also possible that the RF is affecting your main amplifier, especially if one of the cables from the phono preamp to the amp has lost its shield ground, or if there is separate circuitry in the main amp, for the phono input. Are you able to try the preamp plugged into something else?
Is there any change in radio station reception if the turntable is unplugged from the phono preamp?
Does your phono preamp operate from battery power? If so, you/we might have to give some thought to how the cable shields ought to be connected, at the ends of the input and the output cables of the phono preamp. And if so, are the battery leads tightly twisted together?
And how about the internal wiring for the signal inputs and their ground conductors? Shielded twisted pair? Or, if wires, are they at least tightly twisted together?
Have you tried the already-suggested small capacitor between the center and ground connectors of each input jack? Try 20-50 pF just held across the connectors and see if it changes the radio station reception.
Please let us know how it goes.
Cheers,
Tom
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There has been some progress.
The Radio Shack 42-2111 phono preamp is battery powered and the schematic is available in this Audioexpress review:
http://www.audioxpress.com/reviews/media/403hansen2090.pdf
The radio station reception was much reduced by disconnecting the turntable (which is a Kenwood KD-600, with Signet XK50 arm and Adcom XC/MR II cartridge).
The interference, which as I said was on the right channel only, moved with the cable connecting the phono preamp to the preamp. In other words, swapping the connections of the cables at the phono preamp outputs had no effect, but swapping the cable connections at the preamp input caused the radio station interference to move to the left channel.
The cables were old Monster interconnects that are supposedly directional. I suspect they may be constructed with the shield connected only at the source end, which could make a nice antenna.
I grabbed another pair of similar cables. With these I had interference on *both* channels. I looked around and found another set of cables, non-directional ones, that I believe originally came with some piece of Sony gear.
No interference. I am now peacefully listening to some Purcell.
I have yet to try the dishwasher.
The Radio Shack 42-2111 phono preamp is battery powered and the schematic is available in this Audioexpress review:
http://www.audioxpress.com/reviews/media/403hansen2090.pdf
The radio station reception was much reduced by disconnecting the turntable (which is a Kenwood KD-600, with Signet XK50 arm and Adcom XC/MR II cartridge).
The interference, which as I said was on the right channel only, moved with the cable connecting the phono preamp to the preamp. In other words, swapping the connections of the cables at the phono preamp outputs had no effect, but swapping the cable connections at the preamp input caused the radio station interference to move to the left channel.
The cables were old Monster interconnects that are supposedly directional. I suspect they may be constructed with the shield connected only at the source end, which could make a nice antenna.
I grabbed another pair of similar cables. With these I had interference on *both* channels. I looked around and found another set of cables, non-directional ones, that I believe originally came with some piece of Sony gear.
No interference. I am now peacefully listening to some Purcell.
I have yet to try the dishwasher.
I can now report.
First I did a sanity check with the current (Sony?) cables, and convinced myself that there was no shortwave interference.
Then I reconnected the original Monster cables in their intended direction. WHRI may have stopped their broadcast on 3.215, but I brought in a Spanish language music station. I had interference in both channels. Plus there was another station that was interfering with the Spanish language station.
Then I reversed the direction of the Monster cables. And I still had interference.
Finally I put back what I believe are the Sony cables and had no interference.
Good job!
If you have a multimeter or an Ohmmeter, it would be a good idea to check the cables (each cable in both sets), to see if the shield is connected all the way through or not, so you know which way it needs to be.
If the ones that work without RF interference DON'T have their shields connected all the way through, then I would try reversing them and see what happens. In that case, if one way works and one way doesn't, then I'm not sure how you could tell which end of the shield was not connected, unless you could tell by looking at them, somehow, or if the connectors were the type that could be opened.
It would also be interesting to see if the outer ground rings on all of the jacks are connected, between inputs and outputs, on the phono preamp and the main preamp. I would guess that they are at least connected to a common ground, internally. But you never know.
Sounds like the dishwasher breaker is on the same phase as the stereo. A zero cost thing to try is to remove the cover of your breaker panel. Locate the dishwasher and stereo breakers. Count the breakers and see if they are both on odd or even count counting from the top. The phases alternate. Breakers 1, 3, 5, 7, etc... will be on phase A, breakers 2, 4, 6, 8, etc... will be on phase B.
Make sure that the dishwasher and stereo are on opposite phases. If they are on the same phase then remove the breaker for the stereo and one below or above it and swap them and plug them back in. This will put them on opposite phases and reduce the transients from the motor starting. Make sure that your fridge is not on the same phase as the stereo too as this can have a similar effect. This is one that I would make sure of since the dishes are intermittent, the fridge always needs to run.
While you are in there just tighten each breaker wire and neutrals and grounds. Turn the main off before doing any work for safety.
Also, as pointed out it may just be interference picked up through your pre cables. Try twisted pair, they tend to have good cancellation characteristics. The set you have with the single ended ground are intended to reduce noise from ground loops as there is no physical ground connection at one end so it does shield the wire but does not actually ground the two components together. This will eliminate ground loops but can introduce RF into the system.
Make sure that the dishwasher and stereo are on opposite phases. If they are on the same phase then remove the breaker for the stereo and one below or above it and swap them and plug them back in. This will put them on opposite phases and reduce the transients from the motor starting. Make sure that your fridge is not on the same phase as the stereo too as this can have a similar effect. This is one that I would make sure of since the dishes are intermittent, the fridge always needs to run.
While you are in there just tighten each breaker wire and neutrals and grounds. Turn the main off before doing any work for safety.
Also, as pointed out it may just be interference picked up through your pre cables. Try twisted pair, they tend to have good cancellation characteristics. The set you have with the single ended ground are intended to reduce noise from ground loops as there is no physical ground connection at one end so it does shield the wire but does not actually ground the two components together. This will eliminate ground loops but can introduce RF into the system.
The cables that work indeed say "Sony" on them in small letters.
I think I'd have to cut the Monster cables open to get at the shields. I believe they are constructed with two conductors plus shield, with the shield connected only at one end. The ends are marked accordingly.
Brian, I live in an apartment and I hesitate to make changes in the breaker box. Thank you for the information though. I was more concerned with the dishwasher bringing out the symptom of the interference problem, rather than the dishwasher being a problem in itself. I'm just glad it no longer leaks.
I think I'd have to cut the Monster cables open to get at the shields. I believe they are constructed with two conductors plus shield, with the shield connected only at one end. The ends are marked accordingly.
Brian, I live in an apartment and I hesitate to make changes in the breaker box. Thank you for the information though. I was more concerned with the dishwasher bringing out the symptom of the interference problem, rather than the dishwasher being a problem in itself. I'm just glad it no longer leaks.
Question? Did the interference with the phono stage start after you fixed the leak in the dishwasher????
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