Victor and Mark,
thanks for sticking this out with me. Yes Victor you are correct, amp is connected via 2 prong (polarized) plug. Preamp is connected to amp with rca interconnects. (I have tried several different pairs that I know are good.)
I will get on the grounded clip lead test as soon as I can, hopefully tomorrow.
Mark, 1. I tried pulling the plugs as one of the first attempts, no difference with any configuration. I replaced the tubes too. 2. When the preamp is unplugged I get no voltage across the secondary, when it is plugged in I get .001-.002 Volts. I have no idea if this is significant leakage. 3. I knew I forgot to do something. I'll unsolder it ASAP.
An observations and a question:
1. The hum diminishes (by about half) when I hold the chassis.
2. I know that all the other lights and appliances can cause differing ground potentials and so one of the initial experiments I did was to plug this simple preamp/amp combo with no sources connected to my bathroom's GFI. It is the only 3-prong outlet I have. I checked the circuit panel and it seems that it has it's own breaker but I am making the assumption that this is a legitimately grounded outlet. Now I'm suspicious because this building (3 apartments) has seen several landlords over the last few years, each have done spotty renovations here and there to add value to the place..."modern 1 1/2 bath apartment for rent..." You get the idea. What is the simplest and safest way to verify that the GFI is a truely earth grounded outlet and not sharing another ground somewhere else in the house?
More to come soon,
gary
thanks for sticking this out with me. Yes Victor you are correct, amp is connected via 2 prong (polarized) plug. Preamp is connected to amp with rca interconnects. (I have tried several different pairs that I know are good.)
I will get on the grounded clip lead test as soon as I can, hopefully tomorrow.
Mark, 1. I tried pulling the plugs as one of the first attempts, no difference with any configuration. I replaced the tubes too. 2. When the preamp is unplugged I get no voltage across the secondary, when it is plugged in I get .001-.002 Volts. I have no idea if this is significant leakage. 3. I knew I forgot to do something. I'll unsolder it ASAP.
An observations and a question:
1. The hum diminishes (by about half) when I hold the chassis.
2. I know that all the other lights and appliances can cause differing ground potentials and so one of the initial experiments I did was to plug this simple preamp/amp combo with no sources connected to my bathroom's GFI. It is the only 3-prong outlet I have. I checked the circuit panel and it seems that it has it's own breaker but I am making the assumption that this is a legitimately grounded outlet. Now I'm suspicious because this building (3 apartments) has seen several landlords over the last few years, each have done spotty renovations here and there to add value to the place..."modern 1 1/2 bath apartment for rent..." You get the idea. What is the simplest and safest way to verify that the GFI is a truely earth grounded outlet and not sharing another ground somewhere else in the house?
More to come soon,
gary
gary h said:
Boo on the two prong polarized plug. Always use a three prong grounding plug with the third ground prong connected to the preamp chassis for safety.
When the hum reduces by holding the chassis it sounds like your body is acting as an antenna to apply ambient AC field hum out of phase and is partially canceling your induced hum. Sound crazy? It isn't.
Regarding your one grounded outlet, don't assume anything. Short of tracing the line to the basement power box to check the ground, you could try using an ohmmeter between the center ground of the outlet to the nearest "cold" water pipe. I might first do an AC voltage measurment between these points. You should get zero or very-very low fractional levels both for volts and ohms for a properly grounded outlet.
Another test you could make would be to take everything to a friends house, with known good wiring, and try it there. I once lived in an older appartment building and know what screwy things can be done over the years.
Victor,
I meant the outlet(s) I use have two poles, that is they have no dedicated ground. The remote box I have the transformer in now has a 3prong plug but because it is lifted, (unless I use my bathroom,) there is nothing to plug it into.
Also, my transformer has only + and - 120 input leads, no ground in. I have the red/yellow high voltage ground lead strapped directly to the new star ground I put in on the chassis, (see pics.)
Is there something else I can do to make this safer?
gary
I meant the outlet(s) I use have two poles, that is they have no dedicated ground. The remote box I have the transformer in now has a 3prong plug but because it is lifted, (unless I use my bathroom,) there is nothing to plug it into.
Also, my transformer has only + and - 120 input leads, no ground in. I have the red/yellow high voltage ground lead strapped directly to the new star ground I put in on the chassis, (see pics.)
Is there something else I can do to make this safer?
gary
Victor,
the bathroom GFI ground fluctuates between 1-5 ohms. I tried connecting it with both nearby hot and cold feeds. I'm going to take this show on the road. My wife works at a hospital and their labs purportedly have some pretty bomber electrical supplies. I'll let you know how it goes, (provided they let some weirdo toting a stereo, multimeter, and test speaker through the door.)
gary
the bathroom GFI ground fluctuates between 1-5 ohms. I tried connecting it with both nearby hot and cold feeds. I'm going to take this show on the road. My wife works at a hospital and their labs purportedly have some pretty bomber electrical supplies. I'll let you know how it goes, (provided they let some weirdo toting a stereo, multimeter, and test speaker through the door.)
gary
Without a solid earth ground through the AC outlets, your chassis will be floating. As long as nothing goes bad internally, nothing will happen. If a transformer shorts to the core, (worst case) the chassis will become hot and could hurt or kill you should you touch it when holding onto a water pipe or radiator or something that was grounded. A floating system could conceivably be contributing to the hum problem. An older building without grounded outlets does pose a problem. Replacing the outlets with grounding types is a job for a licensed contractor. Even then using the existing armored BX cable as a ground path isn't kosher, but would be better then nothing I guess.
One to five ohms isn't the best or the worst I've heard of. I'd call it acceptable. It's a lot better then 100. The fluctuation is probably contact resistance of your probes.
These transformers do not isolate the ground. Hospitals are ground freaks when it comes to patient safety. These transformers, like the ones made by Topaz, have an extremely low capacitive coupling between primary and secondary. On the order of femtofarads to reduce/elimate noise throughput.
Victor
One to five ohms isn't the best or the worst I've heard of. I'd call it acceptable. It's a lot better then 100. The fluctuation is probably contact resistance of your probes.
gary h said:
These transformers do not isolate the ground. Hospitals are ground freaks when it comes to patient safety. These transformers, like the ones made by Topaz, have an extremely low capacitive coupling between primary and secondary. On the order of femtofarads to reduce/elimate noise throughput.
Victor
Hi Gary, Looks like Victor is on the right track. I’m still dealing with a tube tester and only scanned the newest posts. I was hoping to eliminate the PT as a source of difficulty.
The leakage I was talking about is between the primary and secondary with the transformer unplugged and disconnected from the circuit. The question is: Is there any shorting between the primary and secondary. Check it with an ohm meter. If it isn’t auto-ranging then use a high-ohm scale like 100K and Meg-ohms.
Also, the screw in the wall plate should go to earth. If the grounded-neutral is wired properly there should be zero volts between the wide spade and the screw. If there is zero volts then check to see if there is a short between them with an ohm-meter.
If you have the screw going to the earth then grounding the chassis to the screw may eliminate the hum.
It is not uncommon for a polarized wall plug to be wired backwards, so be careful and check for zero volts from wide spade (neutral) to the screw in the center of the wall plate, FIRST.
Also, does the hum change with the tubes removed?
The leakage I was talking about is between the primary and secondary with the transformer unplugged and disconnected from the circuit. The question is: Is there any shorting between the primary and secondary. Check it with an ohm meter. If it isn’t auto-ranging then use a high-ohm scale like 100K and Meg-ohms.
Also, the screw in the wall plate should go to earth. If the grounded-neutral is wired properly there should be zero volts between the wide spade and the screw. If there is zero volts then check to see if there is a short between them with an ohm-meter.
If you have the screw going to the earth then grounding the chassis to the screw may eliminate the hum.
It is not uncommon for a polarized wall plug to be wired backwards, so be careful and check for zero volts from wide spade (neutral) to the screw in the center of the wall plate, FIRST.
Also, does the hum change with the tubes removed?
Mark, Victor,
I disconnected the PT and connnected preamp and amp. Still hums, maybe slightly less but not much. Still diminishes noticeably when I grip the chassis.
My multimeter shows no continuity between primary and secondary, (it goes to 40 MOhms.)
I get varying readings all less than 0.3 Volts when I measure several of the plugs in my apartment between the large spade plug and face plate screw/ground. No short though. (What causes the small potential?) I ran power from both bathroom (GFI) and kitchen (3 prong) to the stereo and using their earth ground didn't improve the hum, didn't change it at all from the 2 prong outlets everywhere else. I also tried lifting the ground from these outlets without improvement.
Hum doesn't change with tubes removed, I tried different configurations with the amp on/off/unswitched/unplugged.
I think the next most useful step is to try plugging in to a known well grounded outlet. I'll get on that this weekend and get back to you. If this doesn't yield a positive then I'm going to assume that somewhere I have a short and recheck all my connections. I'll bring my test leads with me so I can check all my connections to ground.
I got an isolation transformer for $50 on eBay before reading Victor's post that it probably won't help. Oh well, at least I'll have a gourmet surge protector.
Enjoy your weekend.
gary
I disconnected the PT and connnected preamp and amp. Still hums, maybe slightly less but not much. Still diminishes noticeably when I grip the chassis.
My multimeter shows no continuity between primary and secondary, (it goes to 40 MOhms.)
I get varying readings all less than 0.3 Volts when I measure several of the plugs in my apartment between the large spade plug and face plate screw/ground. No short though. (What causes the small potential?) I ran power from both bathroom (GFI) and kitchen (3 prong) to the stereo and using their earth ground didn't improve the hum, didn't change it at all from the 2 prong outlets everywhere else. I also tried lifting the ground from these outlets without improvement.
Hum doesn't change with tubes removed, I tried different configurations with the amp on/off/unswitched/unplugged.
I think the next most useful step is to try plugging in to a known well grounded outlet. I'll get on that this weekend and get back to you. If this doesn't yield a positive then I'm going to assume that somewhere I have a short and recheck all my connections. I'll bring my test leads with me so I can check all my connections to ground.
I got an isolation transformer for $50 on eBay before reading Victor's post that it probably won't help. Oh well, at least I'll have a gourmet surge protector.
Enjoy your weekend.
gary
Gary,
Did you see if the 3-prong ground was active? You should get 120 from the hot (narrow spade) to both the ground and the neutral, if it really is a grounded neutral.
I am going to look at your pictures sometime tonight.
What do you mean by "lifting the ground".
This is common with a.c. readings. I have assumed that it is due to capacitance somewhere when there is no closed circuit for the meter to measure.
You may not get surge protection from an isolation transformer. It may help some, but it is not a surge protector. You are already isolated from the mains with a standard PT. Possibly hospitals use isolation transformers so that the potential for shock is reduced. Instead of having the full force of the power station turbine there is only the small capacity of the isolation transformer secondary. Mark
Did you see if the 3-prong ground was active? You should get 120 from the hot (narrow spade) to both the ground and the neutral, if it really is a grounded neutral.
I am going to look at your pictures sometime tonight.
What do you mean by "lifting the ground".
This is common with a.c. readings. I have assumed that it is due to capacitance somewhere when there is no closed circuit for the meter to measure.
You may not get surge protection from an isolation transformer. It may help some, but it is not a surge protector. You are already isolated from the mains with a standard PT. Possibly hospitals use isolation transformers so that the potential for shock is reduced. Instead of having the full force of the power station turbine there is only the small capacity of the isolation transformer secondary. Mark
I looked at your pictures 5 and 6. What I would do next, if your trip to a different house doesn't improve things, is to go ahead and take the board out of the steel chassis. Also, have you shorted the inputs?
Was it Sherlock Holmes that started looking for the impossible after the improbable? M
Was it Sherlock Holmes that started looking for the impossible after the improbable? M
Gary, I was looking at one of your earlier pictures. The two large black capacitors are the .33uf couplers at the output?
If so, the two semi-circular symbols on the case may mean the outer-foil. If these are in backwards they may be picking up the hum.
I have read that the OF is not necessarily supposed to be directed toward ground. They are suppose to be directed toward the power supply, either positive or negative rail. Looks like they may be in backwards. Mark
If so, the two semi-circular symbols on the case may mean the outer-foil. If these are in backwards they may be picking up the hum.
I have read that the OF is not necessarily supposed to be directed toward ground. They are suppose to be directed toward the power supply, either positive or negative rail. Looks like they may be in backwards. Mark
Mark,
Ok, I will totally understand if you never reply again but here goes...I might be missing something very basic. I get 4.5 Ohm resistance between input and ground where they connect to the board. (But no continuity at the input jack.) Have I screwed up on one of my numerous re-wirings. The resistance grows over a few seconds, does this mean that one of my capacitors is leaking/misconnected (perhaps the output caps you mentioned) or have I just miswired the new pot I put in. Do tubes leak? Pics here:
http://home.comcast.net/~garyworld/pot1.jpg
http://home.comcast.net/~garyworld/pot2.jpg
or all of them: http://home.comcast.net/~garyworld/site/
I will reverse the polarity of the output caps (C303-.33uF 400V) tomorrow. The line section schematic (http://home.comcast.net/~garyworld/schematic1.jpg) doesn't show this as a polarized cap. Out of curiosity, how does one determine this?
Cheers,
gary
hailteflon said:
Ok, I will totally understand if you never reply again but here goes...I might be missing something very basic. I get 4.5 Ohm resistance between input and ground where they connect to the board. (But no continuity at the input jack.) Have I screwed up on one of my numerous re-wirings. The resistance grows over a few seconds, does this mean that one of my capacitors is leaking/misconnected (perhaps the output caps you mentioned) or have I just miswired the new pot I put in. Do tubes leak? Pics here:
http://home.comcast.net/~garyworld/pot1.jpg
http://home.comcast.net/~garyworld/pot2.jpg
or all of them: http://home.comcast.net/~garyworld/site/
I will reverse the polarity of the output caps (C303-.33uF 400V) tomorrow. The line section schematic (http://home.comcast.net/~garyworld/schematic1.jpg) doesn't show this as a polarized cap. Out of curiosity, how does one determine this?
Cheers,
gary
hailteflon said:
I get around 120 V from hot to both neutral and ground.
By "floating the ground" I meant that I first plugged the preamp/amp into this socket via a 3-prong plug, and then bypassed the ground with a 2-prong adaptor using the same socket. I don't know what that would tell me but I thought it was worth the 60 seconds.
gary
Gary, The resistance readings are probably related to the position of the potentiometer shaft. The input to the board is at ground when volume is at minimum.
Give me the information on the caps including the manufacturer and I will see if I can find a data sheet on the web.
To check the .33uf postions take a jumper and short the cap with the preamp connected to your amp, but NOT plugged into the wall. If they are picking up hum then it should stop when you put a jumper across the cap. Mark
Give me the information on the caps including the manufacturer and I will see if I can find a data sheet on the web.
To check the .33uf postions take a jumper and short the cap with the preamp connected to your amp, but NOT plugged into the wall. If they are picking up hum then it should stop when you put a jumper across the cap. Mark
Hi Mark,
regarding the pot, I measured the 4 Ohms with the preamp turned all the way down, I guess I was expecting that it would go to 0, but there is probably a slight input leak. I don't remember hearing any input signal with the pot turned down when I had a source connected. Plenty of hum though.
Here is a picture of the .33uF 630 Volt cap:
http://home.comcast.net/~garyworld/cap.jpg
On my parts list it is referred to as Mouser# C-FSD-33-630. I couldn't find it there but Google turned up some results, this is a Solen Dielectric polypropylene filmcap and the logo is actually their "S". I can't tell if there is a direction for this cap, I assumed it wasn't polarized because there are no other markings. I did try hooking a jumper before and after the cap to the chassis and the hum diminished significantly. In fact with the jumpers connected and holding the chassis with the amp turned all the way up the hum was almost quiet. This gives me hope but I reversed the caps as you suggested (shown in above pic) and it didn't make a difference. Could we be narrowing this down? What do you think?
gary
regarding the pot, I measured the 4 Ohms with the preamp turned all the way down, I guess I was expecting that it would go to 0, but there is probably a slight input leak. I don't remember hearing any input signal with the pot turned down when I had a source connected. Plenty of hum though.
Here is a picture of the .33uF 630 Volt cap:
http://home.comcast.net/~garyworld/cap.jpg
On my parts list it is referred to as Mouser# C-FSD-33-630. I couldn't find it there but Google turned up some results, this is a Solen Dielectric polypropylene filmcap and the logo is actually their "S". I can't tell if there is a direction for this cap, I assumed it wasn't polarized because there are no other markings. I did try hooking a jumper before and after the cap to the chassis and the hum diminished significantly. In fact with the jumpers connected and holding the chassis with the amp turned all the way up the hum was almost quiet. This gives me hope but I reversed the caps as you suggested (shown in above pic) and it didn't make a difference. Could we be narrowing this down? What do you think?
gary
Hi Gary, The 4 ohms reading is normal. Pots are not perfect.
Yes, we are getting closer to the problem. Every clue helps. I will look at the schematic again and hope to see something, after I look up this cap on the web. The Mouser number helps.
I am very curious as to the cause of the hum.
What type of solid state amp are you plugging the tube curcuit into?
Does it hum we connected to any other amps?
This is an edit:Solen site
I can't see it in their list, could it be obsolete? Mark
Yes, we are getting closer to the problem. Every clue helps. I will look at the schematic again and hope to see something, after I look up this cap on the web. The Mouser number helps.
I am very curious as to the cause of the hum.
What type of solid state amp are you plugging the tube curcuit into?
Does it hum we connected to any other amps?
This is an edit:Solen site
I can't see it in their list, could it be obsolete? Mark
Mark,
I found this page for MKP type non-polarized caps on the Solen site, mine could be one of these?
http://www.solen.ca/v1/caps/mkp.htm
All parts came as a kit from http://tubes4hifi.com/pre3.htm
They are likely bulk parts which might explain why this cap could be obsolete. (The tubes were new but came in a really old box.) I do feel that it is important to say here though that the preamp really sounds nice, the problem here is almost definitely my lack of electronics understanding.
The amps I have tried are Adcom GFT 5500, Samson Servo-260 and now my testing rig is a Dayton 150W plate amp connected to a sub-woofer with the crossover set to 140 Hz. The hum is much more pronounced on my "nicer" speakers (a DIY pair of Craig Selah's Peridot design) going through the Adcom.
So I'm planning an expedition this week to a place where I can spend some time plugged into a 3-prong earth grounded outlet, (the kind that doesn't snake it's way through 40 years of jury-rigged rewirings.) I'll take Victor's advice and jump the preamp output ground directly to earth and work my way back until the hum stops. Should I disconnect anything connected to the starground before I do this?
gary
I found this page for MKP type non-polarized caps on the Solen site, mine could be one of these?
http://www.solen.ca/v1/caps/mkp.htm
All parts came as a kit from http://tubes4hifi.com/pre3.htm
They are likely bulk parts which might explain why this cap could be obsolete. (The tubes were new but came in a really old box.) I do feel that it is important to say here though that the preamp really sounds nice, the problem here is almost definitely my lack of electronics understanding.
The amps I have tried are Adcom GFT 5500, Samson Servo-260 and now my testing rig is a Dayton 150W plate amp connected to a sub-woofer with the crossover set to 140 Hz. The hum is much more pronounced on my "nicer" speakers (a DIY pair of Craig Selah's Peridot design) going through the Adcom.
So I'm planning an expedition this week to a place where I can spend some time plugged into a 3-prong earth grounded outlet, (the kind that doesn't snake it's way through 40 years of jury-rigged rewirings.) I'll take Victor's advice and jump the preamp output ground directly to earth and work my way back until the hum stops. Should I disconnect anything connected to the starground before I do this?
gary
Hi Gary, you still haven't posted the marking on your .33uf capacitors. If I have this I can probably find out exactly what they are. One of the pictures on the Solen site for the PP film caps shows the type number stamped on the cap. It is two letters.
I don't know what to tell you about your star ground. I haven't seen it. The PT isolates the PS for your tube circuit through the magnetic field from primary to secondary. If you have a star ground and have everything isolated from the chassis, including the input and output grounds then you can connect the chassis to ground for shielding. You can try connecting the preamp PS ground to the earth, but always make sure the wall socket is wired correctly. Miswired wall sockets are quite common.
The question is, how is the power amp wired. Is the PS connected to the chassis and is the chassis connected to the earth at the wall plug? I don't explect you to have the answer to this.
There may be a ground problem, and maybe not. The problem may be an unintended characteristic in your preamp that makes it an antenna for hum.
I simply can't see the whole picture. You said that jumping the .33uf got rid of a lot of the hum. This is significant. I need to find out what type of caps they are before looking elsewhere. Mark
I don't know what to tell you about your star ground. I haven't seen it. The PT isolates the PS for your tube circuit through the magnetic field from primary to secondary. If you have a star ground and have everything isolated from the chassis, including the input and output grounds then you can connect the chassis to ground for shielding. You can try connecting the preamp PS ground to the earth, but always make sure the wall socket is wired correctly. Miswired wall sockets are quite common.
The question is, how is the power amp wired. Is the PS connected to the chassis and is the chassis connected to the earth at the wall plug? I don't explect you to have the answer to this.
There may be a ground problem, and maybe not. The problem may be an unintended characteristic in your preamp that makes it an antenna for hum.
I simply can't see the whole picture. You said that jumping the .33uf got rid of a lot of the hum. This is significant. I need to find out what type of caps they are before looking elsewhere. Mark
Now I can see what you have. I didn't know that it was a kit from an outfit like this one. I thought that you had possibly made the board yourself. It should work or they wouldn't have been able to market it. I have an astigmatism and reading every little thing is almost impossible.
The MKP-FC appears to be what you think it is. The "05" after France is probably the code for 2005. Your cap doesn't have the PB size code, but it appears to be a non-inductive wind. This means it doesn't have to be put in any certain position. They appear to be the "world's best" caps so they should work OK.
They show it in a Dyna chassis so you aren't doing something radical.
After you plug the whole thing into more modern wiring post the results. Mark
The MKP-FC appears to be what you think it is. The "05" after France is probably the code for 2005. Your cap doesn't have the PB size code, but it appears to be a non-inductive wind. This means it doesn't have to be put in any certain position. They appear to be the "world's best" caps so they should work OK.
They show it in a Dyna chassis so you aren't doing something radical.
After you plug the whole thing into more modern wiring post the results. Mark
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