Hello everyone,
I have had quite a few problems with my old ARC SP8 pre amp. ALL of these have been fixed with your combined help, so THANK YOU for your creative, smart, and knowledgable support.
Now the system has been sounding fabulous and I had got the levels of noise and hum to a very low level you could barely hear even at the speaker position.
BUT last night both speakers were accompanying the normal background low level noise with a (guess 100Hz) zizz, in both channels, and one that increased with the volume. The noise was independent of source, and was gone, not surprisingly, on mute. I had changed nothing in the preamp for quite a while, and it had been fault free for 18 months or more I would guess.
I swapped out all the valves including the power supply ones, and the zizz remained.
I did a very quick check on voltages around the valves and power supply and they all seemed as usual, I should repeat more carefully.
Music plays as normal, accompanied by zizzz
I don't own a proper oscilloscope but I have done some testing cheating with REW software recording before.
So my thought are as below:
I have already changes a few and also when sorting a problem with the phono stage so there are not that many left.
Any thoughts welcome
I have had quite a few problems with my old ARC SP8 pre amp. ALL of these have been fixed with your combined help, so THANK YOU for your creative, smart, and knowledgable support.
Now the system has been sounding fabulous and I had got the levels of noise and hum to a very low level you could barely hear even at the speaker position.
BUT last night both speakers were accompanying the normal background low level noise with a (guess 100Hz) zizz, in both channels, and one that increased with the volume. The noise was independent of source, and was gone, not surprisingly, on mute. I had changed nothing in the preamp for quite a while, and it had been fault free for 18 months or more I would guess.
I swapped out all the valves including the power supply ones, and the zizz remained.
I did a very quick check on voltages around the valves and power supply and they all seemed as usual, I should repeat more carefully.
Music plays as normal, accompanied by zizzz
I don't own a proper oscilloscope but I have done some testing cheating with REW software recording before.
So my thought are as below:
- Zizzz 100Hz is likely from power supply
- if it is in both channels and independent of input it is more likely power supply
- I should start looking at capacitors first (in the power supply)
I have already changes a few and also when sorting a problem with the phono stage so there are not that many left.
Any thoughts welcome
Thanks for all the feedback and logic.
So here is some more information, and intrigue!
So here is some more information, and intrigue!
- The noise is not consistent, I have had a couple of times when it is not there (once it went while it was on, I was listening to music for a few tracks to see if there was any other artefacts of the sound, none noticed and when I stopped playing I noticed the zz had gone). When I switched in on the next morning it was back again.
- I have switched off everything nearby, my Macbook, Dac, USB Bridge, network switches, my wife's computer next room etc etc. This made no difference when the zZZZ was happening.
- I live in a detached house, and I have a dedicated power line into the hifi consumer unit that splits incoming after the meter. I also use parallel mains filters that are capacitors across Live>Neutral on this line after the hifi consumer unit, I am not sure of the measured affect of these, but they will likely have no benefit at relatively low frequencies. Switching these on and off made no difference to the zZZZ.
i found this on Steve Hoffman's site,
"I have an Audio Research Search SP-8 that has been making static sounds at random every few seconds to almost continuously, to not at all for an hour or so. It finally became so bad I couldn’t turn it on. I re-tubed it with new Mullard tubes. The problem was solved for a few hours then started again. I searched the web for weeks looking for possible reasons. There are many, from a resister in the base of the tube(s), to a bad tube or I put another bad tube in. I was about to send it off to Audio Research, but I thought I would have one last look at the circuit board and components to see if there was anything out of the ordinary. The nut on the rear panel common ground lugs for rack mount grounding on the back had come loose. I took the brass nut off and wire connector and polished the tarnish off with 3,000 grit sandpaper and screwed it back on. It’s perfect now !"
so check the ground!
"I have an Audio Research Search SP-8 that has been making static sounds at random every few seconds to almost continuously, to not at all for an hour or so. It finally became so bad I couldn’t turn it on. I re-tubed it with new Mullard tubes. The problem was solved for a few hours then started again. I searched the web for weeks looking for possible reasons. There are many, from a resister in the base of the tube(s), to a bad tube or I put another bad tube in. I was about to send it off to Audio Research, but I thought I would have one last look at the circuit board and components to see if there was anything out of the ordinary. The nut on the rear panel common ground lugs for rack mount grounding on the back had come loose. I took the brass nut off and wire connector and polished the tarnish off with 3,000 grit sandpaper and screwed it back on. It’s perfect now !"
so check the ground!
Thanks for this.
My set up is secure from a circuit ground perspective. I have kept the safety ground for the chassis through the power mains plug, and then in my case I have used the chance to separate the circuit ground through a separate plug that is star earthed to the power amp and DAC with low impedance cable.
I had static sounds that was actually a bad 12BH7A valve that ws internally sparking, but that's a separate story = bad valve
My set up is secure from a circuit ground perspective. I have kept the safety ground for the chassis through the power mains plug, and then in my case I have used the chance to separate the circuit ground through a separate plug that is star earthed to the power amp and DAC with low impedance cable.
I had static sounds that was actually a bad 12BH7A valve that ws internally sparking, but that's a separate story = bad valve
What is your sound source? A PC? I had an issue recently where I had a bad noise problem. My main sound source is my PC. PC's are notorious for digital noise. In my case I solved it with isolation tfmrs.
To try and track down the cause try pulling the inputs to the amp and using shorting plugs on the IP's. Next try various sound sources like a phone, turntable etc.
Andy.
To try and track down the cause try pulling the inputs to the amp and using shorting plugs on the IP's. Next try various sound sources like a phone, turntable etc.
Andy.
So maybe I just swap out all the old diodes and caps in the PSupply and keep my fingers crossed.
Rich
My source is a USB DAC, that receives it's digital stream from an Allo USB signature Bridge, that receives the content from tidal through audirvana on a MacBook both connected on ethernet.
I have turned off everything, just leaving the just the power amplifier, and Sp8 on, it made no difference unfortunately including unplugging the DAC. It's also on all inputs
I have turned off everything, just leaving the just the power amplifier, and Sp8 on, it made no difference unfortunately including unplugging the DAC. It's also on all inputs
No. Randomly swapping components will more than likely confuse you more. You need to think logically not cosmically.
1) Disconnect every input source from the amp: is it still noisy? Answer -Yes, then it's not the source it's the amp -therefore fault find amp.
2) Answer No, then it's either a faulty source, IE your DAC or a source + amp fault, like an earth loop.
3) Is it the DAC? Connect to another amp. Ok or Not ok.
4) If the amp is noisy with No input, then it's the amp.
5) Measure the power supply rails with both a DC and AC volt meter. Is the DC reading on spec? If you have approx 100mV of AC ripple on your HT/B+ check the power supply caps. Also while your at it do a thorough visual inspection looking for anything that's iffy. EG loose wires, dry joints, burnt leaky, bulging components.
Hope that helps. Andy
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1) yes it's the amp
2) see above
3) see 1
4) yes noisy on all channels irrespective if they have an input in them or not
5) Can I measure AC on a DC loaded power rail? DC is on specification as it was before, but whne I try to look at AC on the DC rail my meter just jumps around
Finally if it is on both channels can we assume it must be the power supply at cause as this is across both channels?
2) see above
3) see 1
4) yes noisy on all channels irrespective if they have an input in them or not
5) Can I measure AC on a DC loaded power rail? DC is on specification as it was before, but whne I try to look at AC on the DC rail my meter just jumps around
Finally if it is on both channels can we assume it must be the power supply at cause as this is across both channels?
Listen with power on.
Then unplug amp from power outlet.
It will continue to play for a while as the reservoir caps discharge.
Is it noisy or quiet?
My preamp makes a terrible and disturbing thump on power off, however I could turn the volume of the power amp down (it has an incoming volume pot) and then turn off the SP8 and then wait for the thump to occur and then turn the volume back up.
I do know from experience that my power amp is noisy with nothing connected to the input in normal use
Then unplug amp from power outlet.
It will continue to play for a while as the reservoir caps discharge.
Is it noisy or quiet?
My preamp makes a terrible and disturbing thump on power off, however I could turn the volume of the power amp down (it has an incoming volume pot) and then turn off the SP8 and then wait for the thump to occur and then turn the volume back up.
I do know from experience that my power amp is noisy with nothing connected to the input in normal use
Not a good idea in the UK, it might be illegal & void any insurance policy.
Probably but maybe not. I have several Tek 500 series scopes built in the 1960's and most big HV caps are still fine.
AC reading jumping about, might be your meter though most DMM's can read AC @ 50hz/60hz or it could there's little on no ripple but then & again it could indicate a floating supply (from chassis ground that is) Where where your meter probes attached? Check the HT power supply negative is connected to chassis ground, mains earth by doing a continuity test with the power OFF and the caps discharged.
Have you got the means to knock up a high voltage supply? An old HV mains tfmr, bridge rectifier and HV cap will do. Pull the PSU caps out and do a leakage test as per the attached schematic. The circle marked mA is your meter set to mA DC.
Andy.
Attachments
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Thanks for the continued ideas
Last night it had the same response, ZZZzzz when first turned on and then after warmed up with a few songs it disappeared again!
I don't have anything to create a HV supply unfortunately.
HT supply is in a separate unit/box, that contains diodes and the main smoothing caps, and takes HT+ and circuit GND and safety Earth to the Sp8. The valve regulator circuit is in the Sp8 chassis.
Circuit GND is taken to 0V via a separate mains plug only connecting GND to earth in the Sp8 so safety earth for the chassis is separate to GND, joined only in the consumer unit.
Last night it had the same response, ZZZzzz when first turned on and then after warmed up with a few songs it disappeared again!
I don't have anything to create a HV supply unfortunately.
HT supply is in a separate unit/box, that contains diodes and the main smoothing caps, and takes HT+ and circuit GND and safety Earth to the Sp8. The valve regulator circuit is in the Sp8 chassis.
Circuit GND is taken to 0V via a separate mains plug only connecting GND to earth in the Sp8 so safety earth for the chassis is separate to GND, joined only in the consumer unit.