Hi All,
I would appreciate a little help with a problem that has become a bit of a head scratcher.
I have recently fired up my turntable front end after having built the Transcendent Sound phono stage and whilst initially everything was fine with a Cartridge Man Music maker, it all started to go down hill when I switched over to my Wilson Benesch Carbon low output MC.
I had a pair of Sowter SUT's which have been installed in the Transcendent phono stage, giving me both MM and MC options. Whilst the Benesch cartridge plays music superbly through the SUT's, there is a lot of hum which I cannot eliminate. I therefore started investigating the build of a battery powered head amp
Having built the Hart Electronics 1450 Linsley Hood phono stage some years ago, I was digging through the web and came across Paul Kemble's excellent site where he has a schematic for a low voltage head amp designed by Linsley Hood, which is basically exactly the same circuit topology as on the input stage of his phono amp, just with different resistor values to accommodate the lower supply voltage. Bingo. So I built it, and it works superbly well, except for one big problem.
With it in circuit I constantly get popping and spitting noises through the speakers, and this is WITHOUT the turntable playing or rotating, so it is nothing to do with record surface noise.
With the Benesch cartridge plugged into the SUT's there is no spitting, just hum.
So am at a bit of a loss to know what may be causing it and how to solve it. Hopefully some-one on the forum will be able to point me in the right direction. Schematic is below. Have made a few mods. As I couldn't get matched NPN and PNP transistors, have substituted BC549B's and BC559B's which whilst not perfectly matched are a lot closer than the original BC214's and 414's that I had managed to get hold of. Even so, was not able to zero the output, so have got rid of the 68k resistor and the 47k trimmer, and have put a blocking capacitor on the output.
Ironically, in desperation, I dug out the old Linsley Hood phono stage and plugged that in circuit. It did exactly the same thing with the spitting and popping.
So in summary. No record playing or spinning, just everything at idle.
Music Maker into Transcendent MM phono stage - No popping and quiet
Benesch into SUT's in Transcendent phono stage - No popping but hum
Benesch into JLH Head amp and then into Transcendent MM stage - Popping, but no hum
Benesch into old JLH 1450 phono stage - Popping and some hum (I assume as mains powered)
I look forward to your responses.
Thanks.
I would appreciate a little help with a problem that has become a bit of a head scratcher.
I have recently fired up my turntable front end after having built the Transcendent Sound phono stage and whilst initially everything was fine with a Cartridge Man Music maker, it all started to go down hill when I switched over to my Wilson Benesch Carbon low output MC.
I had a pair of Sowter SUT's which have been installed in the Transcendent phono stage, giving me both MM and MC options. Whilst the Benesch cartridge plays music superbly through the SUT's, there is a lot of hum which I cannot eliminate. I therefore started investigating the build of a battery powered head amp
Having built the Hart Electronics 1450 Linsley Hood phono stage some years ago, I was digging through the web and came across Paul Kemble's excellent site where he has a schematic for a low voltage head amp designed by Linsley Hood, which is basically exactly the same circuit topology as on the input stage of his phono amp, just with different resistor values to accommodate the lower supply voltage. Bingo. So I built it, and it works superbly well, except for one big problem.
With it in circuit I constantly get popping and spitting noises through the speakers, and this is WITHOUT the turntable playing or rotating, so it is nothing to do with record surface noise.
With the Benesch cartridge plugged into the SUT's there is no spitting, just hum.
So am at a bit of a loss to know what may be causing it and how to solve it. Hopefully some-one on the forum will be able to point me in the right direction. Schematic is below. Have made a few mods. As I couldn't get matched NPN and PNP transistors, have substituted BC549B's and BC559B's which whilst not perfectly matched are a lot closer than the original BC214's and 414's that I had managed to get hold of. Even so, was not able to zero the output, so have got rid of the 68k resistor and the 47k trimmer, and have put a blocking capacitor on the output.
Ironically, in desperation, I dug out the old Linsley Hood phono stage and plugged that in circuit. It did exactly the same thing with the spitting and popping.
So in summary. No record playing or spinning, just everything at idle.
Music Maker into Transcendent MM phono stage - No popping and quiet
Benesch into SUT's in Transcendent phono stage - No popping but hum
Benesch into JLH Head amp and then into Transcendent MM stage - Popping, but no hum
Benesch into old JLH 1450 phono stage - Popping and some hum (I assume as mains powered)
I look forward to your responses.
Thanks.
Attachments
Sounds like its picking up electrical radiated or induced noise due ( possibly ) to a slight impedance mismatch or too much gain.
Entirely possible , on the public help website I was on for years many posters asking for help on interference etc boiled down to LED lighting/ thermostat switching / faulty TV,s /microwaves --DECT phones/mobile phones /baby alarms and a whole host of interference .
Thats why I bought a small RF signal tracer ( spy tracker ) from Maplin before it went out of business --still got it even picks up my large PC --add in LED street lighting and traffic signals as well as Bluetooth .
Before I left it was a woman,s husband complaining his hi-fi was crackling at night turned out his wife ( secretly ) put food in the microwave as she was hungry late at night -- it took a week to track it down --faulty microwave.
Thats why I bought a small RF signal tracer ( spy tracker ) from Maplin before it went out of business --still got it even picks up my large PC --add in LED street lighting and traffic signals as well as Bluetooth .
Before I left it was a woman,s husband complaining his hi-fi was crackling at night turned out his wife ( secretly ) put food in the microwave as she was hungry late at night -- it took a week to track it down --faulty microwave.
Hi Guys,
Thanks for the suggestions.
I have finally made some headway and have managed to eliminate the problem, but not before a lot of trial and error and heavy use of the solder sucker.
Last night I was reading Merlin Blencowe's excellent book, Designing High Fidelity Tube Preamps. There is a small section in there talking about MC head amps, but as tubes are not really suited to this application, there is very little of substance. One bit of information however did stand out and that was the point that according to Blencowe, there should always be a blocking capacitor at the input to protect MC cartridges from damage due to bias currents flowing through them.
So I tried it, and it didn't work. Back to square 1
Again trawling through the internet, on Rob Elliot's site he also has JLH's phono input stage, but this version has additional capacitors in parallel with the input, and also between the base and emitters of the input transistors, presumably to aid stability. As I was starting to believe I had a stability problem, I added in what capacitors I had, which were very close to the values in the schematic. Result - still popping and spitting. By this time, whilst getting very frustrated with the whole issue, I started to think that as nothing that I had done to the head amp had made the slightest improvement, perhaps the problem was with the the Transcendent phono stage, or the interaction between the two, even though the Benesch cartridge worked fine with just the phono stage and SUT's.
This was then when I had the light-bulb moment. Some years ago, I recall having some instability problems between a pre-amp and power amp, which was resolved accidentally by plugging them together with a much longer interconnect lead. Longer lead means more resistance (As well as more capacitance) so out of interest I added a resistor in series with the output of pre-amp, and all was well.
So bearing this in mind, I added a 1K resistor in series with the input of the phono stage (As it was easier to do that than take the head amp to bits again) and hey presto, popping and spitting gone, just a little bit of background hum that I can happily live with.
So happiness returns to the bat cave, but a couple of final questions if I may -
Can some-one please tell me why adding this resistor into the signal path between head amp and phono stage has eliminated the popping and spitting.
And will the additional capacitors have any impact on Sound Quality.
Thanks and Best Regards,
Steve.
p.s. The head amp is excellent, definitely worth giving it a go if you are looking for something like this.
Thanks for the suggestions.
I have finally made some headway and have managed to eliminate the problem, but not before a lot of trial and error and heavy use of the solder sucker.
Last night I was reading Merlin Blencowe's excellent book, Designing High Fidelity Tube Preamps. There is a small section in there talking about MC head amps, but as tubes are not really suited to this application, there is very little of substance. One bit of information however did stand out and that was the point that according to Blencowe, there should always be a blocking capacitor at the input to protect MC cartridges from damage due to bias currents flowing through them.
So I tried it, and it didn't work. Back to square 1
Again trawling through the internet, on Rob Elliot's site he also has JLH's phono input stage, but this version has additional capacitors in parallel with the input, and also between the base and emitters of the input transistors, presumably to aid stability. As I was starting to believe I had a stability problem, I added in what capacitors I had, which were very close to the values in the schematic. Result - still popping and spitting. By this time, whilst getting very frustrated with the whole issue, I started to think that as nothing that I had done to the head amp had made the slightest improvement, perhaps the problem was with the the Transcendent phono stage, or the interaction between the two, even though the Benesch cartridge worked fine with just the phono stage and SUT's.
This was then when I had the light-bulb moment. Some years ago, I recall having some instability problems between a pre-amp and power amp, which was resolved accidentally by plugging them together with a much longer interconnect lead. Longer lead means more resistance (As well as more capacitance) so out of interest I added a resistor in series with the output of pre-amp, and all was well.
So bearing this in mind, I added a 1K resistor in series with the input of the phono stage (As it was easier to do that than take the head amp to bits again) and hey presto, popping and spitting gone, just a little bit of background hum that I can happily live with.
So happiness returns to the bat cave, but a couple of final questions if I may -
Can some-one please tell me why adding this resistor into the signal path between head amp and phono stage has eliminated the popping and spitting.
And will the additional capacitors have any impact on Sound Quality.
Thanks and Best Regards,
Steve.
p.s. The head amp is excellent, definitely worth giving it a go if you are looking for something like this.
Because its stopped insipid oscillation or as I said above radiated RF interference as in grid stopper.
I would have to sim this to confirm it, but I think what is happening is that the pre this is feeding into along with the cable capacitance is placing an extra pole in the overall response, and that’s causing the JLH to become unstable. The common emitter OPS on the JLH means the output Z is high wrt to an emitter follower that’s typically used in opamps.
By inserting the 1k resistor in series with the JLH output, you have effectively isolated it from load capacitance and stopped it from misbehaving.
Most small signal circuits (discrete or op-amp) place some resistance in series with the OP for excacty this reason. For integrated opamps, the value is typically 47 to 220 ohms.
Without knowing the details of the load, it’s hard to say what effect 1k will have over say a more conventional value like 100 or 220 Ohms.
I would suggest you put the resistor at the output of the JLH - this will isolate it from the cable capacitance and give you more protection. 220 Ohms might be a better value as well - try it and see if that does the trick.
Edit: I see on the Kemball diagram there is indeed a 330 ohm in series with the output. Did you install this on your build?
By inserting the 1k resistor in series with the JLH output, you have effectively isolated it from load capacitance and stopped it from misbehaving.
Most small signal circuits (discrete or op-amp) place some resistance in series with the OP for excacty this reason. For integrated opamps, the value is typically 47 to 220 ohms.
Without knowing the details of the load, it’s hard to say what effect 1k will have over say a more conventional value like 100 or 220 Ohms.
I would suggest you put the resistor at the output of the JLH - this will isolate it from the cable capacitance and give you more protection. 220 Ohms might be a better value as well - try it and see if that does the trick.
Edit: I see on the Kemball diagram there is indeed a 330 ohm in series with the output. Did you install this on your build?
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Thanks Duncan. Yes, you are spot on. Have just checked the schematic for the phono stage and guess what, no grid stoppers! Doh.
Ah Well. Lesson learned.
Thanks again.
Steve.
Ah Well. Lesson learned.
Thanks again.
Steve.
Hi Bonsai,
Yes, I did put the 330 ohm resistor in circuit, but also added in a 1uF capacitor between it and the output as I couldn't zero the output voltage, and didn't want to feed dc into the phono stage. Not sure if this capacitor will have contributed to the problem.
Yes, I did put the 330 ohm resistor in circuit, but also added in a 1uF capacitor between it and the output as I couldn't zero the output voltage, and didn't want to feed dc into the phono stage. Not sure if this capacitor will have contributed to the problem.
Hmm. Seems the problem might lie downstream from your MC head amp.
Anyway, main thing is its working.
Anyway, main thing is its working.