Since the JMo2 is JFET input, its quite insensitive, I would go so far as to say impervious, to the input impedance.
But... operating a large value potentiometer at the 70% position does significantly increase the risk of noise pickup, as the impedance to ground is the maximum (about 1/4 of the pot value). Still, realistically, this is not going to be of any consequence with any style of potentiometer having a value 20k or less.
So yes you can try any volume control you like, but ultimately the less-than-ideal situation of high(ish) impedance will not change until you add more gain to the signal chain.
PS.
"I have some little noise when connect it to TRV tube pre-amp."
Your tube pre-amp has a much higher output noise than the line out a solid state CD player.
But... operating a large value potentiometer at the 70% position does significantly increase the risk of noise pickup, as the impedance to ground is the maximum (about 1/4 of the pot value). Still, realistically, this is not going to be of any consequence with any style of potentiometer having a value 20k or less.
So yes you can try any volume control you like, but ultimately the less-than-ideal situation of high(ish) impedance will not change until you add more gain to the signal chain.
PS.
"I have some little noise when connect it to TRV tube pre-amp."
Your tube pre-amp has a much higher output noise than the line out a solid state CD player.
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Hi Richard,
Thank you for detailed explanation.
Yes, I'll try step attenuator too. Lets see then.
I''ll also try Salas DBC1 buffer with has attenuator (I'm assembling it right now) and I'll not worry about input impedance, but it has x1 gain. Lets see, lets see then....
Some point out of our subject:
I do see that my TRV pre-amp Earth GND is not connected at all. It is not in use from entrance of IEC. Only N and L is utilized.
PSU and Signal GND is connected as star to chassis.
I assume that such way is a violation of safety in USA, since it is not double isolation and no Earth GND either. Does such wiring way is OK in Japan?
My noise might be partially related to that architecture.
I'll use that simple way of GND management (Grounding issue and vinyl care - Page 2) #17 to test it.
Thank you for detailed explanation.
Yes, I'll try step attenuator too. Lets see then.
I''ll also try Salas DBC1 buffer with has attenuator (I'm assembling it right now) and I'll not worry about input impedance, but it has x1 gain. Lets see, lets see then....
Some point out of our subject:
I do see that my TRV pre-amp Earth GND is not connected at all. It is not in use from entrance of IEC. Only N and L is utilized.
PSU and Signal GND is connected as star to chassis.
I assume that such way is a violation of safety in USA, since it is not double isolation and no Earth GND either. Does such wiring way is OK in Japan?
My noise might be partially related to that architecture.
I'll use that simple way of GND management (Grounding issue and vinyl care - Page 2) #17 to test it.
Older houses like mine only have two-conductor AC wiring. There is no earth at all, except at the point of entry from the street.
The additional noise you hear with the tube preamp is mostly likely just a function of what it is, the gain and the devices and the circuit topology. It doesn't necessarily point to a grounding or earthing fault.
You were absolutely right and new GND arrangements based on Grounding issue and vinyl care - Page 2 did not change a thing. That light noise is starting to be noticeable at 50% and up of Pre-amp volume pot position. So, I revised everything back to its original configuration. I also removed my Alps potentiometer form your amp and connected it to Tri pre-amp. I satisfy now to listen to it at 30-40% of Tri pre-amp potentiometer. Thank you. It really nice design and very-very good sound...
Thank you.
Thank you.
Hi Richard
Please excuse my persistence, but I just figured out how that noise is coming through.
I use your TRV-M300SE monoblocks and I connect them to the same output on TRV-4SE as I connect my new headphone amp.
So and during the test
1. My monoblocks and phone amplifier were connected to the same outputs on TRV-4SE back panel.
2. Mooblocks were powered Off.
3. Noise was obvious on my headphones through headphone amp.
4. I disconnected Monoblocks interconnect cables from TRV-4SE outputs and noise was gone, completely disappeared. TRV-4SE was absolutely dead-quite.
I heard very clear sound when I played music. Amazing!!!
5. So, I connected Monoblocks interconnects RCAs back to TRV-4SE and noise came back.
100% noise is related to connection of TRV-M300SEs. Is it input impedance issue?
Any advice how to fix that since I would like to keep using monoblocks sometimes to listen speaker and phone amplifier to listen headphones?
Thank you.
Please excuse my persistence, but I just figured out how that noise is coming through.
I use your TRV-M300SE monoblocks and I connect them to the same output on TRV-4SE as I connect my new headphone amp.
So and during the test
1. My monoblocks and phone amplifier were connected to the same outputs on TRV-4SE back panel.
2. Mooblocks were powered Off.
3. Noise was obvious on my headphones through headphone amp.
4. I disconnected Monoblocks interconnect cables from TRV-4SE outputs and noise was gone, completely disappeared. TRV-4SE was absolutely dead-quite.
I heard very clear sound when I played music. Amazing!!!
5. So, I connected Monoblocks interconnects RCAs back to TRV-4SE and noise came back.
100% noise is related to connection of TRV-M300SEs. Is it input impedance issue?
Any advice how to fix that since I would like to keep using monoblocks sometimes to listen speaker and phone amplifier to listen headphones?
Thank you.
I found the problem!!!!!
I opened first Monoblock and saw all GND was connected to the chassis as well as Earth GND.
So, I installed GND device based on the same known circuit (35A monolithic rectifier/10R 5W resistor/0.1uF 450V cap) into that monoblock and "Voilà", it is dead-quite!!!!!
Second one (which is not upgraded yet) is pushing noise in.
So, I'll fix it tomorrow.
It is a GND loop.
I opened first Monoblock and saw all GND was connected to the chassis as well as Earth GND.
So, I installed GND device based on the same known circuit (35A monolithic rectifier/10R 5W resistor/0.1uF 450V cap) into that monoblock and "Voilà", it is dead-quite!!!!!
Second one (which is not upgraded yet) is pushing noise in.
So, I'll fix it tomorrow.
It is a GND loop.
The output coupling cap is the unavoidable elephant in the room. Choosing the J-Mo II (i.e. a MOSFET single-ended source follower) means choosing to live with that. If anyone hates the very idea of running the output signal through a large electrolytic, there are plenty of directly-coupled push-pull output stages as ready alternatives. For example.
Black Gates are essentially lost to the mists of time. The various MUSE models are pretty good though. The top of the range is the "fine gold" series.
Black Gates are essentially lost to the mists of time. The various MUSE models are pretty good though. The top of the range is the "fine gold" series.
Hi Richard,
Just for my curiosity....
I see in similar concept schematics, people use to bypass output Electrolytic capacitor (in or case 1000uF) with some small value PIO or Polypropylene capacitor (value 0.22 - 0.47uF). Should we try that technique too and see if any improvement will appears?
Please let me know your opinion.
Just for my curiosity....
I see in similar concept schematics, people use to bypass output Electrolytic capacitor (in or case 1000uF) with some small value PIO or Polypropylene capacitor (value 0.22 - 0.47uF). Should we try that technique too and see if any improvement will appears?
Please let me know your opinion.
Well, it's no sweat to give it a try and easily removed if you don't like it. Just solder a bypass capacitor across the leads of C1.
From an electronics standpoint, any audible distortion produced by C1 will not, or can not be removed by adding a small film capacitor as the impedance of C1 is many times smaller than the bypass capacitor over the entire audio spectrum.
The whole idea of a bypass caps is for the power supply, when you are interested in frequencies at several tens of MHz and the electrolytics have high impedance. Bypassing an AC coupling cap in the signal path is a similar way is pointless. The real solution is to invest in an electrolytic capacitor for C1 which has low distortion (or at least sounds good!).
From an electronics standpoint, any audible distortion produced by C1 will not, or can not be removed by adding a small film capacitor as the impedance of C1 is many times smaller than the bypass capacitor over the entire audio spectrum.
The whole idea of a bypass caps is for the power supply, when you are interested in frequencies at several tens of MHz and the electrolytics have high impedance. Bypassing an AC coupling cap in the signal path is a similar way is pointless. The real solution is to invest in an electrolytic capacitor for C1 which has low distortion (or at least sounds good!).
Thank you for prompt response which was always an exceptional support. Well, very known Black Date N Series is out of production for quite awhile. That Cap would be the best in that position. I see some shops still have them for sale, but price is insane: Black Gate N Series 1000µF 50V, Sonic Craft
Most DIY agreed that Elna RFS Silmic II is close-performance one, but I never tested it head-2-head. Second, BG N is by-polar as film caps vs. Enla is not.
I use Elna RFS 1000uF 50V now and I'll try to bypass it with 0.22uF. I have a pair of Vitamin Q PIO. Also, I have couple of 0.1uF, 0.033uF and 0.001uF Russian K40Y also PIO. I'll report soon.
Most DIY agreed that Elna RFS Silmic II is close-performance one, but I never tested it head-2-head. Second, BG N is by-polar as film caps vs. Enla is not.
I use Elna RFS 1000uF 50V now and I'll try to bypass it with 0.22uF. I have a pair of Vitamin Q PIO. Also, I have couple of 0.1uF, 0.033uF and 0.001uF Russian K40Y also PIO. I'll report soon.
Fortunately the J-Mo II circuit biases C1 to several volts, this should help to keep distortion in check. Then, I'd go with "audio grade" electrolytics and finally I'd install the smallest value capacitor I think I could get away with for the headphone impedance.
For example, if you normally use 300 ohm headphones C1 only needs to be 100 uF.
For example, if you normally use 300 ohm headphones C1 only needs to be 100 uF.
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