I'll be making the optimized MJ amp designed (http://home.swbell.net/acavalli/images/MJ_Headphone_Amp.gif) by Alex Cavelli. I will also be using the tube rectifier power supply (http://home.swbell.net/acavalli/images/MJ_Power_Supply_2.gif) also designed by Alex.
I just need comments/feedback/suggestions on the points of the main "star"
1. from ground from plate supply (tap from negative lead of first capacitor)
2. from ground from heater supply (tap from negative lead of first and only capacitor)
3. from ground loop breaker
4. from ground of left channel
5. from ground of right channel
6. from ground of input female RCA
7. from ground of the volume control
Ground point for the individual circuits will be going to a single point. for example, the ground connection for the 2nd and 3rd capacitors in the plate supply will be connected to the negative lead of the 1st capacitor.
I also plan to connect input female RCA ground to the volume control ground directly. I will be using a twisted pair with 1 wire carrying signal from input female RCA to volume control and the other line is ground
Thanks for the replies.
Jayel
I just need comments/feedback/suggestions on the points of the main "star"
1. from ground from plate supply (tap from negative lead of first capacitor)
2. from ground from heater supply (tap from negative lead of first and only capacitor)
3. from ground loop breaker
4. from ground of left channel
5. from ground of right channel
6. from ground of input female RCA
7. from ground of the volume control
Ground point for the individual circuits will be going to a single point. for example, the ground connection for the 2nd and 3rd capacitors in the plate supply will be connected to the negative lead of the 1st capacitor.
I also plan to connect input female RCA ground to the volume control ground directly. I will be using a twisted pair with 1 wire carrying signal from input female RCA to volume control and the other line is ground
Thanks for the replies.
Jayel
I am assuming that the mains ground is connected to chassis. I'm also assuming that with your suggestion, this ground lug will have contact with the chassis.
so with your suggestion, will there be a ground loop?
and the grounding scheme I just stated has nothing mystical in it I think. Well as far as I know there's nothing 'snake oil" about it.
Thanks for the replies.
jayel
so with your suggestion, will there be a ground loop?
and the grounding scheme I just stated has nothing mystical in it I think. Well as far as I know there's nothing 'snake oil" about it.
Thanks for the replies.
jayel
Star earth.
I'm not quite sure what you mean by your question. If you're going to star earth (definitely a good idea) then the physical location of the star is largely down to mechanical convenience. I would suggest that you put it somewhere in the middle of the audio circuitry. I am assuming that you are going to do a true star earth here, and that there will be one wire per component coming to the star - with no components sharing a wire.
Bonding your star down to the chassis is a separate issue, but if the star is in the middle of the audio circuitry, it's an easy matter to bond it to the chassis. Whether, or not, you bond your star to the chassis, make sure the chassis (and transformer E/S screen, if fitted) is properly bonded to mains earth.
Does that answer your question?
I'm not quite sure what you mean by your question. If you're going to star earth (definitely a good idea) then the physical location of the star is largely down to mechanical convenience. I would suggest that you put it somewhere in the middle of the audio circuitry. I am assuming that you are going to do a true star earth here, and that there will be one wire per component coming to the star - with no components sharing a wire.
Bonding your star down to the chassis is a separate issue, but if the star is in the middle of the audio circuitry, it's an easy matter to bond it to the chassis. Whether, or not, you bond your star to the chassis, make sure the chassis (and transformer E/S screen, if fitted) is properly bonded to mains earth.
Does that answer your question?
Hi Jarthel;
Since I use nonconductive chassis on my homebrew amps, I have to run discrete ground lines for everything. That said, I usually just use 3 substars and a single main star. The substars are for the PS filters and heaters (same star), the output valves, and the signal valves. If there is a separate driver it gets it's own substar. The main star connects directly to the safety ground on the IEC. All the metal fittings and trafo cases are just daisy chained by ground shackles directly to the main star.
It's probably more work than it needs to be but my amps have all been very quiet thus far (*knocking on wood for luck to avoid jinxing myself after typing that!!*).
By the way, I've built the MJ headphone amp, albeit to the circuit over at headwize.com (using a fixed feedback loop and with a different PS) and it's really a good little amp, particularly in the optimised form! I think you'll be most pleased with it.....
Good luck with your amp!
All the best,
Morse
Since I use nonconductive chassis on my homebrew amps, I have to run discrete ground lines for everything. That said, I usually just use 3 substars and a single main star. The substars are for the PS filters and heaters (same star), the output valves, and the signal valves. If there is a separate driver it gets it's own substar. The main star connects directly to the safety ground on the IEC. All the metal fittings and trafo cases are just daisy chained by ground shackles directly to the main star.
It's probably more work than it needs to be but my amps have all been very quiet thus far (*knocking on wood for luck to avoid jinxing myself after typing that!!*).
By the way, I've built the MJ headphone amp, albeit to the circuit over at headwize.com (using a fixed feedback loop and with a different PS) and it's really a good little amp, particularly in the optimised form! I think you'll be most pleased with it.....
Good luck with your amp!
All the best,
Morse
I'm using a Hammond 369GX and according to the datasheet, there should be a grey wire that needs to be connected to ground. Well this grey wire is absent in the transformer that I have.
Should I scrape some paint in the mounting holes in the xformer and use that to connect the xformer to ground? Is it mains ground or circuit ground?
Should I scrape some paint in the mounting holes in the xformer and use that to connect the xformer to ground? Is it mains ground or circuit ground?
Jayel,
Ground is ground - many will argue with me on that, but it's true. "Ground loops" occur between COMPONENTS, not within a single circuit - provided you don't do anything weird. Use a single point. How you get each component to that point is up to you - use a bus or individual lines - it doesn't matter as long as the connections are as short as you can make them, and use decent size wire.
Yes - bolt the transformers to the chassis. And "circuit ground" is the same as "chassis ground" to me at least - and in most commercial amplifiers.
Make sense?
Joel
Ground is ground - many will argue with me on that, but it's true. "Ground loops" occur between COMPONENTS, not within a single circuit - provided you don't do anything weird. Use a single point. How you get each component to that point is up to you - use a bus or individual lines - it doesn't matter as long as the connections are as short as you can make them, and use decent size wire.
Yes - bolt the transformers to the chassis. And "circuit ground" is the same as "chassis ground" to me at least - and in most commercial amplifiers.
Make sense?
Joel
Re: Re: Star earth.
I'm afraid I meant every individual resistor, capacitor, transformer connection, input, and output connection. And yes, I know, that's an awful lot of wires to go to one point. It's not easy, but you can get all those wires onto a ceramic stand-off if it's the kind that has four wings rather than two.
This solution solves your last question perfectly. The transformer body wants to go to the chassis, which is mains ground.
jarthel said:
I'm afraid I meant every individual resistor, capacitor, transformer connection, input, and output connection. And yes, I know, that's an awful lot of wires to go to one point. It's not easy, but you can get all those wires onto a ceramic stand-off if it's the kind that has four wings rather than two.
This solution solves your last question perfectly. The transformer body wants to go to the chassis, which is mains ground.
Re: Re: Re: Re: Star earth.
No, it's not a problem. The addition of even 12" of wire (and that should easily be the longest you need) will not add signficant resistance to affect a component. At valve impedances and audio frequencies, even the inductance of that wire is insignificant. OK, if you were daft, and routed one of these wires all the way round the mains transformer, it could pick up some hum, but you will route the wires to be as short and direct as possible.
Tha advantage of star earth is that all the currents flow in the right places without developing unwanted voltages across small resistances. OTL amplifiers deliver significant audio current directly from the HT, so thinking about currents is a good idea.
jarthel said:
No, it's not a problem. The addition of even 12" of wire (and that should easily be the longest you need) will not add signficant resistance to affect a component. At valve impedances and audio frequencies, even the inductance of that wire is insignificant. OK, if you were daft, and routed one of these wires all the way round the mains transformer, it could pick up some hum, but you will route the wires to be as short and direct as possible.
Tha advantage of star earth is that all the currents flow in the right places without developing unwanted voltages across small resistances. OTL amplifiers deliver significant audio current directly from the HT, so thinking about currents is a good idea.
Morse
Hi Jarthel;
>>>...where do you connect the ground for the output?...<<<
Sorry, I should have mentioned that! Normally on an SET I leave the OPT's secondary floating. Of course the MJ design is an OTL design so.....I connected the ground lines from the left and right channels together then tied them to the daisy chain of grounded chassis fittings.
If you look at the pictures at http://www.diyaudio.com/forums/showthread.php?s=&threadid=14035&highlight=pics you can see what I mean by chassis plates - all those metal fittings on the wood chassis. The PS trafo is also tied to that daisy chain via one of it's mounting bolts (had to chip away some paint for that to work though).
All the best,
Morse
Hi Jarthel;
>>>...where do you connect the ground for the output?...<<<
Sorry, I should have mentioned that! Normally on an SET I leave the OPT's secondary floating. Of course the MJ design is an OTL design so.....I connected the ground lines from the left and right channels together then tied them to the daisy chain of grounded chassis fittings.
If you look at the pictures at http://www.diyaudio.com/forums/showthread.php?s=&threadid=14035&highlight=pics you can see what I mean by chassis plates - all those metal fittings on the wood chassis. The PS trafo is also tied to that daisy chain via one of it's mounting bolts (had to chip away some paint for that to work though).
All the best,
Morse
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