I am building a SE stereo tube amp, a la Tubelabs.
I have a few questions: (1) Which internal wires would benefit from twisting? (2) Would using a shielded wire eliminate the need for twisting and finally (3) Which wires should not be run close together?
Thanks in advance for you help.
I have a few questions: (1) Which internal wires would benefit from twisting? (2) Would using a shielded wire eliminate the need for twisting and finally (3) Which wires should not be run close together?
Thanks in advance for you help.
If you are using George's circuit board, most of the critical wiring is done for you. If you're doing point to point, the filament wires should be twisted and run close the chassis and away from signal wires. If a signal wire (or componet) must cross the filament line, do so at 90ºs. Input and output lines should be kept reasonably separated. Putting the filament wires inside shielding can't hurt, but I've found that it generally isn't necessary if you adhere to the above procedure.
With point to point, grounding will be a concern. A central "star" ground or a short ground buss (made from heavy solid copper wire) grounded at one point is proper practice. That point is usually at the input or centralized on the chassis. It can even be near the power supply if that is convenient (depending on location) and produces low hum. I prefer the ground buss approach because it provides for neatness with a convenient place to anchor componets and make signal grounds. The final chassis ground point can be easily found (for lowest hum) with a single wire connection. This is somewhat like adjusting a hum pot across the filament.
Obviously channel 1 and 2 signal wires should not be closely paralleled together to avoid crosstalk pickup. Input signal lines will be helped by using shielded wire, especially if they are long. For short runs, twisting together with a ground wire will provide some shielding.
Follow these simple guidelines and you'll be OK. You could also purchase the book "Building Valve Amplifiers" (Morgan Jones) for more detailed information regarding placement of transformers and other parts.
With point to point, grounding will be a concern. A central "star" ground or a short ground buss (made from heavy solid copper wire) grounded at one point is proper practice. That point is usually at the input or centralized on the chassis. It can even be near the power supply if that is convenient (depending on location) and produces low hum. I prefer the ground buss approach because it provides for neatness with a convenient place to anchor componets and make signal grounds. The final chassis ground point can be easily found (for lowest hum) with a single wire connection. This is somewhat like adjusting a hum pot across the filament.
Obviously channel 1 and 2 signal wires should not be closely paralleled together to avoid crosstalk pickup. Input signal lines will be helped by using shielded wire, especially if they are long. For short runs, twisting together with a ground wire will provide some shielding.
Follow these simple guidelines and you'll be OK. You could also purchase the book "Building Valve Amplifiers" (Morgan Jones) for more detailed information regarding placement of transformers and other parts.
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Thanks for the quick and thorough response. So, assuming that I don't mix wire types, i.e., output and mains, filiment and input, etc., is it safe to go ahead and twist everthing?
No. Don't twist everything. It isn't necessary unless you really like the twisted look. Only the filament wires require it. And this is only necessary if you are using AC to light them. You may twist the input connection together with a ground wire to help prevent hum pickup if you don't use a piece of shielded cable. If the run is short (couple inches) this may not be needed, especially if you are using a metal chassis which provides some shielding itself.
Without knowing just how you're building this, I'll mention one more thing regarding grounding. If you use a metal chassis and plan to mount your input connectors on it, they should be insulated from the chassis. This way they can be grounded by wiring them to the central point and avoid a ground loop. This, of course, assumes your ground point is somewhere other then the the input.
Thanks again. I am using a particle board chassis and plan to install a ground bus and connect the case of all the metalic components (power xfmr, OPT, choke, capacitor, PCB, etc) to it then connect the bus to the mains ground.
Hi.. Seeing this is on the same topic, i chose to revive this.
Can you tell me which of these wire combinations need to be twisted? I want to stop twisting unnecessary wires. This is not only limited to tube amp. Also, for 3 wires: do twisting or braiding? (you know like a girl's hair)
1. Main power line (Line + Neutral), 2 wires
2. Transformer secondary single polar, 2 wires (say 0V and 25V)
3. Transformer secondary, center tapped, 3 wires (say 25-0-25).
4. Heater wires using DC Supply, 2 wires
5. Heater wires using AC supply, 2 wires --> this obviously needs tight twisting
6. DC supply unipolar, 2 wires (say +35V and GND)
7. Symmetrical Power Supply with ground, 3 wires (say +35, GND, -35)
8. Signal wire single ended, 2 wires (i use shielded for this but i throw this in just to make a complete list)
9. Signal wire balanced, 3 wires
10. Anything else? What other wire did i miss that we usually find in power amps?
Or is there a rule of thumb i can remember so that i don't have memorize all of the above? Usually i go with "Twisted for AC, Shielded for Signal, Do Whatever for DC". I'm not sure it's correct..
One more thing: AC coupling capacitors between tube stages, i assume they should be closer to the later stage than the earlier? My output tubes is separated from the preliminaries and i need to connect them together (using shielded cable). I'm guessing the AC coupling cap should be nearer to the output tubes, meaning that my shielded cable will carry high voltage DC with superimposed AC signal --> better hum resistance?)
Can you tell me which of these wire combinations need to be twisted? I want to stop twisting unnecessary wires. This is not only limited to tube amp. Also, for 3 wires: do twisting or braiding? (you know like a girl's hair)
1. Main power line (Line + Neutral), 2 wires
2. Transformer secondary single polar, 2 wires (say 0V and 25V)
3. Transformer secondary, center tapped, 3 wires (say 25-0-25).
4. Heater wires using DC Supply, 2 wires
5. Heater wires using AC supply, 2 wires --> this obviously needs tight twisting
6. DC supply unipolar, 2 wires (say +35V and GND)
7. Symmetrical Power Supply with ground, 3 wires (say +35, GND, -35)
8. Signal wire single ended, 2 wires (i use shielded for this but i throw this in just to make a complete list)
9. Signal wire balanced, 3 wires
10. Anything else? What other wire did i miss that we usually find in power amps?
Or is there a rule of thumb i can remember so that i don't have memorize all of the above? Usually i go with "Twisted for AC, Shielded for Signal, Do Whatever for DC". I'm not sure it's correct..
One more thing: AC coupling capacitors between tube stages, i assume they should be closer to the later stage than the earlier? My output tubes is separated from the preliminaries and i need to connect them together (using shielded cable). I'm guessing the AC coupling cap should be nearer to the output tubes, meaning that my shielded cable will carry high voltage DC with superimposed AC signal --> better hum resistance?)
Current always flows in loops, so if you have a 'go' wire and a 'return' wire for a particular current, it is a good idea to twist them. This cancels the magnetic field radiated from that pair of wires. It also reduces the voltage induced in those two wires from their own magnetic field, or any other magnetic field.
There is a similar logic for voltage. If two conductors have equal and opposite AC voltage on them, by twisting them we cancel the electric field radiated from them and cancel the pick up of electric fields. Also, by keeping a single conductor with an AC voltage on it close to a ground conductor, we minimise electric field radiation and pick up.
Remember that DC connections can have ripple, or other noise on them. They are also susceptible to picking up AC magnetic and electric fields. So twisting them, or at least keeping the 'go' and 'return' close, is also useful.
There is a similar logic for voltage. If two conductors have equal and opposite AC voltage on them, by twisting them we cancel the electric field radiated from them and cancel the pick up of electric fields. Also, by keeping a single conductor with an AC voltage on it close to a ground conductor, we minimise electric field radiation and pick up.
Remember that DC connections can have ripple, or other noise on them. They are also susceptible to picking up AC magnetic and electric fields. So twisting them, or at least keeping the 'go' and 'return' close, is also useful.
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In other words..
Yes?
In the case of:
#3. Transformer secondary, center tapped, 3 wires (say 25-0-25 VAC).
#7. Symmetrical Power Supply with ground, 3 wires (say +35, GND, -35)
How do you twist them? Simply twist all three wires together? Or you make braids?
An externally hosted image should be here but it was not working when we last tested it.
Yes?
In the case of:
#3. Transformer secondary, center tapped, 3 wires (say 25-0-25 VAC).
#7. Symmetrical Power Supply with ground, 3 wires (say +35, GND, -35)
How do you twist them? Simply twist all three wires together? Or you make braids?
Hi,
Please read this thread:
http://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-good-bad-ugly.html
Ciao, 😉
Please read this thread:
http://www.diyaudio.com/forums/tubes-valves/211731-heater-wiring-good-bad-ugly.html
Ciao, 😉
When three wires need to be twisted, just twist them.
Braiding is for 'audiophile' cables when some RF pickup is desired to add 'detail' to the music.
Braiding is for 'audiophile' cables when some RF pickup is desired to add 'detail' to the music.
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