Wire lengths and twisting
Are they rules of thumb about how long or short hookup wire should be? And should pairs always be twisted together? Is the idea that AC mains are a big source of RF noise? Are other wires susceptible to this noise and so does twisting them make them less so...? Just wondering what the underlying principles are.
I’m planning to place my transformer in the front as I had envisioned building the F6 and per 6L6’s thinking thought to keep it away from the transformers on the F6 amp boards. So this puts it across the enclosure from the back panel. I’m also thinking of running lines to the primary under the chassis.
Or should we file this under “The dept of overthinking?”
Thanks!
Are they rules of thumb about how long or short hookup wire should be? And should pairs always be twisted together? Is the idea that AC mains are a big source of RF noise? Are other wires susceptible to this noise and so does twisting them make them less so...? Just wondering what the underlying principles are.
I’m planning to place my transformer in the front as I had envisioned building the F6 and per 6L6’s thinking thought to keep it away from the transformers on the F6 amp boards. So this puts it across the enclosure from the back panel. I’m also thinking of running lines to the primary under the chassis.
Or should we file this under “The dept of overthinking?”
Thanks!
I'd file it in the dept. of thoughtful planning and understanding.
I look at other people's builds, but here is what I've accumulated.
Twist - Twist AC (that means your signal too). DC is foggy to me. I twisted my rail supplies. Others chime in.
Length - There will be tradeoffs.
Input wires short as possible, but long enough to be carefully away from noisy things. Why? Dinkiest AC signal => any noise relative to the input signal is larger and then gets amplified along with your signal. Don't rely on differential signaling/noise cancellation. Route properly.
Output wires short as you can practically make them, but taking care of routing. Less relative importance than input, but keeping some distance from anything that may impart noise is likely better than a short wire running right across your power transformer.
Mains / primary / secondary - Depends on other compromises like keeping the power transformer away from input/output wiring and the autoformer in your F6 as an example. Do you want your IEC and your mains switch on the front? If so, that would likely shorten up lots of wires. Many people don't like that, so we compromise with longer wires, twisting them, and routing.
Keep the mains/primaries/secondaries away from signal wiring (I/O) and rail supplies.
Keep rail supplies and I/O away from the power transformer.
Hope that's helpful. People with more technical knowledge can chime in. I've read articles on wire routing and wire dressing, but it hasn't sunk in.
I look at other people's builds, but here is what I've accumulated.
Twist - Twist AC (that means your signal too). DC is foggy to me. I twisted my rail supplies. Others chime in.
Length - There will be tradeoffs.
Input wires short as possible, but long enough to be carefully away from noisy things. Why? Dinkiest AC signal => any noise relative to the input signal is larger and then gets amplified along with your signal. Don't rely on differential signaling/noise cancellation. Route properly.
Output wires short as you can practically make them, but taking care of routing. Less relative importance than input, but keeping some distance from anything that may impart noise is likely better than a short wire running right across your power transformer.
Mains / primary / secondary - Depends on other compromises like keeping the power transformer away from input/output wiring and the autoformer in your F6 as an example. Do you want your IEC and your mains switch on the front? If so, that would likely shorten up lots of wires. Many people don't like that, so we compromise with longer wires, twisting them, and routing.
Keep the mains/primaries/secondaries away from signal wiring (I/O) and rail supplies.
Keep rail supplies and I/O away from the power transformer.
Hope that's helpful. People with more technical knowledge can chime in. I've read articles on wire routing and wire dressing, but it hasn't sunk in.
I put my transformers at the front, then ran the secondaries to the back where I had the rectifiers, which fed off short leads to the capacitor boards. This allowed me to have the DC power available basically right in the middle of the chassis and kept the DC lines to the boards short. I twisted everything where possible. For me it was a combination of trying to keep runs short but also keeping access to the boards and such for assembly. Your input and output leads are basically going to be determined by the board layout and geometry from the side panels to the back panel...not much room to get creative there.
If you desire the quitest amp possible, twist all wires.
That means all AC wires and DC wires:
- power in: AC live and neutral
- transformer primaries and secondaries: wires for each winding twisted together
- rectifiers: positive and negative twisted together
- from power supply to amplifier boards: for bipolar supply twist positive, ground, and negative together. For unipolar supply twist positive and ground together.
- input jacks to amplifier boards: twist signal and ground together
- speaker jacks to amplifier boards: twist signal and ground together
Keep transformer and AC wires away from signal wires and amplifier boards.
The best approach is to assume that you have very sensitive speakers or will have, so do your best to build your amp to be as quiet as possible.
If you have speakers of low sensitivity, you can get away with being sloppy, and think your amp is quiet, and that twisting wires together is unnecessary.
Proper grounding is also important. Twisting wires is only one part of the solution. Even something as simple as plugging all of your sound system electronics into one wall socket to avoid ground loops can make a difference.
Here is an article by diyAudio member Bonsai that has helped me greatly. The practical tips and advice is towards the end:
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf
That means all AC wires and DC wires:
- power in: AC live and neutral
- transformer primaries and secondaries: wires for each winding twisted together
- rectifiers: positive and negative twisted together
- from power supply to amplifier boards: for bipolar supply twist positive, ground, and negative together. For unipolar supply twist positive and ground together.
- input jacks to amplifier boards: twist signal and ground together
- speaker jacks to amplifier boards: twist signal and ground together
Keep transformer and AC wires away from signal wires and amplifier boards.
The best approach is to assume that you have very sensitive speakers or will have, so do your best to build your amp to be as quiet as possible.
If you have speakers of low sensitivity, you can get away with being sloppy, and think your amp is quiet, and that twisting wires together is unnecessary.
Proper grounding is also important. Twisting wires is only one part of the solution. Even something as simple as plugging all of your sound system electronics into one wall socket to avoid ground loops can make a difference.
Here is an article by diyAudio member Bonsai that has helped me greatly. The practical tips and advice is towards the end:
http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf
And back to our regularly scheduled programming ... ;-) ... I've posted the next installment of the n00bs guide, wherein we power up the amp boards and do initial bias and offset adjustments:
Building: Amp Board Power Up and Test
I also updated Introduction: Tools You Will Need based on my build experience, adding a good DMM leads kit, magnifying glass, and infrared thermometer to "must have" tools.
And I updated Building: Amp Boards on Heat Sinks to use a Euroblock on the amp board signal input contacts. This should make hooking up input connectors much easier, and make it easy to swap XLR to RCA.
And I also updated Parts: the Rest of the BOM with a refreshed saved Mouser cart, adding all the additional parts that I've needed (connectors, pot trimmer tool, add'l Euroblock, etc, etc).
As usual, comments and suggestions welcomed!
Next on the roadmap are:
1. going back and revising Building: Power Supply Assembly and Test in light of all your great suggestions;
2. what should be the final post, covering chassis assembly, signal input wiring, and final adjustments.
Building: Amp Board Power Up and Test
I also updated Introduction: Tools You Will Need based on my build experience, adding a good DMM leads kit, magnifying glass, and infrared thermometer to "must have" tools.
And I updated Building: Amp Boards on Heat Sinks to use a Euroblock on the amp board signal input contacts. This should make hooking up input connectors much easier, and make it easy to swap XLR to RCA.
And I also updated Parts: the Rest of the BOM with a refreshed saved Mouser cart, adding all the additional parts that I've needed (connectors, pot trimmer tool, add'l Euroblock, etc, etc).
As usual, comments and suggestions welcomed!
Next on the roadmap are:
1. going back and revising Building: Power Supply Assembly and Test in light of all your great suggestions;
2. what should be the final post, covering chassis assembly, signal input wiring, and final adjustments.
Coax on input...
I have some 28 AWG Belden coax I've been thinking of using for inputs; what did you do with the shield?
A. Attach at input only
B. Attach both ends
C. Attach board/chassis end only
Thanks!
I have some 28 AWG Belden coax I've been thinking of using for inputs; what did you do with the shield?
A. Attach at input only
B. Attach both ends
C. Attach board/chassis end only
Thanks!
Unless they've rewired it again from previous pictures, Mkane77g did not use coax for input wiring. The only reason I call that out is you cited the post, so it may have influenced your decision.
Either way, what specific Belden cable were you thinking of using? I don't see a 28AWG except in their standard hook-up wire, but I could have easily overlooked something.
Are you using RCA inputs, XLR inputs, or both?
Either way, what specific Belden cable were you thinking of using? I don't see a 28AWG except in their standard hook-up wire, but I could have easily overlooked something.
Are you using RCA inputs, XLR inputs, or both?
Attach the cable shield at the input end only.
Think of the cable shield as an electrical extension of the chassis. This is not connected directly to audio ground, but through a ground lift circuit of some sort.
The 'hot' and 'cold' or 'neutral' legs of the shielded coax have specific connections. 'Hot' is the signal and 'cold' is signal return, usually audio ground.
Another, perhaps easier, way of connecting the incoming audio inputs is with CAT5 twisted pair. No separate shield, just audio signal and return.
Are you using the coax's shield as 'cold'/return? If so, I'd say you better connect it as in (B)
(a signal wire should/must (?) consist of 2 connections: hot/cold resp. signal/return, doesn't it?)
@ItsAllInMyHead: I'm pretty sure it's been discontinued for years: Belden B8700. After some of the XLR/RCA discussions, I'm now thinking of at least leaving the option to include XLR connectors. I'm still in planning/parts acquisition stage.
@TungstenAudio: Thank you for the shield-chassis metaphor with lift...that's very helpful. If there's no clear advantage to coax, I'll stick with the CAT5 twisted pairs, get it running, and then possibly experiment.
@TungstenAudio: Thank you for the shield-chassis metaphor with lift...that's very helpful. If there's no clear advantage to coax, I'll stick with the CAT5 twisted pairs, get it running, and then possibly experiment.
That's why I asked what cable. It's a solid core coax. You can use it, but... you may want something different.
If you connect it as TungstenAudio suggests, you will get no signal. He may have thought you had two or three conductors and a shield.
Either way, if you do use it, just use it for RCAs. Connect shield to the tab of your input jack and the shield to (-) input on the board. Don't forget your jumper on the board.
Solid core to from center of jack to (+) input on the board.
If you decide to go with XLRs, or XLRs + RCA, I'd use a different cable.
If you connect it as TungstenAudio suggests, you will get no signal. He may have thought you had two or three conductors and a shield.
Either way, if you do use it, just use it for RCAs. Connect shield to the tab of your input jack and the shield to (-) input on the board. Don't forget your jumper on the board.
Solid core to from center of jack to (+) input on the board.
If you decide to go with XLRs, or XLRs + RCA, I'd use a different cable.
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I chose for mine and recommend XLR for the input connection. If you start with XLR, then it's a simple adapter to switch to RCA (Neutrik makes one, $20/pr), or you can get RCA to XLR cables (Monoprice offers start at $16/pr). Electrically, using either of these approaches looks to be identical to the standard hookup connection for RCA jacks (where -IN jumpered to GND).
Whether you opt for RCA or XLR, I also recommend installing Euroblock connectors across -IN, +IN, and GND contacts of the amp boards (it's a perfect fit!), which will make it much easier to swap to XLR later (no desoldering from the amp boards). This convenient idea comes from @Pechelman's excellent list of suggestions.
Great post, yet again.
I read below as a bit strong and "scary". That may not have been your intention.
"Ideally, you should have no input signal wires connected ...you don't need them for initial testing, and you don't want an accidental short if the ends are exposed and touch)."
There's no harm, and a number of people intentionally short the inputs for biasing and nulling the offset. It's 6 of one and a half-dozen of another.
Aah, I guess I thought a little too short about coax (one core, and coaxial to it, a shield) and did not consider the variant of the usual, twisted, shielded wires commonly used for XLR etc. (which aren‘t real coax but called like that for convenience)
The confusion‘s my bad...
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