Internal cabling
For cabling the input RCA connectors to the PCB, I've found some decent shielded audio cable which seems to work well. However, for cabling the speaker (signal out) connectors I'm not sure what to use. The distance is about one foot. Since it's very short, would just cheap thin speaker wire be appropriate? Should it be shielded?
What about the power cabling? Does it matter what kind of cables go from the IEC socket to the transformer? How about from the transformer to the bridge rectifiers? I'm just using the same thin wire I use for everything else at the moment, but since the transformers come with very chunky leads I'm wondering if I should be hooking them up with similar cable...
For cabling the input RCA connectors to the PCB, I've found some decent shielded audio cable which seems to work well. However, for cabling the speaker (signal out) connectors I'm not sure what to use. The distance is about one foot. Since it's very short, would just cheap thin speaker wire be appropriate? Should it be shielded?
What about the power cabling? Does it matter what kind of cables go from the IEC socket to the transformer? How about from the transformer to the bridge rectifiers? I'm just using the same thin wire I use for everything else at the moment, but since the transformers come with very chunky leads I'm wondering if I should be hooking them up with similar cable...
the noise from the amplifier due to switching elsewhere can enter from three routes.
1.) radio waves due to the "spark" at the switch. Suppress the switch. Build a Faraday cage (metal chassis) around the amplifier. Fit a Thiele network to the output of the amplifier, preferably the Pi type rather than the L type.
2.) voltage glitches and spikes on the mains. Suppress the switch and fit an EMI filter at your amplifier mains input.
What is the filter frequency at the power amp input?
3.) the interference is affecting a source component and coming in with the audio signal. Suppress the switch and filter the faulty source component.
1.) radio waves due to the "spark" at the switch. Suppress the switch. Build a Faraday cage (metal chassis) around the amplifier. Fit a Thiele network to the output of the amplifier, preferably the Pi type rather than the L type.
2.) voltage glitches and spikes on the mains. Suppress the switch and fit an EMI filter at your amplifier mains input.
What is the filter frequency at the power amp input?
3.) the interference is affecting a source component and coming in with the audio signal. Suppress the switch and filter the faulty source component.
the internal cabling should be sized to suit the current passing and to suit interference.
Input and other low level cable can be UTP (unshielded twisted pair).
Speaker cable can be 1.5sqmm to 2.5sqmm mains cable or can match your external speaker cable.
Mains cable should be double insulated mains cable.
Input and other low level cable can be UTP (unshielded twisted pair).
Speaker cable can be 1.5sqmm to 2.5sqmm mains cable or can match your external speaker cable.
Mains cable should be double insulated mains cable.
Thanks for those ideas about finding/removing the noise, Andrew - I don't understand them all yet, but that's given me enough to search for that I'm sure I can work it out from here.
Jeremy,
The math is fantastic, but it may also be influenced by the turn on and turn off speed of the diodes in the bridge. If you use ultrafast soft recovery diodes with tns of 25nS, as a general rule you can eschew these switching caps. I found that they make a big difference and now use nothing else.
Switching thumps from domestic appliances can be minimised with power supply design tricks, such as using two caps per rail, and decoupling between those caps with a small resistor, to reduce charge pulse currents in the final cap.
Hugh
The math is fantastic, but it may also be influenced by the turn on and turn off speed of the diodes in the bridge. If you use ultrafast soft recovery diodes with tns of 25nS, as a general rule you can eschew these switching caps. I found that they make a big difference and now use nothing else.
Switching thumps from domestic appliances can be minimised with power supply design tricks, such as using two caps per rail, and decoupling between those caps with a small resistor, to reduce charge pulse currents in the final cap.
Hugh
Adding a small resistor sounds like something even I can do! So each resistor would be in parallel with the last cap? Or every cap? What size might be appropriate?AKSA said:
Jeremy
I would add that "if it ain't broke, don't fix it !"
None of my amplifiers in the last 10 years or so have had any problems with mains appliances or light switch etc. switching spikes. DTV STBs, now that's another story! Andrew's tips will definitely help in that regard. Even the interior light switch on a refrigerator can sometimes upset them. Sensible routing and minimum length of speaker cables helps too.
Alex.
I would add that "if it ain't broke, don't fix it !"
None of my amplifiers in the last 10 years or so have had any problems with mains appliances or light switch etc. switching spikes. DTV STBs, now that's another story! Andrew's tips will definitely help in that regard. Even the interior light switch on a refrigerator can sometimes upset them. Sensible routing and minimum length of speaker cables helps too.
Alex.
Hi Jeremy,
Two caps per rail, cap #1 connect directly to rectifier output, cap #2 passes current to amp. Put in two 1W 0.1R resistors between the caps, on both electrodes.
This also reduces intermodulation of the voice coil earth return current and the charge pulses coming off the rectifier.
Hugh
Two caps per rail, cap #1 connect directly to rectifier output, cap #2 passes current to amp. Put in two 1W 0.1R resistors between the caps, on both electrodes.
This also reduces intermodulation of the voice coil earth return current and the charge pulses coming off the rectifier.
Hugh
AKSA is describing a CRC PSU.
Look up PASS and others, because it's often used with ClassA equipment. It is good for removing mains voltage artifacts from the supply rails, when currents are higher.
Look up PASS and others, because it's often used with ClassA equipment. It is good for removing mains voltage artifacts from the supply rails, when currents are higher.
I've got the power wiring now done, including the cap over the transformer outputs (but not including any of the recent suggestions re external noise from AKSA and AndrewT).:
(The wires aren't routed/tidied yet, as you see - that'll wait until the front panel is done so I know where I want them all exactly).
For those playing along at home, here's a couple of tips (probably obvious to all the gurus here, but perhaps useful to the quiet lurkers!) Firstly, note that a 22nF 3kV cap fits quite perfectly between the inputs of the bridge rectifier. I used a 'piggyback' spade connector to get an easy connection point - you can see the two cap's fairly clearly in this pic:
Secondly, the unused inputs on the power supplies (for the extra windings of the transformer, designed for powering a speaker protector) provide connectors the perfect size for adding a fuse to the input to each transformer:
Be aware that the outside pins of these connectors are joined by a trace on the PCB, so you'll have to flip the board over and cut this trace.
(The wires aren't routed/tidied yet, as you see - that'll wait until the front panel is done so I know where I want them all exactly).
For those playing along at home, here's a couple of tips (probably obvious to all the gurus here, but perhaps useful to the quiet lurkers!) Firstly, note that a 22nF 3kV cap fits quite perfectly between the inputs of the bridge rectifier. I used a 'piggyback' spade connector to get an easy connection point - you can see the two cap's fairly clearly in this pic:
Secondly, the unused inputs on the power supplies (for the extra windings of the transformer, designed for powering a speaker protector) provide connectors the perfect size for adding a fuse to the input to each transformer:
Be aware that the outside pins of these connectors are joined by a trace on the PCB, so you'll have to flip the board over and cut this trace.
Hi, are those fuses 240Volt AC. If they are I suggest using proper 240 V fuse holders. What you have there is deadly.
Terry
Terry
Jeremy,
For your reference, never have any point inside a chassis where 240V wriring is exposed. After installing the 240 V fuses in the back panel cover the fuse holder with tape or heatshrink. Any exposed switch contacts should also be covered. Just pretend there is a child poking around. If we all follow these rules then it is safe to work on other peoples projects. Otherwise one deft touch and you could die.
For your reference, never have any point inside a chassis where 240V wriring is exposed. After installing the 240 V fuses in the back panel cover the fuse holder with tape or heatshrink. Any exposed switch contacts should also be covered. Just pretend there is a child poking around. If we all follow these rules then it is safe to work on other peoples projects. Otherwise one deft touch and you could die.
alfredrofe said:
No, not sufficient. Parts of the underside of the board will still be exposed. Also, none of the tracks on that board are designed to carry or insulate against high current 240 Volts.
Thanks guys - that makes perfect sense now you mention it. I've got some fully covered plastic fuse holders which I'll use instead. Pity - I was so pleased that they fit so well!...
Yes and one day the probe, screw driver, whatever, drops......oops......and you let the smoke out. Or you let the smoke out when retrieving said errant whatever. By the way, consider what the full voltage is across your speaker leads. Is it dangerous? Your secondary voltages are in the lethal range. Have you considered these facts. If not take a few moments to consider.
Terry
Terry
Jeremy
For your own protection,use something like below, with heatshrink covering it .
Alex
Jaycar CAT. NO. SZ2034 RRP $1.95
M205 SAFETY FUSE HOLDER
Similar to our SZ- 2036 below.- Panel hole 12mm....more...
QTY
1+ $1.95
CAT. NO. SZ2036 RRP $2.75
3AG SAFETY FUSE HOLDER
Fuse retainer is released by simply depressing catch by inserting a screwdriver or any similar tool or object in to the small rectangular hole on top ...more...
QTY
1+ $2.75
P.S.
You may want to consider using it in conjunction with something like this :
Jaycar CAT. NO. HM3194 RRP $1.75
5 AMP 12-WAY SCREW TERMINAL STRIP
Nylon terminal strips are suitable for many applications. Sold in a standard length of 12 way - they can always be cut down to a smaller size if requi...more...
QTY
1+ $1.75
OR
CAT. NO. HM3196 RRP $1.95
10 AMP 12-WAY SCREW TERMINAL STRIP
Nylon terminal strips are suitable for many applications. Sold in a standard length of 12 way - they can always be cut down to a smaller size if requi...more...
QTY
1+ $1.95
For your own protection,use something like below, with heatshrink covering it .
Alex
Jaycar CAT. NO. SZ2034 RRP $1.95
M205 SAFETY FUSE HOLDER
Similar to our SZ- 2036 below.- Panel hole 12mm....more...
QTY
1+ $1.95
CAT. NO. SZ2036 RRP $2.75
3AG SAFETY FUSE HOLDER
Fuse retainer is released by simply depressing catch by inserting a screwdriver or any similar tool or object in to the small rectangular hole on top ...more...
QTY
1+ $2.75
P.S.
You may want to consider using it in conjunction with something like this :
Jaycar CAT. NO. HM3194 RRP $1.75
5 AMP 12-WAY SCREW TERMINAL STRIP
Nylon terminal strips are suitable for many applications. Sold in a standard length of 12 way - they can always be cut down to a smaller size if requi...more...
QTY
1+ $1.75
OR
CAT. NO. HM3196 RRP $1.95
10 AMP 12-WAY SCREW TERMINAL STRIP
Nylon terminal strips are suitable for many applications. Sold in a standard length of 12 way - they can always be cut down to a smaller size if requi...more...
QTY
1+ $1.95
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