Rapid sell 1% 600mW metal film from ~£1.50 per hundred.@Jwilhelm and Andrew: thanks!
This will be the way to go, then. I may have to ask the supplier for a better price, though, since the entire package is turning out more expensive than I had previously anticipated...
500VA each, I plan to use the DIYAudio softstart device, as listed in the DIYAudio store.
How can I determine if the quality of C4 is good enough? I have found a 63V Visaton cap, but I don't have very much faith in their loudspeakers...
Assuming the green led has a 2v forward voltage drop. . .Oh, and about R51-52, for the LEDS:
I want to use standard green LED's, rated at ca 20mA each. I use 56,5V rail. According to my calculations, accounting for 5V voltage across the LED, I get 2,2 - 2,5k for R51-52, in stead of the 22k and 100k mentioned in the BOM. Am I correct??
22k is correct to stay within the safe capacity of an ordinary 1/4w resistor.
You could use 12k if you have a 1/2 watt resistor.
Remember, except for about 2v, the rest makes heat in the resistor.
Got a strange problem. First a few hundred Hz noise appeared in one channel just after switch on but it would disappear within about 30 sec. A couple of weeks later mains fuse blew. I took HB modules out, checked PS first, perfect. Then I connected the quiet module to my bench PS (300VA 2x25V toroid with 50A bridge and 2x10mF caps giving about 2x36.5V DC with one module connected), offset zeroed and AC about a few hundred uV at the output. Mains noise. Connected the noisy module and again no problem, offset zero and AC at the output closer to 1mV. DC voltages I measured at a few randomly selected points correct.
Then I shortened input hoping that noise would completely disappear but it jumped up to over 100-150mV and is similar to noise between FM stations. Mostly several hundreds Hz up to a few kHz masking mains noise completely. That is my frequency guess as I listened to this noise with my test wide range speaker connected (8 ohm).
The other channel behaves similarly with input shortened but noise is about 10-20mV.
When placed in the amp's case with amp's PS noise behavior is similar with both modules but the quieter module is quieter. What's wrong?
cheers,
Then I shortened input hoping that noise would completely disappear but it jumped up to over 100-150mV and is similar to noise between FM stations. Mostly several hundreds Hz up to a few kHz masking mains noise completely. That is my frequency guess as I listened to this noise with my test wide range speaker connected (8 ohm).
The other channel behaves similarly with input shortened but noise is about 10-20mV.
When placed in the amp's case with amp's PS noise behavior is similar with both modules but the quieter module is quieter. What's wrong?
cheers,
Attachments
the "shorting the input" seems to be increasing the noise.
This is the symptom we hear when a long lead is connected to an input.
The long lead acts as an aerial due to the high input impedance when there is no Source connected.
That makes me think you are not actually shorting the input.
Could you show a pic of what you are doing and describe what you are doing when you "short the input"?
This is the symptom we hear when a long lead is connected to an input.
The long lead acts as an aerial due to the high input impedance when there is no Source connected.
That makes me think you are not actually shorting the input.
Could you show a pic of what you are doing and describe what you are doing when you "short the input"?
Just RCA plug with screen soldered together with the input pin. No cable whatsoever. That's why it seems strange. And why the mains fuse blew a couple of times? PS fuses unaffected, voltages/currents as should be.
Could the input cap became strangely damaged so when its input is connected to ground it creates together with resistors some sort of an aerial or an oscillating circuit?
Thanks,
cheers,
Could the input cap became strangely damaged so when its input is connected to ground it creates together with resistors some sort of an aerial or an oscillating circuit?
Thanks,
cheers,
you are not alone, i am really scared powering up equipment for the first time, even if i know i did everything right....i make myself a short checklist, and the lamp tester in series with the line is a real life saver...
Well, it's been a couple of years since I have been able to work on my amp and I am thinking its time to hand it over to someone else. Anyone in the Los Angeles area interested in buying a nearly complete amp in the Deluxe 4U chassis? I went with mundorf and clarity caps. Had it nearly working at one point but had some grounding noise and then let out the magic smoke. I haven't looked at it since.
Thanks AJT,
Nice to know I'm not the only one who gets nervous....
I will use the lamp tester when I juice it up. 60W or 80W should be fine.
Test all transistor legs to ground / heatsink first.
I'll post pictures sometime soon if all goes well. (crossed fingers)
Is there any benefit to using a variac and turning up the power slowly?
Or as the build guide suggests, just a momentary on/off at full power?
Ron
i have a 1.5kva variac but i use it mostly for doing short circuit testing of newly built traffos and for providing variable B+ on breadboard tube circuits...
i use the lamp tester exclusively for new amps livening up for the first time...
momentary on and off is very risky, you will be amazed at how quickly solid state devices can fry when there is a fault in the circuit...
i use the lamp tester exclusively for new amps livening up for the first time...
momentary on and off is very risky, you will be amazed at how quickly solid state devices can fry when there is a fault in the circuit...
I haven't solved my problem yet as I spent may Sunday away from home.
Anyway, on powering up I use only a soft start unit and a globe. Never experienced problems with such arragement.
As my recent problem clearly demonstrates parts which are faulty only under certain conditions can became a real pain.
cheers,
Anyway, on powering up I use only a soft start unit and a globe. Never experienced problems with such arragement.
As my recent problem clearly demonstrates parts which are faulty only under certain conditions can became a real pain.
cheers,
Ostripper and JojoD wrote very good build guides, if you followed them to letter, then the amp should work the first time...
My amp worked very well until last week. First, a couple of weeks ago I got noise in one channel after powering up for about 30 sec but that happenned only occasionally and then last week amp's mains fuse blew.
The only partial fault I discovered was weak soldering on the positive supply to the board. I discovered it when I used pliers to check strenght of PS joints as blades do not solder very well. Anyway, on my test bench everything seems fine and noise (about 120-150mV) appears only when I shorten the input.
cheers,
The only partial fault I discovered was weak soldering on the positive supply to the board. I discovered it when I used pliers to check strenght of PS joints as blades do not solder very well. Anyway, on my test bench everything seems fine and noise (about 120-150mV) appears only when I shorten the input.
cheers,
