0 Members and 1 Guest are viewing this topic. Read 5565 times.
Would this be the suitable replacement?http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BC2361-ND
I'd think about rated for AC not less than 600V capacitors. On the secondary (C101) the capacitor is under 550V (if everything in the load is OK). The fact that it is in serial with 10k resistor is not so important (for 60Hz the capacitor will have around 265k, so the resistor will drop only about 20V).About your list of "important" parts.IMHO C300-C303, D101-D104, R302, R303, R306, R307-R312, R300 (or something instead of it - i'll drop it completely), R301 (or something instead of it - I have some other thoughts (comparing to your choices) about its implementation, but I'm afraid I can't mention it here - could be seen as advertising), S300, J300-J302, J304, J305 is critical.C100-C102, C103, C106, C304-C306, D100, R100, R101-R108, R304, R313, R314 is rather common quality could be enough.C303 bypass - is not the method which works well in non-controlled environment (you don't know the following stage load impedance). IMHO I'd prefer to put the single capacitor here.The main note (mostly for myself of course ) - the preamp is the central point of control in your stereo system. Todays technology allows us to use remote controls, perfect low-signal relays, nice indicators - and all of that for only slight increase in cost! I'd add some convenience to the circuit, but you can certainly do what you wish!
I looked for two hours trying to find a replacement for that ceramic cap. Would like to get something from Digikey so just one order could be made. Do you have any suggestions?
I've not looked into remote control, as the cheap ones I've heard sounded exactly like that, cheap and bad. The good ones cost a good chunk of money, and to be honest, it's not worth 1/3 or more of the cost of the preamp to me. I'm not so lazy I can't get up and walk 8 feet to the stereo But if you have some suggestions on those I'd be more than willing to hear your opinions. You can always PM with ideas if you would rather not express them publicly on the circle.
Taking some time to understand things... Strictly speaking digikey doesn't have such capacitors. But... If we agree on some assumptions we'll found that there are capacitors rated X1-X3 (Y1-Y4), which are capable to withstand impulses up to 4000-1200V (8000-2500V, Y3=only 250VAC). You can assume (at yours own peril) that the impuls=AC and live with it. Then you can easily use the capacitor you mentioned in the first posting.(I mean http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BC2361-ND) Yes, will write you as soon as possible.
For the AC 10nF cap I found #495-1301. That 250V is an AC line voltage rating. The capacitors are of special construction for mains operation.jh
Could you explain what do you mean?Your suggestion is dangerous and misleading. The capacitor you have suggested can't be used in the circuit. It is unsafe in the first thing! C101 must have minimal AC ratings of 600V (because it is directly connected to the secondary 550VAC). C100 must have minimal ratings of 250V (because the transformer is universal and can be used in the 240VAC power networks). If you look at the datasheet for the capacitor you have mentioned (http://www.epcos.com/inf/20/20/db/fc_2009/MKP_B32620_621.pdf look at B32620A4103J code) you learn that the capacitor can be used with AC up to 200V RMS only!
So this looks like it has a 1kV rating, same temp rating as the original? # 490-4250
This isn't worth it, over a capacitor. Built a handful of kits and never had this issue.
I'll just put a volume pot on the next amp and call it good. I was looking forward to building a new system around this pre with all the good reviews it gets.
Aren't these just power supply filtering caps to get rid of small spikes?
Can't we use a 0.02uf or greater as long as it is rated for the recommended 2kV?
Is the 2kV a conservative design? Why won't the run of the mill 1kV ceramic disc work?
I found a couple 0.022uf ceramic discs rated at 1kV in my inventory, I am just going to use those until a suitable replacement is issued for C100 and C101. Hopefully it will be short term as poty has got me worried.Blooze: You may want to place an order for those Panasonic caps ASAP if you haven't already, inventory is running thin at digikey.Also, how do previous builders print those nice labels with white lettering? My board came with labels consisting of a white background with black lettering.Thanks,Brad
When something is about safety I'm very conservative. I don't like to feel sitting on a powder keg.It's your choise of course. Yes they are, but speakes are not small. At the working point the spikes of current is rather high, provoking the high spikes on the secondary of the transformer (because of inductance). Yes, we can. As soon as the AC rating is suitable. The question is - what for the rating is? If for DC - then it could be as much as twice less in AC rated field (you can look at the JH-suggested capacitor to see the difference). The other capacitors' dielectric may be broken by high AC currents.
OK, I've looked again at Digikey and it looks like the caps that are rated for higher AC voltages are film caps. Yes, a lot of ceramic caps are tested at high AC voltage for a small period of time, but most are not rated for continious use over 250VAC. So my question is can a film cap be used in this position? Leads can be bent easily to fit the required spacing as long as the body size will fit.
Yes, the film caps can be used in the circuit.Following my own concern I asked Vishay through their site about using their DC rated ceramic capacitors. They have pointed me to caution notes in the capacitors' datasheets. It states:"When sinusiodal or ripple voltage applied to DC Ceramic Disc Capacitors, be sure to maintain the peak-to-peak value or the peak value of the sum of both AC + DC within the rated voltage.When start or stop applying the voltage, resonance may generate irregular voltage.When rectangular or Pulse Wave Voltage is applied to DC Ceramic Disc Capacitors, the self-heating generated by the capacitor is higher than the sinusoidal application with the same frequency. The allowable voltage rating for the rectangular or pulse wave corresponds approximately with the allowable voltage of a sinusoidal wave with the double fundamental frequency.The allowable voltage varies, depending on the voltage and the waveform.Diagrams of the limiting values are available for each capacitor series on request....During operation in a high-frequency circuit or a pulse signal circuit, the capacitor itself generate heat due to dielectric losses.Applied voltage should be the load such as self-generated heat is within 20 °C on the condition of environmental temperature 25 °C."It means that for the secondary the capacitor should withstand not less than 550V*sqrt(2)*2~1555V. Then the 2kV is not conservative voltage, but a must!The Vishay support (following my requested environment) suggested S103M69Z5UP63K7R (digikey part #1256PH-ND) as the best substitution for the missed capacitor.I've looked through other candidates and found similar capacitor DEBF33D103ZA3B from Murata (digikey part #490-4254-ND).Both capacitors have lead spacing 7.5mm (as on the PCB).
