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Creating parallel resistance and capacitance kit

DaveyW said:
Fully understand and appreciate your angle Cyto :thmbsp:

I did re-cal the pots (new cover hand marked up) after the first couple of months of usage - I do periodically check and both appear to have settled down OK.

Also my switching fears have been somewhat erroded with time.
I do occasionally hit the bypass and 2nd range switches on the loading box while the volume is low.

OK - So it's really down to the convienience of infinitely variable v's precise loading.
Yep difficult call :scratch2:
Very much down to personal preference isn't it.

Good stuff!
Dave
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Well said. I think most fears can be softened with a good design and build.

I wonder if the people from Musical Fidelity and other pre-amp makers are seeing the need here?
 
To create the parallel capacitance loading kit that I discuss in my first post, which voltage caps would I need to get?

Also, silver mica caps have been suggested, but I note that DB Systems uses polystyrene caps. Are there relative advantages to one over the other?
 
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steelglam said:
To create the parallel capacitance loading kit that I discuss in my first post, which voltage caps would I need to get?

Also, silver mica caps have been suggested, but I note that DB Systems uses polystyrene caps. Are there relative advantages to one over the other?
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Any voltage will be OK - you don't have to worry about large voltages, or you'd have more expensive problems (e.g. blown cartridge coils) to worry about. If you want to be pedantic, say anything over about 20V.

http://en.wikipedia.org/wiki/Silver_mica_capacitor
http://en.wikipedia.org/wiki/Types_of_capacitor

Cost is one factor that may make one better than the other - either will be OK, if you can get them in the correct sizes.
 
steelglam said:
To create the parallel capacitance loading kit that I discuss in my first post, which voltage caps would I need to get?

Also, silver mica caps have been suggested, but I note that DB Systems uses polystyrene caps. Are there relative advantages to one over the other?
Click to expand...

Personally I use Polystyrene or Polypropylene, these types are very transparent and normally not so expensive.
gusten
 
OK, thanks folks. That's very helpful.

ETI_5000: When you say don't use large voltages, what do you have in mind? Like I said, I'm new to this territory so I'm not sure what defines "small" and "large" voltages. Would resistors that are 50V be too high for this application? 100V? 200V? More than that?
 
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As a follow-up to my last post, I found some 450V capacitors in the values that I need (50-500pf) at my local electronics surplus store. Would this voltage be OK (i.e., not too high) for creating these parallel capacitance plugs?
 
steelglam said:
OK, thanks folks. That's very helpful.

ETI_5000: When you say don't use large voltages, what do you have in mind? Like I said, I'm new to this territory so I'm not sure what defines "small" and "large" voltages. Would resistors that are 50V be too high for this application? 100V? 200V? More than that?
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No - the only thing you have to worry about with capacitors are when the working voltage rating of the capacitor is less than the voltage that is in the circuit, and that higher voltage would be applied to it. They usually go bang when that happens! Because the voltage that a typical cartridge will put out is in the millivolt range, you don't need a working voltage much more than that, but if you have ones that will handle 450V, that will be "more than adequate"!

steelglam said:
As a follow-up to my last post, I found some 450V capacitors in the values that I need (50-500pf) at my local electronics surplus store. Would this voltage be OK (i.e., not too high) for creating these parallel capacitance plugs?
Click to expand...

That will be OK. You actually don't need any more than about 350pF anyway, since the preamplifier itself will also have an input capacitance, which may be anywhere from 50pF to 270pF, and the turntable leads will contribute anything from 70pF to 200pF. They all add up when they're in parallel, so if you have 100pF leads and 100pF input capacitance in the preamp, with an external 350pF capacitor you'll end up with a total 550pF (350+100+100), which is more than enough for any cartridge, and too much for most.
 
OK, thanks ETI_5000. I understand this now.

By the way, does it work the same way with resistors and wattage? In other words, is it OK to use higher wattage resistors in place of lower wattage ones? Like, it seems that folks use 1/4W resistors to build their parallel resistance kits, but could you use 5W or 10W ones in their place?
 
steelglam said:
OK, thanks ETI_5000. I understand this now.

By the way, does it work the same way with resistors and wattage? In other words, is it OK to use higher wattage resistors in place of lower wattage ones? Like, it seems that folks use 1/4W resistors to build their parallel resistance kits, but could you use 5W or 10W ones in their place?
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Well, theoretically you could, but the reason it isn't done is that they are a lot more expensive than resistors with lower wattages, and in some cases, to get that high wattage, they are wirewound resistors, and can be inductive. They are also quite a bit larger than low wattage resistors. It's much cheaper to use lower wattage (1/4W or 1/2W) resistors - they won't receive any significant wattage at the input to an amplifier.

I was going to give you a lecture on Ohms Law, but decided not to - I don't want to bore you. I'll just tell you the figures I worked out for a MM cartridge which puts out 10mV - into a typical 47kΩ loading resistor at the input of a phono preamp, the wattage....wait for it....will be just over a massive 2 nanowatts (0.000000002 watts)! See why you don't need high power resistors?:D
 
ETI_5000 said:
Well, theoretically you could, but the reason it isn't done is that they are a lot more expensive than resistors with lower wattages, and in some cases, to get that high wattage, they are wirewound resistors, and can be inductive. They are also quite a bit larger than low wattage resistors. It's much cheaper to use lower wattage (1/4W or 1/2W) resistors - they won't receive any significant wattage at the input to an amplifier.

I was going to give you a lecture on Ohms Law, but decided not to - I don't want to bore you. I'll just tell you the figures I worked out for a MM cartridge which puts out 10mV - into a typical 47kΩ loading resistor at the input of a phono preamp, the wattage....wait for it....will be just over a massive 2 nanowatts (0.000000002 watts)! See why you don't need high power resistors?:D
Click to expand...

Thanks much, ETI_5000! I understand now. I didn't know that about the relationship between hire wattage resistors and inductors. Someday I'm going to have to sit down and make a concerted effort to understand all of this stuff...someday when I have more time!

I would have appreciated the lecture on Ohm's law! :yes: But what you say in that example makes sense.

Btw, I really appreciate everything that's been shared in this thread. Highly informative. Thanks much folks!
 
Hi folks...I was going to purchase the resistors to create the parallel resistance loadings, and I have a quick follow-up question.

Per others' suggestions, I would like to create 62k and 75k loadings, to try it out with some Shure's and what not. For the several preamps that I have that include both 47k and 100k input resistance loadings, I would use the 100k setting and then use parallel loading plugs to lower it down to 62k and 75k.

My calculations indicate that one would need to use 165k and 300k resistors to lower the stock 100k loading down to 62k and 75k, respectively. Is this correct? If so, the problem is my local electronics surplus store does not carry resistors in those particular values. The closest it has are 150k, 180k, 270k, and 390k. I'm assuming those values would not work to get to the 62k and 75k loadings, unless my calculations are incorrect. Is this true?
 
150k gets you around 60k... which is close enough!
270k gets you 73k - again, that seems about right to me.

If once you are using 60 & 73k, you feel the need for further adjustment, you can then shop via mail order online...

But a 2k difference at 60 to 75k is going to be very very minor

bye for now

David
 
Another quick question on the resistors. Does anyone know if NTE brand resistors are good? That's what my local electronics surplus store carries. If these are considered to be good quality resistors, I will get them. But if they're not, I will look elsewhere. Thanks!
 
NTE are a very good brand, and a major part of their component manufacture used to be branded Philips, who were well known for quality.
 
Bringing up an old thread of mine here. I have a few follow-up questions relating specifically to the capacitance kit that I'd like to create.

1.) Are ceramic capacitors such as these OK to use for this application: http://www.mouser.com/Vishay-Cera-M...0x7yzZ1z0x7yuZ1z0x7p2Z1z0x7z0Z1z0x74kZ1z0x7x4

2.) Do you know of a good source that generally stocks the values of the caps that I need to create this kit--integrals of 50pF, beginning at 50pF and ending at 400pF--and at a real good price, like $0.75 or less per cap? I need to place a huge order from Mouser for other stuff, so I was hoping to include these caps in the order as well. But Mouser either doesn't seem to stock all of the values that I need or they are too expensive.

3.) If I can't resolve the issue of finding a source that has all of the values of caps that I need, do you think there is enough room in an RCA plug to wire in more than one cap in parallel? Like would it work to wire a 220pF and a 33pF cap in parallel inside of an RCA plug to get 253pF (which is close to 250pF)?

Thanks in advance!
 
Hi folks,

A follow-up to my last post...

I did a bit more searching on Mouser for caps, and am wondering:

1.) Would Xicon ceramic caps such as these be OK for creating the parallel capacitance kit? http://www.mouser.com/ProductDetail...Y6bF4iPirSpnBw0aLQnL4/rcPp%2bQIXsOIwzczDt5vk=

2.) Is a 50V cap sufficient for this application?

3.) Is it OK to mix different voltages when creating the different capacitance plugs? Most of the caps I refer to above are available in 50V versions, but a few are only available in 500V versions.

4.) If I want to create plugs in increments of 50pf, beginning at 50 and ending at 400pf, how "close" to the actual value do you need to be for it to be effective? I ask because several of the values that I need are unavailable. Specifically, can I use: A.) a 47pf or 51pf cap for a 50pf loading/plug; B.) A 330pf cap for a 350pf loading/plug, and C.) A 390pf for a 400pf loading/plug? Are those values "close enough" to the desired loading? If not, in your opinion is there sufficient room in an RCA plug and is it an OK practice to solder two caps in parallel to create the exact desired loading?

Thanks in advance!
 
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