Hi im looking for some advice please, im planing to make a passive pre to control my pc's soundcard output.
Im hoping it will drive a Naim NAP140 to a decent volume. Im thinking alps blue for the volume pot but im unsure which value to get - im looking at probably either 50 or 100k value, can anyone help.
Cheers
Im hoping it will drive a Naim NAP140 to a decent volume. Im thinking alps blue for the volume pot but im unsure which value to get - im looking at probably either 50 or 100k value, can anyone help.
Cheers
The higher the pot value the more the cable to the amp will affect the highs. The input circuitry of the amp will also affect the outcome. A lower value is better but if too low it will load the output of the sound card making it work harder = more distortion. So it is a balancing act. The general consensus with solid state gear is 10k.
Thanks Fredex, im planning on using some of DNM's new interconnect wire for internal wiring because thats what im using for the rest of my inters so keeping capacitance low.
Stunning wire IMO, so's his new speaker cable.
BTW, any tips on where i can source a quality pot with that low a value?
Stunning wire IMO, so's his new speaker cable.
BTW, any tips on where i can source a quality pot with that low a value?
it depends on which sound card out you use. the line out would work best with a 10k or 20k pot, while the headphone out would work best with a 1k, 2k, or 5k pot. if it's an actual speaker out, use a 100 or 500 ohm pot.
I don't know how good or bad the PC's soundcard output is, so I suggest you cobble together a very cheap 10k pot with DC blocking cap on the input and a high value grounding resistor from the wiper.
Keep your cables as short as possible (less than 1m) for this first test set up.
If you get a sound that seems acceptable then try to source a better attenuator that suits the PC source and suits the Naim load.
Keep your cables as short as possible (less than 1m) for this first test set up.
If you get a sound that seems acceptable then try to source a better attenuator that suits the PC source and suits the Naim load.
Thanks all, it appears that most if not all Naim poweramps have an input impedance of 18k.
Not sure about the soundcard, i did'nt fit it but im told it's decent,
Creative Audio PCI (ES1371,ES1373) (WDM) - at least thats what my pc tells me is fitted, makes no sense to me at all may as well be in urdu or chinglish.
So what value pot suits an 18k impedance?
Cheers
Not sure about the soundcard, i did'nt fit it but im told it's decent,
Creative Audio PCI (ES1371,ES1373) (WDM) - at least thats what my pc tells me is fitted, makes no sense to me at all may as well be in urdu or chinglish.
So what value pot suits an 18k impedance?
Cheers
I would fit a 100k linear taper pot. The 18k input impedance will load the pot to give a good approximation to a logarithmic characteristic.
but the 25k source impedance of the 100k pot will demand a very low capacitance between pot and power amp.
40pF will create a filter with F-3dB = 16kHz
4pF will give a much more acceptable treble roll off characteristic.
What is the value of the RF filter capacitor inside the Naim?
What is the parasitic capacitance of the internal wiring and connectors in the Naim?
40pF will create a filter with F-3dB = 16kHz
4pF will give a much more acceptable treble roll off characteristic.
What is the value of the RF filter capacitor inside the Naim?
What is the parasitic capacitance of the internal wiring and connectors in the Naim?
Sorry you've lost me with science, im a bit of a novice when it comes to electronics i flunked out of an electronics course in the early 90's and hav,nt advanced much since. I can solder well though but my previous experience is pretty basic, limited to kit building.
Sorry i've no idea what value the rf filter is or the parasitic capacitance. Can you provide a basic diagram of your proposed circuit with input blocking cap value and appropriate grounding resistor value please, if possable go for middle ground, i can change values later to get best sound. Hope im not being to simplistic but my knowlege is sketchy at best.
Cheers
Sorry i've no idea what value the rf filter is or the parasitic capacitance. Can you provide a basic diagram of your proposed circuit with input blocking cap value and appropriate grounding resistor value please, if possable go for middle ground, i can change values later to get best sound. Hope im not being to simplistic but my knowlege is sketchy at best.
Cheers
fit a 5k or 10k pot to suit the Zin=18k of the Naim.
add a 4u7F cap in series before the pot to block DC.
Use very short cables from pot to Naim (try 300mm or so).
If the PC can drive the 5k pot then that would be my preference.
add a 4u7F cap in series before the pot to block DC.
Use very short cables from pot to Naim (try 300mm or so).
If the PC can drive the 5k pot then that would be my preference.
is this a "set and forget" situation, or are you going to be using the control often? if it's a set and forget a linear will do. if it's one you will be adjusting often, go with a log taper.
I am sorry to say that your soundcard (what card btw?) will probably not drive your NAP140 well. This is not a question of input level and impedance alone. NAIM amps like to be "driven" (actually they must be driven) by a very load tolerant low impedance output. Soundcards are usually not very able to do that. Try it with a decent preamp or buffer and you will hear a massive difference. I have tried that with quite poor resulting sound without a preamp. It might be possible with a pro soundcard to use a passive pot alone.
you might want to consider a pair of NIC's (Negative Impedance Convertor) to drive the amp if it's a low Z input. a NIC provides MORE drive as the impedance drops. that's why a few preamps on the market use them.
Thanks, can you suggest a suitable pair of NIC's and where i can source them, preferably in the UK, also circuitry/how to connect them. Sorry my experience limit has been reached and passed.
Cheers
Cheers
To be honest, given that the Naim has a low input impedance, and soundcards don't really like driving low impedance loads (theyre designed to be connected to active speakers usually) then you would be far better off with an active preamp.
Although, if memory serves, that kind of soundcard does have an amp onboard that you can activate with jumpers. I wouldn't recommend it though as if memory serves it's a fairly average Philips chip amp.
An active preamp is not neccesarily a bad thing if correctly implemented. If you were building one, you could probably get away with a single opamp configured as a unity gain buffer to drive your pot, and then take this to the Naim amp.
Although, if memory serves, that kind of soundcard does have an amp onboard that you can activate with jumpers. I wouldn't recommend it though as if memory serves it's a fairly average Philips chip amp.
An active preamp is not neccesarily a bad thing if correctly implemented. If you were building one, you could probably get away with a single opamp configured as a unity gain buffer to drive your pot, and then take this to the Naim amp.
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