Ok to use a 50k pot in place of 250k one?

[tschanrm]

My volume pot on my 1010 is really starting to go, bad tracking, left/right channels do not stay equal throughout the entire 300 degree turning radius. I've got an Alps Blue Beauty 50k Dual pot that's just laying around, and want to just put it in.

My question is: what is the effect in doing so? I figure three things can happen:

1)There would be 6-8db of attenuation (probably more....) at full range, thus only being able to turn the reciever up so loud. Turning the pot to the 12 O' Clock position is ear bleeding loud, so would it even matter?

or...

2)I would never be able to turn the receiver all the way down, or in otherwords the lowest position I could turn the pot would still result in a moderate sound level.

or....

3) Volume is controlled by the ratio between wiper-to-output and wiper-to-ground, thus will have no immediate effect. Side effect from using the smaller value could mean I would need lower impedance input sources.

Which one is going to happen? I think it is #3, but I'm not positive. I'm not about to tear this monster apart only to find out there is too much attenuation. I don't want to blow another $25 for a nice 250k pot if I don't have to, so I'm willing to use resistors in series with the pots output legs as well. Can anybody help me with this question? I've got schematics for the 1010 if anybody wants to help solve this mystery with me. :scratch2:

EDIT: Oh yeah,if it matters, I don't use or ever plan on using the phono section of this receiver (although it works).

 

[bigphil]

I wouldn't mess around with the resistance value on the volume... theres a major difference between 50K and 250K, replace it with the same value, its not worth the hassle IMO... of course I may be wrong

 

[ferninando]

I think all of what you say will happen to one degree or another. Even 100K Rs in series at each end won't work cause there will always be 100K of resistance at each end of the wiper, affecting volume max/min. Additionally I think you'll be affecting the impedance the volume control circuit will 'see' if you replace a 250K pot with 50K possibly influenceing it's operation. You'll be far better off forking over the $25 for a 250Kr, IMHO. Not using the phono is irrevelant as tape, am/fm, aux all use the vol. control.

 

[agger]

I have looked into the schematics and see 2 problems:

1. The volume pot is in series with the balance pot. If you go down to 50k, this would influence the balance function. After leaving the center the signal will go down very fast.

2. The original pot has a center tab connected to the loudness filter network. I dont know if your Alps pot has that. If not, loudness function is gone. If yes, it will not work as intended because the turnover frequencies change factor 5.

For the load to the signal in general it´s not such a big problem. I won´t put any series resistor. But for 1+2 I would say get a replacement with the correct value.

 

[tschanrm]

I have looked into the schematics and see 2 problems:

1. The volume pot is in series with the balance pot. If you go down to 50k, this would influence the balance function. After leaving the center the signal will go down very fast.

2. The original pot has a center tab connected to the loudness filter network. I dont know if your Alps pot has that. If not, loudness function is gone. If yes, it will not work as intended because the turnover frequencies change factor 5.

For the load to the signal in general it´s not such a big problem. I won´t put any series resistor. But for 1+2 I would say get a replacement with the correct value.

Thanks for the input everyone, I appreciate it.

Yeah, I noticed that about the balance control, but like I said I'm willing to take some comprimises. And for #2, I have not been able to source a 250k pot that still has a loudness tap on it and is still has three pin gangs. Alps and noble both make a potentiometer with a loudness tap, but they are four pin gangs, making the spacing wrong for a three pin pc mount in the 1010.

So really I'm only concerned about the load to the input signal. Agger, you say it isn't an issue, but I wonder what the input impedance of the pre-amp would change to? Currently the input impedance is 70k, what would that change to by using a 50k pot? I may just end up ordering a 3 pin alps if I can't figure out what the 50k pot will do in the circuit.....

 

[agger]

Yes, this will lower the imput impedance for i.e. the aux input. But 50kOhms should not be an issue for any HiFi equipment

 

[tschanrm]

Just wanted to let everyone know that I put in the 50k pot temporarily into the 1010. Agger, you were right about the balance issue, turning left or right from center detent rapidly changes the balance. I tested all the inputs to see what the difference would be in sound. Overall, the noise floor seems a little quieter, but for the phono section it is A LOT quieter. The phono section has almost as low of a noise floor as the aux input now. I have to use a different volume knob because the alps isn't splined, but its an aluminum machiend knob that looks similar to the original knob. So for now I'm keeping in the alps 50k pot for now until I find a replacement 250k pot that has a splined shaft or at least a loudness tap.


I just have one last question:

OK, as far as I understand, using a higher impedance potentiometer makes the load easier for the source going into the pre-amp. But, using a higher impedance pot also increases the noise of the pre-amp. Using a low impedance pot, such as a 10k pot, lowers the noise but makes the source drive with more current , possibly causing added distortion.
...............So, why would Pioneer choose to use 250k potentiometers when a 50k (or even a 25k, maybe) is still high enough for most sources to easily drive? Is it that the input impedance of the pre-amp is high enough that using 250k pots does not add any more noise than a 50k?

 

[agger]

Sorry for my late answer, I was off for the last 3 weeks.
Its right that lower resistance generates lower noise. But also the load for the feeding inputs is higher. If you overload the inputs, this can cause some degradation in the frequency curve, additional phase shifts and so on. so the sound quality could be worth.
If you use the phono input with much lower noise now, how is it sounding? Same as before , or maybe a bit less hights? Did you notice a difference?

 

[Pioneer727]

Why don't you ask for a vol pot in the parts swap area? It could be that the vol pot from a 939 or 838 would work. just my 2 cents.

Ron

 

[packrat]

Why don't you ask for a vol pot in the parts swap area? It could be that the vol pot from a 939 or 838 would work. just my 2 cents.

Ron

Maybe post a picture of the original pot with a part number? I see lots of wanted ads for specific parts, but a picture and part number would really help out in case the required part is common to other models or even other manufacturers.

 

[goldear]

250K pots are highly unusual these days. I know that alps used to make a 250K unit as a replacemnt for the Dyna Pas 3 unit, but these are probably long gone.

FYI - There is a way to make you ballance work again with the 50K pot. Simply put a couple of high-quality 200K resistors (one for each channel) in series with the input signal end of the pot. This will result in a significant decreas in the overall gain of your unit (possibly by as much as 10dB), but it will fix your ballance issue.

The net result of doing this is that you will have to turn your volume control up higher position to get the same volume, but if you were running on the low end of the control anyway, then who really cares?