Measuring volume potentiometer.

heiney9

I have a nice inexpensive Norh SE9 tube integrated amp that really should have a little nicer volume pot. The stock pot is cheaper, not as cheap as some, and it scrapes sometimes when your rotating it.

I have been looking at an ALPS Blue Velvet Plastic Pot like the one pictured here.

http://www.partsconnexion.com/product7384.html

I have searched high and low for a schematic, but can't find one and Norh seems to be out of business as emails go unanswered. I have no idea of it's 10K, 50K, 100K or 250K. The only odd ball thing is according to the owners manual the pre-amp section is passive. I assume that would mean the vol pot has to have more gain than in a typical integrated.

Is there a way to measure the current vol pot? Can it be done in the circuit? What's the procedure in or out of the circuit? This attaches the main PCB by wire so it's not mounted in the PCB.

Any suggestions, help, advice, etc appreciated.

H9

ShinAce

You should be able to measure it in circuit.

You'll see one or two sets of 3 prongs. Forget about the middle pring(tab) and measure resistance between the two outside prongs. That should give you its resistance. Otherwise, you'll need to cut one of the wires and measure it.

Now you need to find out if it is linear or logarithmic.

audiobilly

You can measure it in circuit, but not advised, the reading will be off. Better to get it out of circuit.

Typically you will have three pins on the pot. The outer two are the actual resistor, and the inner pin will be the wiper. If you measure across the outer two pins you will then have the value of the potentiometer. The taper of the pot is also a consideration, either liner or log (logarithmic). Most audio circuits use the log taper, but not always.

Here is some Wiki to help show some general pictures and ideas.
http://en.wikipedia.org/wiki/Potentiometer

If the pins are not in a row, you can try different configurations of the ohm meter to determine what pin is the wiper and what pins are the "top" and "bottom" of the resistor.

heiney9

ShinAce wrote: »

You should be able to measure it in circuit.

You'll see one or two sets of 3 prongs. Forget about the middle pring(tab) and measure resistance between the two outside prongs. That should give you its resistance. Otherwise, you'll need to cut one of the wires and measure it.

Now you need to find out if it is linear or logarithmic.

Will it matter what position the volume knob is in? How will I know if it's linear or logarithmic? What will the meter indicate if the stock pot is linear or log?

Thanks

H9

heiney9

One other thing that may help, the stock pot has a detent when it's exactly 1/2 way. The indicator marking on the knob is pointing straight up when you hit the detent on the stock pot meaning it's 1/2 way between the min and max. I have been also trying to figure out why that would be.

H9

audiobilly

A linear pot will be half value at the mid point. A log pot will be significantly "not half" at the mid point.
A little more reading,
http://sound.westhost.com/pots.htm#taper

Very rare that a linear pot is used in a audio circuit, put stranger things have happened.

Center detents are usually for a Balance type pot, so you know when you are in the center, neither left or right. Can also be used for a level reference in a EQ circuit, Center detent means no cut no boost. Just for idea references.

heiney9

audiobilly wrote: »

Center detents are usually for a Balance type pot, so you know when you are in the center, neither left or right. Can also be used for a level reference in a EQ circuit, Center detent means no cut no boost. Just for idea references.

Thanks!

I thought it was wierd to use a center detent pot for a volume control. I'm sure it's a log pot, but atleast I have an idea of where and what to look for. Any ideas about other brands besides ALPS. Needs to be reasonably priced because this is amp is budget concious, used in a secondary rig so I'm not going all out. Looking for something that will sound nice and be reliable.

H9

audiobilly

Alps is a good pot. It also depends on physical limitations, will it fit in the "place" you have or, do you have to or are you will to modify, bla bla.

Other pot manufactures,, Bourns are good, Vishay might have something,

FTGV

I prefer Nobles to the popular ALPS blue beuties,and prefer Valabs stepped attenuators to the Nobles.

TECHNOKID

ShinAce wrote: »

You should be able to measure it in circuit.

You'll see one or two sets of 3 prongs. Forget about the middle pring(tab) and measure resistance between the two outside prongs. That should give you its resistance. Otherwise, you'll need to cut one of the wires and measure it.

Now you need to find out if it is linear or logarithmic.

Reading/measuring while in circuit can lead way off base as anything in the circuit that is of lower value will be closer to your actual reading. The let's say 10K pot with a 2K resistor could well be read as a paralell circuit and gives you an average value of let's say 6K.

IMHO, removing the pot and looking around it for markings would provide you with data for searching for the right one. Unless fairly recent gear which uses cheap out of country manufacturing, there is pointer on the parts as to its value or part number which can then be search on the selected aftermarket provider site for equivalent match.

TECHNOKID

According to http://www.ehow.com/how_5995013_check-potentiometer.html;

4
Isolate the potentiometer by unsoldering two of its leads if it's connected by wires or by unsoldering it from its printed circuit board (PCB). Testing it while connected to its related circuitry will produce a false reading because of the other components in the circuit

FTGV

TECHNOKID wrote: »

According to http://www.ehow.com/how_5995013_check-potentiometer.html;

That would only apply depending on where a pot is in the circuit.The majority of the time (not always)the volume pot will be directly at the the input thus sometimes it's value could be measured accurately as Shin Ace suggests.

heiney9

TECHNOKID wrote: »

Unless fairly recent gear which uses cheap out of country manufacturing, there is pointer on the parts as to its value or part number which can then be search on the selected aftermarket provider site for equivalent match.

Norh is assembled in Thailand and it's rife with Korean and Chinese manufactured parts. The PS caps are SANWHA. They did use WIMA MKP10 coupling caps but I'm swapping those for Auricaps or Obliggato's, but I'm afraid there won't be enough real estate for Obliggato's.

I have no doubt the vol pot is of foreign origin probably Chinese or Korean, it's decent enough but can be easily improved by even an entry level ALPS or Noble.

H9

heiney9

FTGV wrote: »

That would only apply depending on where a pot is in the circuit.The majority of the time (not always)the volume pot will be directly at the the input thus sometimes it's value could be measured accurately as Shin Ace suggests.

I'm almost positive is directly at the input. I just hope since the pre section is passive it's not some wierd type of part. I assume it's just a higher gain pot vs. a standard integrated amp with an active pre section with a direct input signal.

H9

FTGV

heiney9 wrote: »

I assume it's just a higher gain pot vs. a standard integrated amp with an active pre section with a direct input signal.

H9

A pot can only attenuate it can't add gain,but if it is just passive input as in just a pot you might try a multi meter across the outside pins as Shin suggested.

TECHNOKID

I tought with new high technology this would have changed but it seems wired wound pots are still the best available.

Material Manufacturing Method Common uses Power (Typ)
Carbon Deposited as a carbon composition ink on an insulating (usually a phenolic resin) body Most common material, especially for cheap to average quality pots. Has a reasonable life, and noise level is quite acceptable in most cases. (DC should not be allowed to flow through any pot used for audio control) 0.1 to 0.5W

Cermet Ceramic/metal composite, using a metallic resistance element on a ceramic substrate High quality trimpots, and some conventional panel mount types (not very common). Low noise, and high stability. Relatively limited life (200 operations typical for trimpots) 0.25 to 2W
(or more)

Conductive Plastic Special impregnated plastic material with well controlled resistance characteristics High quality (audiophile and professional) pots, both rotary and linear (slide). Excellent life, low noise and very good mechanical feel 0.25 to 0.5W

Wire wound Insulating former, with resistance wire wound around it, and bound with adhesive to prevent movement High power and almost indefinite life. Resistance is "granular", with discrete small steps rather than a completely smooth transition from one resistance winding to the next. Low noise, usually a rough mechanical feel. 5 to 50W
(or more)

FTGV

TECHNOKID wrote: »

I tought with new high technology this would have changed but it seems wired wound pots are still the best available.

Not for audio use.The stepped attenuator using discrete metal film resitors rules the roost.

Face

FTGV wrote: »

Not for audio use.The stepped attenuator using discrete metal film resistors rules the roost.

I agree. I'm a big fan of Goldpoint.

heiney9

FTGV wrote: »

Not for audio use.The stepped attenuator using discrete metal film resitors rules the roost.

Face wrote: »

I agree. I'm a big fan of Goldpoint.

I would defer to both of you and agree, but once again a $400 integrated amp used in a secondary rig just doesn't warrant that nice of a part. There is nothing wrong with the stock part, it's dead silent, but I don't like the feel of it and I know for about $25-30 I should be able to get something a little nicer.

H9

Face

Alps it is!

FTGV

heiney9 wrote: »

but once again a $400 integrated amp used in a secondary rig just doesn't warrant that nice of a part....about $25-30 I should be able to get something a little nicer.

H9

Yes I was replying to TK's wire wound reference..However don't let the price fool you,I have been using one of these in a DIY fet based pre for about a year and have no complaints. http://cgi.ebay.ca/Valab-23-Step-Attenuator-Potentiometer-10K-Stereo-Log-/270644208873?pt=LH_DefaultDomain_0&hash=item3f03a6e4e9 Ofcourse stepped attenuators don't allow for ultra fine adjustment which may be a deal breaker.

As for standard conductive plastic types I have used ,I have found the Nobles to have tighter inter channel tracking than the Alps blues.

thsmith

FTGV wrote: »

Yes I was replying to TK's wire wound reference..However don't let the price fool you,I have been using one of these in a DIY fet based pre for about a year and have no complaints. http://cgi.ebay.ca/Valab-23-Step-Attenuator-Potentiometer-10K-Stereo-Log-/270644208873?pt=LH_DefaultDomain_0&hash=item3f03a6e4e9 Ofcourse stepped attenuators don't allow for ultra fine adjustment which may be a deal breaker.

As for standard conductive plastic types I have used ,I have found the Nobles to have tighter inter channel tracking than the Alps blues.

I replaced the Alps blue pot in my Wright preamp for the one linked from ebay.

I prefer this over the Alps. Actually I think it was Mr. Daniels is who turned me on to this one.

ShinAce

GV, you're making my life too easy!

All I gotta do is give the generic answer and let the trolls shoot at me, and then you specify what I meant. It's awesome!!!

Technokid:
Keep in mind a volume pot is usually a resistor, in parallel with the input stage, which feeds the input via its wiper. The other components the multimeter will see are:
-the output transistors of the source(negligible as the meter has a low voltage to read ohms)
-the input transistors/tube of the amp itself(again, negligible. Essentially 0 effect if it's a FET)
-the cap in series with the input(negligible once the meter charges it, if that occurs)
-input conditioning circuits(which often involve zener diodes for clamping which will make that 'leg' negligible).

I've got a 500 page amplifier design handbook somewhere if you want to read it. Heavy stuff, but it covers the working theory of amps quite well.

mmadden28

Have you tried to clean the existing pot yet?