I have an Audio Refinement integrated amp with a level imbalance. The right channel is noticeably louder than the left. I traced the problem to the motorized pot.
The right channel also goes into cilpping a little before the left which makes sense, it works perfectly well other wise. Seeing this is a 20year old amp, I think it`ll be next to impossible to find a replacement pot. There is a part number on it 742t 100K AX2 but a search of that didnt come up with any hits.
I found one that is nearly identical differing only in the shaft. The one I need is a rather short split and knurled type while the replacement looks like it has a split but its longer and isn't knurled.
Alps 100K Blue Velvet, Stereo Motorized Potentiometer
In the event that a suitable replacement doesnt exist, would it be possible to repair this one or perhaps add some resistors to compensate for the gain mismatch?
Many thanks in advance.
The right channel also goes into cilpping a little before the left which makes sense, it works perfectly well other wise. Seeing this is a 20year old amp, I think it`ll be next to impossible to find a replacement pot. There is a part number on it 742t 100K AX2 but a search of that didnt come up with any hits.
I found one that is nearly identical differing only in the shaft. The one I need is a rather short split and knurled type while the replacement looks like it has a split but its longer and isn't knurled.
Alps 100K Blue Velvet, Stereo Motorized Potentiometer
In the event that a suitable replacement doesnt exist, would it be possible to repair this one or perhaps add some resistors to compensate for the gain mismatch?
Many thanks in advance.
Attachments
I agree.
And no one normally runs an amp into clipping - that's abuse.
Besides, there could be other issues involved in the extreme high volume imbalance.
A quick ohmage check at varying positions will likely show it's winthin tolerences.
By analogy with 'voltage', 'amperage' and 'wattage' its just as precise and meaningful a term, albeit informal and infreqnently seen.
That's correct.
I don't adhere to "strict" rules regarding descriptions, but alas, the grammar police sometimes get disturbed.
The clipping was experienced only on a scope and not on a speaker
Due to it`s position, it`s extremely difficult to take accurate measurements of the pots but I did measure abnormalities.
Shunting both wipers results in equal volume on both channels.
The pot is literally hard-wired to the mother board by means of thin, solid wire that I dont want to disturb needlessly. I would have to remove the entire board if a wire snapped and I really dont want to do that.
Attachments
The Alps RK27 pots are normally quite good, but they are actually spec'ed to something like 2 or 3dB mismatch between channels. If you are sure that this is the reason then it would probably be possible to replace the pot with one that has better tracking. As to whether it's possible to compensate in other ways I think that requires a schematic to be able to answer accurately.
Attachments
This version of the DS says 3dB gang error and 5dB at the low end (which is where people normally have problems)
http://analogmetric.com/specification/ALPS/ALPS RK271 datasheet.PDF (top of p. 373)
In principle, increasing R101 on your schematic would lower the input voltage for the loudest channel (because R101 and R102 form a voltage divider), but whether it gives any other audible differences I am not sure (don't think so). However, you'd need measurements to verify how much to drop the input.
Oh, and the fix will be the same across the whole gang range of the pot, whereas the gang error might not be, so not 100% it's worth the effort to be honest - but YMMV.
http://analogmetric.com/specification/ALPS/ALPS RK271 datasheet.PDF (top of p. 373)
In principle, increasing R101 on your schematic would lower the input voltage for the loudest channel (because R101 and R102 form a voltage divider), but whether it gives any other audible differences I am not sure (don't think so). However, you'd need measurements to verify how much to drop the input.
Oh, and the fix will be the same across the whole gang range of the pot, whereas the gang error might not be, so not 100% it's worth the effort to be honest - but YMMV.
Please show me any service document or measurement device that uses the bastardised formats of 'ohmage/ampage/wattage'.
I feel by allowing the use of these words we are responsible for the decline of the industry.
Since americans have issues with the letter 'L', maybe we should petition companies to rename their products to 'sodder' and 'soddering irons'.
Heck while we're at it why not get rid of the pesky AC and DC monikers. After all it's all just ampages and voltarages anyway.
Last edited:
You guys are making a good case for using an IC volume control like the PGA2310. 1/2 dB steps
with excellent tracking channel to channel. Motorized pot implies remote control. You need a
microcontroller to load the PGA or similar chips but this makes remote control trivially simple. ICs
don't wear out or get noisy either. Something to consider.
G²
I`d rather not change out the knob as there is another identical to it on the other side.
I just placed an order for a new pot/motor assembly. I`m debating whether to continue the split on the solid shaft some more and then cutting it down to size or leaving it as is and tap a hole into the knob for a set screw however, it`s large and solid metal.
I`ll have a better idea when it arrives from Germany, hopefully soon.
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.