Hi all,
Just a quick question based around an all to common problem with the Pioneer A400 amps and their volume and 'balance' pot combo.
Recently acquired an A400 from the Bay with the usual duff right channel problem caused by the rear pcb of the 100K pot cracking.These pots are unobtanium, using an Alps 100K8X2 with 40% loudness, pinout is (looking from the front):
1-CCW
2-Wiper
3-CW
4-Loudness tap (40%)
Now, I know I can replace with one of the slightly fake looking Alps pots with loudness from eBay, but the amp would lose it's 'balance' (read that as 2 x mono, L&R).
I've found a dual linear 100k with loudness pot which appears to use identical pcb's as the original Alps and plan to use one of the carbon tracked pcbs in the original Alps, but the new one is 50% loudness.
I might be being dumb, but can I use a resistor on the loudness tap to reduce this from 50% to 40% on the new rear board, or should I just swap both boards in the pot to the new 50% ones? Or should I sack off using the old pot entirely and just pop a new Alps in?
Thanks in advance (pic of the old pot attached for ref)
Just a quick question based around an all to common problem with the Pioneer A400 amps and their volume and 'balance' pot combo.
Recently acquired an A400 from the Bay with the usual duff right channel problem caused by the rear pcb of the 100K pot cracking.These pots are unobtanium, using an Alps 100K8X2 with 40% loudness, pinout is (looking from the front):
1-CCW
2-Wiper
3-CW
4-Loudness tap (40%)
Now, I know I can replace with one of the slightly fake looking Alps pots with loudness from eBay, but the amp would lose it's 'balance' (read that as 2 x mono, L&R).
I've found a dual linear 100k with loudness pot which appears to use identical pcb's as the original Alps and plan to use one of the carbon tracked pcbs in the original Alps, but the new one is 50% loudness.
I might be being dumb, but can I use a resistor on the loudness tap to reduce this from 50% to 40% on the new rear board, or should I just swap both boards in the pot to the new 50% ones? Or should I sack off using the old pot entirely and just pop a new Alps in?
Thanks in advance (pic of the old pot attached for ref)
Attachments
If that's a common problem, is the cause also known? There's only two things I can think of, either excessive mechanical stress (possibly abuse?) or swelling / cracking of the phenolic (the stuff doesn't like petroleum based products, like WD40, or acetone).
This doesn't look like it couldn't be cleaned up, epoxied back together, the gaps bridged using conductive silver ink or similar, relubed and reassembled.
I am not at all convinced that the 50% tap with external resistor would work quite the same as the 40%. This may have to be measured and simulated, but my gut feeling says no.
This doesn't look like it couldn't be cleaned up, epoxied back together, the gaps bridged using conductive silver ink or similar, relubed and reassembled.
I am not at all convinced that the 50% tap with external resistor would work quite the same as the 40%. This may have to be measured and simulated, but my gut feeling says no.
I stopped reading all the complaints after 4 hi-fi website had posters complaining of the same fault , cycling quickly through more the answer even from their gurus is-----tough ! -IE- no answer .
Lots of head scratching try this Alps or that to no avail .
I then tried for spares at -
Replacement Pioneer Vintage Stereo Parts / Spares.
But he conveniently missed out A400 but he says phone him anyway for advice .
Another Pioneer spares website had everything bar this control but the prices !!!
There even was a guy in the West of Scotland looking for one in 2013 and used the same words----unobtanium .
Lots of head scratching try this Alps or that to no avail .
I then tried for spares at -
Replacement Pioneer Vintage Stereo Parts / Spares.
But he conveniently missed out A400 but he says phone him anyway for advice .
Another Pioneer spares website had everything bar this control but the prices !!!
There even was a guy in the West of Scotland looking for one in 2013 and used the same words----unobtanium .
Thanks for the replies 🙂
Yeah, the only way it seems to get a direct replacement is via saccing another amp (A300,400, 337 or 447).
Currently having an experiment with some JB Weld and Vallejo steel pigment (basically graphite powder) to make a paste to repair the broken carbon trace.
When the 50% loudness pots get here I'll have an experiment with resistors, but i think you're right in that its placement on the pot that dictates resistance, adding a resistor probably wouldn't make it equivelant to 40%
Yeah, the only way it seems to get a direct replacement is via saccing another amp (A300,400, 337 or 447).
Currently having an experiment with some JB Weld and Vallejo steel pigment (basically graphite powder) to make a paste to repair the broken carbon trace.
When the 50% loudness pots get here I'll have an experiment with resistors, but i think you're right in that its placement on the pot that dictates resistance, adding a resistor probably wouldn't make it equivelant to 40%