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 Forum index » Instruments and Equipment » General Discussion
My Paia 2700 hummmmmmmmmmmmms... and other issues
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patrickvf1976



Joined: Aug 08, 2011
Posts: 181
Location: Gig Harbor

PostPosted: Sun Oct 13, 2013 9:19 pm    Post subject: My Paia 2700 hummmmmmmmmmmmms... and other issues
Subject description: Need help getting this thing fixed.
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I have recently received my Paia 2700, which I have purchased on Ebay. To my dismay there is a very noticeable hum eminating from some (but not all) of the modules, mainly the VCA, VCO (along with the signal), Inverter/buffer (especially with 5V offset switched on). I have also noticed that the hum coming from the VCA module has a higher pitch tone to it? Could this be an isolated problem? Also, the PWM effect on the VCO is weird - first off it sounds distorted, kind of like fuzz/overdrive/feedback and gets very loud at it's peak. Also the range is very narrow, so that if I move the knob just a couple cents the tone stops completely either way. The over all output is very low unless I route the VCA through the inverter/buffer to the 20db input, which also multiplies the hum level. I'm not sure where to begin at resolving the issues but I take any suggestions you throw at me.

PS: The keyboard tuning and glide are out of whack too, as in when I turn up the glide level, the pitch goes down - Any ideas? Another thing I should point out is that the VCO, EG and BPF have extra switches and dials that I didn't see in other Paia 27xx machines (modded?)

The modules present are: Power unit with patch panel, VCO, Sine/PWM source, ASR envelope generator, control oscillator, VCA, BPF, LPF, inverter/buffer, envelope follower.
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Blue Hell
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Joined: Apr 03, 2004
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PostPosted: Mon Oct 14, 2013 7:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Sound like a power supply issue to me - likely the filter caps in the PSU not being large enough, or being too old and leaky. Or maybe an error in the ground connections.
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patrickvf1976



Joined: Aug 08, 2011
Posts: 181
Location: Gig Harbor

PostPosted: Mon Oct 14, 2013 8:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I was already thinking that there might be some bad caps somewhere, but I wanted to hear some other opinions first. So why does the hum from the VCA have a different pitch? And any suggestions about the PWM feature?
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Blue Hell
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Location: The Netherlands, Enschede
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G2 patch files: 318

PostPosted: Mon Oct 14, 2013 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Dunno - is it a related pitch? like double the frequency maybe? Could imagine that to happen, if its an unrelated pitch it would be strange.

The PWM behavior .. when the power supply is not stable the level used to compare the saw wave with might not be stable ... or there might be a sine super imposed on the saw - both would make it work weird for sure.

Can you measure any hum on the PSU output? A scope on AC or when no scope a DVM on AC should show it ....

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patrickvf1976



Joined: Aug 08, 2011
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PostPosted: Mon Oct 14, 2013 10:09 am    Post subject: Reply with quote  Mark this post and the followings unread

All I have a voltmeter from Radioshack, but how can I measure a frequency with a meter that mainly measures voltage and resistance?

PS: Were you referring to the Sine/PWM module? I was talking about the PWM of the VCO, but I didn't try it that sine/PWM module yet.

Also, the hum from the VCA is static just like the line hum but a slightly higher pitch. I'm beginning to suspect that the VCA has a grounding issue as well, independent from the line hum.
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patrickvf1976



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PostPosted: Wed Oct 16, 2013 6:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

So.. I took a peek into the Paia just to see what all these extra switches and dials are about, and I have kind of a curious question - Theoretically, each and every module would only be connected to the power/ground rails and not interconnected in any way, right? Well.. The VCO seems internally wired with the sine/pwm module, and the LFO, The EG also has a connection from the VCO to the +/-5V output, bridged with a resistor, and the lowpass filter seems to have connections to some switches on the bandpass filter. I'm gonna follow up with some pictures, so you all can see what I'm talking about. Maybe someone (the builder perhaps) can tell me what's going on. By the way here's the link to the (closed) auction of the synth that I won, so maybe someone will recognize it and tell me what the mods are all about.

http://www.ebay.com/itm/190909978617?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

Have a great hump eve! Smile
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