Wierd clipping & barking at slightly low line (110VAC)

[nevetslab]

Throne Transducers

Himm.. I think I'd one of those transducers might be just the thing to make those pesky intermittent faults show up on so much of the gear I see.

Here's a photo Porter & Davies had sent me a while back of the two types they've used in their seats:



I can't quite make out the P/N labels.....the one on the right is a current PD TT2, the one on the left was early production from Clark Synthesis. I don't know who they're getting the TT2's from. Tim Porter indicated the TT2 is 219 pounds + shpg.

Update: Tim indicated they're getting these seat transducers made for them by Precision Devices
http://www.precision-devices.com/ I didn't see anything like it in their standard product line-up, so it's definitely an OEM product.

The power xfmr in the amp that has regulation issues is a current updated xfmr, so when I go back into the unit to swap out their 3-terminal regulators, I'll be looking for whatever is loading down the low current bipolar supply rails.

[nevetslab]

Here's a photo Porter & Davies had sent me a while back of the two types they've used in their seats:

[ATTACH=CONFIG]54279[/ATTACH]

I can't quite make out the P/N labels.....the one on the right is a current PD TT2, the one on the left was early production from Clark Synthesis. I don't know who they're getting the TT2's from. Tim Porter indicated the TT2 is 219 pounds + shpg.

Update: Tim indicated they're getting these seat transducers made for them by Precision Devices
http://www.precision-devices.com/ I didn't see anything like it in their standard product line-up, so it's definitely an OEM product.

The power xfmr in the amp that has regulation issues is a current updated xfmr, so when I go back into the unit to swap out their 3-terminal regulators, I'll be looking for whatever is loading down the low current bipolar supply rails.

The LM2940T-12 and LM2990T-12 Low Dropout 3-terminal voltage regulators arrived this afternoon, and I swapped out the LM7812T and LM7912T's with those, same pin-out. The Unregulated supply voltages are still low, and I didn't find anything besides the 12V output relay on the amp board to account for that lower + Unreg voltage. There's only two IC's on the preamp board, nothing running hot, nor is the 8A bridge that runs them.

Powering the Drum Throne again, monitoring the input signal and output signal of the power amp, while monitoring the AC Mains current...same setup I had been using (Roland TD-10W controller for my kick drum pattern), I can now drop the AC mains down to 105VAC without having any issues. Below that, I begin to see the preamp clipping. So, that WAS a worthwhile change. Still waiting to compare notes with Tim on what their unregulated supply voltages are. I can now send this back to my client. Interesting exercise.

[SoulFetish]

The LM2940T-12 and LM2990T-12 Low Dropout 3-terminal voltage regulators arrived this afternoon, and I swapped out the LM7812T and LM7912T's with those, same pin-out. The Unregulated supply voltages are still low, and I didn't find anything besides the 12V output relay on the amp board to account for that lower + Unreg voltage. There's only two IC's on the preamp board, nothing running hot, nor is the 8A bridge that runs them.

Powering the Drum Throne again, monitoring the input signal and output signal of the power amp, while monitoring the AC Mains current...same setup I had been using (Roland TD-10W controller for my kick drum pattern), I can now drop the AC mains down to 105VAC without having any issues. Below that, I begin to see the preamp clipping. So, that WAS a worthwhile change. Still waiting to compare notes with Tim on what their unregulated supply voltages are. I can now send this back to my client. Interesting exercise.

I knew it was the regulators

[g1]

I knew it was the regulators

So they probably all do it then.

[nevetslab]

Another Porter-Davies BC2 came in, this time with broken Master Volume pot. The knob must have been hit, as it snapped off the pot mounting bushing, leaving the pot dangling on the wiring cable. I dug out my bag of Porter-Davies parts, finding they did send me replacement pots....these were (as luck would have it), larger bushing size than the one that broke off, so I had to ream out the mtg hole. Relying on memory as to where the Shield, WHT and RED wires were attached, I removed them, and wired the new pot in. Wasn't getting signal, then found I wired the pot backwards! Nothing wrong with my memory! Claribel did it! Claribel did it! Stupid heat shrink kept shrinking prematurely during the restoration of that mix-up.

Got the pot mounted, then I wasn't getting any drive under load, but had full signal open circuit. Somehow I managed to plug in an NL4 to T/S, phased correctly that until I measured it, didn't have continuity between the TIP and 1(-) on the NL4. Changed cables, now had output.....and, I was also getting nasty transient barking. That rang a bell, and found in my notes from July 2019, I had been down that road, but I didn't record the Post date of this thread. Had to wander thru all of my posts to find it in the "W's". And, at the end, found I had improved on the problem, finding it was at low line voltage that the problem was occurring. Changed out the LM7812T and LM7912T's with these LM2940T-12's and LM2990T-12's, both being Low Drop-out regulators.

So, this is one of the units that didn't get this update. I dug thru my semiconductor box, and found the two bags at the very bottom (figures). I had only purchased two pcs of each, one pair installed in the one I was battling with.

Now, it didn't come over to me with any complaints about this odd distortion. I suspect one's behind can't really tell if there's transient barking going on at low AC Mains line (which can no doubt occur on kick drum hits if the sound system pulls the mains down on those transients). I had already put the unit back together, but was sure I had been down this road already.

I'll mention it to the client, only having a marginal upgrade. The real change would have to come from Porter-Davies in their power xfmr design. 105VAC is easy to come by under transient bursts.

[nevetslab]

My conscience got the better of me, and I opened up the unit this morning, pulled the two common LM7812T and LM7912T regulators, replaced with LM2940T-12 and LM2990T-12 Low Dropout regulators. Checked the results under system drive as I had done previously in this 2019 thread, and got the improved results. I'll have to order more parts, as I haven't done this on CenterStaging's units. I also found in reviewing the previous invoice on that client's unit from July 2019, I see I failed to bill for these parts. So, caught that on the rebound for this billing.