PLC1 MKII Passive pre help.

audiobliss · « **on:** 29 Nov 2014, 03:32 pm »

Hi guys, my first time posting here. I had a issue with one of my PLC1 a few days ago. I have one in the tube system, and one in the HT system. I have the one in the HT system configured for bypass on input four, and I am using the tape input as input five for my turntable.

Well a few days ago I decided to play a LP in the HT system. I got the TT and phono stage going, lowered the arm on the LP, went to switch inputs from my tuner on input two to the phono input, but mistakenly hit input four, which of course produced no sound because that's HT bypass, then realizing that, I went straight to the tape input. The system then came on FULL blast, like the PLC let through the full volume to the amp.

I dived for the volume control, but that had no effect, I had to hit the power switch on the amp to save the speakers.

After I settled down from trying to figure out why that happened, muted the PlC then went to tape input again and the TT played normally.
So what I would like to know for sure is, did that happen because I went from HT bypass to the tape input and the PLC was still in pass trough mode ?
Will that happen only with the tape input ?
Should I always get out of the HT bypass before going to the tape input.This was the first time I went straight from HT bypass to tape input, I have gone from HT bypass to the other inputs without any problems.

I hope this can by explained, because I can't figure a reason why that should have happened except for some glitch.

AB.

CIAudio · « **Reply #1 on:** 1 Dec 2014, 09:07 pm »

I can only guess that maybe you connected the phono output to the HT bypass by mistake.
The tape input is connected to the volume control (just like the 1st three inputs).

audiobliss · « **Reply #2 on:** 1 Dec 2014, 09:35 pm »

No, the phono has always been going to the tape input. I am tempted to try the same procedure again, but I have to use some cheap disposable speakers

Thanks for your reply anyway, good to know that the tape input is independent like the first three.

Btw, its a great sounding unit, just whats needed in a pre and nothing more. The LEDs could be a little softer, less bright, especially with three or four on at the same time.

Allan.

RDavidson · « **Reply #3 on:** 1 Dec 2014, 11:00 pm »

Well, since the inputs are (assumingly) controlled via a microcontroller, which sometimes hiccup, it is possible that it didn't switch inputs accordingly. Did you switch inputs via the remote or by hand? Sometimes small electrostatic shocks can make the microcontroller go wacky. Seen this happen on a couple of components. It doesn't seem to damage anything, but may cause the unit to lock up and it may need to be reset (turned off or given another command). In the winter months, with less moisture in the air, electrostatic shock becomes more common. I suggest always using the remote....plus you keep finger prints and grime, like Cheetos particulates, off your gear.

audiobliss · « **Reply #4 on:** 2 Dec 2014, 03:24 am »

I think you might be on to something, at least it fits my glitch theory. I did use the remote, but sometimes I notice there seems to be some confusion between the remote and the unit, I will hit the mute button and the unit will go to the tape input instead, then I have to hit the mute again.

RDavidson · « **Reply #5 on:** 2 Dec 2014, 03:55 am »

Have you ever tried unplugging the unit and plugging it back in (to reset it)?
If it glitched in the past, but has never been reset or only occasionally reset, it might continue to glitch as the microcontroller still hasn't been cleared of the hiccups. That's my theory anyway. I'm no genius, but experience and things I have read seem to hold water.

audiobliss · « **Reply #6 on:** 2 Dec 2014, 05:37 am »

I will do that, thanks.

Allan.

CIAudio · « **Reply #7 on:** 2 Dec 2014, 05:44 pm »

It could have possibly been a microprocessor glitch, although I've never experienced this.
Each input has a relay to connect it to the volume control. When an input command is given, the current input is first disconnected, then the chosen input is connected to the control. There is no way for the micro to connect the signal to anything but the volume control.

If the micro had a glitch, it would have to be that the HT did not disconnect from the output, so when the tape input was selected it was in parallel with the HT input, causing the control to be by-passed.

If this happens again (or any other command issues), I would suggest sending it to us for re-programming.

OldiesButGoodies · « **Reply #8 on:** 19 Apr 2017, 03:55 am »

Quote from: audiobliss on 29 Nov 2014, 03:32 pm

Hi guys, my first time posting here. I had a issue with one of my PLC1 a few days ago. I have one in the tube system, and one in the HT system. I have the one in the HT system configured for bypass on input four, and I am using the tape input as input five for my turntable.

Well a few days ago I decided to play a LP in the HT system. I got the TT and phono stage going, lowered the arm on the LP, went to switch inputs from my tuner on input two to the phono input, but mistakenly hit input four, which of course produced no sound because that's HT bypass, then realizing that, I went straight to the tape input. The system then came on FULL blast, like the PLC let through the full volume to the amp. I dived for the volume control, but that had no effect, I had to hit the power switch on the amp to save the speakers.

After I settled down from trying to figure out why that happened, muted the PlC then went to tape input again and the TT played normally.
So what I would like to know for sure is, did that happen because I went from HT bypass to the tape input and the PLC was still in pass trough mode ?
Will that happen only with the tape input ?
Should I always get out of the HT bypass before going to the tape input.This was the first time I went straight from HT bypass to tape input, I have gone from HT bypass to the other inputs without any problems.

I hope this can by explained, because I can't figure a reason why that should have happened except for some glitch.

AB.

FYI - This happens with my PLC1 mkII as well - I need to watch out when I go from HT to Tape Loop mode. It is reproducible, not a random occurence. I am a heavy user of the tape loop and HT bypass, so I ran into the issue quickly after buying the PLC1 four months ago. My solution has been to get out of HT bypass before going to the tape input. It can be scary the 1st time it happens.

Good luck,

J

CIAudio · « **Reply #9 on:** 19 Apr 2017, 04:31 am »

Can you call me so we can try to figure out what is happening?
The tape input is no different than any other input and is fed directly into the volume control.
The only way I can see this happening is if both the HT input and Tape input are somehow active at the same time.
We tried to duplicate the problem Audiobliss described a few years ago and couldn't cause it to happen.
Since then we've sold hundreds of these and have never heard of another instance until now.
If this is something that is repeatable on your unit, I'd love to put it on the bench too see what's going on.

audiobliss · « **Reply #10 on:** 19 Apr 2017, 04:27 pm »

Quote from: OldiesButGoodies on 19 Apr 2017, 03:55 am

FYI - This happens with my PLC1 mkII as well - I need to watch out when I go from HT to Tape Loop mode. It is reproducible, not a random occurence. I am a heavy user of the tape loop and HT bypass, so I ran into the issue quickly after buying the PLC1 four months ago. My solution has been to get out of HT bypass before going to the tape input. It can be scary the 1st time it happens.

Good luck,

Well, good to know i am not the only one. Did you buy yours new or used ?
Just wondering if you ended up with the one I had.

AB

J

OldiesButGoodies · « **Reply #11 on:** 21 Apr 2017, 12:41 am »

Quote from: audiobliss on 19 Apr 2017, 04:27 pm

I bought it new from Music Direct if I remember. Christmas gift to me

Dusty - will try to give you a call when I am home some time during business hours week days (which is not very often - though you are West coast and I am in the East so it may work out) so I can share the details. The problem with sending the unit back to you is that I have developed a bit of an addiction to it and use it daily. That said I can look at it myself more carefully and see what may be going on in more detail, maybe take a video.

Regards

OBG

OldiesButGoodies · « **Reply #12 on:** 23 Apr 2017, 04:45 pm »

Dusty - sent you a PM with a youtube video link of the issue when switching from HT bypass to the tape loop.

Regards,

Jose

CIAudio · « **Reply #13 on:** 23 Apr 2017, 05:10 pm »

Quote from: OldiesButGoodies on 23 Apr 2017, 04:45 pm

Dusty - sent you a PM with a youtube video link of the issue when switching from HT bypass to the tape loop.

Regards,

Jose

Your YouTube link says "this video is unavailable".

OldiesButGoodies · « **Reply #14 on:** 23 Apr 2017, 07:16 pm »

Just fixed it - my bad.

CIAudio · « **Reply #15 on:** 25 Apr 2017, 11:33 pm »

ok... after watching your video, it is obvious as to what's going on.

The tape input is a "tape monitor", which means the selected input is fed to the "tape out" (tape recorder) for recording purposes.
When the tape input is selected, you can listen to (monitor) the recording while the selected input is fed to the recorder.

When in HT bypass, the volume control is taken out of the loop and the #4 input is fed directly to the output.
So... if you select "tape monitor" while HT bypass is selected, the tape input is fed directly to the output (full volume).
By selecting a different input before tape, you are exiting HT mode and signal is then routed through the volume control when tape is selected.

How do we fix it?
Well, if we want to keep tape as a "monitor" and not just an "input", the solution is to modify the software so that HT bypass is turned off when tape monitor is selected. The problem is that there will be no monitor function on input #4 when used as a standard input.
So the other software change needed is to make each press of #4 toggle the input, so it can be reselected.
Not as elegant of a solution as I'd like but the only way to keep all functions and eliminate the full volume issue.

I'll post here when I have new software tested and ready.
For those wishing to send their unit in for reprogramming... it will be done at no charge.

audiobliss · « **Reply #16 on:** 25 Apr 2017, 11:47 pm »

Who really use a tape monitor these days ? Why not just make #4 A regular input and forget tape monitoring.

AB.

CIAudio · « **Reply #17 on:** 26 Apr 2017, 12:42 am »

Quote from: audiobliss on 25 Apr 2017, 11:47 pm

Who really use a tape monitor these days ? Why not just make #4 A regular input and forget tape monitoring.

AB.

Personally, I'd be more inclined to get rid of the HT bypass.

audiobliss · « **Reply #18 on:** 26 Apr 2017, 01:42 am »

I think HT is much more popular than tape monitoring.

AB.

CIAudio · « **Reply #19 on:** 26 Apr 2017, 01:54 am »

Quote from: audiobliss on 26 Apr 2017, 01:42 am

I think HT is much more popular than tape monitoring.

AB.

True, so my final decision is a small compromise to keep all functions.
Tape will be turned off when going into & out of input #4.
Inputs 1-3 will remain as is and will have monitoring capabilities.
Input 4 will be for playback or HT bypass only.
Sound reasonable?