Angelo

Still trying to track the issue down. Just to summarize. This is not an issue with the input board, this is not an issue with the tubes, and this is not an issue with the tube bias. There are two inputs on the front of the amp, and they are both working as normal to the input board. The part where the nomenclature gets confusing are the signals coming out of the input board. I'm looking at the signals GIN_LO+, GIN_LO-, GIN_HI+, and GIN_HI- There is a 20x gain difference between the two signals. If my memory serves me correctly, this is used for the ADC Crossfade Gain Switching. The way that works is the DSP is listening to both signals and uses the high gain channel at low levels to provide better SNR and then switches to the low gain channel at higher input levels to provide better headroom. What I believe is happening is that the DSP is never switching over to the GIN_LO+, GIN_LO- pair so I never get the benefit of the higher headroom. In the pictures, I am probing the test points between GIN_LO+ and GIN_HI+, for a signal of 290mV RMS on GIN_LO+, I get 4.7V RMS on GIN_HI+. This is right at the edge of clipping for the GIN_HI+ channel. To me, this exonerates the input section up to the Codec. So now I suspect the Codec may have issues, but I have never experienced just a single channel going bad on a Codec. Again, I hate to scrap my DT-50. It works perfectly when used through Line 6 link with my POD HD. It is just that the input switching isn't working properly Best, Angelo

Okay, I've swapped out the TLC084C. That did not fix the issue, but I have more information. Coming out of the DT-50's input board are differential signals for a High Gain and Low Gain signals that go to the codec. These differential channels go to the codec are used for gain switching in the DSP. When you are playing quietly the DSP uses a peak follower to select the High Gain differential channel to keep your guitar input signal level higher than the noise floor of the electronics. When your input crosses some threshold, the DPS selects the Low Gain differential channel to provide you with more headroom. This gives you the best of both worlds, low noise when you need it, and higher headroom when you need it. This tracks exactly with my problem. When I play quietly, the guitar sounds crystal clear (I'm on the High Gain differential channel), but when I dig in to the strings the signal cuts out and clips, which means there is a problem with the Low Gain differential channel, or possibly an issue with the Codec (a Cirrus Logic CS42436). I highly doubt just a single channel went bad on the codec, I've never heard of that happening. Partev, do you have any clues? Have you had any other DT-50 failures with the input gain switching? I'll keep probing to see if I can find the fault. I hate to have to scrap my DT-50 when it is otherwise working perfectly! Best, Angelo

I haven't been able to swap out the TLC084C to narrow down the issue yet. Is the DT-25 guitar input board compatible with the DT-50 (electrically)? They have the same header https://www.fullcompass.com/prod/270207-line-6-50-02-0209-guitiar-input-pcb-assembly-for-dt25-amp

Interesting. If it turns out that the TLC084C is okay. Are there other parts in the input audio path that could contribute to severely lower headroom if they fail? Diodes maybe?

yeah, that's what I was thinking of trying first. The part # is TLC084C. I was posting to see if it was a common problem, but it looks like it might only be me. :)

Both

yes, correct tubes and bias I have no clipping if the HD Rack does the conversion of the guitar signal from analog to digital, and then sends the digital audio to the DT-50 via L6 Link. I only get the clipping if I plug my guitar directly into the front of the DT-50.

Ok great, then that exonerates the tubes. The tubes are working perfectly. If I go: Gibson SG -> HD Pro rack -> L6 Link -> DT-50, I have no issue at all There is clipping somewhere between the DT-50's guitar in and the codec of the DSP on the mainboard.

Ok, thanks for the part number and the tube tips. Aren't the 12AX7's after the DSP main board? I am nearly certain that they are.

Also, what is the correct part number? If 35-00-0385-1 is the unstuffed pcb, then what is the fully populated pcba? My guess is 55-02-0385, but just a stab in the dark based on the DT-25 input board number. Thanks for all the speedy replies

A pair of Ruby 12AX7AC5 HG+ tubes and a pair of Sovtek tubes for the power amp. Changing the the tubes made no difference at all in the performance, so I swapped back. I don't think I am describing my test cases clearly enough. My L6 Link signal flow - no input clipping - sounds great: Gibson SG -> HD Pro rack -> L6 Link -> DT-50 In this case the input board of the DT-50 is not being used My DT-50 signal flow - input clipping - sounds bad: Gibson SG -> DT-50 In this case the input board of the DT-50 is being used It is only when I connect my guitar to the input of the DT-50 that I get the weird lack of headroom and clipping

Hi Partev! I just replaced all four tubes in the DT-50 Using L6 Link means that the guitar input board is not used, and the digital audio goes into the DSP and then to the tube power amp. Since the DT-50 functions perfectly when L6 Link is being used, it means that the DSP and the power amp are not where the problem is. If you open up the DT-50 you will see that there is a daughterboard for the guitar input that is separate from the mainboard. The part number for the daughterboard is 35-00-0385-1 Do you know where I can get a replacement for the daughterboard to try out?

HI, After years of working great, my DT-50 has extremely harsh clipping on the guitar input. Symptoms: Plugging my guitar straight into the amp, I get clipping when playing chords at a normal volume. If I turn my guitar volume way down I don't experience any clipping at all. It seems like a bad diodes or bad op-amp. Things I tried: I connected the DT-50 via L6 Link with my HD Pro rack; when I do this the DT-50 sounds perfect. It is definitely something related to the guitar input. Changed the tubes on the DT-50 - no difference at all. It wasn't the tubes. Input Board part number: Opening up the amp, the guitar input board is over on it's own. The part number on the input board is 35-00-0385-1 The input board has the TLC084C opamp package on it. You can but the DT-25 input board on Full Compass, but the DT-50 input board is not for sale on Full Compass. I'm suspecring the Any ideas, Anybody else experience the same thing?

dead thread bump I'm getting this with firmware version 2.10 on an 89F; it sounds like a triggered envelope is being applied. I can hear this across all models and pickups, and still occurs even when the neutral body model is selected. Maybe everyone has moved on, just mentioning with the hope that someday this is something that can be addressed. I have no facts but guessing that the floyd + graphtech pickups added more sustain and a triggered envelope was added to counter act. Sorry, just wild speculation, but if that is the case, then an off switch would be much appreciated.