Jump to content

DT50 BIAS VOLTAGE FREAKOUT IN VOICE III


mtreehugger
 Share

Recommended Posts

Can anybody tell me if it's normal to have a radically different bias voltage for voice III.  I'm in Class AB (of course) pentode mode, and in voices I, II, and IV both pins check in at 35mv ±1mv.  But when in voice III, the voltage freaks out.  I'm actually measuring 18 Volts, which is 500 times as much voltage as the other voices!!!

 

I just got my amp back from the shop.  I had asked the tech multiple times to check this but apparently he failed to do so.  After replacing teh DSP board, he said he tested it thoroughly and gave it a clean bill of health.

 

???

 

It occurs to me that if voice III is actually Class A or somesuch that this condition could be normal, however, without any knowledge that it is normal I'm not going to operate the amp.  Another possibility is that the voltage I'm seeing at the test pins with my voltmeter is not what the tubes are actually seeing in voice III.  Neither of these notions seems likely, though.

 

Can anybody check their amp in this regard?  (remember, I'm checking at the test pins)

 

THANKS!

  • Upvote 1
Link to comment
Share on other sites

Can anybody tell me if it's normal to have a radically different bias voltage for voice III.  I'm in Class AB (of course) pentode mode, and in voices I, II, and IV both pins check in at 35mv ±1mv.  But when in voice III, the voltage freaks out.  I'm actually measuring 18 Volts, which is 500 times as much voltage as the other voices!!!

 

I just got my amp back from the shop.  I had asked the tech multiple times to check this but apparently he failed to do so.  After replacing teh DSP board, he said he tested it thoroughly and gave it a clean bill of health.

 

???

 

It occurs to me that if voice III is actually Class A or somesuch that this condition could be normal, however, without any knowledge that it is normal I'm not going to operate the amp.

 

Can anybody check their amp in this regard?

 

THANKS!

 

I was under the understanding that the bias is not affected by the voicings. I can't check it 'cause my DT50 HD is still in for servicing. I don't think your going to get much concrete info on this but my hopes are high. The III voicing was always the noisiest for me, sounded good when played though. Have you done a support ticket? or called Line 6? You should if you haven't. Good Luck I'll be following.

Link to comment
Share on other sites

I was under the understanding that the bias is not affected by the voicings. I can't check it 'cause my DT50 HD is still in for servicing. I don't think your going to get much concrete info on this but my hopes are high. The III voicing was always the noisiest for me, sounded good when played though. Have you done a support ticket? or called Line 6? You should if you haven't. Good Luck I'll be following.

 

I got ahold of the tech 1 hour after posting this.  He said that according to the schematic, what I'm reporting is impossible without frying resistors and tubes and junk, which is pretty much what I'm afraid of.  I'm bringing the amp back this afternoon and he'll verify my measurements.  He'll expedite this to the best of his ability, and hopes that Line 6 is able to expedite whatever they may need to do as well.

  • Upvote 1
Link to comment
Share on other sites

So my tech calls me up and tells me that he observed the same voltage change that I did, however, he also observed that when switching to voice III my amp was also switching to Class A.  And in class A, 18 volts at the bias test pins is normal.  I had no idea my amp was doing this, but answers from another thread of mine by Phil (Phil_M I think) tell us that the FW 2.0 update changed it so that each voice will "remember" the Class and pentode/triode settings so that if you switch voices and then go back it's where you last left it.

 

I familiarized myself with the amp  under FW 1.x and was unaware of the functionality change that took place after I did the update.  So I'm in there, measuring the voltage, completely oblivious to this, and unable to see the front of the amp.  Dang good thing my tech spotted that--he's a keeper!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...