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Author Topic: Presence  (Read 8641 times)
Gerome
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« on: July 29, 2009, 01:47:15 AM »

Amp sounds good but the presence does not seem to be working. The amp is really bright! The presence would be a very good feature to have right now.  Does anyone have any suggestions for trouble shooting this issue?
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Gerome
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« Reply #1 on: July 29, 2009, 02:32:50 PM »

Also some hum issues. Huh?? Anyone got any ideas?
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cmoore
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« Reply #2 on: July 29, 2009, 03:46:04 PM »

Is the amp new?   Who put it together?
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Gerome
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« Reply #3 on: July 29, 2009, 04:45:07 PM »

I just put it together. The tubes aren't even burned in yet. I'm so far pretty happy with the way it sounds but there will be a bit of tweaking however. My first objective is to fix the presence and reduce the hum. a couple of other comments on what I want to achieve. I would like the amp to clean up a little quicker when I roll off the volume on the guitar and maybe a bit cleaner overall. I will be experimenting with tubes, but I would like to get as much out of the amp first. I use most of my amps for recording so hum is an issue. Thanks ahead of time to anyone that can help.
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cmoore
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« Reply #4 on: July 30, 2009, 02:13:11 AM »

Can you post a few pictures.   
Regards the presence, triple check your amp to the schematic.   Go real slow, physically touch the paper as you trace the path of travel.   Make sure you have made every connection, make sure all the components are correct, make sure the pot is working/passing signal, stuff like that.
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wyatt
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« Reply #5 on: July 30, 2009, 03:21:04 AM »

Well, their layout and their chassis pics are different on the Presence control.  Which does yours look like?

I would disconnect the Presence from the OT tap outright and take it out of the equation, if the amp is still bright, then it isn't the Presence control (setting Presence to 0 is the same as having no Presence at all)
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Gerome
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« Reply #6 on: August 03, 2009, 02:40:02 AM »

The Latest. Ok. Found a mistake. I forgot to jump between pins 3 and 8 on the pre tube, but when I do that the amp takes off with what sounds like an oscillation. VERY LOUD. It i then disconnect the presence from the OT. It now is very noisy with allot of gain....    Huh???  I have tried this with both methods of wiring the presence, (Expression and Liverpull)  Hummmmmm.
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cmoore
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« Reply #7 on: August 03, 2009, 04:10:32 AM »

This starts to get pretty confusing (at least it does for me).   So I assume 1/2 of your phase inverter was not working.   Now that you have both halves going, you have more trouble than you did before.   You are probably going to need help from somebody better than me but, I would say you need to check your wiring again.   Verify that you have the proper volt readings everywhere.
Double check all of the "under the board" wiring and be sure that you did not miss something.   Make sure you judiciously check ALL of your work, from the input jack to the output jack.   
Bad oscillation on a newly wired amp can be caused by the OT.  You might try reversing the brown and blue wires fro you power tubes to the OT.   You will know if that was the problem or not.   It will either fix the oscillation, or make it 100 times worse.  Other than that, I do not know what to say.
Your original complaint was that your amp was too bright.   After jumping the PI cathode with one wire, you now have trouble with oscillation.   So all I can say is:
Check all of your amp against the layout, and take your time. 
You really need to check all of the important voltages throughout your amp.  I realize you do not have a schematic, maybe Nik can help you put with some expected voltages.
Flip the OT wires and see if that helps your oscillation.
Reconnect your presence.
Good Luck
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Gerome
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« Reply #8 on: August 03, 2009, 03:54:02 PM »

Ok, reversing Brown and Blue worked. Presence is now working as well. Is there possiably something reversed B4 this that would account for the reverse issue? The hum issues are still a problem but the overall sound of the amp is pretty good, so, were getting close. THANKS FOR THE HELP!!!!!
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cmoore
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« Reply #9 on: August 03, 2009, 05:04:01 PM »

No, the brown and blue wires were the problem.   They are not compensating for something further back in the circuit.
As far as hum..... I would triple check all of your ground connections.   Make sure you have continuity.   Re-flow any joint that looks the least bit suspicious.   Other potential problems are your ground systems themselves.   Also, as always, lead dress can be critical.   Moving a wire 1/4' inch can make a big difference.    Again, make sure all of your ground connections are short, tight, and non-invasive as possible.   You may as well start chop sticking, see what you can improve. 
That is probably about all the help I can be for you.    You may need the service of an amp tech.   Posting some pictures may still prove to be a big help.
Good Luck
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Gerome
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« Reply #10 on: August 08, 2009, 02:21:33 AM »

OK, THIS IS WHERE WE STAND, The amp is functioning properly,and sounds good, BUT, THERE IS NOW A HUGE HUMM. the initial issue was the presence not working, I missed hooking together pins 8 & 3 on the 3rd pre tube. now the presence is working but there is a huge humm, I tried using the presence layout on the Expression and it voice is a bit different but the huge hum is still there. I don't have much experience with amp building but I'm RALLY REALLY SMART, so I bet I can figure this out. All help will be appreciated. I will post pic tomorrow   
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Gerome
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« Reply #11 on: August 15, 2009, 09:59:44 PM »

Issues resolved. Thanks everyone
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jerrydyer
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« Reply #12 on: May 17, 2010, 05:34:49 PM »

just an FYI
if you use the Mercury ot for this amp its brown then blue. brown starts. the schem or layout for this amp and its OT oare blue brown.  You can always just switch the wires off the plates of the PI too.. a little easier.   
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