Harmony Central Forums
Announcement Announcement Module
Collapse
No announcement yet.

amp hum after mod - help!

Page Title Module
Move Remove Collapse









X
Conversation Detail Module
Collapse
  • Time
  • Show
Clear All
new posts

  • #16
    Good luck with your work. I hope you get it all figured out. I have also done what you did, but on a $100,000 piece of Air Force communication equipment. And I'm still in the Air Force 14 years later.

    You will get good and you won't make the same mistake twice. You have to learn something and along the way all of the VOODOO will go away.

    Remember the guys in white coats in the glass lab working on computers....its just the same voodoo.

    Some folks will spend over $5000 a year recycling amps, paying techs $40 to bias tubes, $25 to replace pick ups and so what if you blow your **************** up. Your right, if you learn, then you done good.
    My Band:
    http://www.stuckingearrocks.com/sig/Home.html
    Positive Transactions with:
    DarkCide, Rfaranda, Lord Megatron, Sixtonoize, Derekb, Bigmark, 35091

    For Sale
    Peavey JSX Head- Great Condition - Make Offer

    Comment


    • #17
      Gus, I read about that cap that limits the bass on another forum. I also understand that theres bright caps that can be clipped that smoothes out the treble response(less buzzy). I have modded the effects loop so that it works as a series loop. Now I can use my DSL401 as a slave amp taking a signal from my 2204's preamp. That EL84 power section sounds pisser with the 2204's preamp going into it. I think if someone could mod the existing DSL401 preamp for a more classic vibe this amp would be the ticket. Also upon removing the chassis one would do good to inspect every solder joint. These amps are notorious for cold solder joints. I had mine gone over 4 1/2 years ago and no problems yet. Good luck with your mods and if you feel up to it feel free to post some.

      P.S. I've read a few articles that claim that the OD channel volume is a Post Phase Inverter Master. Can you confirm this?
      Marshall JCM800 2204
      Marshall Lead 100 Mosfet
      Laney AOR ProTube 50

      Comment


      • #18
        Originally posted by guitarzan
        ...you will not cover tube therory in EE class except maybe one afternoon outlining history. ..... Be sure to pick up some worthy text. At least an old RCA tube manual.


        No kidding! Tubes don't get any respect these days!! About the only time they get any mention if CRT for TV's and computers... it kinda sad really... There's just something about the glow of a tube that make my heart warm....

        I have two tube manuals that I downloaded ftom the internet... I think I actually understood them the third time around. I just finished Dan Torres's book, which got me started and really helped me narow down components to use on my next completely crazy DIY amp project (512 different tone cominations). I just ordered The Ultiimate Tone, and that seems to have a lot of great stuff in switching, etc.

        If I want to get really technical and learn about tubes I general, I have checked out a few books from the 1940s-50s from the tech library about tubes (they were WAY over my head then), and there are books on tubes circuits and even Morgan's Valve Amplifiier books. Turns out my Grandpa's brother wrote a few of those books - too bad his health is failing as well as his mind - he could teach me TONS!!

        Sadly the tech Library somehow lost the Radiotron designers handbook, so I won't be able to look at that one for while...

        anyone else suggest more good reading material as far as tube circuits go?

        Comment


        • #19
          Originally posted by cap'n'crunch
          Gus, I read about that cap that limits the bass on another forum. I also understand that theres bright caps that can be clipped that smoothes out the treble response(less buzzy). I have modded the effects loop so that it works as a series loop. Now I can use my DSL401 as a slave amp taking a signal from my 2204's preamp. That EL84 power section sounds pisser with the 2204's preamp going into it. I think if someone could mod the existing DSL401 preamp for a more classic vibe this amp would be the ticket. Also upon removing the chassis one would do good to inspect every solder joint. These amps are notorious for cold solder joints. I had mine gone over 4 1/2 years ago and no problems yet. Good luck with your mods and if you feel up to it feel free to post some.

          P.S. I've read a few articles that claim that the OD channel volume is a Post Phase Inverter Master. Can you confirm this?


          The cap that limits the Bass (C92) isn't necessary - supposivley it was put in there to elimate any pops from occuring when the relay switches the channel - I didn't notice any pops with it out - probally die to the circuits that "ducks" the volume when the channel is switched... Just remember to replace it with a wire if you take it out or you won't be hearing anything!!

          The bright caps (C100, C97) could be clipped out..... it turns out that my amp had the bright cap (C97) on the clean section modded it was replaced with a 100pF - it sounded beautiful!! Resotring to the 470pf stock value made it REALLY shrill!! Woah!! Changing that one to a 100pF will still keep the channel bright without the harshness of the 470pF. I'm definately going to change mine back!! No wonder people hate this amp when they hear it, and no wonder the ones at the guitar shop didn't sound as good as mine!!

          I haven't done any experiments with the cap on the overdrive, but it does sound good without it in there ( My wire was about 5mm to short and so it pulled out when I put everything back together...) I'm not sure if this one got modded or not...

          By they way, You don't need a serial effects loop to use the DSL401 as a slave power amp. You can plug it into the effects return and use the FX mix as a volume control. The GREAT thing is that it comes into the amp before the tonestack if you put your amp on the OD1 channel (OD2 will work, but might cause noise). So you can tweak your tone even more- if you want to run it straight through with no volume contol or whatever you can just use the clean channel...

          Yes, the DSL401 has a post-phase inverter master volume control- this is my problem... one side has a volume control and the other doesn't know what is going on at this point!!

          The person who had my amp before me also modded it with a fan, and probally touched up the cold solder joints, too...

          Within the next few months I will be posting a website dedicated to the DSL 401... I will include, tips, tricks, mods, sound clips, etc. I really think that this is a great amp... just a few things that can be done to improve it if you have the patience.

          Comment


          • #20
            Try The Ultimate Tone (TUT) series

            Comment


            • #21
              Originally posted by clay_finley
              Try The Ultimate Tone (TUT) series


              Just ordered it a few days ago.... can't wait to jump into it!!

              Comment


              • #22
                I have a page about old Marshalls too:
                Marshall Circuits

                Comment


                • #23
                  sweet!! That is my next project!!!

                  its gonna be the craziest amp ever, with all the switches it will have it will have 512+ tone combinations!!

                  Comment


                  • #24
                    Originally posted by gusfinley


                    No kidding! Tubes don't get any respect these days!! About the only time they get any mention if CRT for TV's and computers... it kinda sad really... There's just something about the glow of a tube that make my heart warm....

                    I have two tube manuals that I downloaded ftom the internet... I think I actually understood them the third time around. I just finished Dan Torres's book, which got me started and really helped me narow down components to use on my next completely crazy DIY amp project (512 different tone cominations). I just ordered The Ultiimate Tone, and that seems to have a lot of great stuff in switching, etc.

                    If I want to get really technical and learn about tubes I general, I have checked out a few books from the 1940s-50s from the tech library about tubes (they were WAY over my head then), and there are books on tubes circuits and even Morgan's Valve Amplifiier books. Turns out my Grandpa's brother wrote a few of those books - too bad his health is failing as well as his mind - he could teach me TONS!!

                    Sadly the tech Library somehow lost the Radiotron designers handbook, so I won't be able to look at that one for while...

                    anyone else suggest more good reading material as far as tube circuits go?


                    I have not seen any Torries books but have heard some good things about his FX loop. Ultimate tone is a super book as are any of the London Power series and Kevin is a great guy a I mentioned before. I have access to a military library just stacked full of tube stuff if the need be. Old books rule and a library that stocks them is my kind of place. Too bad the Radiotron is gone from yours, you may want to buy one if you get real serious. One other very famous book for tubes is Jack Darr's "Guitar Amplifier Handbook" It covers more about servicing than design but it is great and easy to read. I have no schematics for newer Marshalls. I assume the preamp in a DSL/TSL is simular to a 800. Would still like to see it if possible. Is there a link for them? At least then I would know exactly what you are doing or intending to do...

                    Comment


                    • #25
                      here is the schemtic.....

                      There are a lot of extra components compared to the earlier marshalls - probably too facilitate the switching....

                      pdf link

                      this is a great site for you basic marshall history with plenty of schematics....

                      Comment


                      • #26
                        The TUT book has a huge chapter on switching.

                        Comment


                        • #27
                          Originally posted by gusfinley
                          here is the schemtic.....

                          There are a lot of extra components compared to the earlier marshalls - probably too facilitate the switching....



                          OMG I get dizzy looking at that! No wonder I prefer vintage or DIY. I can see now why the DSL I did play was without the feedback and screams of older Marshalls. See all those caps in parallel with the anode Rs. Everyone of them sucks a certain amount of high range out of the signal. This is great if you want to boost the amp in front without high range feedback. I wonder though if it could be done another way? Usually I increase my filter caps and use better grounding for that sort of stuff. Interesting. So which cap did you remove? The one I normally take out in older Marshalls with too much highs is right after the first stage. Usually a 470pf cap in parallel with a 470K resistor just before the gain pot.

                          Comment


                          • #28
                            The caps on the anodes that shunt highs are used in high gain amps to get rid of squeals.

                            Comment


                            • #29
                              Originally posted by clay_finley
                              The caps on the anodes that shunt highs are used in high gain amps to get rid of squeals.


                              I know but not all high gain amps have them.

                              Comment


                              • #30
                                Originally posted by guitarzan


                                OMG I get dizzy looking at that! No wonder I prefer vintage or DIY. I can see now why the DSL I did play was without the feedback and screams of older Marshalls. See all those caps in parallel with the anode Rs. Everyone of them sucks a certain amount of high range out of the signal. This is great if you want to boost the amp in front without high range feedback. I wonder though if it could be done another way? Usually I increase my filter caps and use better grounding for that sort of stuff. Interesting. So which cap did you remove? The one I normally take out in older Marshalls with too much highs is right after the first stage. Usually a 470pf cap in parallel with a 470K resistor just before the gain pot.


                                Yeah, this schematic still makes me dizzy!! I've got it about 70% figured out.... I removed capr C92, i think - the one between the tonestack and the cathode in the cathode follower circuit - BIG difference - at least on the clean channel..

                                The other filtering may be there to compensate for the lack of negative feedback in the amp... I'lll have to check out the schematic again and look for the shunt caps on the plate load resistors.....

                                this has become quite the good discussion!!!

                                Keep it coming!!

                                Comment



                                Working...
                                X