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Vox Escort Lead 50 repair/tone problems

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  • #31
    Originally posted by drewl View Post
    Is the cabinet cool looking?

    EDIT: WOW! They are great looking, it would make a perfect AC15!
    Hehe, well, you may say that It was very much a sad garage find when I got it, someone had put a hole through the speaker and the amp was noisy as I've ever heard. The grill cloth was basically tatters so I've taken it as a learning amp. I've went over it all and it now works well, albeit with the crappy sound from the factory design. But along the way, rather than get a Vox grill cloth I just used some leftover parrot tropical fabric to practice my upholstery on , so depending on your stance its now either a unique, fun oddity or an absolute abomination!!

    Actually, making the cabinet and tolexing it to look like an old Vox is something I'm a lot better at, I have access to a full woodwork facility etc. so the value of the box is less for me..but building an amp to put in it is probs out of my ability right now, so I want to use this as a learner for the electronics side. But I love the idea, in future, of making a great little amp and re-appropriating old shells!

    The badge is long gone...

    BTW, does anybody know what the name of that gold edging strip is called for the purposes of purchase? Would like to get a new, nicer one, but any word combo I can think of for the name just gets a tonne of carpeting strips..
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    • #32
      Originally posted by OwenM View Post

      BTW, does anybody know what the name of that gold edging strip is called for the purposes of purchase?
      Like this? Some terms you can search for anyway, https://www.tubeampdoctor.com/en/sho...X_AC30_size_43
      (gold fascia strip, vox)
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


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      • #33
        Originally posted by OwenM View Post

        Just double checking, the dot next to the old .01 and the .022 / 47k caps and resistor, is that left unconnected?

        I know almost anything will work, but any preference for what type the 0.01uf cap is?
        That was the old bright input. Those components aren't needed anymore. For a future experiment you could connect a footswitch to short that terminal to ground. It would be some kind of treble boost.

        Or you can steal the .01 cap for the mod. Those yellow caps are good quality, at least from my experience.
        Last edited by dmeek; 06-15-2019, 02:20 AM.

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        • #34
          Originally posted by dmeek View Post
          That was the old bright input. Those components aren't needed anymore...
          I got the bits and did the mod today, and it turned out really nicely! Its softened all the weirdness in the sound, its fairly flat on neutral eq and you've got a fair bit of beef and a nice bit of extra treble if needed, the mid control is really useable. Whatever funkiness was going on in the impedance mismatch was meaning the eq circuits were pushing and pulling around some really odd shaped signal by the time it got to them... Now it just works exactly as you'd expect, nothing to write home about, but certainly a nice little amp to have around!

          Thanks so much for your help Dmeek and everyone else, been a good learning project for me!

          Just one thing I'm not too sure of, and would like to ask, what's the purpose of the 0.01uf cap added? Does it form part of a radio frequency filter circuit? I had to fiddle around with the position of that one for the least hum and ended up with it siliconed to the underside of the board, though I may go in with a small bit of universal PCB and make a slightly more robust board if I find the time.

          I assume the 68k resistors at the input jacks are best kept as close as possible to those jacks though, am I right?

          All the best

          Owen
          Last edited by OwenM; 06-19-2019, 10:31 PM.

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          • #35
            There is DC voltage on Pin 2 (and pin 1 and 3) of the op-amp. I think about 15 Volts. The .01 cap isolates the DC from the input, but lets the audio pass through.
            Without the cap there would be 15 Volts on the input jacks which would get shorted out by the guitar pickup. That would throw the amp into a non-working state.

            The connection from the input jack to the op-amp might have to be shielded to reduce hum because the impedance is now very high at 1Meg.
            Keeping the wires as short as possible may be good enough. If not, one trick is to wrap the input jacks, wire and .01 cap with masking tape,
            then wrap tinfoil over that and ground the tinfoil.
            Last edited by dmeek; 06-19-2019, 10:50 PM.

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            • #36
              I'll go pore through my archive of Vox schematics. It sure seems like there was an Escort Lead 50 in there.

              As a side possibility, I made up a PCB for the preamp section of the UK Vox 700 series - 715, 730, 760, etc. If you get too disgusted, you might want to consider a soul transplant.
              Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

              Oh, wait! That sounds familiar, somehow.

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              • #37
                Originally posted by dmeek View Post
                There is DC voltage on...
                Thanks, makes sense, I need to read up on op amps and what voltage is where on em but I understand the principle!

                I may try shielding, but really, the hum is pretty minor. You can run the amp at a loud 'room volume' and notice nothing. I was chop-sticking the placement of the cap around at a really high volume and found the sweet spot there so that's probably enough but I may tin foil it in the future if I fancy going in again and perfecting it!

                Thanks

                O

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                • #38
                  Originally posted by R.G. View Post
                  I'll go pore through my archive of Vox schematics....
                  Sure! If it pops up I'd love to see it, and yeah I'm up for making it a part of a bigger project later, upgrading the whole preamp section! It has no real value to me other than something to learn solid state on, and its been great for that purpose so far!

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                  • #39
                    I did a little poking through the archives. No luck. It must be the bass 50 I remember.

                    But I did come up with some thoughts. Both the US and UK Vox folks liked to do mix and match designs. I wonder if the preamp of your amp is the preamp of the Escort Lead 30 grafted onto the power amp of the Bass 50. It would be very Vox-ish if that were true.
                    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                    Oh, wait! That sounds familiar, somehow.

                    Comment


                    • #40
                      Originally posted by R.G. View Post
                      I'll go pore through my archive of Vox schematics. It sure seems like there was an Escort Lead 50 in there.

                      As a side possibility, I made up a PCB for the preamp section of the UK Vox 700 series - 715, 730, 760, etc. If you get too disgusted, you might want to consider a soul transplant.
                      Do you have pix of the boards on your site?
                      I'm not seeing them. I'd love to take a look a the 7- series boards and your incredible work.

                      Comment


                      • #41
                        Originally posted by R.G. View Post
                        I wonder if the preamp of your amp is the preamp of the Escort Lead 30 grafted onto the power amp of the Bass 50. It would be very Vox-ish if that were true.
                        No the lead 30 is oddly enough not at all like the 50, the Lead 50 has an inverting OpAmp preamp stage similar to the Bass 50, and although it has the normal/bright (labelled high/low) it gets it's change in tone through a little cap / resistor after each input and then goes to the - of the preamp op-amp.. So it's a little unlike both really... Anyway, dmeek wrote me a mod to give it a proper impedance on the input and now the high/low is gain instead and it sounds really pretty nice, definitely loads better from where it was!

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                        • #42
                          Originally posted by drewl View Post
                          Do you have pix of the boards on your site?
                          I'm not seeing them. I'd love to take a look a the 7- series boards and your incredible work.
                          There aren't any pictures of that board. I can put up some pics of the bare board, but my amp tech friend coaxed me out of the first-article assembled item. I'm have to assemble another one to get a picture of one with parts. Could happen... They're 10" x 2" overall.
                          Originally posted by OwenM
                          No the lead 30 is oddly enough not at all like the 50, the Lead 50 has an inverting OpAmp preamp stage similar to the Bass 50, and although it has the normal/bright (labelled high/low) it gets it's change in tone through a little cap / resistor after each input and then goes to the - of the preamp op-amp.. So it's a little unlike both really... Anyway, dmeek wrote me a mod to give it a proper impedance on the input and now the high/low is gain instead and it sounds really pretty nice, definitely loads better from where it was!
                          Interesting. Did you happen to do enough tracing to know the actual schematic of the Lead 50, or all the differences from the Bass50? I'd be willing to draw/document the schemo for the Lead 50 and post it for reference.
                          Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

                          Oh, wait! That sounds familiar, somehow.

                          Comment


                          • #43
                            Originally posted by R.G. View Post

                            Interesting. Did you happen to do enough tracing to know the actual schematic of the Lead 50, or all the differences from the Bass50? I'd be willing to draw/document the schemo for the Lead 50 and post it for reference.
                            I'm halfway there with the Lead 50 schematic. I can finish it in a day or two.

                            edit: Here it is. A few capacitor values I couldn't see, The power amp section looks to be identical to the bass 50

                            https://music-electronics-forum.com/...1&d=1561230494
                            Attached Files
                            Last edited by dmeek; 06-22-2019, 07:09 PM.

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                            • #44
                              Originally posted by dmeek View Post
                              I'm halfway there with the Lead 50 schematic. I can finish it in a day or two.

                              edit: Here it is. A few capacitor values I couldn't see, The power amp section looks to be identical to the bass 50

                              https://music-electronics-forum.com/...1&d=1561230494
                              If you like I could open up again and look at the values of those caps you couldn't see the value of, maybe if you circle which ones they are on the board I'd be able to get a better look at them. If its those blocky, yellow Phillips 'chicklets' then they are all either 470n for the big ones and 10n for the smaller ones.

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                              • #45
                                OK thanks. There's just one other capacitor and I wasn't sure if the 3 circled resistors were 470 ohms or 4.7K. Also need the pot values. And the little disc cap in the upper right
                                I'll post an updated schematic.

                                https://music-electronics-forum.com/...1&d=1561335487
                                Attached Files
                                Last edited by dmeek; 06-24-2019, 12:26 AM.

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