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Sounded good until I started messing with it ...

Discussion in 'Shock Brother's DIY Amps' started by HiFiFreq, Sep 8, 2020.

  1. HiFiFreq

    HiFiFreq TDPRI Member

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    I re-built a circuit into an old chassis with what I had hanging around . Sounded pretty good until I tried adding a presence control and that's why I am posting . One of the parts I had hanging around was an old Hoffman Stout turret board . It was probably my first or second build and it never really sounded good . More than likely it was my lack of experience in building that was the reason for the poor sound quality. Either way I cleaned up the board and repopulated it with some mods to the layout . Most of the mods are in the pre-amp section that I took from a Matchless design with a 12ax7 parallel triode input . I'll get to that in a little bit . The problem I'm having is in the phase inverter section . In my crude drawings you will see a .01 capacitor connected to pin 7 of the 12ax7 PI . In the "Stout" PI it is in parallel with a 470k resister and then in series with a 47k resister to ground . In the "Matchless" PI the .01 cap is connected at pin 7 and then to ground . Trying to figure out why . I have the PI built like the Stout is built . In my attempt to come up with a presence control I changed it to look like the Matchless PI . As I stated earlier It sounded good until I started messing with it ... Before it was dead quiet and with the change in the .01 cap it became noisy , hissy , not quiet . The Stout PI seems to be different than all of the other LTP types in respect to this .01 cap . Can anyone school me on this ?
     

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  2. HiFiFreq

    HiFiFreq TDPRI Member

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    Here is a schematic of what I have that works . Matchless like front end and tone stack into the Stout PI and on to the 6v6 output section . The amp is very quiet (no hum no hiss) and very clean even cranked all the way up . It breaks up when you dig in . I like it so far but I feel that it is not quite as loud as it should be .
     

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  3. HiFiFreq

    HiFiFreq TDPRI Member

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    Here are a few before and after pics of the re-build .
     

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    Nickfl likes this.
  4. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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  5. HiFiFreq

    HiFiFreq TDPRI Member

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    Thanks Lowerleftcoast . I was just looking around Rob's site as I thought I might find some answers there. I had a look at the Aiken and Valve Wizard sites last night as well . I'll have a read now and see what I can make of it .
     
  6. HiFiFreq

    HiFiFreq TDPRI Member

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    I'm back with an update . I have a feeling that I had the circuit wired incorrectly . After some research and reading I have become a little more familiar with the LTP circuit but I wouldn't say I understand it . Got lost in a very helpful thread where I thought two members might strangle each other but they finally worked it out . A thread I'll be revisiting . Regardless I was able to implement the circuit so that it worked and also made some changes over all to the circuit . I did away with the "Matchless" parallel triode circuit and changed the input circuit to resemble a more traditional Fender type using only one of the triodes in the first 12ax7 leaving one triode unused . Had a little space on the Stout board so I added a trem circuit like the one in a 6g3 circuit . This is my second attempt at a trem circuit . My first attempt was with a Silvertone 1471 inspired build using a pentode tube and I liked the results . While I was at it I changed the bias circuit of the output tubes from a fixed? biased to a cathode? biased circuit like the 6g3, I may have those terms confused hence the question marks . In order to get my voltages closer to the schematics I was using I had to make some changes to the power rail which ended up looking more like the 6g3 circuit. The more I messed with it the closer it came to resembling the Fender 6g3 schematic . I have a few updated pics and a few more questions . Pics first ...
     

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  7. HiFiFreq

    HiFiFreq TDPRI Member

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    BTW I nixed the presence control in favor of a negative feedback circuit . Also I implemented a master volume control . I still have to wire up a second input jack and I have either the speed or intensity control wired backwards that I have to change . This trem circuit seems to be suffering from the thumping effect that I have read a little about . Had to walk away from this one for a while as I was getting frustrated . Thing is while this project was on hold I built another amp into an old Hammond AO29 chassis based on the 6g3 circuit but stripped way down . No trem , no tone control , volume and master volume controls only , Parallel triode input and a pot added to the power tube negative bias circuit so I can make adjustments in plate voltage and current flow simultaneously . I'm really impressed with the adjustable bias circuit and how much it affects tone and volume . My god this thing is loud !
     
  8. HiFiFreq

    HiFiFreq TDPRI Member

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    I would like to post a schematic and voltages . I would also like to stop posting my usual "LoFi" pics and drawings . I've read about some free software for creating schematics . I wonder if someone could point me in the right direction to find and use one of these programs . This site is absolutely fantastic ! So much knowledge and so many generous people ! I offer my sincere thanks to all of you for this bounty of information !
     
  9. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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  10. HiFiFreq

    HiFiFreq TDPRI Member

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    Thanks for that Tom ! I downloaded the program and have half of the schematic drawn . Fairly easy to use as is . Awesome !
     
  11. HiFiFreq

    HiFiFreq TDPRI Member

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    I spoke too soon . It's not that easy ... I have the schematic drawn out with all of the components . I have not yet assigned values to any of them as of yet . I need to print a copy to take to my bench in order to reverse engineer what I have completed . Once I've recorded values I can transfer that information to the schematic . I can't get the print out enlarged big enough to see it when printing directly from DIYLC . I converted it to a PDF and that helped a little . What do you do with a file once finished ? I need a larger print out and some guidance for uploading it to this post when I'm finished .
     
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  12. HiFiFreq

    HiFiFreq TDPRI Member

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    ???
     

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  13. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    If you want to upload a DIYLC file here, use Save As PNG. Then use the 'upload a file' button, or just drag the png into this 'compose' box. If, rarely, a big file is too big as PNG, use any image app to convert to JPG.
     
  14. jhundt

    jhundt Doctor of Teleocity

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    how old is that Stout board?

    I remember several years ago I etched a board based on the Stout design. In the end, I never built the project, but I seem to recall a problem:

    There was a fault in the original published circuit for the Stout, that remained uncorrected for a long time. I think I might have read about it in the Hoffman forum, a year or two after I etched the board, when I was considering re-starting the project.

    I never built the Stout, and I can't comment any further about the design, nor can I recall what the error was on the schematic and/or layout that I used. But there was something.
     
  15. HiFiFreq

    HiFiFreq TDPRI Member

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    I have a revised schematic . Saved as a PNG . Complete with voltages etc...
    By the way the "stout board" is close to ten years old I think .
     

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