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    ST70 chassis mods

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    dmag

    Posts : 30
    Join date : 2010-10-05
    Location : North Shore,Ma.

    ST70 chassis mods

    Post by dmag on Sat Mar 03, 2012 4:50 pm

    After doing a couple ST70's on stock chassis', I'd like to do a few changes .
    So here's my thought, and I know it wouldn't be worth the trouble already. Just a way to use parts and a hacked chassis.
    On epay it's common to see a chassis with paint,wood trim, bias test jacks on front etc.

    I've never seen anyone move the inputs to the rear, power switch to front or bias pots to the front of a stock type board.(or leave original pots on top and add balance pots to front or top ie Dynakit.)
    It's basically more esthetically pleasing to me.
    But I wonder, Is there any technical reason not to do these things?
    And a more advanced option , to use a VTA board and relocate the bias pots to the front panel if used in a ventilated cabinet where access would be a pain.

    Any opinions appreciated



    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: ST70 chassis mods

    Post by heyraz on Sun Mar 04, 2012 2:33 am

    All of the low level signals that are sensitive to RFI are brought in up front close to the driver board's inputs. This keeps them away from all of the noisy stuff like power lines, switches and transformers, which are kept at the rear. It's a simple configuration to minimize noise. Function over fashion.
    Even though your cabinet is ventilated, the general consensus is that the amp should be looking at the ceiling when in use. It will get hot, which will shorten it's life. Just my 2 pennies. Rich

    dmag

    Posts : 30
    Join date : 2010-10-05
    Location : North Shore,Ma.

    Re: ST70 chassis mods

    Post by dmag on Sun Mar 04, 2012 2:40 pm

    Thanks,
    I appreciate the input.
    I figured there was a technical reason nobody seems to have moved the inputs.

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: ST70 chassis mods

    Post by Luddite on Mon Mar 05, 2012 2:19 pm

    dmag wrote:Thanks,
    I appreciate the input.
    I figured there was a technical reason nobody seems to have moved the inputs.

    Just for the record, back in the 90's I built an ST70 with a NOS chassis, transformers, and cage. I used the Van Alstine driver board and did indeed locate the inputs on the rear as well as locating the power switch on the front. Additionally, I located the bias pots in place of the front panel sockets and installed test jacks where the inputs would have been. This amplifier was very quiet and served me well for many years until I sold it. I'm not necessarily encouraging anyone to do likewise, but am just confirming that it can be done.

    Best Regards,
    Charlie

    dmag

    Posts : 30
    Join date : 2010-10-05
    Location : North Shore,Ma.

    Re: ST70 chassis mods

    Post by dmag on Mon Mar 05, 2012 10:40 pm

    Thats good to hear.
    I had pretty much decided it was worth trying.
    Worst case I' d have to move inputs back forward.
    Did you go with shielded wire, twist or strait runs.
    I have some Straightwire coax I thought might be just the ticket.
    It is after all a learning curve.No pain no gain.
    ,

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: ST70 chassis mods

    Post by Luddite on Mon Mar 05, 2012 11:55 pm

    dmag wrote:Thats good to hear.
    I had pretty much decided it was worth trying.
    Worst case I' d have to move inputs back forward.
    Did you go with shielded wire, twist or strait runs.
    I have some Straightwire coax I thought might be just the ticket.
    It is after all a learning curve.No pain no gain.
    ,

    I used foil shielded wire with two inner conductors, running straight from the driver board to the input connectors which were mounted on both sides just inside each of the speaker output terminal strips. Note: the shield was only connected on one end to avoid any potential ground looping. That being said, I have also successfully used coax in similar applications with other projects. Hint: be careful not to let the input signal wiring pass directly below the bottom (cover) of the power transformer.

    Best Regards,
    Charlie

    dmag

    Posts : 30
    Join date : 2010-10-05
    Location : North Shore,Ma.

    Re: ST70 chassis mods

    Post by dmag on Thu Mar 29, 2012 5:32 pm

    Thanks Charlie.
    That's helpful. I'v pretty much figured my layout, similar to what you did.
    Collecting my parts now..Curious though, if you used "stock" type components or went
    with different type caps etc.
    I think i'll getsome new transformers and save the cloth leads to do a complete stock ST70 that I''ve been saving and matching parts for.
    I was brought an old guitar amp with point to point wiring ,and as soon as that's done it will be time to start.
    sf

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: ST70 chassis mods

    Post by Luddite on Thu Mar 29, 2012 7:03 pm

    dmag wrote:Thanks Charlie.
    Collecting my parts now..Curious though, if you used "stock" type components or went
    with different type caps etc. sf

    Nothing exotic. I just used the best grade of Panasonic for both electrolytics and polypropylenes and metal film resistors (may have been Dale brand). That was in the early 90's and there weren't really any specialty caps on the market to speak of.

    Best Regards,
    Charlie

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