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    Stereo/Mono Switch....

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    wolverine

    Posts: 60
    Join date: 2010-02-20

    Stereo/Mono Switch....

    Post by wolverine on Wed Mar 10, 2010 8:29 am

    I would like to get some opinions on the removal of the switch. My basic question is...."should I remove the switch from the circuit first of all, and if so then what is the proper method of doing so for a stock board". Thanks to all who reply, your experience is greatly appreciated by me.... :}

    wolverine

    Bob Latino
    Admin

    Posts: 1821
    Join date: 2008-11-26
    Location: Massachusetts

    Re: Stereo/Mono Switch....

    Post by Bob Latino on Wed Mar 10, 2010 1:30 pm

    wolverine wrote:I would like to get some opinions on the removal of the switch. My basic question is...."should I remove the switch from the circuit first of all, and if so then what is the proper method of doing so for a stock board". Thanks to all who reply, your experience is greatly appreciated by me.... :}

    wolverine

    There is no real reason to remove the stereo/mono switch other than maybe a couple of less solder connections between you and the music. Removal of the switch will make no audible difference in the sound of your amp.

    What many Dynaco ST-70 users don't realize is that when you JUST flick this switch to mono you do not have now a 70 watt mono amplifier. What you have when you just flick the switch to mono is two 35 watt amps carrying the same audio signal. In order to truly have a 70 watt mono amp you must also, in addition to flipping the switch to mono, run a wire between the two output transformers. If you have 8 ohm speakers you must run the wire between the two 16 ohm taps. If you have 4 ohm speakers you must run a wire between the two 8 ohm taps. Now you have a 70 watt mono amplifier and you can connect your speaker to EITHER transformer output. You can connect your input interconnect to either input jack.

    If you do want to remove the switch wiring do this ...

    1. Remove the wire that runs from lug #3 of the stereo/mono switch to the positive terminal of the right channel input jack.

    2. Remove the wire that runs from lug #2 of the stereo/mono switch to the positive terminal of the left channel input jack.

    3. Remove the end of the 470,000 ohm resistor connected to lug #1 of the stereo/mono switch and reconnect it to the center positive lug of the left input jack.

    Check the photo below ...

    Bob



    wolverine

    Posts: 60
    Join date: 2010-02-20

    Thanks Bob... :}

    Post by wolverine on Wed Mar 10, 2010 2:39 pm

    I have for some time envisioned a different chassis for one of my ST-70's. I have seen some really nice ones done by DIY'ers and I thought I would enjoy designing my own chassis. Since I NEVER use the switch I though why in the world make a cut-out for it in a new chassis build. I really had no clue as to whether or not this little switch was integral to the workings of the amp at all, though I cannot see where it has any function other then to send the same signal to both sides of the amp.

    Bob I truly appreciate your time. Thanks for your support, and thanks to all you other folks who have contributed your time and energy in answering stupid questions from dumb old farm boys like me!.... :}

    wolverine

    GP49

    Posts: 467
    Join date: 2009-04-30

    Re: Stereo/Mono Switch....

    Post by GP49 on Thu Mar 11, 2010 9:36 am

    But even after doing all that, you don't have a PROPER 70 watt mono amplifier.

    For one thing, if you put it on the test bench, you will find it won't make 70 watts, anyway.

    And...worse...the two amplifiers will then share the same negative feedback signal to the input stage, which is incorrect because it is virtually impossible that the error correction needed by each amplifier channel will be identical in both. The combined negative feedback signal won't match the errors in each channel, since it will be a mongrel composed of both feedback signals, combined.

      Current date/time is Fri Apr 25, 2014 3:20 am