Forte Model 3 Amp

cjmustang69
cjmustang69 Posts: 117
edited June 2009 in Vintage Speakers
I recently purchased a set of SDA SRS speakers and plan to drive them with a Forte Model 3 amplifier. I've searched and cannot determine if this is a common ground amp. Can anyone confirm if this amp is common ground? Thanks, Denny
Post edited by cjmustang69 on
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    I don't know the specifics of that model but if it's like Nelson Pass's other Forte designs it will have resistors isolating the channel grounds from each other and chassis ground.If this is the case then it can be made common ground by strapping the two negative speaker posts together.If you have a multi meter you can check the resistance between the two neg binding posts and chassis.If the resistance value is under 100 ohms or so, you are safe to strap them together.
    Testing
    Testing
    Testing
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  • cjmustang69
    cjmustang69 Posts: 117
    edited June 2009
    Thank you for the information. I'm quite new at this - so I have a few follow up questions:

    1. If the resistance between the negative post and chassis is over 100 ohms - does this mean the amp is common ground?

    2. If the resistance is less than 100 ohms (between negative post and chassis)
    what should I use to strap the negative posts tpgether? Would speaker wire be ok? Thanks, Denny
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  • heiney9
    heiney9 Posts: 25,214
    edited June 2009
    I asked this question of Nelson also. It was for a different model Forte, but I *think* the designs are very similar.

    http://www.diyaudio.com/forums/showthread.php?s=&threadid=105335&highlight=

    This link may or may not help

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • Systems
    Systems Posts: 14,873
    edited June 2009
    cjmustang69 wrote: »
    1. If the resistance between the negative post and chassis is over 100 ohms - does this mean the amp is common ground?
    High resitance would indicate non common ground.
    2. If the resistance is less than 100 ohms (between negative post and chassis)
    what should I use to strap the negative posts together? Would speaker wire be ok? Thanks, Denny
    Yes a short piece of 12 or 14AWG would be fine.
    Testing
    Testing
    Testing
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  • cjmustang69
    cjmustang69 Posts: 117
    edited June 2009
    H9 - thanks for the link regarding Forte amps. I had used this Model 3 with my SDA 2B's for a short period of time - I didn't have any problems. I'm thinking it must be common ground, but would like to make certain before using with my SRS's. GV#27 - thank you clarifying how to interpret the resistance readings which I should get when I do my checks.
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