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120v centertap transformers, what to do with them? *PIC*

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  • 120v centertap transformers, what to do with them? *PIC*




    I have a few transformers that have dual 60v outputs. I was going to use them for a chip amp but the voltages are too high for any chip amps that I have found. What should I do with them (no, I am not going to get rid of them)? Do I have to learn how to build an amplifier with discreet components to use them, or is there a chip amp that can handle 60V rails (no, I don't want to build a regulated PS to get lower voltage rails). Also, which caps are suggested for a simple power supply? I was looking at the Nichicon HE 820uf 100v caps (using a few per side). They have a high ripple current and low impedance.

    <A HREF="http://www.bc-2.com/test/nichicon/en.../pdfs/e-he.pdf">http://www.bc-2.com/test/nichicon/en.../pdfs/e-he.pdf</A>

    I also have PE's buyout 14Vct transformers which will give me a little under 10 volts (unloaded) per rail. Is this enough to power an LM1875T (I have a few of these)? I am only looking to use it as an amp for SpeakerWorkshop, so I hardly need any power at all.
    <A HREF="http://www.partsexpress.com/pe/showd...number=129-082">http://www.partsexpress.com/pe/showd...number=129-082</A>


  • #2
    Re: 120v centertap transformers, what to do with t


    > I have a few transformers that have dual 60v
    > outputs. I was going to use them for a chip
    > amp but the voltages are too high for any
    > chip amps that I have found. What should I
    > do with them (no, I am not going to get rid
    > of them)? Do I have to learn how to build an
    > amplifier with discreet components to use
    > them, or is there a chip amp that can handle
    > 60V rails (no, I don't want to build a
    > regulated PS to get lower voltage rails).
    > Also, which caps are suggested for a simple
    > power supply? I was looking at the Nichicon
    > HE 820uf 100v caps (using a few per side).
    > They have a high ripple current and low
    > impedance.

    If it has dual 120V primaries, you could use it as a 30/0/30 at about half the VA rating. That would be a little more into chip amp territory at +/-42V. If you're solidly stuck at 60/0/60, you could always build the Leach Super Amp.

    Caps? 6 of those 820 uF per side would be a *start*, but I think it would really take 10 or more. Many smaller caps *is* better if you're trying to fit it all on one circuit board, but at what you end up spending, it might be worth it to try to find surplus 100V soup-can caps.

    > I also have PE's buyout 14Vct transformers
    > which will give me a little under 10 volts
    > (unloaded) per rail. Is this enough to power
    > an LM1875T (I have a few of these)? I am
    > only looking to use it as an amp for
    > SpeakerWorkshop, so I hardly need any power
    > at all.

    With THAT low a rail voltage, I would be thining about some of the older chip amps used for car audio - like the TDA2003/4/5. It will end up dropping to 7 or 8 volts under load, and I doubt the 1875 will put out more than your sound card will at that voltage.

    Comment


    • #3
      Re: 120v centertap transformers, what to do with t


      > I have a few transformers that have dual 60v
      > outputs. I was going to use them for a chip
      > amp but the voltages are too high for any
      > chip amps that I have found.

      Depending on the VA, you could isolate the secondaries to run two chips independently around +/-42V. Again, that's borderline for most and you'll need enough current to supply the chip at that voltage.

      Tim

      Comment


      • #4
        Re: 120v centertap transformers, what to do with t


        > I also have PE's buyout 14Vct transformers
        > which will give me a little under 10 volts
        > (unloaded) per rail. Is this enough to power
        > an LM1875T (I have a few of these)? I am
        > only looking to use it as an amp for
        > SpeakerWorkshop, so I hardly need any power
        > at all.
        >
        > <A HREF="http://www.partsexpress.com/pe/showd...number=129-082">http://www.partsexpress.com/pe/showd...number=129-082</A>

        If you have two of those transformers you could both of them together to get +-20 volts which would be good for the LM1875.

        Comment


        • #5
          My bad, 42vAC = 60cDV. thx for the responses !!!


          I realized that I had written the AC voltage wrong. They are 42v secondaries, so I am getting 60vDC.

          Warren - I have an older SB 32bit soundcard that only has line-level outputs. So even the smallest gain from the 1875 would be more than the output from the soundcard (am I right in saying this, or does the line-level outputs have enough power to use for testing purposes, I haven't finished the jig yet, so I haven't tried the outputs yet).

          colby - I do have 2 of them, and was thinking about that, but I didn't want to waste 2 of them for just one chipamp (I only have 2 of them). Maybe I should go this route for now though. Thanks for the suggestion.

          Tim - I don't know what the VA is on these, but they are running some pretty hefty wiring. They weigh a few pounds each.

          Comment


          • #6
            Re: My bad, 42vAC = 60cDV. thx for the responses !


            > I realized that I had written the AC voltage
            > wrong. They are 42v secondaries, so I am
            > getting 60vDC.

            Same thing applies - if you can wire the primary for 240 and put in 120, you get half the voltage. And +/-30 has a lot more possibilities for chip amps than +/-42. At +/-60 it would be in the 100-150 wpc/8 ohm range for a discrete amp. What *I* would do with them is put two in series for quad 60V rails and getting 1500 watts bridged class H, but that's just me :-)

            > Warren - I have an older SB 32bit soundcard
            > that only has line-level outputs. So even
            > the smallest gain from the 1875 would be
            > more than the output from the soundcard (am
            > I right in saying this, or does the
            > line-level outputs have enough power to use
            > for testing purposes, I haven't finished the
            > jig yet, so I haven't tried the outputs
            > yet).

            You'll get gain - but the output voltage swing on the 1875 is 6 volts *less* than the supply rails on each side. Only a volt or two isn't much output. Since you don't need gobs of power and you won't be running the tranny near its max VA capacity, why not add a few turns of wire to up the voltage? Just use standard insulated wire, wrapped over the tape.


            Comment


            • #7
              Re: 120v centertap transformers, what to do with t


              Have you looked at the Cerwin Vega amp mod over on the Apex Jr. web site done by Neil Davis? For $50 + s/h you would have a pretty scookum full range amp!

              Andy



              (Originally posted by: Andy D.)

              Comment


              • #8
                Listen to you Warren, if 'I' were you. U da Man, W


                I "like" your way of thinking. Now I just need to figure out how to make an H class amplifier. I would love to run mucho power to my 15" DVC (3.5' sealed) with a Linkwitz transform circuit (which isn't on there yet). May just have to buy another 15"DVC in that case and build 2 amps (I have 7 of those transformers).

                I guess that I will just go with 2 of the buyouts secondaries wired in series and run the 1875 with 18v per side.

                BTW Warren. You told me to go with a BP102 and a compression driver for my bass some time ago. I am still building the cabinet (I am lazy sometimes), but just wanted to thank you again for the advice. That is one very nice driver for practicing and should hit the low note for my 4 string just fine (just don't ask my neighbors their opinion on the matter).

                > Same thing applies - if you can wire the
                > primary for 240 and put in 120, you get half
                > the voltage. And +/-30 has a lot more
                > possibilities for chip amps than +/-42. At
                > +/-60 it would be in the 100-150 wpc/8 ohm
                > range for a discrete amp. What *I* would do
                > with them is put two in series for quad 60V
                > rails and getting 1500 watts bridged class
                > H, but that's just me :-)

                > You'll get gain - but the output voltage
                > swing on the 1875 is 6 volts *less* than the
                > supply rails on each side. Only a volt or
                > two isn't much output. Since you don't need
                > gobs of power and you won't be running the
                > tranny near its max VA capacity, why not add
                > a few turns of wire to up the voltage? Just
                > use standard insulated wire, wrapped over
                > the tape.

                Comment


                • #9
                  Re: Listen to you Warren, if 'I' were you. U da Ma


                  > I "like" your way of thinking. Now
                  > I just need to figure out how to make an H
                  > class amplifier. I would love to run mucho
                  > power to my 15" DVC (3.5' sealed) with
                  > a Linkwitz transform circuit (which isn't on
                  > there yet). May just have to buy another
                  > 15"DVC in that case and build 2 amps (I
                  > have 7 of those transformers).

                  7 of those transformers???? Let's see, that's two each for the sub amps, two for the mid amp, and one for an ultra-high quality class AB amp for the horns..... If you had a decent stash of power transistors and heatsinks, that's about $2200 worth of amplifiers waiting to get built - enough to power a whole PA. :-)

                  Class H amps aren't that hard in principle - if you have quad rails available, just about any discrete class AB design can be "converted" by switching the volatge on the outputs and leaving the rest of the amp running off the high rail. But you do have to know what you're doing.

                  > I guess that I will just go with 2 of the
                  > buyouts secondaries wired in series and run
                  > the 1875 with 18v per side.

                  > BTW Warren. You told me to go with a BP102
                  > and a compression driver for my bass some
                  > time ago. I am still building the cabinet (I
                  > am lazy sometimes), but just wanted to thank
                  > you again for the advice. That is one very
                  > nice driver for practicing and should hit
                  > the low note for my 4 string just fine (just
                  > don't ask my neighbors their opinion on the
                  > matter).

                  I hear a table saw calling your name. The driver said he would be a lot happier in the cabinet, too. But the neighbors won't be any happier - it will mean *more* bass.

                  Comment


                  • #10
                    Re: My bad, 42vAC = 60cDV. thx for the responses !


                    > colby - I do have 2 of them, and was
                    > thinking about that, but I didn't want to
                    > waste 2 of them for just one chipamp (I only
                    > have 2 of them). Maybe I should go this
                    > route for now though. Thanks for the
                    > suggestion.

                    With two of the transformers you could easily power two LM1875 ICs for a stereo chipamp.

                    Comment


                    • #11
                      How about Hypex UcD400? *PIC*



                      Provided Link: http://www.hypex.nl/


                      It uses +/- 60 volt rails. 200 watts @ 4 ohms.

                      C
                      Curt's Speaker Design Works

                      "It is the mark of an educated mind to be able to entertain a thought without accepting it."
                      - Aristotle

                      Comment


                      • #12
                        That's funny, cuz I was reading yr post from below


                        I followed your shortcut from the other day, but could not find any prices on those amplifiers. Those do look inviting for sure.

                        Thanks for chiming in there Curt.

                        Comment


                        • #13
                          Well if you really really want 'em

                          Provided Link: http://www.adireaudio.com/Home/UcDAmps.htm


                          Here's the link to Adire's web page. I would love to try them out too.

                          shawn
                          My favorite woofer is a Labrador retriever.

                          Comment


                          • #14
                            Re: 120v centertap transformers, what to do with t


                            If you buile a choke imput filter instead of a cap imput filter , you get .9*AC rather then 1.414*AC. Costs a lot more but it is a lot earyer on the diodes and the trans doesn't ring as much ether.

                            Celeste

                            Comment


                            • #15
                              Re: 120v centertap transformers, what to do with t


                              > If you buile a choke imput filter instead of
                              > a cap imput filter , you get .9*AC rather
                              > then 1.414*AC. Costs a lot more but it is a
                              > lot earyer on the diodes and the trans
                              > doesn't ring as much ether.

                              > Celeste

                              But choke input filters don't work as well under light loads. If the load is too light, the conduction through the inductor becomes discontinuous and the voltage rises. Which brings us back to 1.4X Vac. That type of filter worked well in the days of tubes, when you always had a significant bias current that was a sizeable fraction of full load.

                              Comment

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