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JBL s312ii and a big amp = problems???

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  • #16
    Originally posted by philthien View Post
    Amplifier clipping can sound a bit like voice coils slapping.
    I could confirm this with the o-scope on the output of the amp

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    • #17
      Originally posted by djg View Post
      I have several Outlaw Audio monoblocks at 200/ 8 ohms 300/ 4 ohms. I have a Yamaha M80 downstairs. I have two Class D Audio 250/ channel. I think I know what a monster amp is, and I don't consider any of my amps "monsters".

      Just my opinion.
      It’s all relative to your perspective. What does it have to do with the question?

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      • #18
        Well the question i think was is my new Denon amp too much for my JBLs.

        I asked if you were sure it was in good repair being somewhat vintage. No reply.

        I asked if things were fine before the Denon, and what you were using before the Denon. No reply.

        I suggested that 150 watts per channel is not a "monster" amp, despite the huge transformer and caps. That got a response, read up on the amp.

        I guess I'm too stupid to help you, sorry for wasting your time. Good luck.

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        • #19
          Originally posted by Mountainman Bob View Post

          The source input on that amp is 1v.
          More than likely it’s less than your old one......try the attenuation (which I see it does have) at 1 or 2 o’clock instead of pegged.
          I gave been playing around there... but what about using the “High Cut Filter In”? 1.41v and starts it’s rolloff at 40khz

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          • #20
            Seeing as that's about 20kHz higher than the source material or speaker pass band I doubt it would do anything.

            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

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            • #21
              Originally posted by billfitzmaurice View Post
              Seeing as that's about 20kHz higher than the source material or speaker pass band I doubt it would do anything.
              i understand that most source matterial is 20hz to 20khz (or less in many case). And most of us can’t even hear that... that wasn’t why I was suggesting I might use that input

              Bob had suggested that the amplifier needs a 1v input and, so my thought is the high cut has a input of 1.41v and should be a little less hot.

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              • #22
                The mash up I was referring to is replacing a woofer in a designed system without changing the crossover. I read the owners manual and it says never to run two pairs of 8 ohm speakers - implication is that it doesn't like 4 ohms. If I had to guess, I think it's clipping.

                Agree with you about modern 500 watt home theater receivers that draw 200 watts. My Accuphase P-300s produce 400 watts at 4 ohms and draw 10amps and weigh 55lbs - old school real power.
                Last edited by dwigle; 03-14-2019, 10:18 PM.

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                • #23
                  Originally posted by Ericfx1984 View Post

                  I could confirm this with the o-scope on the output of the amp
                  That's a nice amp - I love those old meters! The scope on the outputs would seem to be the best next step. See if there's any clipping - also check in the MHz ranges for oscillation. Heck, it could be your speaker cable not playing well with the amp. It's been known to happen. If everything looks good, it's time to eliminate possible causes. Bypass the Modi if you can - maybe play something right out of your phone or computer directly into the amp. Use the Win/OSX main output control so system alerts & sounds won't play full blast. Still hear the problem, it's not the Modi. Haul your speakers over to your friend's place and see if they play fine in his system.
                  Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

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                  • #24
                    I tested the MODI this morning as well as my TASCAM US-600 (DAC/interface). Using a 1khz sine wave, there was no clipping seen on either and they had the same output on the oscope’s screen.

                    so on the the Carver c-1 (later tonight). I will check it at the output with the Modi hooked up to it

                    If that all passes I will move on to testing the output of the amplifier

                    I actually learned a lot about doing this when I started building guitar amplifiers. Basically a friend of mine came over and said, “Eric, we should start building tube guitar amplifiers...”

                    well for some reason the first one I built, which mind you was completely from salvage components, produced almost no sound. I scratched my head scratched my head some more and scratch my head again. Then I looked at the schematic that I had designed loosely based off of a Fender champ, and decided I should trace a signal through it, well come to find out The issue was simple, the salvaged resistor that I chose to use, was not the correct value, I had missed read the final band, what I have done was added so much negative feedback that it nearly shut the amplifier down, this became very easy to figure out due to doing a signal trace

                    And that’s really all that I’m doing on this, it’s a little different in that what I’m looking for is clipping or some type of signal distortion



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                    • #25
                      OK fellas, now we are getting somewhere. the C-1 is the issue(so far)

                      I ran the MODI into the C-1, and hit it with a sine wave, it looked clean, as first, then as i approached a higher volume it started clipping fast... right before 3 o'clock on the volume it started to clip. It looks almost like a Square wave by the time it hits full volume.

                      I pulled out my NAD 314, which has low power on the Amplifier side, but I perfectly working preamp, I have not had TIME to signal trace it and find the problem. BUT IT's preamp WORKS! I can run that thing until I repair the C-1

                      Another thing to note on the Carver C-1 is it does not fill the screen on my Oscope nearly as much as the NAD...

                      My guess is that the Carver is causing issues with the amp long before it becomes visible on the Oscope.

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                      • #26
                        I found a thread on AudioKarma that mentions a Carver service bulletin regarding changing the gain of the C-1 by swapping some resistors. Looking at the schematic, it's just a voltage divider at the rca jacks. That only effects the Main 1 outputs, so you'll probably get more signal on Main 2 output jacks. If you have a flakey op-amp or two, you can still get the RC3146. It has a strange pin-out and a few say they would buy a Brown Dog adapter board to run some better spec chips, like the good ole' NE5532.
                        Co-conspirator in the development of the "CR Gnarly Fidelity Reduction Unit" - Registered Trademark, Patent Pending.

                        Comment


                        • #27
                          So I read your problem as ... I got a more powerful amp and it's power can bottom out the woofers. And, the original woofer has been replaced (likely with a high power rating?).
                          So my question is ... was the replacement woofer selected (i.e. modeled) for the JBL enclosure (its volume and port tuning)?

                          Putting any woofer in any box can lead to excessive cone excursion (bottoming out) at lower power due to a poor match with the enclosure. That's obvious as you mention the kick drum. The kick drum's acoustic power peaks between 55 and 60 Hz. Any decent 12" woofer in a matched enclosure would not bottom out in that frequency range.

                          This can be modeled in 5 minutes. You need (1) The PE woofer mfg and model #; (2) The volume of the JBL enclosure (inside); and the size of the port (LxW). Most any regular member hear can model that using their current software package of choice (mine - WinISD). That will tell you what's going on with the woofer (graphs of cone movement by frequency at given power levels, caviar, etc.).

                          The solution might be as simple as lengthening the port. Though it's more likely the box is too big for the particular replacement woofer. An excessive "extended bass shelf" (EBS) alignment (e.g., box to big for the particular woofer design) causes severe peaks in the freq response above the shelf. Modelling will tell you that and also validate replacement woofer choices. If the JBL mid and tweet can handle more power, you could up your SPL game with a new woofer - confident it will perform well. Party on Wayne ...

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                          • #28
                            Originally posted by tom_s View Post
                            I found a thread on AudioKarma that mentions a Carver service bulletin regarding changing the gain of the C-1 by swapping some resistors. Looking at the schematic, it's just a voltage divider at the rca jacks. That only effects the Main 1 outputs, so you'll probably get more signal on Main 2 output jacks. If you have a flakey op-amp or two, you can still get the RC3146. It has a strange pin-out and a few say they would buy a Brown Dog adapter board to run some better spec chips, like the good ole' NE5532.

                            You bring up a really good point. I have read that service bulletin. I also noticed when I first got this that there were some resistors that it been changed out near the main output of that preamp. They were larger than the original components. My guess is that they are incorrectly spec’Ed causing this unit to drive into clipping

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                            • #29
                              OK. I’ve swapped to a different preamp now that I’ve discovered the problem with my preamp. And it is definitely better a lot better. Looks like I’m going to have to start working on the car for preamp

                              This is what I get for not confirming it to be fully functional chasing my tail for no reason at all damn I feel stupid

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