I took it in to the lab and looked at the outputs. Everything seems perfect and in-phase. I am not sure what the problem is. Maybe it dosnt like my speaker cables or somthing. I will try another set of cables, and try another set of RCA cables from my CD player. We'll see if that straightens things out.
-have a good one.
-Paul Hilgeman
-have a good one.
-Paul Hilgeman
Could you be asking more of the LM3875 than it can deliver? This chip is really designed to work into an 8 ohm load, and if you take a careful look at the datasheet, you can see that it does not do well into 4 ohm loads (this is from memory, so I don't have specifics). Since you have an MTM, you probably have a 4 ohm (approximately) load over much the bass and midrange. As I recall, you can run into problems with current limiting. If this is the case, try the LM3886.
Just something to check into.
John
Just something to check into.
John
Paul
Do you still have the "old" amp you mentioned ? Is the problem gone when you connect the speakers back to this one?
If the problem persists then I have a suspicion:
Did you ever take apart one of the speakers (I sometimes do such things out of curiosity) ?
If you, for instance, unplugged the woofers (or are they soldered ?)and wired them the wrong way again, then the described effects can happen.
Bass will only be in-phase when one of the speaker cables is wired out of phase. But then the tweeters will be out of phase which isn't contributing to good imaging at all (apart from the fact that you will have a bump or a dip in the crossover area).
Regards
Charles
Do you still have the "old" amp you mentioned ? Is the problem gone when you connect the speakers back to this one?
If the problem persists then I have a suspicion:
Did you ever take apart one of the speakers (I sometimes do such things out of curiosity) ?
If you, for instance, unplugged the woofers (or are they soldered ?)and wired them the wrong way again, then the described effects can happen.
Bass will only be in-phase when one of the speaker cables is wired out of phase. But then the tweeters will be out of phase which isn't contributing to good imaging at all (apart from the fact that you will have a bump or a dip in the crossover area).
Regards
Charles
Power Supply
Paul and John,
Could this be a power supply issue? At what are the voltage rails operating? If this IC is run between 25 V and 27 V it is a beast. It actually produces more power into a 4-ohm load than into 8-ohms. I think that It would pretty much rock on the Dayton III's.
If it is not the power supply, It sounds like a possible capacitance issue.
Later,
Paul and John,
Could this be a power supply issue? At what are the voltage rails operating? If this IC is run between 25 V and 27 V it is a beast. It actually produces more power into a 4-ohm load than into 8-ohms. I think that It would pretty much rock on the Dayton III's.
If it is not the power supply, It sounds like a possible capacitance issue.
Later,
Attachments
Voltage should do fine
Hi Poul.
It´s a shame your amp doesn´t work
The voltage you are using should be fine, I have used a 29-0-29v trafo and driven 4ohm MTM´s without any problems, other than the chip getting hot.
Why dont you try to hardwire everything together instead of using a pcb ?
I never could get a pcb to work a good .
Regards
Kim
Hi Poul.
It´s a shame your amp doesn´t work
The voltage you are using should be fine, I have used a 29-0-29v trafo and driven 4ohm MTM´s without any problems, other than the chip getting hot.
Why dont you try to hardwire everything together instead of using a pcb ?
I never could get a pcb to work a good .
Regards
Kim
From my limited experience, it almost sounds like the speakers have a common path to ground that has too much impedance.
If you have ever lost the ground connection to your headphones you will know what I mean.
I used to build with board like this until I went beyond AF.
I use circuit board material and cut the traces i need with a dremmel tool...results in very good ground planes.
If you have ever lost the ground connection to your headphones you will know what I mean.
I used to build with board like this until I went beyond AF.
I use circuit board material and cut the traces i need with a dremmel tool...results in very good ground planes.
Issues Resolved
Hey Guys,
Thanks for all of the support. Last night I did about 6 hours of research and testing. I 'reverse' wound my transformer and got it down to 19-0-19 VAC, I incrased the capacitence to 3300uF per rail plus 1000uF per rail, per chip right near/on the chip.
Lastly, and this is pure dumbness on my part. I have my system in a 12x16 room, and if you do the calculations on this, there is a huge hole starting at 35Hz, going all of the way to 55Hz of about -8dB.
So, the combination of all of these iterations of research has brought me to the conclusion that the am sounds incredible, more so with the lowered PS voltage (this made the largest difference), and the increased capacitence (this made a difference in that the lower mids are much more 'meaty' and bold), and the realization that I had a 6dB bass boost on my old amp that I had totaly forgoten that I had turned on 8 months ago when I had goten this room 'flattened' out.
So, the moral of the story and what my ears heard is that the lower supply volage is very very important, even when driving nominal 6 or 8 ohm speakers. I would just stick with 18-0-18 no matter what, or possibly 20-0-20. I had ordered 25-0-25, and with my higher than average wall voltage was getting about 27-0-27 which was too high for the 3886 to handle.
Second moral, after probably 6 to 8 hours of listening, I do prefer a slightly higher capacitence (I still have the original 1000uF caps near the chips though). I will of course remove these additional 3300uF caps closer to the PS in a couple of weeks when the amp is broken in and see how it sounds.
Third moral, even if you set your previous amp up months ago, and then sold it and couldnt see what the settings were, try and remember if you had a bass boost. to remove or help out some of your room modes. I was burned by this one, and now that I am listening to a flat amp, I have nulls of about -8dB in the bass region, which is killing some things pretty bad. I will desing a cicruit to correct this though.
Thanks again
-Paul Hilgeman
P.S. I will post final pictures soon!!!
Hey Guys,
Thanks for all of the support. Last night I did about 6 hours of research and testing. I 'reverse' wound my transformer and got it down to 19-0-19 VAC, I incrased the capacitence to 3300uF per rail plus 1000uF per rail, per chip right near/on the chip.
Lastly, and this is pure dumbness on my part. I have my system in a 12x16 room, and if you do the calculations on this, there is a huge hole starting at 35Hz, going all of the way to 55Hz of about -8dB.
So, the combination of all of these iterations of research has brought me to the conclusion that the am sounds incredible, more so with the lowered PS voltage (this made the largest difference), and the increased capacitence (this made a difference in that the lower mids are much more 'meaty' and bold), and the realization that I had a 6dB bass boost on my old amp that I had totaly forgoten that I had turned on 8 months ago when I had goten this room 'flattened' out.
So, the moral of the story and what my ears heard is that the lower supply volage is very very important, even when driving nominal 6 or 8 ohm speakers. I would just stick with 18-0-18 no matter what, or possibly 20-0-20. I had ordered 25-0-25, and with my higher than average wall voltage was getting about 27-0-27 which was too high for the 3886 to handle.
Second moral, after probably 6 to 8 hours of listening, I do prefer a slightly higher capacitence (I still have the original 1000uF caps near the chips though). I will of course remove these additional 3300uF caps closer to the PS in a couple of weeks when the amp is broken in and see how it sounds.
Third moral, even if you set your previous amp up months ago, and then sold it and couldnt see what the settings were, try and remember if you had a bass boost. to remove or help out some of your room modes. I was burned by this one, and now that I am listening to a flat amp, I have nulls of about -8dB in the bass region, which is killing some things pretty bad. I will desing a cicruit to correct this though.
Thanks again
-Paul Hilgeman
P.S. I will post final pictures soon!!!
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