Very Clever! The parallel resistor is a nice idea. That way you can tune the affect of the inductor.
Last night I tried a 0.5 Ohm resistor in parallel with that previous 2.6mH inductor. It turned out very good. No more horrible on/off cone movements. Buzz noise didn't come back. 2 main goals were done.
Brief listening impression was very similar to the previous [inductor only] stage. As expected, there's a slight change in response curve, a little bit more SPL in 30-40Hz range, so a tad of heaviness. In fact the difference is very little, and I'm satisfied with the result. 😀
Brief listening impression was very similar to the previous [inductor only] stage. As expected, there's a slight change in response curve, a little bit more SPL in 30-40Hz range, so a tad of heaviness. In fact the difference is very little, and I'm satisfied with the result. 😀
OK, here I summarize all these as follows:
Driver's Qes = 2 * Pi * fs * Mms * Re / BL ^2
And any series R in between driver and the [driving source] should be added into the "Re" in the above formula, thus we got a new (real) system Q. Or, we may set a target system Q, and determine how much series R is needed.
And the series R is made by http://sound.westhost.com/project56.htm
This is the simplied circuit diagram of my current setting (modification) of the plate amp for sub:
And for those who might be interested, attached spread sheet is my 'forecast tool'. In the table, you have to insert your own set of numbers, like the impedance data of the driver. Mine are exported from the mearsurement by WT3.
Any comments are welcome, and I hope someone can correct me on those calculations if anything wrong.
Driver's Qes = 2 * Pi * fs * Mms * Re / BL ^2
And any series R in between driver and the [driving source] should be added into the "Re" in the above formula, thus we got a new (real) system Q. Or, we may set a target system Q, and determine how much series R is needed.
And the series R is made by http://sound.westhost.com/project56.htm
This is the simplied circuit diagram of my current setting (modification) of the plate amp for sub:
An externally hosted image should be here but it was not working when we last tested it.
And for those who might be interested, attached spread sheet is my 'forecast tool'. In the table, you have to insert your own set of numbers, like the impedance data of the driver. Mine are exported from the mearsurement by WT3.
Any comments are welcome, and I hope someone can correct me on those calculations if anything wrong.
It works with chip based amp, too. I think it'd be easier to try the concept with chips😉
Here:
http://www.diyaudio.com/forums/chip-amps/150767-lm3886-current-feedback.html#post2332047
Here:
http://www.diyaudio.com/forums/chip-amps/150767-lm3886-current-feedback.html#post2332047
Hi,
I don't use T-bass circuit with this. T-bass needs high current/ low output impedance. Quite the opposite of this modded amp. (similar overall effect, but I won't call it a 'replacement'... )
The inductor in the current sensing element adds another pole to the 'filter'. It may or may not be a good thing. In the spreadsheet, Rp and Rs appear in the sheet for "inductor // R as Rfb". They mean 'the resistor in parallel with the inductor' and 'the DC impedance of the inductor'. You may see the Rfb is changing with the frequency. Also, you may see in the formula how it's calculated. Refer to https://en.wikipedia.org/wiki/Electrical_reactance#Inductive_reactance
You need a small overall impedance in series with your woofer (R3, or Rfb) to get a smaller loss.
Feel free to experiment, but keep your steps small.
I'd like to add that the voltage feedback is still there controlled by R1 and R2. When making up a combination of desired gain / output impedance, it can be overdone on these numbers. I had once set both gain and output impedance too high. That made the whole thing unstable -- visible long and slow stroke of the cone.
Dipole bass needs a LOT of compensation in the low end. I found it'd be better to spread it in many stages. We have many tools along the signal chain to play with -- digital EQ, line level (passive or active), between amp and driver (what this thread and T-bass are all about). Several dB in each stage is better than 20 dB in one. And, healthy 30 Hz would be a better goal than flapping 20.
I don't use T-bass circuit with this. T-bass needs high current/ low output impedance. Quite the opposite of this modded amp. (similar overall effect, but I won't call it a 'replacement'... )
The inductor in the current sensing element adds another pole to the 'filter'. It may or may not be a good thing. In the spreadsheet, Rp and Rs appear in the sheet for "inductor // R as Rfb". They mean 'the resistor in parallel with the inductor' and 'the DC impedance of the inductor'. You may see the Rfb is changing with the frequency. Also, you may see in the formula how it's calculated. Refer to https://en.wikipedia.org/wiki/Electrical_reactance#Inductive_reactance
You need a small overall impedance in series with your woofer (R3, or Rfb) to get a smaller loss.
Feel free to experiment, but keep your steps small.
I'd like to add that the voltage feedback is still there controlled by R1 and R2. When making up a combination of desired gain / output impedance, it can be overdone on these numbers. I had once set both gain and output impedance too high. That made the whole thing unstable -- visible long and slow stroke of the cone.
Dipole bass needs a LOT of compensation in the low end. I found it'd be better to spread it in many stages. We have many tools along the signal chain to play with -- digital EQ, line level (passive or active), between amp and driver (what this thread and T-bass are all about). Several dB in each stage is better than 20 dB in one. And, healthy 30 Hz would be a better goal than flapping 20.
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