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Old 30th June 2007, 07:12 PM   #1
durxter is offline durxter  Netherlands
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Default ACE-bass amplifier design

I am very much interested in the ACE-bass principle, invented by K.E. Stahl back in the seventies. Iíve found the patent of the principle and did a lot of searching on the internet. In this tread on DIYAUDIO I found a circuit of a prototype of Bjornoís ACE-bass amp design.

I am planning to build such a thing to experiment with, and maybe when it give satisfying results build a sub for daily use.

Bjorno mentioned in one of his posts of the tread that the amp part can be replaced by an ďgaincloneĒ amp. This would be very practical since Iíve already built a Gainclone amp, which I can use for this project.

I have redrawn Bjornoís circuit diagram with a Gainclone amp instead of the original amp. My question is: will this work, or am I forgetting some critical things here?

Bjorno, what does P4 (100k) do at the + input of uA748 do? Offset or something?

I am hoping that any of you can give me some feedback on this design.

Thanks,

Durxter
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Old 30th June 2007, 10:16 PM   #2
bjorno is offline bjorno  Sweden
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Quote:
Bjorno, what does P4 (100k) do at the + input of uA748 do? Offset or something?...
durxter,

Thank you for re-writing my old schematic , it looks good as far as I can see. Iíve tested with a 3886 amp and it worked well.

Tip;You should insert a 10 K Ohm pot P (Rrs) in series with the Rrs resistor to trim the negative output resistance starting at max pot R value, then vary between this pot and pot P4, i.e. for every setting of P (Rrs) the output will drift and has to be counteracted with P4.

If you also have a PSpice program available then itís very easy to model any driver in a closed box with a fixed Qtc and alter the virtual T/S parameters to target a new more suitable and preferred value of the Qtc at another chosen corner frequency.

b
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Old 30th June 2007, 10:52 PM   #3
bjorno is offline bjorno  Sweden
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Forgot to add:

R14 = 22k Ohm, seed value for Ra = 330k Ohm, R19 = 68 k Ohm, seed value for Rrp = 150k Ohm, seed value for Rlp = 68k Ohm, seed value for Ccp = 47nF, seed value for Ci = 0.22 uF.

b
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Old 1st July 2007, 10:35 AM   #4
durxter is offline durxter  Netherlands
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Bjorno,

Thanks for the quick reaction to my post!

Quote:
R14 = 22k Ohm, seed value for Ra = 330k Ohm, R19 = 68 k Ohm, seed value for Rrp = 150k Ohm, seed value for Rlp = 68k Ohm, seed value for Ccp = 47nF, seed value for Ci = 0.22 uF.
I didn't put those values in my circuit because they have to be calculated to get the parameters you want. But I don't understand how to determine the Amplification Constant (G) to get Rg. I hope you can explain that to me.

Another question about the ACE bass principle in common:
What is the advantage when using ACE-bass with a sealed box over a Linkwitz Transform Circuit? In a Dutch Elektor book about speaker design, the author mentions that for closed cabinets the ACE principle has no advantages over LT. I hear different stories about that. I thought that one of the advantages of ACE bass is that you donít need much extra power to go low, as with LT ( or ELF).

For the first tests I plan to use standard 7inch Focal woofers (in sealed enclosure), they donít have an extreme X-max and a max power of only 60 Watts. I hope this works out.

Durxter
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Old 1st July 2007, 04:45 PM   #5
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Quote:
Tip;You should insert a 10 K Ohm pot P (Rrs) in series with the Rrs resistor to trim the negative output resistance starting at max pot R value, then vary between this pot and pot P4, i.e. for every setting of P (Rrs) the output will drift and has to be counteracted with P4.
Or use a first order highpass with low cutoff-frequency at the input of the power amp (like Stahl's patent suggests !). It worked well for me with a 2Hz cutoff.

Regards

Charles
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Old 1st July 2007, 05:51 PM   #6
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Here is my effort. It only does negative resistance Qe whereas the ACE
tweaks the Compliance (VAS) and the moving mass
Will give much better results than a sealed box with LT in terms of cone excursion, voice coil heating and depth of bass from a given size box.
R26 should goto the junction of C16 and r15 to avoid DC offset problems.
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Old 2nd July 2007, 11:44 AM   #7
bjorno is offline bjorno  Sweden
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Quote:
..But I don't understand how to determine the Amplification Constant (G) to get Rg.
The global gain G relies of the open loop gain through the band pass filter (closed through the gyrator feedback) x the closed loop of the power amplifier = Ao being much larger than G.

As G is 1/R14 x (R18xR26)/(R46xR25) you can think of Ao as an inverting amplifier (in reality positive gain) with the input series resistor = R14 and the feedback resistor =(R18xR26)/(R46xR25).

Quote:
What is the advantage when using ACE-bass with a sealed box over a Linkwitz Transform Circuit?
I have never compared with LT and in a sealed box, I used my amplifier for small volume ported boxes (large ports) only and my favourite driver is the low inductance SS 21W85550.

The power transistors runs very cool as the energy transfer from the amplifier to the speaker has no troublesome VSWR at all, compared to the opposite when using LT at higher gain losses.

Quote:
Or use a first order highpass with low cutoff-frequency at the input of the power amp (like Stahl's patent suggests !). It worked well for me with a 2Hz cutoff.
Thank you Charles for this reminder, it would be very easy to incorporate this safety approach if a first order HP pole is placed at or below 2 Hz.

At time when I worked with the my amplifier I tested with 2 series 100 uF capacitors and 1N4148 diodes for the leak currents, connected bipolar at the inputs of R16 and R28 but later when I made circuit boards I eliminated these bulky capacitors with the offset pot.

b
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Old 2nd July 2007, 02:20 PM   #8
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Quote:
I have never compared with LT and in a sealed box, I used my amplifier for small volume ported boxes (large ports) only and my favourite driver is the low inductance SS 21W85550.
The real advantage IMO is indeed only when this circuit is used with a ported box. The interaction between drivers and box is as if the drivers actually had the simulated parameters - something that wouldn't happen if the "un - ACEd" driver(s) were used with the same box and tuning. But it can't change the laws of physics and so the efficiciency remains low at low frequencies. But it is able to take advantage of the reflex loading, especially in terms of driver displacement.

I assume that it has about nil advantage over an LTF in a closed box.

Regards

Charles
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Old 2nd July 2007, 07:30 PM   #9
durxter is offline durxter  Netherlands
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So actually ACE bass might not be worth the effort when using it with a sealed enclosure? Wouldn't it be easier then to use the patent of Yamaha (only negative resistance), since you will not get the simulated parameters when using ACE with a sealed box.

Do you have experience with that circuit?

Thanks
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Old 2nd July 2007, 08:43 PM   #10
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The desirable properties of a driver for a small vented box are low Vas (stiff compliance) low Fs and low Qts. The ACE is used to achieve these parameters. With a sealed box the matching of parameters is not so difficult and the response can simply be flattened with a LT. However when you look at the excursion its much lower with a vented box,
especially with a high pass filter making a sixth order design.
I do not think there is any advantage in using a complex ACE amplifier with a sealed box. Interesting idea though!
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