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Old 15th April 2012, 06:42 PM   #2401
hahfran is offline hahfran  Germany
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Three amps for a 2 1/2 way speaker are much cheaper than hi grade passive crossovers
one tin foil 10F 150 Volt (DC not AC!!) capacitor alone costs almost as much as the parts for 3 amps not to mention the even more expensive inductors. In fact BJTs resistors transfomers elcos heatsinks cost me nothing as I have those. The only expense so far is 6 complimentary pairs of On semi therm traks for 30 euros. A handful of caps opamps trimmers for 6 amps may cost another 30 euro at most and that's it for two speakers.
The most expensive of all will be the case of the speakers its a complicated design and solid hard oak.
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Old 15th April 2012, 07:12 PM   #2402
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Quote:
Originally Posted by hahfran View Post
Basically this is not new thinking anymore , the makers of active speakers are considering amp and speaker and box and acoustics of listening rooms as one system, not as independent separated devices.
If the package is considered as a system than you could easily transform it in a way to work with noninverting amp.

SSA can be used as inverting amp, I draw you sch in post#2392, only that in this case an input impedance drops to 1,5 kohm.
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Old 15th April 2012, 07:15 PM   #2403
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Originally Posted by guitar89 View Post
LC, also with your BIBGT HP SSA, what is the heat dissipation of input & cascode, and VAS ? If its too low then the need to more thermal compensation, and vice versa ?
Power dissipation can be calculated for each part at idle state conditions, start with input bias current level and than go gradually from part to part.
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Old 15th April 2012, 07:33 PM   #2404
hahfran is offline hahfran  Germany
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Originally Posted by keantoken View Post
The BC5x0 have low noise and far better Vce characteristics at low voltages. The BC337/327 have even better Vce characteristics, but different gain specs. The BC5x0 should perform exceedingly well here I think.
for all BJTs of the epi planar technologies the same rule applies : the min of noise ( there are several causes of noise and several types of noise) is achieved at ic around 200 A to 500 A this comes combined with low fT or min of GBW and worst hfe/ic linearity. The best hfe/ic linearity and max of GBW comes at ic 10 mA. There noise has a maximum. This is just semiconductor physics. Also pnp can be made with less noise than npn.
The semiconductor designer and process engineer of BJTs has more parameters to optimize than the ones for FETs. Thus it is indeed possible to have very closely matching complimentary BJTs but not so for complimentary FETs. There are no truely complimentary junction FETs. Also complimentary
MOSFETs are impossible because of the gate source capacity. If rds on matches, the gate source capacity of the p channel must be twice as high as for the n channel. If in turn the capacities match then rds on will not match. There is no way to bypass semiconductor physics.
While power Bjts as ring emitter or multi emitter can be made perfectly complimentary if these are current driven, i.e. in terms of hfe/ic, the capacities CB , BE , are also different by around factor 2. This has to do with the majority carrier velocity , "electrons" are two times faster than "holes".
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Old 15th April 2012, 07:37 PM   #2405
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Since I was not pleased with thermal stability of this one, I tested improved CCS today. It looks that this one is going to end in SSA BIGBT HP.

Specifications are quite impressive for home DIY conditions, especially DC stability, load current regulation (1 uAmax/25C), thermal current drift dependency (5 uAmax/25-75C). AC performance also get a little better from previous version, noise floor is still well below -100 dB, but signal rejection ratio went down to -84 dB/100 kHz/100 ohm (8 Vpp 100 kHz sine signal according to 0,5 mVpp ripple on 100 ohm load resistor).

This one is confirmed, finally.
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Last edited by Lazy Cat; 15th April 2012 at 07:48 PM.
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Old 15th April 2012, 07:44 PM   #2406
hahfran is offline hahfran  Germany
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Originally Posted by Lazy Cat View Post
If the package is considered as a system than you could easily transform it in a way to work with noninverting amp.

SSA can be used as inverting amp, I draw you sch in post#2392, only that in this case an input impedance drops to 1,5 kohm.
no that would not yield a CS amp.

The problem is that using the amp as inverting as you proposed , it becomes unstable as seen as ringing at square wave edges. This can be avoided by making the OL bandwidth lower
- not higher to my suprise- thus that OL bandwidth is about 20 kHz. However
as not inverting OL BW is > 100 kHz with perfect rectangle even at complex load. I think I have to have on a nice PC board to avoid any coupling or whatever effects.
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Old 15th April 2012, 09:47 PM   #2407
mikelm is online now mikelm  England
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Quote:
Originally Posted by Lazy Cat View Post
only that in this case an input impedance drops to 1,5 kohm.
If non inverting i/p is grounded the inverting i/p's become one diode drop above/below virtual earths.

Feeding the i/p signal into these two offset virtual earths via the gain resistors gives an i/p Z of Rg/2 which would be of the order of about 100R

Or did I miss something ?

Last edited by mikelm; 15th April 2012 at 09:53 PM.
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Old 15th April 2012, 10:01 PM   #2408
mikelm is online now mikelm  England
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Quote:
Originally Posted by hahfran View Post
no that would not yield a CS amp.

The problem is that using the amp as inverting as you proposed , it becomes unstable as seen as ringing at square wave edges. This can be avoided by making the OL bandwidth lower
- not higher to my suprise- thus that OL bandwidth is about 20 kHz. However
as not inverting OL BW is > 100 kHz with perfect rectangle even at complex load. I think I have to have on a nice PC board to avoid any coupling or whatever effects.
If you are not really interested in the fantastic speed of this design or you have to slow it down very much to make it work well in your scheme - you seem to be moving away from the core design feature of SSA.

I think it would be much easier for you to realise your project with a different topology.

I think a folded cascode would work better if speed is of interest to you or any LTP design if it isn't.

mike
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Old 15th April 2012, 11:07 PM   #2409
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Quote:
Originally Posted by mikelm View Post
If non inverting i/p is grounded the inverting i/p's become one diode drop above/below virtual earths.

Feeding the i/p signal into these two offset virtual earths via the gain resistors gives an i/p Z of Rg/2 which would be of the order of about 100R

Or did I miss something ?
Exactly, even lower, 50 ohm (two 100 ohm parallel), me too fast, no thinking ...
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Old 16th April 2012, 06:13 AM   #2410
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by mikelm View Post
If you are not really interested in the fantastic speed of this design or you have to slow it down very much to make it work well in your scheme - you seem to be moving away from the core design feature of SSA.

I think it would be much easier for you to realise your project with a different topology.

I think a folded cascode would work better if speed is of interest to you or any LTP design if it isn't.

mike
I have an even faster topology which is an inverting current feedback but with that it is difficult to take advantage of the therm trak.
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