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Old 27th October 2003, 09:45 PM   #1
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Default Line level XO and gainclones

Hi

I'm building 4 inverting gain clones which are to be used to drive my 2 way setup. (Fostex FE206E OB and jbl2225 sealed)

I was planing to do something like Pedja (http://www.geocities.com/react_71/au.../gainclone.htm)

For high/midrange I planing to use a 6db hp filter and some lp filter to remove hf garbage and a 6 or 12 db filter for the bass.

The best documentation I have found so far is:
http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
http://www.silcom.com/~aludwig/Sysde....htm#Bi_amping
It have given me some clues, but also some questions.

And now for the questions:
For the lowpass, 2 resistors in series will affect the gain right? Should I just add the value of all the resistors in series and use that to calculate the gain?
For the highpass how do I calculate the values when I need to combine a hp and a lp filter?
Or better yet, where can I read about this (see some examples (LLXO for dummies))?
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Old 27th October 2003, 11:25 PM   #2
GregGC is offline GregGC  Canada
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If you can post a schematic it'll help?
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Old 28th October 2003, 12:00 AM   #3
GregGC is offline GregGC  Canada
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If you are looking at the Pedjaís circuit those HF filters are kind of weird. The higher the frequency, the higher the gain of the amp. Starts at F=6.3*(Rout +R1)*C1). C2 makes it even more complicated. The gain goes up but the filter suppresses the HF more, so itís pretty tricky. Mind you the effect becomes smaller the smaller the Rout+R1 is compare to the 9k resistor. So if Rout+R1 has similar value to 9kOhm, than the gain will increase 2 times for HF. So if Rout+R1<<<9k, then F=1/6.3*(Rout+R1)*C1 if C2 is not installed and the gain will change very litle.
For the LF, F=1/4.7uF*6.3*(R1+9k).
I hope Iím not missing anything.

Greg
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Old 28th October 2003, 08:09 AM   #4
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I haven't got a schematic yet. I wanted to do an XO without using opamps.

Wow it is that simple (joke).

If I add a buffer more after the XO I will get a more "normal" filter response. So I end up with: buffer -> hp -> hp -> buffer -> gainclone.

How about combining a 6db lp and a 6 db hp after each other? How will they affect each other? Should they also be separated by a buffer to get some normal filter responses?
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Old 28th October 2003, 09:06 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Quote:
I haven't got a schematic yet. I wanted to do an XO without using opamps.
May I humbly suggest looking at THIS

Ridiculously simple but works very well (and no opamps)!
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Old 28th October 2003, 02:43 PM   #6
Previously: Kuei Yang Wang
 
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Default Re: Line level XO and gainclones

Konnichiwa,

Quote:
Originally posted by Flemming J P

For the lowpass, 2 resistors in series will affect the gain right?
Yes.

Quote:
Originally posted by Flemming J P

Should I just add the value of all the resistors in series and use that to calculate the gain?
Yes and no. This is a little complex. You may be better off using fully active filters placed around the Chip Amplifiers. AD (IIRC) has a suitable on-line calculation tool that handles inverting filters up to high order, HPF and LPF.

Here it is, I did RC....

http://www.analog.com/Analog_Root/st...er/filter.html

Simply select MFB LP (or MFB HP) and fill in the blanks and it gives you a schematic for the whole filter. If you like, tell me what Order X-Over you want and what particular frequency and I run the Filter Designer and post the results here.

Sayonara
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Old 28th October 2003, 03:32 PM   #7
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by Nuuk


May I humbly suggest looking at THIS

Ridiculously simple but works very well (and no opamps)!
There is a way to simplify even more. As long as you use even numbers of filter sections you can alternate NPN Transistors as follower with the J-Fet CCS to the negative rail with PNP Transistors as follower with the J-Fet CCS to the positive rail for the LPF. If the NPN and PNP transistor are thermally coupled you remove the output offset completely and you can dispense with coupling capacitors entirely.

Equally, if you include an added PNP Follower after the final HPF section (maybe implementing a mild LPF while at it?) you can limit the cap's used again strictly to those in the filter.

Sayonara
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Old 28th October 2003, 04:53 PM   #8
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what about that AC-coupled in and out jfet stage? it makes a high input impedance inveting amplifer.

also, what happens when the gain is dropped below 10 on the gainclones? for inverting you could just add a cap either in series with the input for highpass or in parallel with the feedback for lowpass, unless it would mess up with a gain < 10. national does this near the edge of the audio spectrum in the datasheets.
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Old 28th October 2003, 09:04 PM   #9
Pedja is offline Pedja  Serbia
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Hi Flemming,

First, if you use FE206E (96dB/W(m)) and expose the tweeter directly to the ampís out, then with buffer Iíd strongly suggest usage of delayed power-up for the output opamps. (The only good buffer that I can think of at the moment and which still can make you pretty free of power up thump is the diamond transistor.)

I think the thing can be done two ways. First, you can use two whole buffer/filter/opamp circuits, one for each section. The second option assumes one buffer. I can only guess what will be better.

(those triangles at left are symbols for the buffers and not for the opamps )

Click the image to open in full size.

In fact, in both cases either section is band passed. As crossover elements, the coupling capacitor would be used for high-, and shunt capacitor for low-passing. Gregís equations are ok with that addition, considering necessary capacitance for the LPF, R1 should be probably in the kOhm range, and hence 9k resistor should be calculated in parallel with Rout + R1. For the 2SK170 buffer biased between 5 and 10mA, Rout is between 30 and 25 Ohms, so if R1 is 1k or more, Rout can be neglected.

To make the designing of the filter more controlled: donít tune the frequency by the resistors, first estimate what would be optimal values of the series resistors, then determine appropriate feedback resistor. Use the caps to tune the filters frequencies.

If you have some determined crossover frequency I could simulate the passive LLXO. Let me know. Also, what is the sensitivity difference between the drivers (if you intend to match their levels using the adequate gain in the amp sections)?

Second order filter might be a bit longer story.

Pedja
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Old 28th October 2003, 10:04 PM   #10
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I have a question about using either passive or active XO that are located between power amp and preamp.The drivers are connected directly to the amps.
But what about the tweeter.Does it have to have some cup (say some 50uF) to protect it from DC.Maybe delay relay at the output of the amp would be enough.Any thoughts on that topic?
Bartek
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