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Old 9th July 2004, 02:14 PM   #21
moamps is offline moamps  Croatia
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Default Re: Re: Industrial SMD Gainclone - group buy

Quote:
Originally posted by Kuei Yang Wang
How about an active 2-Way bi-amplifier build around LM3875 with an inverting Highpass (3rd Order) and an Inverting Op-Amp as subtractive Filter for the LF. Then apropriate EQ networks in the NFB of the LF section (correction for usual rising MF in most moder "Bass/Mid" drivers) and possibly in the HF section for the high frequencies.
New-old idea?
Quote:
Originally posted by Kuei Yang Wang
I for one would like to see someone make a minimalist "BiAmpliFiddler" design with LM3875 and a subtractive X-Over plus switchable suitable HF & LF EQ circuits with bridge Amp's for woofer and Tweeter to be used in activating the common 2-Way HiFi Speakers. Now for that a neat layout (grounding etc) and vestigal PCB would be great.
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Old 9th July 2004, 02:17 PM   #22
tiroth is offline tiroth  United States
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Quote:
Originally posted by peranders
http://www.apexjr.com/alesis.htm
Not exactly as my project but similar.
Check out this cute pcb!
Hey, I still have a couple of those. They are now missing the LM ICs though.
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Old 9th July 2004, 02:33 PM   #23
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Default Re: Re: Re: Industrial SMD Gainclone - group buy

Konnichiwa

Quote:
Originally posted by jackinnj
I worked out the PCB design for the above -- enough op-amp power for the buffer, cascaded LR (1) XO and a phase correction circuit (2). As I read more I decided that it would be a lot more than a beginner/kit project, and if not implemented carefully would lead to "the weaping and gnashing of teeth !", i.e. unhappy customeres.
You clearly misunderstand what I propose, namely:

1) Input Buffer
2) 3rd order inverting highpass around the Power Op-Amp (Chip Amp) to drive the tweeter (good reason for 3rd order)
3) Inverting summing circuit that combines the Tweeter signal and the fullrange input signal to derive the lowpass for the LF Driver, LF Eq if required in the feedback loop of the LF Chip Amp

It means the addition of minimum of parts, the provision of the only possible "squarewave perfect" crossover and the needed LF eq with a minimum of added parts. No Op-Amp's other than the Power Amp's, buffer to be open loop.

Quote:
Originally posted by jackinnj
Without some method of measuring the output -- both magnitude and phase (not everyone has a portable PC with a sound card, or an FFT analyzer) it just looked to me as a project which would frustrate more than help.
Given that we'd replace simple build in X-Overs with a usually very low parts count - nope, using the right "perfect summing" crossover and equalising the woofer only works fine. Try it. The LF Eq can be tuned usually by ear and/or guesswork very close.

Sayonara
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Old 9th July 2004, 04:11 PM   #24
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Default Re: Re: Re: Re: Industrial SMD Gainclone - group buy

Quote:
Originally posted by Kuei Yang Wang
Konnichiwa

You clearly misunderstand what I propose, namely:

1) Input Buffer
2) 3rd order inverting highpass around the Power Op-Amp (Chip Amp) to drive the tweeter (good reason for 3rd order)
3) Inverting summing circuit that combines the Tweeter signal and the fullrange input signal to derive the lowpass for the LF Driver, LF Eq if required in the feedback loop of the LF Chip Amp

It means the addition of minimum of parts, the provision of the only possible "squarewave perfect" crossover and the needed LF eq with a minimum of added parts. No Op-Amp's other than the Power Amp's, buffer to be open loop.

Given that we'd replace simple build in X-Overs with a usually very low parts count - nope, using the right "perfect summing" crossover and equalising the woofer only works fine. Try it. The LF Eq can be tuned usually by ear and/or guesswork very close.

Sayonara
Model the above before you solder it up.
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Old 9th July 2004, 04:18 PM   #25
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Default Re: Re: Re: Re: Re: Industrial SMD Gainclone - group buy

Konnichiwa,

Quote:
Originally posted by jackinnj
Model the above before you solder it up.
I designed and build something along these lines in the mid 1980's. Trust me, it works quite well.

Subtractive X-Overs and wrapping the X-Over around the Power Amplifier are ancient concepts and have been repeatedly documented.

Sayonara
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Old 9th July 2004, 04:37 PM   #26
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Default Re: Re: Industrial SMD Gainclone - group buy

Quote:
Originally posted by Kuei Yang Wang
While I like the SMD part, may I ask why not make something unusual, instead of just another 1/2 Channel Amp?
Unusual, how many SMD Gainclones are there out there, I mean complete products? This is the first so I may not call it common.

The other reason I want to do this is because it's rather small as a project. My time is limited so I can only work on small projects.

Active cross-over is a good idea Thorsten, but not for me at the moment.

The challange for me here is to make a perfect solution with the given specifikations. The last QRP01 project went very well. A 100% correct pcb without any prototyping, perfect function out. Everybody are pleased. This was really cool to achieve such result. Ok, I worked on the design for over 6 months on and off.

The concept here is a simple buffered inverting Gainclone, nothing more. I want also to keep the number of parts down so it won't get to mighty for the skilled builder. Note that by skilled I mean people with a decent soldering iron, a pair of good tweezers... and steady hands. As long as you see well and don't tremble too much this is not going to be hard. My other SMD projects have been very easy to get going. Noone have had ANY problems. Can you believe that?
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Old 9th July 2004, 05:49 PM   #27
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Default Re: Re: Re: Re: Re: Re: Industrial SMD Gainclone - group buy

Quote:
Originally posted by Kuei Yang Wang
I designed and build something along these lines in the mid 1980's. Trust me, it works quite well.

Subtractive X-Overs and wrapping the X-Over around the Power Amplifier are ancient concepts and have been repeatedly documented.
I expressed my interest in this project already on previous occasions, and if you are still game for that, we might do some prototyping. This of course requires your input with filter calculation and overall support. I believe Brian wouldn't mind coming up with few test boards and the whole project could be made on purely non-profit basis, as an excercise in proving ancient concepts
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Old 9th July 2004, 06:30 PM   #28
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Default Re: Re: Re: Re: Re: Re: Industrial SMD Gainclone - group buy

Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,

Subtractive X-Overs and wrapping the X-Over around the Power Amplifier are ancient concepts and have been repeatedly documented.

Sayonara
Model it and look at the phase response.

I am not averse to seeing how it sounds, but am curious to see how the 45 deg phase shift (for the LF) affects the results.
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Old 13th July 2004, 04:11 PM   #29
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Default To Kuei and Peter Daniel,

As a quiet lurker, I would greatly appreciate any progress made on the Subtractive-Active-Current-Clone (SACC) project--and I'm sure I'm not the only one!

As a start, a schematic would be very helpful.

As for the Seas coax, a few have the clear cone (TPX) that is reported to sound quite decent:

T17REXCOAX 17cm
T17RECOAXTV 17cm shielded
T18RECOAXTV 18cm shielded

These drivers are under ~$100 US, easily available in Europe and North America and I think they would make a great experiment base to try different enclosures (sealed, ported, open baffle) and different crossovers (simple passive--cap on tweet, complex passive, active, active with current drive). And the shielded ones could be used for home theater to boot!

The low cost and wide setup possibilities could give us a reference (small "r") from which we could speak a common language. (Another reference could be the Linkwitz headphones (Sony EX71SL ~$50 US) with notch filter--see Linkwitz site)

And finally, a Seas Coax could be used with a dipole woofer (http://www.mfk-projects.com/dipole_pa_system.htm scaled down for 15" with Eminence Beta 15s ~$50 US each) to produce a half-decent system (wide range, reasonable SPL) at low cost.

So please, any progress would be greatly appreciated!
Thanks,
Jeff
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Old 13th July 2004, 09:59 PM   #30
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Now it comes to mind -- Nelson wrote an article for Speaker Builder in 1982 ("Phase Coherent Crossover Networks" SB 2/82) where he discussed the subtractive XO -- the magnitude response has a bump which, he stated, has to be dealt with via manipulation of the Q of the network.

FWIW, I modeled the results of Nelson's paper (He uses Sallen-Key -- without Q manipulation first. Here's a screenshot of the schematic and bode plots. I used MFB and the results didn't look right. I guess this is why Nelson is in the XO biz:

It looks worth a try:
Attached Images
File Type: gif phase.gif (52.2 KB, 553 views)
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