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Old 19th March 2003, 01:00 AM   #31
Diode is offline Diode  United States
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Hey Philo,

Thanks for the web site.... I will look them up. I have built 7 kits that deliver 366W into 4 Ohms. I want to build one from scratch this time. I use the others in my home theater and really like them so far. I have been using a Crown CE-1000 for my subs but the input of pro audio needs to be a lot higher than home stuff and I haven't built a pre-amp to do that yet so my subs are weak. I want to build an amp from scratch and if it does well, I'll build 2 and use them for my subs. My subs are Shiva's and are a bit power hungry. Great sub though!!! Yes, my Crown can handle that but I have another use for it anyway.

Chris
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Old 19th March 2003, 01:53 PM   #32
rickpt is offline rickpt  Portugal
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Hi Chris

The output I use is a triple follower. Exactly equal like the one on the picture with different resistor values, so just one RC on front of the first driver. By the way the one on the picture will work without any modification

And try this amplifier on your main system; maybe itís better than your kit amplifier. I think you will like it

about Randy Sloane amp, I donít like it for the same reason I have mentioned before about the AV800 and it uses the very expensive double die mosfet by semelab. I think the one you are doing with the mods, has better performance and you will learn a lot more doing a design from scratch than doing a kit: cool:

Good luck for your project

Best regards

Ricardo
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Old 19th March 2003, 11:28 PM   #33
Diode is offline Diode  United States
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Thanks Ricardo,

I will be working on it but I will probably still be posting on this thread with other questions and comments. I hope you check in from time to time.......

talk to you later,

Chris
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Old 20th March 2003, 01:04 AM   #34
Philo is offline Philo  United States
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Ricardo,
Your right about the learning process, doing it from scratch is the best to really learn about amp design, but sometimes the hard way. No offense, I just posted Randy's website because of the earlier remarks and he stands behind his designs and products faithfully and will write you back if you have trouble. After building a few older, mod'ed designs, I got tired of doing endless part searches (although, I am back doing it now for some Alephs) it was nice change to build from a kit that already had matched transitors and the gain values were hashed out. I am not sure of what terms you are speaking about when you say "better performance", though.
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Old 20th March 2003, 03:35 PM   #35
rickpt is offline rickpt  Portugal
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Hi Philo

I agree whit your post, I was just talking about the design of that particular amp on the pic you posted I even have a book by Randy Sloane

About performance...
Again I say that I donít think that driving mosfet whit high source impedance is a good design practice...
The output impedance of the vas stage (a cascode vas will be even worse for obvious reasons) with the capacitance of the mosfet will form a very big RC filter and you will end with a very slow and non linear output stage. and in the end, a slow amplifier. Not my cup of tea

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Ricardo
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Old 20th March 2003, 09:05 PM   #36
Philo is offline Philo  United States
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That's what I thought you meant. I agree about the sound but it not always true, keep your capacitance matching on the low side seems to help as well as using some very small bypassing caps. As you mentioned before you have to watch your stability. Judging by Chris's other equipment he has an affinity to the pro-sound and "performance" usually translates to durability and sustained raw power.
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Old 20th March 2003, 11:40 PM   #37
rickpt is offline rickpt  Portugal
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Hi Philo

Why the capacity needs to be low? Why you need bypass caps? And why you have stability problems without them? And why high power amplifiers canít have good audio performance?

Sorry all the questions

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Ricardo
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Old 21st March 2003, 12:29 AM   #38
Diode is offline Diode  United States
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Judging by Chris's other equipment he has an affinity to the pro-sound and "performance" usually translates to durability and sustained raw power.

Yes, performance is key. I am NOT into PA systems and the like. Actually, I bought the Crown amplifier as a last resort because I couldn't find an affordable, high power, good sounding subwoofer. I was ignorant to the input requirements of "pro audio" Those amps need a lot more PK-PK signal to drive them well. Home audio is much more sensetive and can amplify small signals better. My other amps were kits and I got them on a clearance sale. They weren't designed with adequate heat sinking OR output devices. They could stand at least 2 more output devices per rail and a honking big heatsink. The power transformers are a bit under rated. Since I never use their full power output, they run just fine and sound good as well. The rails are supposed to be +/- 75VDC @ 8A but are hardly that. At full power, the rial voltage drops to 68V. With only 2 2N3773 output devices per rail, well, I only get 244W RMS into 8 Ohms. I get 366W RMS into 4 Ohms but the heatsinks get hot enough to fry eggs with. TOOOO hot!!!!! They suggest a fan to cool it with but I'm fresh out of Hurricanes! LOL My thinking and experience about a lot of power. I have always heard high power amps with good speakers and the detail is wonderful and if it needs to go loud and clear, ie. a big transient, it can and still be very clear and responsive. Car audio, for example, I have never heard a good subwoofer, that was clean and extremely responsive, that had a low power amp. They ALWAYS have a huge amp and a lot of headroom. I know that the drivers have a lot to do with it as well but you can see my concept here. Well, I bought my subs and they are called Shiva subwoofers. They can take a lot of power so I don't overdrive the driver or amplifier. Those 2 things, in my book, equal clean, responsive sound.

Chris
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