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Chip Amps Amplifiers based on integrated circuits

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Old 23rd April 2003, 01:12 AM   #41
Philo is offline Philo  United States
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T-guy,
Stick with the 541 for now and short the pin to to the output pins (5&7). Get a working prototype with what you got before you start second guessing. PM and and I have different tastes but IMO the 541 sounds better and more like the LM chips than the 549. I haven't tried the 548 yet as I went back to using 3875s (which I prefer) and 3886s after testing those two. All that aside...it's all a matter of personal taste. Get some of the LMs, test them out and decide for yourself. Its the only way you'll really know for sure. You don't want to be sitting in front of your amp and wondering if you picked the right chip based on our opinion, right?

Edit: PM is also a faster typist than I.
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Old 23rd April 2003, 01:19 AM   #42
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Well, I already have the 541's, so if it works by shorting the current limit pin, I guess it is worth a try. If I don't like it, I'll pull the parts off and change chips.

I am glad the OPA's sound good... I do a lot of work with headphone amps, and prefer the BB chips over anything I have tried so far. There is something about their sound that I like a lot... but I don't know enough of the comparative terms to describe it. Someday... I will add other chips and test. When budget allows...

Thanks for the help.
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Old 23rd April 2003, 01:26 AM   #43
Philo is offline Philo  United States
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No prob. The great thing is the popular chips all sound great but just have a different personality. Note: I put the RC circuit on the +input to ground like in the original Thor amp and used the inverted input. Just sounded better to me.
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Old 23rd April 2003, 09:43 AM   #44
miguel2 is offline miguel2  Portugal
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Quote:
... if it works by shorting the current limit pin...
I made a GC with the OPA541 and I shorted the pins. You just have to put a drop of solder between pins 7 and 8 (I believe these are the numbers, output and limiting pin). Dont bother with pin 5. And when you have it done, please allow it to cool down for a couple of days (and breath deeply because it is functioning ).I found that it sounds very bad in the beginning but then it gets right. And use a test speaker on the first time, so if something goes wrong you dont damage your nice speakers.

Philo, can you describe the differences between the OPA541 and the 3875? I am wondering about it too, but I would like to know more before splashing out 15 euros... Is this a big difference?
Have you tried the RC connection for the + instead of the 18k resistor? Did you have the 22k resistor from - to ground?

Miguel
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Old 23rd April 2003, 03:22 PM   #45
Philo is offline Philo  United States
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I had a 22k resistor and .01uF mylar connected fromthe + input to ground and the signal fed to the - input in an inverting configuration. Basically, Peters design plus the RC. I like the somewhat warmer sound of the LM3875 over the dryer abiet flatter response of the 541. Possibly my old B&W speakers have a dip in their response curve in the mids and the 541 sounds thinner with them. I have only A/B compared the chips using those speakers. The LM chip has more forward vocals and seems more musical and involving to me. Don't get me wrong, I like the sound of the 541, and the differences are minor but I just prefer the sound of the LM chip a little more. I have listened to about a dozen different speakers with my LM3875 amp and have yet to find a combination I didn't like. The funniest comparison was against a high dollar Yamaha A/V receiver of a neighbors who uses Klipsch ceiling speakers for his rear surrounds. The difference was even very noticable there, and yes, we hooked the ceiling speakers to the front outputs of the receiver to make sure the comparison was fair.
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Old 23rd April 2003, 06:51 PM   #46
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I created a pc board layout for this amp last night... however i am at school and do not have my screenshot to show you for checking. Will someone go over it for me and give me some feedback? Thanks

Also... I have a few questions. Should I use a Piher or Alpha/Zicon pot? Is 10k too small a value for this amp? Gain of 21 sound ok?

I also plan to have a sub out... so, I will take the RCA input and split it to go to the amplifiers and to a 1/4" jack (my sub is a prosub with 1/4" inputs). Should I just run both channels together on a mono out? I am pretty sure the amp is mono in. Or, should I use two jacks and run one to each amp input? I may have to put a preamp on this-- no problem whatsoever.

Thanks all
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Old 24th April 2003, 01:50 AM   #47
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OK, I had an idea... hopefully someone can give me some feedback on it. Here goes:

I wanted to include a sub pre-out for a powered pro sub I will be acquiring from a friend. So, I needed an xover for this, and I had planned to buy an inline passive one from PartsExpress. However, it is $15, and I really don't want to spend that. I also wanted to cross the mains over to play 100Hz and up. So... it was going to cost a lot.

But, I read some about active xovers, and figured some up... they can be CHEAP! I have tons of little chips laying around... will probably use OPA2132/OPA2134 for mains xovers and OPA2227 for sub xover. I like the sound of the OPA2132 better than the 2227, which is why they are in this order. So... lets say I put the mains HP at 100Hz, and the sub LP at 120Hz. This should work fine, right? I will also be using active xovers for my mains now... 2000Hz LP for woofer, 2000Hz HP for tweeter. Example:

input-->120HzLP-->sub preamp (gain=4)-->sub volume pot-->sub out
|
-->mains volume-->100HzHP-->2000HzLP-->OPA541 woofer amp-->woofer
____|
____-->2000HzHP-->OPA541 tweeter amp-->tweeter

Will this work? Should I sub the chips in either the tweeter or woofer section?

Thanks
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Old 24th April 2003, 02:02 PM   #48
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A few days ago I found a post with the zip file of the latest gainclone schematic that Peter Daniel uses. I have searched again but I cannot find it. If someone knows the link or has the latest schematic and partlist please post it.

Thanks
George
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