Also thinking of trying this.
Buy an lm1875 kit.
Connect a plug where the chip goes.
use a connector on each amp.
Then I could have a modular amp and test different amps, plugin the lm1875, unplug, plugin lm3875, unplug, plugin opa549, etc., till I find the one I like.
Should be able to use the same +-25 power supply for all of them.
Buy an lm1875 kit.
Connect a plug where the chip goes.
use a connector on each amp.
Then I could have a modular amp and test different amps, plugin the lm1875, unplug, plugin lm3875, unplug, plugin opa549, etc., till I find the one I like.
Should be able to use the same +-25 power supply for all of them.
I'm putting together an OPA541-based sub amp with integral electronic crossover. I used 3/4 of an OPA4134 each side for buffer/filter. As usual, the biggest problem is getting the thing into a case. I considered using bridged 541s, but decided it's not worth the trouble, as my sub is really efficient. Probably the biggest advantage of the National chips over the Burr-Brown/TI equivalents is the higher supply voltage capability. I'll be running my 541s at about +/- 30V to keep away from the 40V supply limit. However, I like the JFET input on the 541s, as it allows yiou to use a film cap instead of an electrolytic cap to make the chip unity gain for DC so as not to pass on any more offset than is necessary. Sound? I'll find out sooner or later...
you could check ti's opa548 based 'complete audio amplifier ' . Don;t forget the Vref pin and you're about set. page 4, fig. 5.
pretty much speaks for itself. except for psu bypassing. You could use the "standard" 100ouF per rail or a regulated supply.
hmm, there's an error in the link given above. On page 4, in fig. 5 r14 (snubber/zobel, whatever you call it) should be 1 ohm in stead of 1 kilo ohm.
pretty much speaks for itself. except for psu bypassing. You could use the "standard" 100ouF per rail or a regulated supply.
hmm, there's an error in the link given above. On page 4, in fig. 5 r14 (snubber/zobel, whatever you call it) should be 1 ohm in stead of 1 kilo ohm.
The schematic I like is using this chip with National's BR-100W circuit in AN-1192 or something like that.
You can download the AN-1192 from www.national.com. And if you want a PCB, I have one that works well (i use it on my home built comp. speakers sub and am very satisfied, especially with the entire system running off of two 16V 10W doorbell transformers. The entire system is two 3886 for the satellite speakers and two bridged 549 for sub). Let me know if you want it, it's on my other computer and I can get it later.
You can download the AN-1192 from www.national.com. And if you want a PCB, I have one that works well (i use it on my home built comp. speakers sub and am very satisfied, especially with the entire system running off of two 16V 10W doorbell transformers. The entire system is two 3886 for the satellite speakers and two bridged 549 for sub). Let me know if you want it, it's on my other computer and I can get it later.
Heres a direct link to AN-1192: http://www.national.com./an/AN/AN-1192.pdf
I can have the pcb by tonight.
I can have the pcb by tonight.
Sorry to throw a wrench into the proceedings here,but... Rebuilt my NI LM1875 amp on the weekend,this time with pc boards,so no more $%#$! broken leads.Sounded awful at first (new parts),but has about 30 hours on it now and sounds much better.Hooked up to my cheap crappy test speakers,the OPA549 amp sounded much better than the LM1875.But-surprise-on my good speakers the LM1875 was better.Thought that since I hadn't heard the OPA amp for about a week that I might be wrong,so after listening to the LM amp for a few hours last night, I hooked the OPA amp back up.No contest- the LM chip wins.In comparison,the OPA chip has an exaggerated midrange which gives the "warm" sound that I liked from this chip,but it is definately more distorted sounding than the LM amp. Not the results that I was expecting,but that's how it turned out. One thing that I should point out here is that I can't help but notice that,in all of the various configurations I have tried the LM1875 in,it has never sounded particularly good driving multi-way speakers,probably due to the low output power.
I think you are asking a question that there is no real answer to- which chip is "better".As I mentioned in the above post the OPA549 sounded better with my test speakers,and the LM1875 sounded better with the speakers I usually use. Does this really mean that the LM1875 amp is the better one??? Or the OPA549??? I think which chip is "better" depends a lot more on the equipment that you are using it with than the chip itself. I will make a suggestion that will hopefully help- the most expensive part of building these amps is the power supply. If you are thinking about trying more than one chip,try to get chips that will operate using the same supply voltage as each other. That way you will be able to use the same power supply for all of the chips that you are experimenting with and keep your costs at a reasonable level.
mrskinny,
Sorry I didn't get back to you earlier, but I only really get onto the forum at weekends at the moment...
So the 549 you built was NI or I? If NI, then definately swap it over, it should be fairly simple. My layout is based on the original Thorsten schematic, not the current PD inspired minimalisation, but rejigged for the pinouts of the OPA.
I use 1000uf per rail at the bridge, with another 1000uf at the chip, and a 0.1uf vifa polyprop across the rails. Oh, and a dual bridge PSU as well. Gain set with 22k/220K resistors.
Sorry I didn't get back to you earlier, but I only really get onto the forum at weekends at the moment...
So the 549 you built was NI or I? If NI, then definately swap it over, it should be fairly simple. My layout is based on the original Thorsten schematic, not the current PD inspired minimalisation, but rejigged for the pinouts of the OPA.
I use 1000uf per rail at the bridge, with another 1000uf at the chip, and a 0.1uf vifa polyprop across the rails. Oh, and a dual bridge PSU as well. Gain set with 22k/220K resistors.
Thanks for the reply Pinkmouse. No hurry,I don't always have the time to spend on the forum myself. The OPA549 amp that I made is an NI amp,used with dual mono regulated supplies.Sounds good in this configuration,but after listening to it for a few weeks I felt that the amp was "missing" something. Next time that I go for some parts I will try this.
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