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Old 11th October 2006, 08:33 PM   #1
juma is offline juma  Germany
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Question Inverted OPA549 - question for those who tried it

Browsing some old threads I found some nice words about OPA549 in inverted topology (Pinkmouse). My friend recently got some of this chips and is pressing me to try them. People who tried it wrote that it gives its best at gain 2-4 as inverted opamp. It calls for a pre-gain stage with gain of about 6. I thought to use AD823 since it swings rail-to-rail and from my previous experience I know that it sounds very good.
With +-17V supply it can swing at least +-16,5 V on 2K load and with OPA549 (+-28V supply) with gain of 3 it should be enough to make a nice amp.
I enclose the preliminary schematic.
If you did something similar please share your experiences (stability, sound, etc...).

Thanks
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Old 11th October 2006, 09:06 PM   #2
Alcaid is offline Alcaid  Norway
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You can use a gain of up to 10 with the OPA549. I've tried both inverting and non-inverting. My main amp is non-inverting OPA549, but now I'm listening to a proto bridged OPA549 with one inverting and one non-inverting driving each phase, input buffered by an OPA627. Made this just to use some low voltage toroids I had lying around.
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Old 11th October 2006, 09:27 PM   #3
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Hi Juma

Iím glad you started this thread.
I had a similar idea a couple of month, I posted a thread but I got side tracked with a speaker project.
I have an amp with the OPA549 in bridge mode with a DRV134. The gain is 13, the gain is a little high but I had to match it to another ampís gain. With this gain the highs are OK but the midrange is better.

When I find the time, I will try it with the OPA541
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Old 12th October 2006, 08:12 AM   #4
juma is offline juma  Germany
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Hi guys,
I'm glad you found this chip worthy of listening in the longer period of time. So, it must be worthy of building an amp around it.
What are your power supply voltages and did you measure the output power? What about the heat(sinking)? Are your's PS regulated - considering that OPA549 hasn't got much of a PSRR in higher freq. region ?

Thanks
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Old 12th October 2006, 09:00 AM   #5
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As this thread is all my fault, it's probably only reasonable if I contribute. My nicest GC yet was a balanced input inverted 549, using the INA137 with a built in gain of two, and the OPA set up to have gain of 10, built for a friend who wanted a small amp to drive monitor speakers from a desk for mobile recording duties. It ran on 25V rails with a conventional PSU of 6000uF of Rubicon ZA per rail, with MBR 20100 rectifiers, dual mono aprt from the trannie, (250VA). That was a couple of years ago, and I believe it's still working hard. I'm into discrete amps at the moment, but if I revisit chip amps I may well take this a little further.
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Old 12th October 2006, 10:10 AM   #6
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I have an unregulated +/- 20 volt power supply with 1000uf at chips' pins and 15000uf per rail, per amp. My heatsink is an aluminum modem case. I have not done any real measurements. I think the output is around 50watt per channel
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Old 12th October 2006, 11:23 AM   #7
juma is offline juma  Germany
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Thanks guys,
I'll let you know when it starts playing music.
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