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Chip Amps Amplifiers based on integrated circuits

opamp plus driver stage and output stage with its own supply, what could happen?
opamp plus driver stage and output stage with its own supply, what could happen?
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Old 26th October 2013, 09:39 AM   #1
Mihkus is offline Mihkus  Estonia
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Red face HV OpAmp as voltage amplifier. Mihkus Version of opamp driven amp trans amp

Yohoo everyone.

I know that some of us have wanted to use opamp as VAS stage for years...
So I took my brainless head and started this thread, my knowledge so far is sadly poor.
But I managed to design and build something, not 100% my design but who cares


And PCB, You can give it a try but all im able to say... This amp sounds better than many chipamps, just my opinion but thats what Im thinking.
Supply voltage for this design should be around 15-16,5V...

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And PCB:

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But that is the final design? NO! I will continue to make it better, whenever I have time.

But the road to this started on protoboard...

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After that... It sounded good, but I wanted something more :d

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I tried with capacitors as diodes to eliminate any switching... Nothing got better, only worse at higher power levels it was VERY UNSTABLE.
After replacing caps for diodes It sounded sweet, but I wasnt happy!
I added driverstage too! and it got better, alot more output power and alot lower distortion. because the opamp had very low output current.

After listening for pop rock for a while...

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(Not mine)


And after that...

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Last edited by Mihkus; 25th January 2014 at 06:24 PM. Reason: Jop.
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Old 26th October 2013, 10:25 AM   #2
Arty is offline Arty
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transistor (or "whatever") boosted opamps are quite a common diy amp builds.
actualy the opamp is used only as a voltage amplifier, and the output stage has a voltage gain of 1.
so it supply current.
if you drive the output part with higher supply, the voltage swing of the opamp will not be larger.
so, the output power remains..

actualy a good opamp can bias an output stage, if the output stage is included in the opamp feedback path. can't elliminate the crossover distorsion, but will reduce it to a level where its more than acceptible.
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Old 29th October 2013, 02:26 PM   #3
ChristianThomas is offline ChristianThomas  United Kingdom
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You''ll never get +-50V from an op amp - at least not one that I know of. The OPA604 or 2604, will do +-24V, which is already amazing. (You might be able to push it a few volts further as well, but be prepared for failures).

If you are looking at simple biasing then how about 3 or 4 diodes? Just to not waste all of that feedback on correcting the crossover distortion. Also, drivers plus o/p will make life easier on the op amp, esp. if you are using it over-voltage. A slightly higher supply on the output stage probably wouldn't go amiss but I suspect the max output of the op amp will already never get above 3 or 4V less that the rails so that's room enough.

A perfectly nice idea.
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Old 29th October 2013, 03:00 PM   #4
geraldfryjr is offline geraldfryjr  United States
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You can using a High Voltage opamp such as Analog Devices ADA4700-1.
Here is a link to the data sheets,

http://www.diyaudio.com/forums/solid...ml#post3652631

However it is in a SOIC package and I had just got one but I have not tried it out yet,

http://www.diyaudio.com/forums/solid...ml#post3663983

It has great specs and looks like it may do well for such applications as this.
This type of application is the very reason I got one to try out.

FWIW

jer

Last edited by geraldfryjr; 29th October 2013 at 03:03 PM.
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Old 29th October 2013, 04:02 PM   #5
ChristianThomas is offline ChristianThomas  United Kingdom
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Wow, you are up to date with that! And apparently there's a Linear one that I didn't know about either (and I get mails and post from them).

BTWm that link isn't to the datasheet, but to the other thread.
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Old 30th October 2013, 11:30 AM   #6
gootee is offline gootee  United States
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Go to linear.com and search for an18. There is a similar app note that national had, which is now at ti.com.
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Old 31st October 2013, 02:04 AM   #7
geraldfryjr is offline geraldfryjr  United States
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The LTC6090 is the new one from Linear teachnology.
It is rated at 140v (+/-70V),

LTC6090 - 140V CMOS Rail-to-Rail Output, Picoamp Input Current Op Amp - Linear Technology

http://cds.linear.com/docs/en/datasheet/6090fb.pdf

It had just came out earlier this year I think.

These are some of the first of their type since the LM143 that had got discontinued some time ago besides the very expensive ones from Apex.

http://www.ti.com/lit/ds/snvs759/snvs759.pdf

jer

P.S. Yes, it was a link to the links that I had already posted on that part.

Last edited by geraldfryjr; 31st October 2013 at 02:15 AM.
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Old 31st October 2013, 10:55 AM   #8
gootee is offline gootee  United States
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In an18 and a similar application note from national, there are amplifier circuits that use regular low-voltage op amps and produce high voltage and/or high power output swings, even in excess of 1000 volts, if I recall correctly.
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Last edited by gootee; 31st October 2013 at 11:00 AM.
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Old 31st October 2013, 11:30 AM   #9
gootee is offline gootee  United States
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http://www.ti.com/lit/an/snoa600b/snoa600b.pdf

http://cds.linear.com/docs/en/applic...note/an18f.pdf
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Old 31st October 2013, 12:38 PM   #10
geraldfryjr is offline geraldfryjr  United States
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Here is yet another method of increasing the output voltage swing of opamps,

http://m.eet.com/media/1152270/24127-45890.pdf

I have not tried this myself yet but I have seen it implemented many times.
Typically this circuit doesn't work in simulators but does in real life applications.
I am wondering if this type of configuration could be used up into the >1kv ranges.

FWIW

jer
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