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Old 30th August 2014, 10:42 PM   #11
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Some links on virtual grounds...
Virtual ground in power amp applications
Virtual Ground Circuits

I never built used the above circuit, but I did test it out and everything worked well enough...
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Old 31st August 2014, 12:55 AM   #12
JMFahey is offline JMFahey  Argentina
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Quote:
The single chip solutions like TC7662 will probably not give me enough power for at least 6 opamps
Your 6 x TL072 (12 individual Op Amps) need 3 mA each or a total of 18 mA.
A single 7662 converter when supplying 18mA has an internal resistance of 50 ohms, for a 0.9V loss, so it will turn raw +18V into -17V .
You can turn both into very clean +/-12V with a pair of 78L12/79L12 for a simple, cheap and compact solution

Much better than very dirty +18V by the way

FWIW I make (among other things) portable guitar, bass and PA amplifiers , fed from a 12V7AH battery for reasonable weight.
I need a negative rail for the preamp TL072 , and I have been making them from the Stone Age on, no fancy pump converters way back then, so I designed my own with available everywhere NE555 .
I get between -9V and -10V (depending on load), plus original +12V to feed my TL072 which are happy with them.
They do not need perfect symmetrical supplies by the way ,)
Here´s the smallest one, 30W biamplified (20+10W RMS, 10" speaker + LeSon tweeter)
Click the image to open in full size.
Click the image to open in full size.
4 x TL072 in total, fed from a non dedicated cheap IC, how´s that?
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Old 31st August 2014, 03:36 AM   #13
gofar99 is offline gofar99  United States
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Hi, Mean Well (source Jameco) has several DC to DC converters that do split regulated outputs. Cheap at about $10 and they are pretty clean I use them all the time. I there is one that does 9-18 input to +/- 12 out. All are encapsulated and about the size of an ice cube.
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Old 31st August 2014, 05:23 AM   #14
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hvergelmir, where are you located? I have some very nice dc-dc converters and would be willing to let one go for only the shipping cost. This is the converter...

BWR-15/330-D12A-C Murata Power Solutions | Mouser

I've used these to power many op-amp projects.
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Old 31st August 2014, 08:15 AM   #15
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Quote:
Originally Posted by theAnonymous1 View Post
hvergelmir, where are you located? I have some very nice dc-dc converters and would be willing to let one go for only the shipping cost. This is the converter...

BWR-15/330-D12A-C Murata Power Solutions | Mouser

I've used these to power many op-amp projects.
I'm in the Netherlands, so if you're stateside then I'm not sure if it's feasible - although I really do appreciate your generous offer

Do the TL072s really draw so little current? I've seen wildly differing figures on the internet - from 2 to 50mA per chip...

BTW, your portable amps look pretty cool JMFahey!
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Old 31st August 2014, 08:19 AM   #16
AndrewT is offline AndrewT  Scotland
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Quiescent current.
You need to add on output current.
and not just for the resistive loads, but for the capacitive (inadvertent) loads and for the feedback loads.

Allow a peak current of half the short circuit current.
That would be ~20mA per opamp channel.
Design for 120mApk
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Old 31st August 2014, 10:22 AM   #17
Mooly is offline Mooly  United Kingdom
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I'm going to disagree with Andrew on this. Practicalities...

I still have my 7 opamp D Self test PCB, and this is a low impedance version that uses 4k7 pots for bass, 2k2 for treble, 1k for treble turnover and 4k7 for bass turnover. So its not really suitable for TL072's because its asking to much to drive it fully... however...

Here it is fitted with TL072's and fed from a 12 to 15/15 convertor with 1 ohm resistors in the supply to determine current draw. This uses 7 opamps.

Current draw quiescent was 23.1 ma
Current draw at 16 volts pk/pk output at 1kHz was 30.6 ma
Current draw at 10 kHz and max treble boost purposely driven into severe clipping was 45 ma The scale on the scope for this was 5 volts/div.

For any normal music input and with levels around a couple of volts the change in current draw from quiescent is minimal.

The small convertors that are rated around 66ma per rail will easily power 6 TL072's under signal conditions.
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Old 31st August 2014, 01:32 PM   #18
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Quote:
Originally Posted by hvergelmir View Post
I'm in the Netherlands, so if you're stateside then I'm not sure if it's feasible - although I really do appreciate your generous offer.
No problem really; 7USD shipping and it would take about a week. PM me if you're interested.
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Old 31st August 2014, 10:01 PM   #19
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Quote:
Originally Posted by Mooly View Post
I'm going to disagree with Andrew on this. Practicalities...

I still have my 7 opamp D Self test PCB, and this is a low impedance version that uses 4k7 pots for bass, 2k2 for treble, 1k for treble turnover and 4k7 for bass turnover. So its not really suitable for TL072's because its asking to much to drive it fully... however...

Here it is fitted with TL072's and fed from a 12 to 15/15 convertor with 1 ohm resistors in the supply to determine current draw. This uses 7 opamps.

Current draw quiescent was 23.1 ma
Current draw at 16 volts pk/pk output at 1kHz was 30.6 ma
Current draw at 10 kHz and max treble boost purposely driven into severe clipping was 45 ma The scale on the scope for this was 5 volts/div.

For any normal music input and with levels around a couple of volts the change in current draw from quiescent is minimal.

The small convertors that are rated around 66ma per rail will easily power 6 TL072's under signal conditions.
Thanks again for the extensive info. The project will be dealing with just transients, but even that should be easily within the limits. TheAnonymous, I'm going to take you up on your offer! PM forthcoming.
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