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googlyone googlyone is offline

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About Me

  • About googlyone
    Electronics engineer, worked on digital, RF, systems engineering, software. Now in management :(
    Adelaide, South Australia
    Strong interest in electronics, particularly analog, power audio and DSP. Hands on, try it out type
    Operations Manager in product design and manufacturing company
    Real Name


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General Information
  • Last Activity: Yesterday 07:33 PM
  • Join Date: 7th November 2006


View googlyone's BlogRecent Entries
Latest Blog Entry

Posted 12th June 2017 at 06:25 AM by googlyone Comments 1
Posted in Uncategorized
I finally got around to doing some measurements on the discrete op amp at G=2 and G=10.

These were non inverting mode - note the voltage was 6-8V p-p, and the rails were +/-15V so there was a fair whack of headroom. Anyway, I will let the measurements speak for themselves.

This is what they looked like...Attachment 2414

I tested a whole bunch of configurations of the DOA, including:

Differential pair current 1, 1.5, 2 and 4mA
Output current 8mA (2* 4mA) and 12mA
VAS current 1.5, 3mA.

The test setup was a dual op amp board, one channel set to G=2 the second set to G=10.

The load for G=2 was 1kOhm. The load on G=10 was 10kOhm. I could go back and retest this... I had not lingered on this during the test.

The first challenge I found was MASSES of noise really messing with the results. It looked a lot like oscillation, and I kid you not, I spent hours trying...

Posted 25th May 2017 at 10:18 PM by googlyone Comments 4
Posted in Uncategorized
Well I am home again, and the PCBs for the discrete op amp beat me home.

I used PCBcart, who have a very competitive prototype PCB service -it is certainly not worth your time to make fiddly double sided boards like these at home!

They came out like this...

Attachment 2397

And no, I don't have a finger the size of a baguette...

More images to give you some scale of these little buggers:

Attachment 2394

Attachment 2395

and thru the microscope which I had to use to solder the bits on:

Attachment 2396

There are parts on both sides of these PCBs.

A this point I am yet to mount the miller cap, as I want to play with this a bit. On the schematics there is a "guaranteed to work" value. I want to measure the phase margin and stability into some odd loads - as overcooking this will directly affect...

Posted 11th May 2017 at 06:28 PM by googlyone Comments 0
Posted in Uncategorized
Well here I am travelling again, and this time stuck for an extra week away from home. The design bug has bit, and this time I tried keeping things small rather than crazy.

I have built a number of discrete operational amplifiers in the past. Usually integrating everything onto the board so that they wind up being preamplifiers rather than operational amplifiers.

If that confuses you - the difference is that an operational amplifier needs to be plugged into a circuit to be useful, a preamp is a standalone PCB.

The inspiration was seeing a burson amp on ebay. I looked and thought to myself "I keep starting that, and keep ending up with a preamp". Then I thought "Do it right for once".

The resultant goals:
- Dual channel op amp
- DIP8 pinout
- Good perfromance
- Class A (vs class AB which many are)
- Minimum size, whilst
- Sticking to 0805 SMD resistors caps, and...

Posted 22nd April 2017 at 04:30 AM by googlyone Comments 4
Posted in Uncategorized
After a few months of playing with loudspeaker drivers and software fixes to code that I wished I had never written in the first place, the lure of the BJT loomed large again...

There I was, sitting at my desk, and pondering where these dark feelings were coming from and how to scratch that evil itch, and my eyes came to rest upon that most ludicrous of things - the amplifier of 100 transistors.

About a year ago, or so it seems to me sitting here, I built this homage to the BC549, or as the engineer in me says, "Laughably stupid thing, which probably shouldn't work. Who would be dumb enough to try and find out?".

It needed a case. It needed a power supply. It deserved each of the above that would allow it to work, and ideally take an equally "left field" approach. it should never have been built, but it had. It should have been put in the back of a very dark, locked cupboard, but it had not.

The idea then...

Posted 21st March 2017 at 11:49 AM by googlyone Comments 0
Posted in Uncategorized
Years ago I moved from the country back into the city. This was a move that required me to clean out heaps of stuff that I really didn't want to clear out. In our old place we had two houses on the block, one of which had been converted into an enormous studio room with NO walls, and a 14 by 14 metre shed. To say that I amassed a collection of speakers and stuff would be an understatement.

One of the things I got rid of were a pair of Richard Allan CG-10 drivers that I never got around to sticking in a box. Indeed, I never even got around to measuring their parameters.

Recently on EBAY I came across a pair of these...

Attachment 2323

Attachment 2324

I was surprised at the condition of these - the cones look new. Needless to say they are not, the date code is 1973.

I have measured and used the CG-12, HD-15 and a bunch of other Richard Allan drivers in the past and found them...
Recent Comments
Well done indeed !
Posted 13th June 2017 at 02:22 PM by kasey197 kasey197 is offline
you're running this...
Posted 9th June 2017 at 08:17 AM by kasey197 kasey197 is offline
nice going and its looking...
Posted 9th June 2017 at 08:14 AM by kasey197 kasey197 is offline
Only G=2 at present...
Posted 8th June 2017 at 01:27 PM by googlyone googlyone is offline
this is pretty interesting...
Posted 7th June 2017 at 12:12 AM by kasey197 kasey197 is offline
Hide this!Advertise here!

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