DOA - Discrete Op Amps

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Sebastian,
I've been on some other projects but now back on it, reviewed everything up to this point for errors oversights and found none.
So be patient , have you tested anything like this before?
(Note: The 1k grid resistor also limits forward grid current in addition to kill oscillation if any tendencies )
Regards
Bruce
 
6DJ8 Unity gain non inverting

Trying to get back into it. I had a 6DJ8 and thought the specs looked interesting so here is a series of tests. This group is unity non inverting.
The readme file has hardware info. The circuit is identical to the one Sebastian drew but a 6DJ8 is used.

Interesting that I attempted this time to use one of those low cost switchers on ebay for 6VDC heater. They are verrrry noisy!

Went back to my low noise dc supply. Its a switcher but has special filters for for use with sensitive radio receivers.

My test board is not yet assembled so these two test runs are on perf board.

The readme file has hardware info.

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Here are tests using inverting gain of 4.7

Note the sight increase in thd is mostly 2nd.

Still remaining are test board assembly, CC diode spreadsheet, PCB fab using new CAD (dropped Eagle) and same project but repeated using grounded grid topology.

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This pic shows general idea, if possible to make pcb dual use.

Stuff with the single opamp package and miniature triode tube footprint for 990 package.

Or stuff with dual opamp package and 9 pin dual triode with dip8 male header.
May have to use 4 layer board but that's better anyway for thermals.
 

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E452 is a Semitec current regulator, 4.5ma.

Here are the eagle v5 files as of today. I have not checked the board 100% , but after will get some Purple boards fab.

Its 2 layer, 1" X 1".

The odd soic pin 8 is for a lower Z, since there are no bypass caps on board.
The compensation C can be omitted, stuffed with fixed value or variable smd or 5mm through-hole varicap.

The 'board' shown is made from balsa wood and some throw down packages. Its just a reality check for clearance.

zip and some pics here.

Any opinions on the purple boards?
OSH Park ~
 

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> What is the part called E452?

See post #35.

More on current regulators. These are fast , I was not really expecting.

I have tested resistor loading and parallel jfets which also work excellent.
But would take up a lot of space. The semitec parts also rated for 100v vs 30-40v jfets.

So the CRD seems to be best choice.

They are somewhat expensive.

E-452 Semitec | Mouser
 

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Cleaned up some pads, tweeked Compx path and reduced number of drills.

Also removed thermals. (Thermals are bad- only helps production) , yes the board must be heated prior to soldering.

So today I think its going to fab.

-
 

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Last edited:
Well I ordered 12 prototypes so we'll see in a few weeks how it sounds.


Amazing how low prices are for board fab now. $5 for three with no setup chg...

Pretty amazing.

Starting on the grounded grid version now.

pic here of the vendors status page.
 

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Will listen to it for a few days and relish the fun. So far no issues.
Its a clamshell so soldering is more difficult and a specific assy order must be followed.

Got tired of taking my DH100 apart so using this $9 preamp tone board for listening.
The power amp is a SAE 2200.


Here are the Gerbers to look at until I finish all the testing. I hate to take it down for the THD measurements.

First tracks used....

#1
Cecilia Bartoli: (Opera)
Mozart: Così Fan Tutte, K 588

#2
Henry Qualls: (Texas Blues)
Shotgun Blues

#3
Red Bar Jazz Band Live Jazz with Chuck Schwartz
Bye Bye Blackbird
 

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