Oktava Schematic?

[zebra50]

Hi Adrianh,
Thanks for the tips. I can scan 600DPI in black-and-white in future, and save to GIF, but I simply never have the time to fix all the errors. I currently lack PDF writing software but I really ought to get that sorted.

Back on the Oktava Mic topic.
I looked at two 219s this weekend (2002 vintage) just 100 serial numbers apart. There were some differences in capacitor brands and some resistor values values.

Looking at Flatpicker's schemo:

Mic 1: R7 = 1.8k, R8 = 1.8k;
Mic 2: R7 = 1.6k, R8 =1.0k;

Also there are different markings on the o/p transformers. One is marked "1,8 1,8" the other is "1,6 1,0". Weird?

In both mics R1 and R2 are 510Meg not 680Meg as shown.

Despite the differences I could not hear any major sonic differences between the two mics.

I have replaced the caps in one mic with some audio grade and increased R1 and R2 to 1 gig. I'll post back when I've had a good listen to them.
Stew

 

[zebra50]

Mic 1: R7 = 1.8k, R8 = 1.8k;
Mic 2: R7 = 1.6k, R8 =1.0k;
Also there are different markings on the o/p transformers. One is marked 1,8:1,8 the other is 1,6:1,0. Weird?

:shock: :idea:
Now I have written it down & read this back I have just realised that the markings on the xformer match the values of the resistors... so the mic circuit is tuned for the transformer? Does this make sense to anyone?

Stewart
:?: :shock: :? :?:

 

[zebra50]

So, I managed to get hold of a MK319 to look at.

The transformer has "1,8 1,6" written on.

Guess what?

R7 = 1.8K; R8=1.6K

I see a pattern emerging. The numbers on Oktava trannies are not simply the ratios. The transformers must be measured before putting in the mic and the resistors adjusted to match some parameter. I don't really understand what effect changing R7 and R8 will have on the circuit.

I plan to measuring ratios tomorrow for these transformers. My plan was to wire up a signal generator to pins 2&3 at the XLR, unsolder at C8 and then measure. Do I need to add a resistor to load the transformer? (I should know this, but it's getting late here & I should quit tinkering before I break something).

Cheers!
Stewart

 

[adrianh]

Transformer ratios should be measured unloaded.
Connect sig gen to pins 2 and 3
Set to 1Khz and .5 volts (ballpark)
Measure exact level at transformer leads record that number.
Lift one lead on the other side of the transformer leave it floating.
Measue with meter (Fluke 77 or better set to AC volts)
the other winding. record that number.
The ratio is second number divided by first number.

 

[guavatone]

I opened up my mk319. iether cap values for C5 and C6 are reversed on the schem. or my mike has them reversed.

OOF!... I just saw the russian schcem... someone mesed it up att the factory.

I have a blue 680pF cap clearly going to ground and the 271pF(tan) cap goes to + side of C8


-Just thought id chime in I'll try to post some pics


PS. Dorsey didn't cover my mic version well enough. He neglects the important point that some of those Russion components up top, eg. resistor actually look like little caps.

-g

 

[dale116dot7]

I doubt that those markings have much to do with the transformer at all - the transformer is just a handy place to write it. I would expect that the board is put together without those two resistors, then the mic is tested with resistance sub boxes in place. Once the gain and bias of the FET is tweaked with the resistance sub box (or two pots?), then the two R values are written on the transformer and then someone else goes and picks those two resistors out of a bin and solders them in during a later step. Oh yes, the bias is set by R7+R8 and the AC gain is set by R7 (R8 is bypassed).

 

[evm1024]

Keeping it in this thread....

Removing c1 (270pf) and associated wiring gets rid of the -10 dB pad. Removing C4 and R5 does the same for the low cut filter. The question is:

What do C5,C6 and R9 do? On one hand they could be part of the low cut filter and thus can be removed. Is it recommended to remove them or are they esential to the MK319?

On a side note the FET used in my MK317 is a (from memory) 7BN2. (In russian the B looks like a squared off 6 and the N like an H). I did not find any references to it on the web. Anyone have a data sheet for it?

I would like to get a copy of the Russian manual should anyone have one.... I could post a translation.

Cheers