Magnum on steroids!

[Toros]

You are fully right!

[perkun]

corrected .

[ivconic]

GB pot. is connected to pin 6 Lm324. should go to pin7.

Yes you are right, according to schematic it is mistake, made by me.
Funny thing is that i made few detectors on such pcb's and those worked just fine!??
I hadn't any problem to adjust GEB or Disc!?
I remember only that audio was slightly weaker than on original, everything else was quite alright.
Very confusing?
I will have to compare it again with original...

[perkun]

Say something about balancing the coil.
I did DD27 balanced to 100mV.
When switch to 18khz jumps to 900mV.
In original GM4 U1 is a TL074?

[ivconic]

Say something about balancing the coil.
I did DD27 balanced to 100mV.
When switch to 18khz jumps to 900mV.
In original GM4 U1 is a TL074?

On some models there is TL074 and on some models there is LM324.
About balancing the coil; read Andy Flind's article.

[Nexus]

Say something about balancing the coil.
I did DD27 balanced to 100mV.
When switch to 18khz jumps to 900mV.
In original GM4 U1 is a TL074?

If the RX offset sf over the coil ends 900 mV is a serious problem, but if the offset is on the input of the 4053 (or what ever else is in use) phase demodulator then it is not the end of the world.

[Nexus]

Say something about balancing the coil.
I did DD27 balanced to 100mV.
When switch to 18khz jumps to 900mV.
In original GM4 U1 is a TL074?

I forgot to mention. You can not use the same windings for both low and high frequencies without expecting some shift in offset voltage. First of all the inductance that is sufficient for high frequencies may be insufficient for low frequencies, which means an inductance calculated for low frequencies can be far too great for high frequencies resulting in extreme quality factor values.
Also it is important to know that any set of windings that are balanced first at low frequencies depending on particular design may require a new balance to work properly at high frequencies.

[ozzy_sv]

About balancing the coil; read Andy Flind's article.

I'm sorry, you can give a link to what exactly you mean in view of ?

[Toros]

I'm sorry, you can give a link to what exactly you mean in view of ?

Perhaps given Andy Flind's article in the Electronics Magazine of 1981. I think you'll find it in Russian language in md4u.ru

[N@SKO]

Say something about balancing the coil.
I did DD27 balanced to 100mV.
When switch to 18khz jumps to 900mV.
In original GM4 U1 is a TL074?

Balance of the coil must be done at 18 khz.When switch to 8 khz will keep balance.

[Toros]

In English language here - http://www.geotech1.com/cgi-bin/page...gnum/index.dat

[ivconic]

In English language here - http://www.geotech1.com/cgi-bin/page...gnum/index.dat

Yes that's the article. I referred it on first page in first post of this topic.
It is there for years, Carl provided it long time ago.
Original Flind's Magnum is working on 15kHz.
Andy Flind explained coil balancing and also provided simple circuitry which helps a lot for that task.
I simply followed his article and everything came on the place easily.
But than again; i mentioned this in my first posts here. No need to repeat.

[Artyom]

perkun Note that on the printed circuit board, the mag redu has an incorrect layer arrangement (mirror image).

[reiv]

Hello, what value has discr. potentiometer?

[Toros]

50k