API 312 Thread!

[Jonkan]

thanks! Ill try my little case then.


Another question. What does the 100k "RL" resistor on the Bauman 312 pcb do? Its the one across the input transformer secondary.

Its not in the original api312 schematic, so im curious.

Is it some kind of loading for the input transformer, and more importantly, does the value thats best differ from transformer to transformer? Do i even need it at all?

I just mounted it without thinking because it was in the schematic.
Im using a sowter 9820, so maybe i dont need it really?

Has anyone experimented with this input transformer btw?

Cause i remember reading about it earlier, but i dont think we ever came to any conclusions about the sowter.


/J

 

[pmroz]

.
CJ, that's from me...
from a cheap Panasonic WR-450 A/V mixer, very small trafo inside.
For your amusement

sent a pm about that stuff... should I send it again, or email?

API2621 is the bigger round can w/bracket from the same box. (says 7200-2621 IIRC can't miss it)
Black plug-ins in there too, one cut open... mystery to me.

btw you didn't have to wind that stuff, thanks man.
i'm sending something else.

Paul

BTW Jonkan

Is it some kind of loading for the input transformer, and more importantly, does the value thats best differ from transformer to transformer? Do i even need it at all?

You're on the right track. Think it's referred to also as termination, to prevent the transformer oscillating. Check the manufacturer datasheet for what they recommend. There's often a schematic with the value in there. Think of it as part of the transformer you use, with a spot provided by Fabio. So to try different trafos you have to change it.
RL depends on the impedance of the transformer secondary, so a 1:8 input needs different RL than 1:10, etc. Also some manufacturers recommend you terminate a transformer with a resistor/cap combo.

And to know the whys and hows, please stare into the dark caverns of the transformer Meta, top of page, from which depths the magnetic eyes of lemmy stare out at you. or google.

 

[Jonkan]

Well,

I actually emailed brian sowter and he replied that he didnt know which values for loading and for zobel that would work with the 9820. So no luck there.


Is there some way to find out what values would work best without using a scope+sig.generator?

Because i dont have any of those, sadly.

You say that the RL resistor depends on the impedance of the transformer secondary.
How do i measure that, and how do i then calculate the proper value for the RL resistor?

I want to get this right :green:
But maybe im being a bit anal about this..lol

/j

 

[pmroz]

.

I emailed brian sowter and he replied that he didnt know which values for loading and for zobel that would work with the 9820. So no luck there.

That's weird... I'd think if anybody would know, it would be the guy who designed/manufactured it.

Impedance (Z) of the secondary is in the 'pro vintage' chart on the Sowter website. And the hotlink for your trafo might give you an idea. There are some values there in the schem for RL and RC.

If you know the primary and turns ratio of any transformer, you can calculate secondary impedance... there's a simple formula.
If you check the basics, you'll get a better idea of other values for RL or C here that you might prefer. Once you get it, it's a snap trying different ratio/quality transformers in the pres. Lower ratios can be nice, as the pres have considerable gain.
The caverns are not that bad... lemmy is friendly.
cheers, Paul

 

[Bauman]

For the sowter clone I'd use the same values on the original 312 schemo to start up.
Then if it works bad (I doubt it) you can mess with the values of RL and RC/CC....

:guinness:
Fabio

 

[Jonkan]

Thanks alot, ill be shure to read that meta when i get the time! Im not shure if i will understand much though at this point in time.

Ok, heres the values for the 9820 taken from the sowter website:
voltage ratio 1:4.37, and 150/600:11.5k,

The last value is the impedance, correct?

How does that value relate to the appropriate loading value?

And also, does the secondary impedance change if i connect the primaries differently? I have the primaries connected in parallel right now. Would that give me about the double voltage ratio, or am i way off here?

Another strange thing is that the voltage ratio are listed differently if you check on sowters website, and on the datasheet on prodigy-pro.


/J

 

[CJ]

paralell means half the pri turns, and the same sec turns, so yes, double the voltage coming out, if you don't load it too bad.

 

[Jonkan]

Cj, thanks. thats what I thought!

Fabio:

For the sowter clone I'd use the same values on the original 312 schemo to start up.
Then if it works bad (I doubt it) you can mess with the values of RL and RC/CC....

Does that mean i should try to not use any RL at all to start with, and see if it sounds good? I dont see any loading at all in the original schemo.

/jonas

 

[mick]

Can anyone help me out here as I'm really close to getting this project finished
and I just need to order the last few bit's, I'm going with Fabio's board's with:
24v relays (with 7824)
22K rev Log pot's
Questions psu first:
I'm hoping to run 4 boards off one psu card is that ok ?
R 1,2 both 10R 5w ?
will I need R10 ? (with the 7824)
R11 2k2 half watt ? ( and the same for led's on pre board)
Mic pre board:
CSW1 upped from 16v to 35v is that enough ?
RPP3 200R ?
C3 which value do I need with a 22K pot ?

 

[mick]

Anyone ? :sad:

 

[AnalogPackrat]

[quote author="mick"]Can anyone help me out here as I'm really close to getting this project finished
and I just need to order the last few bit's, I'm going with Fabio's board's with:
24v relays (with 7824)
22K rev Log pot's[/quote]

>Questions psu first:
>I'm hoping to run 4 boards off one psu card is that ok ?

I'm only running a pair, but I think others have run four. You should make sure you heatsink your regulators well--especially the 7824.

>R 1,2 both 10R 5w ?

I jumpered these for now. Read back through this thread and you'll find some discussion about these.

>will I need R10 ? (with the 7824)

I'm not sure which is best with the 24V relay option. I'm running 12V relays and jumpered from pin 1 of the 7812 to C1 and left R10 out. Actually, thinking about it more...if you run four boards worth of relays, you will really be straining your 48V regulator by usinr R10. I'd jumper back to C1.

>R11 2k2 half watt ? ( and the same for led's on pre board)
Should be close enough. Check with a breadboard or mini-grabbers using the actual LEDs you have. Some of the new ones are really bright and you can get away with even less current (bigger series R).

>Mic pre board:
>CSW1 upped from 16v to 35v is that enough ?

Yep.

>RPP3 200R ?

Go back through this thread--there's a discussion about bleeding CPP by rearranging some of the circuitry around the phantom feed. Now's the time to do that mod.

>C3 which value do I need with a 22K pot ?

Bigger C3 give better bass response. Not sure what the tradeoff is. I'm using 1000uF. The originals used 250uF.

Good luck!

A P

 

[mick]

Thanks A P
C3 was the one I had no idea about, I'll go with the 1000 and see how that goes, I remembered that Fabio had posted some pic's with four in one box, I found them an now (you realize at the beginning of the a project and then forget to take account of ) can see the psu will need to be separate.
I will now go and trawl back through this thread to the points you've made and probably have a ton more questions

Thanks again

 

[mick]

Hi A P
Is this the CCP circuit mod you was talking about ?

http://www.groupdiy.com/index.php?topic=246&postdays=0&postorder=asc&start=255

 

[AnalogPackrat]

[quote author="mick"]Hi A P
Is this the CCP circuit mod you was talking about ?

http://www.groupdiy.com/index.php?topic=246&postdays=0&postorder=asc&start=255[/quote]

Yep--that's the discussion.

 

[mick]

Thanks again, this is hard work trying to find all the little bit's, still I noticed that the SSL thread is half as much again.

 

[mick]

Hi there can someone tell me the correct colour code for a Cinemag CMOQ2S to match Fabio's 312 ? I was of the understanding it was not the same as the profile's ( I might be wrong though)

 

[AnalogPackrat]

[quote author="Bauman"]
you can do this: do not use the PP LED where it was supposed to be but connect it in the PP
going to the input connector. raise the the led resistor to 5k1 at least. it will turn on when the power is on the way to the input connector and will drain the charge when the PP is turned off...
[/quote]

OK, color me dense, but I've read this several times and can't figure out what you mean When you say move the LED to "PP going to the input connector" do you mean the 48V input connector or the Mic In connector? I'm not seeing how either of these discharges CPP when the phantom is switched off. Any help? Feeling a bit stoopid now...

A P

 

[dissonantstring]

hey AP,
i think what fabio means is to raise the RLED1 to 5K1 and instead of having the input leg of RLED1 at the wiper of the DPDT have it go to the 48V trace (CPP + side) going to the mic input. This will drain the CPP as it discharges after the PP is turned off. sorry, i can do the whole circle the graphic thing. hope this makes sense. if not you kick me the next time i see you.:green:
regards,
grant

edit: oops! i meant common, not wiper of the DPDT (or whatever the middle lug is called.)

 

[AnalogPackrat]

That makes sense...then I just need a SPDT switch for PP. I'm using panel mount ones anyway. If it doesn't work, I'll make you listen to me play through your Marshall next week :shock:

Thanks,
A P

 

[AnalogPackrat]

[quote author="mick"]Hi there can someone tell me the correct colour code for a Cinemag CMOQ2S to match Fabio's 312 ? I was of the understanding it was not the same as the profile's ( I might be wrong though)[/quote]

Looks to me like the CMOQ2S color codes match Fabio's board. Go for it.

A P