API 312 Thread!

[laitue5]

I?m trying to modify Fabio?s 312 but I still haven?t found how to do two things.

1. I want to use one rotary switch for all input selection :

• 150 Ω mic input (Cinemag 75101APC)

• 600 Ω mic input (Cinemag 75101APC)

• line input

• Hi-Z input

So I don?t want to use the automatic jack switch?
Do you know how I could wire this stuff?

2. I want to use a gain trim to complete the Grayhill rotary switch. Should I use a 22K Rev Log as if it were the only gain control?

These are the changes I plan to ad :


Do you think it?s correct? :wink: thanks

 

[laitue5]

Do you know if the Cinemag CMOQ-2S is ?color compatible? with the profile 4804 output xformer?
(I also plan to ad an output xformer selector ? I took the idea from the Shadow Hills Industries products: http://www.shadowhillsindustries.com/preamps.php )

 

[guitarmaker]

The two trannies aren't color compatible. The Cinemag colors are on their datasheet. If I remember right red and brown are the primary and blue and orange are the secondaries.

Steve

 

[laitue5]

Thanks Steve

 

[Svart]

i am going to use the Lundahl 1578xl for inputs. lundahl shows RC as 50k and CC as 200pf... anyone confirm this?

and using the servo, does this just output to the "servo out" pins or does it affect the main output too when installed?

 

[Jonkan]

im having a strange problem with one of my two channels.

On of the channels seems to be about 4-5dB louder below 63hz when looking at a frequency analyzer.
It also sounds a bit muddier, which confirms what im seeing.
Otherwise they seem to be pretty matched.

I havent done any really scientific tests, with noise etc. But i have done extensive testing in other ways, and they all lead me to believe that this is true and not only in my head.

Any thoughts on why this is, and how i could possiby fix it?

/Jonas

 

[laitue5]

Let?s build a table:

 

[Guest]

hey i just started going at my 312 (thanks fabio!)

and in the parts list there are some resistors, that couldnt be found in the store.

is it OK to use the closesed i can find?

for instance
RPD1,2 is stated 619, and im using a 620

this is also happening in the gain resistors:
RG7 states 1.15k and i have a 1.1k

another question...
RPP1 and RPP2 state 6K81 with a 1% acuracy
i have found a 6k98 with a 0.25% acuracy
is that ok to use?

and last one:
RPP3 states 200R or 1K
whats better to use? is it depending on something else?

 

[Svart]

Yes all those values should be just fine. usually within 5% is perfectly normal and acceptable deviation for a 1% resistor.. :shock: yeah go figure!

yes the 6k81 should be as accurate as possible, more matched to each other than close to the 6k81 value is better. i use .25% here too since it's easy.

as far as the 200r or 1k, I saw a few of Fabio' pics with that just jumpered so that is what I am doing since this is only going to current limit the 6k81 resistors that are current limiting the phantom.. I think there is no need to have a resistor there if your +48 is clean and stable.

:thumb:

I am still wondering about the servo setup though.. i populated it anyway.

 

[Greg]

I think I posted a parts list somewhere in this thread a while back. I built a couple API 312s several months ago with Jensen input iron and the Profile 4804 as output iron. If you can find that parts list it should give a good start for sourcing parts... you can modify for your particular needs. Good luck this is a great project.

 

[Guest]

on that list there is a C3 cap stated: 220u16 or 1000u16 or 4700u16
what would be the difference when should i choose what

 

[bubba_b]

So, earlier, I had a noise issue in my single channel 312 and found it was the power trafo. If I turned it just right, the noise disappeared. However, I now have installed a second channel into this chassis and now it has the same noise issue. Again, turning the trafo gets rid of it, but the problem is, there is no point of turning that gets rid of this in both channels (gone in one, pops back up in the other). Is there a way to block this interference by another method other than turning it? As you can see by the pics, I am limited in space, so relocating is difficult.

I searched the Power Supply Metas for any info on this issue, but couldn't find anything. Did I miss it somewhere?

 

[Greg]

What DIP are you using in there? Can it drive that Profile 4804? Poof?!?

 

[pmroz]

.
bubba, looks nice! Are those metal guitar knobs for gain?

Maybe try relocating the toroid to the right corner. Also, someone (PRR?) suggested a (well-washed) tuna can covering the toroid. There are links around here for different hum/noise remedies... try a search for tuna. The thread posts explain the theory behind it better than I can. The pres here have a separate PS (and no hum), so I don't reallly have first-hand info to offer. But I did 'can' the toroid, thought it a great idea and tuna can fits perfect.

Would be nice for you not to have to re-rack everything. In that case, putting the PS in a separate box would probably be easier... you could leave the pres and metalwork alone.

Maybe this is stupid... has anyone tried a separate box for the toroid only, and left the PS board racked with the pres? Then you'd only need 4 leads from box to box. I'm thinking of NYDave's cap box here...

Red Muse, i used 3300 for C3. It was a while ago, but i think the explanation I got is that C3 terminates the gain pot/switch, and a larger value lessens the chance/volume of pops with a switch. Usually don't reply if I don't know for sure what I'm talking about, and this is one of those times. But I saw there was no response, so... if that's wrong, I need to be spanked... somebody spank me.

Hope it helps,
Paul

 

[MikoKensington]

[quote author="pmroz"].
Also, someone (PRR?) suggested a (well-washed) tuna can covering the toroid. [/quote]

I think this was discussed as being potentially dangerous. But my memory isn't that trusty.

 

[drpat]

...

 

[matta]

I?ve not built an API so I might be talking out my ass...

But should the OEP?s not be shielded with the optional Mu-Metal screen?
Could having them on board without the cans be a reason for the
interference?

Matt

 

[pmroz]

.
Okay, searched for tuna... Miko had me wondering about potential danger. Here's the thread I remember:
http://www.groupdiy.com/index.php?topic=5035&highlight=tuna

Dr Pat, thanks for the info.

Paul

 

[Guest]

Hey!

after several hectic days of reading the forums, sourcing for parts (not very fun here in israel), soldering (fun!) , testing resistors (eh...) and mainly forgeting all of my responsibilities, i have finished stuffing most of the components on my 4 API boards, 2 psus, 4 2520bcs and 4 melcors.

here are some pix of my current state:
www.o-zen.com/saffi/api

and now for some questions:

* for the relays i used Axicom FP2 D3012 (24v) http://relays.tycoelectronics.com/datasheets/fp2.pdf
are they worthy or am i better off using switches instead?

* on the melcor and 2520BC, instead of the BD139 i used BD441
http://www.ortodoxism.ro/datasheets2/0/01glh2g3agku3e7l7q75q2rt41py.pdf
is that ok?

* will the servo output level be the same as the line out? im thinking of making a switch between them (SW_IRON :green: ), has anyone tested the servo out, and can say how it sounds?

* I'm planning to make a small hatch for each opamp that you can open and change the opamp from melcor to 2520bc at will. i understand there is an issue with the c5 cap. right now i put 220pf, which i read is better for the melcor. will it work ok on the 2520bc aswell? or shoudl i just add another cap on the melcor to balance it (C5=120 + another 100pf on the melcor)

*what are the leds in the PSU for? are the mainly acting as diodes, or do they have some calibrating usage? im wondering if i should mount any of them on the chasis...

* is it possible to have an output level switch in the preamp? im wondering if overdriving it a bit can bring a nice effect, and controling the amount of overdrive would be better controled with a output level.

* was the melcor's oscillation fixed in the end of the proccess of trying to fix it? there is so much technical talk i have lost track of what parts are the problematic ones.

and now for sourcing Trafos! i think im going with the Cinemag 8-PCA and CMOQ-2S

Peace!
Assaf

 

[AnalogPackrat]

I'm sourcing parts for a pair of Fabio's 312 boards and have a question about the relays. I know I can get the TQ2-5V parts at Digikey and/or Mouser. However, I have found a local supply of TQ2E-5V relays that are cheaper (surplus). I can't find any specs on these parts anywhere. I suppose they've been discontinued. Does anyone know what the "E" signifies? I hope it's not "electronic" as in pass FET. The package size is the same as the TQ2-5V part. Any help would be appreciated.

Analog Packrat