API 312 Thread!

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Hello

I discovered somthing strange.

To check the noise I used to plug a headphone into the API output. The API output is a monophonic balanced one, but the headphone plug is a unbalanced stereo. I was trying to record the noise, and what a surprise when I saw on the vu-metre of Sound forge that noise at maximal gain was only around -70dB (at 0dB input gain on Firepod preamp).
I used both balanced and unbalanced cable, and the result was the same !
I got only some "click" when switching pad or phase, but no big buzz or hum !
You can hear the result and tell me if you think noise level is correct or not ( first you'll hear the channel one, in line input, then in mic input, turning the pot from minimal gain to the max, and the same for the second channel, which is the closest to the PSU board)

http://krokro1.free.fr/channel%201and%202-%20Line%20and%20Mic.wav

But the strange thing is when I have the headphone plugged into the first channel and a cable plugged between the second channel and the Firepod input, I've got no hum and buzz at all !!! but if I remove the cable between the API and the firepod, hum and buzz are back ! So, I can't record this hum ( because it disappear when I connect the API on the firepod). Do you think it is normal or not ?


I don't know what to think now.. I feel a bit stupid to haven't hear the noise through the API sooner ... :oops: lol
 
Hi Phasinhead,

as you've wired it, both preamp grounds connect to the psu gnd, so the gnd of the psu card would be your star gnd. These gnd's for the different voltages (except relay gnd) are already connected on the pcb of the preamp- and psu card, so 1 wire for connection will be sufficient.
The xlr-pin 1's all connect to your "flying" star gnd, which is placed in a different spot. May matter.

Did you already try connecting to your firepod by only using pin 2+3, leaving pin 1 of your preamp-output unconnected (ground lift)?
For your oscillation at high gain settings have a look at this tread

Ps.:Take care your regulator heatsinks don't touch the bottom of your case if not isloated, as these are carrying output voltage for the lm317 and input voltage for the lm337.
 
Hello Harpo !

thanks for the advices :razz:

I haven't tried the ground lift yet. Is it better to have ground lift ? ( I heard that it wasn't good.. ). In any case I haven't buzz or hum when connected to the Firepod... so do you think it could make problem on other soundcard ?

thanks for the oscillation solution. Somebody already told me about supply decoupling problem but I'm not enough experienced to try this.. I fear to burn something :green: . I just need to take time to try this, I can have an oscilloscope at school and see where is the oscillation.. but I would prefer to know if somebody already tried this on an API preamp and if it works well :wink:
Actually there are two 100nF decoupling caps for the 2520 DOA.. should I try a lower value or an higher one ?
I also already tried to change the 120pF cap (by a 150 and 220 pF) which is connected between two OpAmp pins, but it haven't changed anything.


for the regulator heatsink, it is spaced of all components and rack bottom.. so I don't think there is problem with it.


as you've wired it, both preamp grounds connect to the psu gnd, so the gnd of the psu card would be your star gnd. These gnd's for the different voltages (except relay gnd) are already connected on the pcb of the preamp- and psu card, so 1 wire for connection will be sufficient.
Click to expand...

mmmm If I undestand right you mean that I could have only one ground wire between preamp PCB and PSU PCB.. which means for example to remove the ground cable of 48V and relay, and just let the +/- 18V ground cable ?


Code: 
The xlr-pin 1's all connect to your "flying" star gnd, which is placed in a different spot. May matter.

I don't understand what you means by different spot... the pin 1 of each XLR and jack are connected together in star ground as you can see it on the picture in the previous page of this thread. What should I do with thoses Pin 1 of Mic input XLR ?
 
Hi everybody!

I'm back for a new and a last problem !! ( I hope so :green: )

I already had the problem and asked here some help, but nobody succed in finding a solution, and I didn't found myself too ! :cry:

so, the problem is : I have 2 preamp board connected to one PSU board ( all PCB and DOA are from fabio). When I switch on the power , resistor R2 ( a big 10 ohm, 5W one) of the PSU comes very hot and I can't touch it with my fingers after 4/5 seconds of running ! then, when I switch off the power, one of the 2 power LED stop glowing instantanely, while the other one stop glowing slowly after 20 seconds. So, I thought it was a short-circuit problem. I checked many things and I found that the problem occur only when the first preamp board was connected to the power supply. I checked the solder on the PSU and preamp board ( to avoid bad solder or short circuit), but no change.
So, could it be the few caps and diode between the PSU and the DOA , or the DOA that could be bad ?

Does somebody had the same problem on his API ? thanks a lot for your help :razz:


P.S : I still haven't tried the modification of the ground wiring, I'll try it soon, but for the moment, the big hum and buzz has disappeared when plugged into the Firepod.. so, it is perfect like this, but noise reduction can be still improved.
 
R2 devient trop chaude a cause de la difference de potentiel.
je n'ai pas utilise de R2, en fait il y a un thread ou ca parle de comment bypasser cette resistance. peut-etre tu n'aurais pas besoin.

Quelle LED reste allume?

bonne chance.
 
merci 3nity !!! je vais lire ça attentivement.. mais même en supprimant R2 ça ne résoudrais pas le problème de court-circuit qui se trouve quelque part aprés R2 :? .... bref, je vais lire et checker tout le reste, quite à dessouder et resouder tous les composants necessaires :?

sinon la led qui s'éteint instantanément est celle reliée à la borne LED- de la PSU. ah ui je précise également que j'utilise les régulateurs d'alim réglé sur + / - 18.5V , le régulateur des relais est en 24V et il reste celui en 48V. J'ai également enlevé R10 et mis un fil entre la jonction R1/C1.
 
[quote author="flintan"]Mick, does your solution work good? It connects the +/- signal to ground via the PP resistors when not using PP. Have you tried it with dynamic or ribbon mics?[/quote]

Sorry it took so long to reply, I've had it checked it out now, and it work's fine as I posted before

http://www.twin-x.com/groupdiy/albums/userpics/phantom_drain_2.bmp

however my friend thought it would be a good idea to add another 1K resistor to Fabio's board if you are planning on using this mod, if you look at the above diagram there is a link wire to the left of the RPP3 resistor which supplies the 48v to the switch, change that link to a 1K resistor. The reason for this is that the CPP1 cap is totally drained (through a 1K resistor) so when you switch the 48v back on it won't hit the (now empty) CPP1 cap so hard, he said this could be wired so you only need one resistor for both jobs but the pads on my boards are not looking so good so I don't want to re-solder them anymore. Hope it helps

Mick
 
Hi everybody !


I have a question : Can I connect two API 312 board in serie for the power supply. I mean to have a wire going from the PSU board to the first preamp board, and then another going from board1 to the second one. here a little schematic of what I mean :

http://rapidshare.com/files/77664908/cablage_API.JPG.html

Does it will have any influence on the sound when both preamp will be working at high gain?


thanks for your advice :wink:
 
Hi everybody

Does somebody have any news from Fabio ??? We (a french DIY group) are trying to contact him for one month now, and he never answer to our message on msn, or our email. Do you know if he had any problem with people here on prodigy ? Some of them have paid for some parts that they never got, and they still wait since 6 monthes ! So ... we thought that he was an honnest guy .. we don't know what to think about him now... :?

let me know if you know something
 
:green: :green: okay guys

but more seriously, I've always got very good contact with him, I used to speak with him very often for our API projet ( that worked fine, even if we had some problem of shipping), but we would like to buy him some 2520 DOA more. Another guys here have not received 1 boards and 2 DOA for Sonetec EQ project, and Fabio told six months ago that he will send it.. guys here are still waiting :roll:
I don't know why he suddenly stopped to answer us.. there are no reasons. When he has not the time to answer he alway tell me and I wait if it needs, but no answer at all, since more than one month now... :?
 
I think he's probably got a lot on his plate. It took me over a year to get some things from him one time. I was once told by somebody that people sell things around here as a favor to the people on this forum, and I should not complain. I disagree... After that, and being burned on a couple of items and one group buy, I just stopped buying stuff from people around here.
 
I'm sure it has been more work than it's worth for him ,
but true without the economy of scale savings , or a unique
pcb , you can control your own destiny with the parts company
yourself , part by part instead of just buying one [ which i would do
in most cases if i had the money ]

Some people [ including him ] have a track record , but sometimes
it is like driving across town to save a nickle .

At one point though no one had api or 1272 boards , so balence
between frugal and in a hurry
 

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