Access-312 Build Thread

[sr1200]

I'd call you very brave for etching your own DOA.  They're small enough to begin with with a LOT of holes that need to be drilled on a 1" x 1" board.

 

[Spencerleehorton]

Hi,

have gone with the GAR2520 boards!!! they arrived and i see what you mean, proper tiny!!!!

regards

Spence.

 

[emtee]

Anyone got any pointers as to where to buy the Mill Max sockets in the UK. I'm drawing a blank everywhere...

Thanks.

 

[emtee]

Well in answer to my own question, I'm going to give these a go -

http://www.ebay.co.uk/itm/80-x-Socket-Pins-for-Nixie-Tubes-IN-12-IN-18-IN-2-IN-8-IV-22-VFD-Valve-PCB-Gold-/161111364744?pt=UK_Sound_Vision_Other&hash=item2582fc5488

May need a little trimming but all the specs seem to add up.

 

[sr1200]

I think i got mine thru whistlerockaudio.com  (same place i got my DOAs and powersupply)

 

[emtee]

Yep, I looked on Whistlerock's site but it ends up being fairly expensive and postage may well be 2 weeks. I should have ordered them from Classic API when I bought the DOAs and trannies.  :

 

[Spencerleehorton]

Hi Guys,

At some point im gonna put together the rest of this API 312 build, just wanted to check a couple of things:
API 312 BOM

R1 = 6k8
R2 = 6k8
R3 = 470R
R4 = 100R
R5 = 10k reverse log pot
R6 = ?
R7 = ?
R8 = 120R
R9 = 470R
R10 = 470R
R11 = 6k8
RC = 150k

C1 = 220uf / 35v
C2 = 220uf / 35v
C3 = 100nf / 35v
C4 = 100nf / 35v
C5 = 220uf / 63v
C6 = 220uf / 63v
C7 = 100pf / 50v
C8 = 220pf / 50v

D1 = 1N4007
D2 = 1N4007

3 x Push button switches DPDT - F2UEE type
1 x LED for 48v

DOA -GAR2520 op amp
Input transformer - OEP A262A3C
Balanced Output board (as per GSSL) or Transformer
Ratio Jumpers

What are R6 and R7?

any other specific requirements i need to watch out for i.e when using the OEP transformer?

Is it ok to use the GSSL psu pcb?

all help appreciated.

regards

SPence.

 

[Spencerleehorton]

HI All,

Im looking for a few answers to the following:

1. the schematic that is on here has an IC in it before the output transformer? this isnt on me pcb's what is it, and is there a another schematic without this IC?
2. when using the OEP transformer for the input what should be the changes in the other values?
3. im planning on using a balancing board as per the Gssl instead of transformer and changes or can this go straight in? also thinking of designing a pcb that will fit in the output transformer space.
4. if a balancing board can be used in replacement for the output transformer can something else similar be use for the input transformer?

all help welcomed.

regards

Spence.

 

[Harpo]

For your previous questions for your BOM (and ignoring your following questions), have a look at my edits from post #310.
The GSSL has its psu on main board.
If you want to adapt all changes from your following questions into this then remaining circuit, the valid parts of this BOM might decrease to 6 remaining resistors, partly missing their power rating, 3 switches, a LED and maybe some molex connectors.

1. the schematic that is on here has an IC in it before the output transformer? this isnt on me pcb's what is it, and is there a another schematic without this IC?

The DOA (discrete operational amplifier).

2. when using the OEP transformer for the input what should be the changes in the other values?

Depends on how you hook up the 1+1:6.45+6.45 primary windings and secondary windings of your OEP A262A3 (ordered with mu metal shielding as separate accesoir). Parts values of R6, R7/RC and C8 are related.

3. im planning on using a balancing board as per the Gssl instead of transformer and changes or can this go straight in? also thinking of designing a pcb that will fit in the output transformer space.

The GSSL has no separate balancing board. No need for the current drive ability of a DOA with following THAT1606/1646, DRV134/135 or SSM2142 balanced line driver chip. A single opamp (maybe on an adapter board to plug in to the DOA sockets) might do as well. YMMV.

4. if a balancing board can be used in replacement for the output transformer can something else similar be use for the input transformer?

Sure. THAT1510/1512, INA103/163/217, SSM2017/2019 with surrounding circuit.
It seems you want the Access-312 board as an oversized carrier for the switches and replace nearly everything else (i/o connectors, phantom and pad circuit might stay) with different circuits on adapter boards ?

 

[Spencerleehorton]

Hi Harpo,

I have four channels so i wanted to do two with transformers (OEP input TXF) and two with something else.
Im interested in if you can use IC's that replicate transformers for the output transformer, what will be the difference if this was also done in replacement of the input transformer, and having these to be able to slot in so if i wanted to change for OEP transformer i could, or if im able to have both and maybe switch them?

The PSU pcb I ment was the SSL 9k psu sorry got confused there, this will be ok right?

Now looking at the schematic i can see that the IC is the (DOA gar2520) thanks for that.

How should i hook up the OEP A262A3? best to get the mu metal can as well yes?

again it was the SSL 9k balancing board i ment, sorry for my mistake.

if you have anymore documentation on any of this i really do need to read up on all this (noob)

regards

Spence.

 

[Spencerleehorton]

Hi Guys,

thought i'd try and put together something which may help, well at least help me, just need to check im walking down the right path!!!

 

[Spencerleehorton]

HI Guys,


Just one more question is the VU-1 and VU-2 connections for VU meters, if so would something need to be put before i connect them?

regards

Spence.

 

[Harpo]

Im interested in if you can use IC's that replicate transformers for the output transformer, what will be the difference

Balanced line drivers come with fixed gain of +6dB, need power supply, are missing galvanic insulation, ... Just look up the parts datasheet. Your output transformer has 3 secondary windings, so can be wired for a 1:1, 1:2 or 1:3 stepup ratio. Standard wiring is a +6dB 1:2 stepup ratio, leaving a spare 1:1 winding that might be used for a VU meter (obviously showing half the level of your other +6dB combined output winding).

if this was also done in replacement of the input transformer, and having these to be able to slot in so if i wanted to change for OEP transformer i could, or if im able to have both and maybe switch them?

I'd trash this idea. This would be a complete transformerless mic preamp circuit, but with fixed gain, set for the input transformers stepup ratio to not mess up your frontpanel gain labeling, would need additional phantom blocking caps, clamping diodes, ...
besides being misplaced in this Access312 build thread.

The PSU pcb I ment was the SSL 9k psu sorry got confused there, this will be ok right?

Ment to 'cheap and cheerful' supply two SSL 9k boards (different circuit with different voltage and current requirement, to be read in context with the mains transformer in front). For four Access-312 preamps, you'd at least need to increase some cap values in the voltage doubler section. I'd use a TL783 for the +48V part.

How should i hook up the OEP A262A3?

Probably input in series, output in series for a 1:6.45 stepup ratio (from Jorge's schematic I'd try R6 24K-33K, R7 47K, C8 220pF) or
input in series, output in parallel for a 1:3.225 stepup ratio (R6 6K25-10K, R7 22K, C8 270pF-330pF). R6 from schematic is 'R6/R7' on silkscreen, R7 is 'RC' on silkscreen.
No idea if the OEP footprint fits on Access-312 pcb.

best to get the mu metal can as well yes?

yupp

is the VU-1 and VU-2 connections for VU meters, if so would something need to be put before i connect them?

VU meter (singular and electro-mechanical device). You connect the meter across these winding ends with IIRC 3K9 resistor in between. A LED meter to mimic a VU meter is a different subject and depending on circuit doesn't need to occupy your spare winding, so you could use this aux.winding elsewhere (FI monitoring, send for psycedelic lightshow, ...).

 

[Spencerleehorton]

HI Harpo,

i just want to be clear with what you have said:
I am wanting to use an input transformer (OEP A262A3) and use a balancing board option.
I have read what you have said and you say about using the OEP and im assuming you mean to use it as the input TFX but wire the output of it in different ways?
Still unclear on what to do for the PSU as this is probably the most important part first of all.
also Jorge has emailed me an 2x 51R resistors, 2x 10K resistors and 2x 470uf/50V which i will try instead of the balancing board, sounds interesting.
If anyone could elaborate on the PSU side of things please?

regards

Spence.

 

[Harpo]

I am wanting to use an input transformer (OEP A262A3) and use a balancing board option.
I have read what you have said and you say about using the OEP and im assuming you mean to use it as the input TFX but wire the output of it in different ways?

AFAIK the Access-312 pcb is layed out for a Cinemag CM-75101APC or a EdAnderson EA2622 (transformer with 8-pin housing). This transformer has two primary windings that can be wired in series or parallel for a 1:5 or 1:10 stepup ratio for the Cinemag or a 1:3.5 or 1:7 stepup ratio for the EA and a single secondary winding. The OEP (transformer with 9-pin housing and different pin order and meaning on secondary side) has two primary and two secondary windings, so these secondary windings can be hooked up in a series or parallel config as well (and you have to pick one option, else it won't work when leaving pins 6 and 7 for the other winding ends unconnected).

Still unclear on what to do for the PSU as this is probably the most important part first of all.

Unless you finaly decide, which parts you will use for your boards (different/additional chips might come with different max.supply rail voltages and will draw additional power), noone could seriously tell you. This will be a minor important part of all.

also Jorge has emailed me an 2x 51R resistors, 2x 10K resistors and 2x 470uf/50V which i will try instead of the balancing board, sounds interesting.

For an impedance balanced output. You lose the +6dB from missing output transformer, so you might decide to use a DOA that allows for higher supply rail voltages for maybe usable increased headroom (the following stage will have max.input voltage limits). Increasing supply rail voltages is not neccessary/contraproductive with output transformer fitted in a stepup config. You cannot make these descisions without context to surrounding parts or requirements.

 

[bieckmusic]

I'm planning out my 4-channel access 312 build and was wondering,  :
at the risk of advertising my lack of experience with impedances 
with the Cinemag CM75101APC input transformer:
Is there a way to wire it, possibly in reverse, or utilizing the combinations of the two transformer primary input taps,  (150 ohm 600ohm) to use that mic input transformer as a D.I. or a line input to the pre?

I've read about people wiring the Neve 31267 in reverse to get a line in?  I'd really want to add a cheap D.I...  and/or line input.

Anyway, if there's any experience on this,
I've looked at the Jensen D.I. box schematic,    http://www.jensen-transformers.com/as/as007.pdf
My thinking is that it wont work because the Jensen D.I. transformer has a 12:1 ratio, which looks like a much higher ratio than the cinemag?

Or, is there an alternate mic transformer that also has a 12:1 tap?

 

[Harpo]

The OEP A262A3 is 1+1:6.45+6.45. With primary windings in parallel and secondary windings in series this is a 1:12.9 ratio.

 

[bieckmusic]

Thanks Harpo!! On their website I found the A262A3E, is that what you were referring to?  150 and 600 primary, secondaries are 6.25k and 25.k, so  primary windings in parallel and secondary windings in series for DI mode, do you know the configuration for Mic mode... 

It says no D.C. through the windings, will the 48v phantom be destructive?

Thanks again, always appreciate all of your feedback on the forum 

 

[Harpo]

Thanks Harpo!! On their website I found the A262A3E, is that what you were referring to?  150 and 600 primary, secondaries are 6.25k and 25.k, so  primary windings in parallel and secondary windings in series for DI mode, do you know the configuration for Mic mode...

Yepp. For DI/line mode you most likeley don't want a 1:12.9 but 12.9:1 ratio and make up the -22.2dB step down loss in the preamp. 

It says no D.C. through the windings, will the 48v phantom be destructive?

With a not broken/shorted mic cable connected there is no DC through the winding. An applied phantom voltage with matched 6K81 resistors (same value is more important than absolute value) is common mode. If either XLR-pin2 or XLR-pin3 is shorted to phantom voltages 0V reference voltage in a broken mic cable, this isn't common mode anymore but 48V differential and there will be 7mA DC current flowing thru the winding. Same might happen if the 6K81 resistors power rating is not sufficient and you had connect a broken cable. This might kill your opamp/DOA as well from missing protection clamping (when you switch on phantom voltage with broken cable connected, opamps noninverting input sees 48V times transformers stepup ratio, far exceeding the opamps supply rail voltages. This switching on from 0V to +48V by definition isn't DC but AC, so the transformer will not block but reflect it to its secondary side).

 

[dirty1_1garry]

Hi!

Just purchase four 312 pcbs.
Is there are any possibilities to insert HPF into 312 preamp?)
Thanks!