Access-312 Build Thread

[mattmartin831]

I am building an 8 channel unit using this build guide, but I am wondering does the rack chassis I use have to have an anodized coating? The rack enclosure I purchased is simply painted black, so I am worried i may end up with a 60 Hz hum being picked up by my preamps. Can anyone shed some light on this for me? I am planning to use an external power supply, but my preamp will be racked with my audio interface as well as another preamp. Any info would be appreciated.

 

[TillM]

As long as you use an external power supply you should have no problem with hum.
I'm also sure that the 312 Preamp has less hum problems, even if the power supply is in the rack.

 

[mattmartin831]

In that case maybe will put the power supply in the rack case. I've been searching for ptownkid's power supply kit to use with this build but I haven't had any luck finding it, can anyone point me in the right direction to find it or another suitable power supply for this build?

 

[Whoops]

I am building an 8 channel unit using this build guide, but I am wondering does the rack chassis I use have to have an anodized coating? The rack enclosure I purchased is simply painted black, so I am worried i may end up with a 60 Hz hum being picked up by my preamps. Can anyone shed some light on this for me? I am planning to use an external power supply, but my preamp will be racked with my audio interface as well as another preamp. Any info would be appreciated.

I dont understand your question.
Whats the problem?

The case should be metal, thats it.

 

[Whoops]

In that case maybe will put the power supply in the rack case. I've been searching for ptownkid's power supply kit to use with this build but I haven't had any luck finding it, can anyone point me in the right direction to find it or another suitable power supply for this build?

The problem is not the PSU but the transformer.

Transformers can induce hum. Just get a Toroid transformer for less EM interference.

As for PSU, you need a 2 rail PSU with a 48V rails, any will do.
With 7815 and 7915 or with LM317 and LM337, any will do.
Plenty of options in the White Market

 

[TillM]

I think the easiest one for your project should be Pier Paolo's PSU, especially designed for the Access 312 or the ML12 PSU from Whislerock. These two PSU's are designed for a 312-style Preamps.
But like Whoops said, there a plenty of options in the White Market.

 

[3nity]

I always used PeterC psu, simple and does the job...
I like to run my pres at 17V that way the regs wont run hot and you get the best from the op amp.
Just my  0.2 cents.

Thanks.

 

[dandeurloo]

You can use these for the PSU.  Very simple and affordable.

http://collectivecases.com/?product=psu-cc-psu1

and if you want to go one step further

http://collectivecases.com/?product=dc-filtering-pcb

 

[mattmartin831]

You can use these for the PSU.  Very simple and affordable.

http://collectivecases.com/?product=psu-cc-psu1

and if you want to go one step further

http://collectivecases.com/?product=dc-filtering-pcb

I am building an 8 channel API 312 preamp, and my next project will be a 4 channel neve 1290 preamp. Would it be possible for me to use those two products  together in order to power all 12 preamps from one supply?

 

[Whoops]

I am building an 8 channel API 312 preamp, and my next project will be a 4 channel neve 1290 preamp. Would it be possible for me to use those two products  together in order to power all 12 preamps from one supply?

Martin, you are still not ready to build those projects. You have to learn more first and understand the basics.

You should do a guitar pedal first, and continue from there, learning, gaining experience and skills.

Also you should do much more reading here in groupdiy.
The rule is "Search before asking"

All those topics have been discussed a lot of times

 

[mattmartin831]

Martin, you are still not ready to build those projects. You have to learn more first and understand the basics.

You should do a guitar pedal first, and continue from there, learning, gaining experience and skills.

Also you should do much more reading here in groupdiy.
The rule is "Search before asking"

All those topics have been discussed a lot of times

I have no use for a guitar pedal, so I do not intend to build one at this time. However, as an employed electrical engineer with 7+ years experience soldering PCBs , modifying microphones, etc, I think I will have little trouble completing these projects. However I do not know the current draw of each preamp channel, so my question was perhaps worded poorly. Would it be possible for the CC PSU with 1.6 Amps over 16 Volts be able to supply enough current to power 8 channels of API 312 preamps and 4 channels of Neve 1290 preamps combined?

 

[Whoops]

However, as an employed electrical engineer with 7+ years experience soldering PCBs , modifying microphones, etc, I think I will have little trouble completing these projects.

Well, that's not really coherent with your questions and posts.

... Anyway, good luck, and I will try to help in what I can.

But you have to read the relevant threads first.
Current Draw of these projects was already stated in quite a few posts.

Also if you've done minimal reading you would know that the voltage needs of an API type circuit are not the same of a Neve circuit. And I guess that's on the first post of each of the project threads. Also easily seen on any of the projects schematics.

There's really no shortcuts, Search and Read before posting.

 

[Pusch3l]

The 16volts are pretty fine for the 312s. But the 1290s are a total different kind. You surely can hook a 16v PSU on them but they will not work as they (and you can read that in the 1290 Thread and Build Manual) need 24volts...

If you Solder the DOAs yourself double and triple check your soldering. Theyre a bit bitchy...

 

[Harpo]

...However, as an employed electrical engineer with 7+ years experience soldering PCBs , modifying microphones, etc, I think I will have little trouble completing these projects. However I do not know the current draw of each preamp channel, so my question was perhaps worded poorly. Would it be possible for the CC PSU with 1.6 Amps over 16 Volts be able to supply enough current to power 8 channels of API 312 preamps and 4 channels of Neve 1290 preamps combined?

Your wording didn't get much better, and you need to read more carefully.
Doesn't read "the CC PSU witch 1.6 Amps over 16 Volts". It says "the PSU can deliver 1.6A of power to symetrical +/-16 volt rails", that is 0.8A for the +16VDC rail and 0.8A for the -16VDC rail, each in respect to their 0V reference in between. +/-16VDC is 32VDC differential, that is  either 8VDC more or 8VDC short than a 24VDC Neve 1290 preamp circuit is designed for. Not knowing your connected load to these preamps (<600R ... >10K) and the type of DOA used (next to different abs.max. parts values, different types of DOAs come with different idle current...) this is next to impossible to answer. (An analogy would be questioning, if a mains fuse would be sufficient for 8 parallel loads and keeping it a secret, if these loads would be night lights or roomheaters...).
The "CC PSU1 also has a +48v (140mA) phantom power output" might be not enough for supplying all (8+4) channels, considering the LEDs current consumption per channel, additionally drawn from this 48VDC rail.

 

[mattmartin831]

Thanks for all the input so far, I think I have my power supply figured out now.

I have another question regarding the input impedance of the circuit. I understand that when the jumper is not active between points 2 and 3 on the schematic, the input impedance is 150 ohms, and that when the jumper is in place it becomes 600 ohms. The line outputs on my audio interface have 300 ohm impedance and it would be nice to able to add some API color to recordings sent to me from other people. I would of course pad the signal down by 40 to 50 dB on the way in, but I'm wondering if there is a way to match the impedance as well. Is there any option to set the input transformer's impedance to 300 ohms with a third setting on a 3 position switch perhaps?

My assumption would be that this probably will not work, but i'm hoping someone can prove to me otherwise.

 

[Whoops]

Thanks for all the input so far, I think I have my power supply figured out now.

I have another question regarding the input impedance of the circuit. I understand that when the jumper is not active between points 2 and 3 on the schematic, the input impedance is 150 ohms, and that when the jumper is in place it becomes 600 ohms. The line outputs on my audio interface have 300 ohm impedance and it would be nice to able to add some API color to recordings sent to me from other people. I would of course pad the signal down by 40 to 50 dB on the way in, but I'm wondering if there is a way to match the impedance as well. Is there any option to set the input transformer's impedance to 300 ohms with a third setting on a 3 position switch perhaps?

My assumption would be that this probably will not work, but i'm hoping someone can prove to me otherwise.

You don't want impedance matching, you want the input to have 10 times higher impedance than the source

Using a resistor PAD will lower the voltage but also lowers the impedance.
A 40dbs Pad on Line inputs, puts the Voltage and Impedance at what a Mic Preamp input likes to see. No need to change anything besides ading a PAD

More Reading:
http://www.uneeda-audio.com/pads/

 

[lachlan.vercoe]

Hi there,
Has anyone ever built these with EA 2623-1 Litz output transformers rather than EA 2503 Litz outputs?
Any issues doing this?

I'm building 8 channels of these and have 2623-1 Litz o/p instead of 2503.
Only thing is the 2623-1s are 6 wire vs the 8 wire 2503s... Looking at the Litz PDFs on the CAPI site isn't calriying things for me, the missing wire colours are White and Yellow, white = Output Pin 2 and Yellow is tied to Grey.

Does anyone feel generous enough to point me in the direction of a way to translate the 6 wire 2623-1s to this application?

Thanks!

 

[Whoops]

Wire the transformer this way

And don't forget to do the grounding this way

 

[chipss36]

Anyone have documentation on the ps universal-ss power supply? Rev1-2011?  Diypartssuppy seems no more,  sad so many broken links on this great project.
Motown will never be the same!

 

[Whoops]

Anyone have documentation on the ps universal-ss power supply? Rev1-2011?  Diypartssuppy seems no more,  sad so many broken links on this great project.
Motown will never be the same!

Is that related to 3nity's Access 312 project?