Just THAT - preamp (Pre Grinder)

[Gustav]

Seems like most issues have been covered, but I'll try to supplement a little.

When I did the prototypes for this, it was a bit of a wiring mess, and I had no problems with noise as long as the grounding was in place. The box I posted here is 1RU and holds the PSU card and one channel with the pot wired.

I would second Nele's suggestion of drawing 15V to the second pole of the DPDT switch. Theres no need to draw 48V for a LED, and from my limited experience, the lower voltage you can get away with, the better.

The PSU card is pretty small, and you wont have any problems bending the caps if you have problems fitting them upright n a 1RU case (Add heatshrink to avoid exposed, long solder terminals)

Hope that helps!?

Gustav

 

[erik_DK]

Seems like most issues have been covered, but I'll try to supplement a little.

When I did the prototypes for this, it was a bit of a wiring mess, and I had no problems with noise as long as the grounding was in place. The box I posted here is 1RU and holds the PSU card and one channel with the pot wired.

I would second Nele's suggestion of drawing 15V to the second pole of the DPDT switch. Theres no need to draw 48V for a LED, and from my limited experience, the lower voltage you can get away with, the better.

The PSU card is pretty small, and you wont have any problems bending the caps if you have problems fitting them upright n a 1RU case (Add heatshrink to avoid exposed, long solder terminals)

Hope that helps!?

Gustav

Hi Gustav.

It certainly helps a lot. I just did not think of using the +15V rail. Possibly because it had to do with the phantom power.

May I ask you then, what does the second potentiometer on your pictured 1-channel device do? My guess was that you had two channels, and just switched phantom and low-cut on both channels simultaneously.

In the application notes from THAT corporation there is also a 20dB pad and a phase switch. Any technical reason not to include them, or was it just to make it an easier build for beginners?

BTW. Kind of akward to write to another Dane (even in the same city?) in English.

Kind regards
Erik

 

[Gustav]

Seems like most issues have been covered, but I'll try to supplement a little.

When I did the prototypes for this, it was a bit of a wiring mess, and I had no problems with noise as long as the grounding was in place. The box I posted here is 1RU and holds the PSU card and one channel with the pot wired.

I would second Nele's suggestion of drawing 15V to the second pole of the DPDT switch. Theres no need to draw 48V for a LED, and from my limited experience, the lower voltage you can get away with, the better.

The PSU card is pretty small, and you wont have any problems bending the caps if you have problems fitting them upright n a 1RU case (Add heatshrink to avoid exposed, long solder terminals)

Hope that helps!?

Gustav

Hi Gustav.

It certainly helps a lot. I just did not think of using the +15V rail. Possibly because it had to do with the phantom power.

May I ask you then, what does the second potentiometer on your pictured 1-channel device do? My guess was that you had two channels, and just switched phantom and low-cut on both channels simultaneously.

In the application notes from THAT corporation there is also a 20dB pad and a phase switch. Any technical reason not to include them, or was it just to make it an easier build for beginners?

BTW. Kind of akward to write to another Dane (even in the same city?) in English.

Kind regards
Erik

You can use groupdiy.dk for a danish conversation (or send me a mail), but the great thing about forums and more universal languages is, that more people benefit, as long as we are not discussing regional issues, like local shops and get-togethers.

I had a limited amount of front panel space to work with, so I opted for a few, central functions. A filter is much more useful than a pad to me, and a phase reverse on a preamp is so 1988.

The last "pot" is the power switch!

Gustav

 

[tanosky]

Hi there


I just built my own PreGrinder last evening.
So far everything went good, no problems soldering the parts onto the PCB.

I startet measuring the psu board and measured 15v between + & ground.
Between - & ground i got -21v, and i have no idea why?!

Every ground connection is made and working.

Any suggestions would be very appreciated.

Thanks in advance


tanosky

 

[Harpo]

Between - & ground i got -21v, and i have no idea why?!

Regulator needs a little load to operate. A temporary 1K...2K between the neg.rail and 0V reference voltage should prove correct operation without your usual load (the preamp) connected.

 

[tanosky]

Thanks for your reply!

It really was the missing load on the output.
Everything is working as expected

 

[tanosky]

Hello guys


One more question: I studied the schematics and found SW1 to be switching between +48V and Ground. I wanted to remotely switch the phantom power by some microcontroller ( still to decide wich one ) and therefore use an optocoupler to do the switching.
For my understanding, i should be able to place the optocoupler to switch +48 on or off, and leave the "ground pin" of the switch unattached, since the phase+ and phase - signals are already connected to ground by c19.

Right? or am i missing something?

Thanks and sorry for my non-native english

 

[Harpo]

For my understanding, i should be able to place the optocoupler to switch +48 on or off, and leave the "ground pin" of the switch unattached,

Probably yes for the pointless ripple LPF @ 160kHz parts values R3 10R and C19 100nF. Probably no with more common FI R3 100R and C19 100uF/63V for a LPF @ 16Hz, where you probably want a cap discharge path to phantom reference voltage thru R3, else a charged C19 will hold phantom voltage for a looooong time.

since the phase+ and phase - signals are already connected to ground by c19.

Connected to shield/phantom reference voltage thru c1,c2,c3 to help keeping RF out.

 

[grrrunge]

Gustav, is that the PSU board you're selling from your shop, you used for the 8 channel version?
What are the specs for the toroidal trafo you used? I've got an itch to build a box like that

 

[Gustav]

Gustav, is that the PSU board you're selling from your shop, you used for the 8 channel version?
What are the specs for the toroidal trafo you used? I've got an itch to build a box like that

PSU board is the same as in the shop, and was lifted off the schematic used for the 9K preamp project by SSLtech - Its what I used for 8 channels.

Power transformer was 2x18V 30VA.

And Harpo - RE R3, yes, can be 0R, just a jumper with a small value.

Gustav

 

[carlmart]

About 14 years ago I designed and built a few circuits similar to this, using the SSM2017.

Basic schematic was the AD mic preamp by Walt Jung.

Now I would like to try THAT's and others, but using single power supplies, powering from 12v batteries at most, adding an inverter for the split supply, and see if there are better ways to generate 48v for the phantom power.

I can upload the circuits I used.

 

[whiskeynipple0088]

Gustav,
thanks a lot for the etch file of the pre grinder - its my first etch. Cant wait to finish it.
have you allowed anyone to do a home etch of the psu board?
that would be sweet as shipping to the states blows
thanks again

 

[kosty]

The pre grinder is one of the project still unfinished on my work bench.
After having ordered the wrong caps the last time, I didn't work on it for a long time.
Now I wanted to finally finish it and was wondering if these caps are the right ones for the 6.8uF : http://mouser.com/Search/ProductDetail.aspx?R=MKS2B046801M00KSSDvirtualkey50520000virtualkey505-MKS2B046801MKSSD

Because I'm doing an 8 channel version I don't want to order the wrong caps again for 150€ :/

Any help is appreciated.
Btw. attached is a pic of my front panel (from Schaeffer)

 

[mylesgm]

Thinking about building this circuit onto a 51x board, what are the pcb dimensions?

 

[Gustav]

Now I wanted to finally finish it and was wondering if these caps are the right ones for the 6.8uF : http://mouser.com/Search/ProductDetail.aspx?R=MKS2B046801M00KSSDvirtualkey50520000virtualkey505-MKS2B046801MKSSD

Looks right to me.

Thanks so much for building it from my design

Gustav

 

[mastertaenia]

a little question...
What's the rated voltage of c10/cg (1000uf)?

 

[BangDAT]

Go easy on me. Im completely green in the world of electronics.

my question is:

The Toroid transformer listed for this pre is:

https://pcbgrinder.com/index.php?route=product/product&product_id=103

The description states is rated for 110v /220v mains.

Can I use this transformer in the USA where the power is rated for 120?

 

[kante1603]

Hello and welcome to the forum,


yes,you can use it in the usa.
For european or 230vac operation the primaries must be wired in series.
For 110/120 vac just wire them in parallel.
Watch the start and end of the windings.


Best,


Udo.

 

[Cosmonaut]

Hi Gustav, could you confirm the dimmesions of the pcb in the etch files? I'm wondering if  it would be possible to put 4 channels in 1 rack unit, maybe wiring pot and switches...or even putting one board on top of another?

Anyone has done 4 channels in one rack unit?

 

[Gustav]

Hi Gustav, could you confirm the dimmesions of the pcb in the etch files? I'm wondering if  it would be possible to put 4 channels in 1 rack unit, maybe wiring pot and switches...or even putting one board on top of another?

Anyone has done 4 channels in one rack unit?

I am working on it...

And etch dimensions can be verified by checking with an IC socket.

Gustav