Just THAT - preamp (Pre Grinder)

[Gustav]

This is a simple pre based on the THAT1512/1646 combo.

I have built a handful of 1 channel versions and a single 8 channel, and the circuit has performed very well in all applications so far.

I hope these will work for self etch, in case anyone is interested.

https://pcbgrinder.com/download/Pre_Grinder_doc.pdf

The High pass frequency can be set by changing C21, and thats about it.

Just wanted to share.

Gustav

 

[dissonantstring]

Cool!  Thanks Gustav!  This might come in handy one day!

 

[sonolink]

Hi
What kind of sound do these preamps have?
Do they compare to others?
Cheers
Sono

 

[seavote]

Thanks.  Have had these ics hanging around for some time. I either got them as samples (mail)or acquired them at an AES convention,don't remember which.

 

[Gustav]

Hi
What kind of sound do these preamps have?

I would say detailed and open, and they are not a clone of anything.

It's just a simple board, which is easy to build, and the schematic is almost identical to THATS own implementation notes.

Gustav

 

[Nele]

Nice!
C21 is cap A/B on the components overlay, right? And what value did you use?
Also some small suggestions:

- maybe include some text in the self-etch file? this way it will be 100% clear which way is up
- add the component numbers to the parts overlay?
- add a bom

Might be overkill but an external filter option would be great. I'm thinking of combining this with the Harrison filter board (minus the (de-)balancing chips). Is using the C21 pads all that's needed in combination with a DPDT-switch?

Thanks for this!

 

[Nele]

One more thing:

Include PCB-dimensions. I etched these from the pdf and they are too small! 

 

[Gustav]

One more thing:

Include PCB-dimensions. I etched these from the pdf and they are too small! 

So sorry about the scale being off. When I printed the output to PDF and sent the PDF to my own printer, it came out in the correct scale, so I hoped that would be universal. I will look into it next week and change the files, so they are correct scale if I can figure out how  - and Ill also add the dimensions.

The rest is up to you or anyone else who might find use for it - and adding a Harrison Ford filter to this would be out of touch with the philosophy behind doing this. I tried to do a board to learn something basic about PCB and circuit design with a simple circuit, I tried to make plenty of room on the board and large pads for a beginner, and i hoped it would sound better than usual soundcard and interface stock preamps. I almost excluded the fixed high-pass, but it is just so damn useful.

I hope you get good result. I am still amazed at how good my rack of 8 sounds - and I am getting recordings in from people using my scattered 1 channel prototypes that are gorgeous. Sound was the parameter i was most worried about, and the chips must be great, cuz I have no idea what I'm doing half the time - and I will not be adding any bells and whistles. I would rather move on to something else

Gustav

 

[Nele]

So sorry about the scale being off.

Hi Gustav,

I double-checked and in the pdf the pcb is about 120 mm long. If I resize it to the correct ic-footprint it ends up around 142mm (width of copper), so there is some strangeness going on.
I noticed on your website that you sell parts-kits but no pcb's for this project. Is that a matter of time? I would be interested in a few. Home-etching is fine but drilling is a pain in the ass!

Cheers,
Corneel

 

[Gustav]

So sorry about the scale being off.

Hi Gustav,

I double-checked and in the pdf the pcb is about 120 mm long. If I resize it to the correct ic-footprint it ends up around 142mm (width of copper), so there is some strangeness going on.
I noticed on your website that you sell parts-kits but no pcb's for this project. Is that a matter of time? I would be interested in a few. Home-etching is fine but drilling is a pain in the ass!

Cheers,
Corneel

Will check the self etch PDF and see if I can get a new one up in the correct scale

Gustav

 

[Spencerleehorton]

HI Guys,

As per the printing the self etched file out there is normally some difference within the accurate output i have found. I think i adjusted my printer to 125% and this fitted ok. bit of a mine field but i used the pins off the IC's as a good guide.
have printed out 2 self etch'd boards just gotta drill and then give them a coating.
If i nickel plated the pcb after drilling would this be ok to solder or should i use something else?

regards

Spence.

 

[gyraf]

Don't nickel plate - that is impossible to solder.

Better tin it, that's the common solution. Or leave it copper, that's the old-fashioned and simple solution.

Jakob E.

 

[Spencerleehorton]

Ah thanks for saving me bacon there!!!

yeah just gonna leave it copper i think!!!

regards

Spence.

 

[burglar]

Hi folks,

These have been around for a while now.  I'd be keen to hear some reviews on the sound.  I'm looking for x8 cost effective clean pre's.  are they based on or close to a commercial product?

 

[Gustav]

Hi folks,

These have been around for a while now.  I'd be keen to hear some reviews on the sound.  I'm looking for x8 cost effective clean pre's.  are they based on or close to a commercial product?

They are simply based on the THAT design notes for a clean, open preamp, and if you self etch, you can do this pretty cheaply and get preamps that a far beyond the usual interface preamps.

I havent included footprints for alternative caps (Wima 6,8uF) but....Note that the input caps are in parallel, and you can add up any caps to get the values with a little twisting, bending and slight of hand.

If you want more than just a few preamps, you can do your own basic layout from the THAT design notes. It is a very nice learning experience.

Gustav

 

[erik_DK]

This is a simple pre based on the THAT1512/1646 combo.

Just wanted to share.

Gustav

Hi.

I am new to this forum, which I came across a couple of days ago. Sorry if this is not the right thread, but I suppose it is. I have been playing in bands for some 40 odd years, and have always been "the guy with the soldering iron", so I know how to solder, and I have some basic knowledge of electronics.

I think of buying two complete kits from PCB-grinder and build a 2 channel version of this pre-amp. I guess that is what you did in your second picture.

I have a 1U 19" case lying around, which is not deep enough to mount the PCBs front to back like you do in the 8 ch. version. They will have to be turned 90 degrees.

Will there be any problems, not having the gain potentiometer and the switches for phantom power and low-cut soldered directly to the board, and instead connect them via short wires? Should I use screened cable for the potentiometer?

For convenience I want the mic-inputs on the front, but as they seem to be connected with wires anyway, I expect no problems here.

I also would like to put in an indicator-LED to show if phantom power is on, just to have a visual warning before plugging in some ribbon-mic. If I make the switch for phantom power a DPST, I could use half of it to turn on a LED connected between the rails of the 48V supply via a suitable resistor. Will this have any negative effects regarding a clean supply to the microphones?

And yes, I know, that the electrolytics for the power supply will have to be mounted off the PSU board.

Regards
Erik

 

[Nele]

Will there be any problems, not having the gain potentiometer and the switches for phantom power and low-cut soldered directly to the board, and instead connect them via short wires? Should I use screened cable for the potentiometer?

I don't think there's any problem. Keeps the wires as short as possible and just twist them together.

I also would like to put in an indicator-LED to show if phantom power is on, just to have a visual warning before plugging in some ribbon-mic. If I make the switch for phantom power a DPST, I could use half of it to turn on a LED connected between the rails of the 48V supply via a suitable resistor. Will this have any negative effects regarding a clean supply to the microphones?

You could use a DPDT switch with two seperate poles so you could also use the +15V powerline to switch the led and keep the 48V clean.

And yes, I know, that the electrolytics for the power supply will have to be mounted off the PSU board.

I don't think this is necessary. You will need a seperate PSU board, but Gustav's standard psu has room for the electrolytics.

 

[Nele]

And welcome to the forum! 

 

[erik_DK]

And yes, I know, that the electrolytics for the power supply will have to be mounted off the PSU board.

I don't think this is necessary. You will need a seperate PSU board, but Gustav's standard psu has room for the electrolytics.

Yes. But a 1unit rack is very low. :

Kind regards
Erik

 

[Nele]

Yes. But a 1unit rack is <b>very low</b>. :

It depends a bit on spacers and cap-height what value will fit. If too low an option would be to keep the leads on the caps long and bend them.
On the other hand I've built quite a lot of gear in 1U cases (neumann eq, ssl comp, forsell comp, nite eq etc) and never had any problems.

Cheers,
Corneel