Single chip makeup stage - is really that simple?

[snaper]

Hi Guys,

Lot of great projects here, and started to build a few of them.
My question is regarding the makeup gain stages.

I would like to use simple opamp gain stages, no need for transformers or balanced outputs...

...but is that really this simple ?

http://www.electronics-radio.com/articles/analogue_circuits/operational-amplifier-op-amp/op-amp_basic_non_inv.gif

 

[JohnRoberts]

Simple in concept but there are always details missing.

Try to find actual schematics with similar functions to what you want, and try to understand all the extra parts, that aren't shown in the simple drawing.

JR

 

[snaper]

Would like to achieve a simple 20db makeup for  a passive pultec, instead of the tube one.
Could you recommend something?

 

[pvision]

I suspect I am as ignorant here as you, but you may find these links to be a help:

Rod Elliott on opamp designs
http://sound.westhost.com/dwopa.htm

THAT chip selection guide
http://www.thatcorp.com/THAT_IC_Selection_Guide.shtml

THAT 1583 details & data sheet
http://www.thatcorp.com/1583_Low-Noise_Differential_Audio_Preamplifier_ICs.shtml
http://www.thatcorp.com/datashts/THAT_1583_Datasheet.pdf

Nick Froome

 

[ruffrecords]

An op amp can work perfectly well as a gain make up amp. You should use the non-inverting configuration for two reasons:

1. The gain setting components do not affect the input impedance.
2. It is quieter than the inverting configuration.

As others have mentioned, there are several praactical details that you also need to take into account.

Cheers

Ian

 

[snaper]

Thanks for the help guys.
I've drawn this for the Gpultec.
Would it work with (for example) with the PoorMans Pultec?
That would be awesome!

On PCB layout plan, there will be enough space to mount a DIP8 based discrete opamp (like the ACSound one)

 

[gyraf]

Looks right, but you'd probably want a 5534 in there instead of the TL071 - just in case you'll want to drive real loads from the output.

Jakob E.

 

[snaper]

Looks right, but you'd probably want a 5534 in there instead of the TL071 - just in case you'll want to drive real loads from the output.

Jakob E.

071 is just used because it was the first single opamp in my eagle library. I think the pinout is the same.

 

[Joechris]

If you want to use it for a poormans makeup, I think you need a fet input opamp with high input impedance. A OPA 604 could be a choise.
I think a 5534 is more happy with a lower input impedance. I could be wrong...

 

[gyraf]

For Pultec filter, anything over 10K does fine, I think

 

[snaper]

Im really confused about these impedance things...
I have a few synths and sampler, I would like to use those with this eq...no microphones or balanced gear in my experimental studio

 

[ruffrecords]

For Pultec filter, anything over 10K does fine, I think

True for a genuine Pultec but not for my poor man's design which prefers a load not much less than 470K (the EQ works at 10K rather than the 600 ohms of the original).

Cheers

Ian

 

[ruffrecords]

Im really confused about these impedance things...
I have a few synths and sampler, I would like to use those with this eq...no microphones or balanced gear in my experimental studio

I think you will be fine with a TL072. Most if not all of your loads will be 10K bridging or a similar impedance unbalanced input. The TL072 will be quite happy driving them.

Cheers

Ian

Edit: If you change R4 to 47K and R5 to a 10K pot you can trim the gain with the pot. You can then remove the pot at +ve input and just leave the 470K.

Ian

 

[mitsos]

Hey man, sorry to spam your thread, but I'm clearing out a bunch of utility PCBs I've had made over time.  Take a look at this thread and see if this'll work for you.  Ive used it for buffered direct outs (usually with gain),  it's just a non-inverting opamp so you can do what you want with it, and it goes out to an impedance balanced TRS jack.

I posted them yesterday in the Black market, and promised a few buyers I would put the schematic up:

http://groupdiy.com/index.php?topic=59043.0

 

[ruffrecords]

Hey man, sorry to spam your thread, but I'm clearing out a bunch of utility PCBs I've had made over time.  Take a look at this thread and see if this'll work for you.  Ive used it for buffered direct outs (usually with gain),  it's just a non-inverting opamp so you can do what you want with it, and it goes out to an impedance balanced TRS jack.

I posted them yesterday in the Black market, and promised a few buyers I would put the schematic up:

http://groupdiy.com/index.php?topic=59043.0

No problem. Looks like a useful little board. One question. On your schematic there is no dc connection to the +ve input necessary to set the dc conditions.

Cheers

ian

 

[mitsos]

Thanks, Ian.  The connection is there, pin 7 on top of the opamp, I had to edit the schematic to get it to fit the screen, and besides being kind of fuzzy looking, the junction ended up in the wrong place, is that what you're seeing?  Both rails and ground are there, as well as 2 ceramic caps from the rails to ground.  The board actually has two sets of pads for power, so by putting a header in one of the pad sets and wiring a female Molex KK to the other, you can daisy chain power from one PCB to the next and still maintain separation of modular channels for console maintenance. 

It's totally doable on perfboard also,  that's how I did the first dozen or so.

cheers!

Hey man, sorry to spam your thread, but I'm clearing out a bunch of utility PCBs I've had made over time.  Take a look at this thread and see if this'll work for you.  Ive used it for buffered direct outs (usually with gain),  it's just a non-inverting opamp so you can do what you want with it, and it goes out to an impedance balanced TRS jack.

I posted them yesterday in the Black market, and promised a few buyers I would put the schematic up:

http://groupdiy.com/index.php?topic=59043.0

No problem. Looks like a useful little board. One question. On your schematic there is no dc connection to the +ve input necessary to set the dc conditions.

Cheers

ian