completed chipamp pre

[Russ White]

Yep I sure will post a schematic for all of them. It will probably be the next day or two , as I am building a case for my Mauro Ref amp right now and that is likely going to consume my day. But don't worry it will come. I will also include a complete BOM and suggestions regarding the optional parts(like compensation caps) and gain setting.

Cheers!
Russ

 

[Russ White]

FreeBird schematic

I have been getting a lot of email asking for the FreeBird schematic. Here is it is, but be prepared, its ugly. I will clean it up later.

 

[Russ White]

And a parts list for a gain of a little more than 5.

C1 47uf CPOL-EUE2,5-6E E2,5-6E rcl 1
C2 47uf CPOL-EUE2,5-6E E2,5-6E rcl 1
C3 100nf C-EU050-030X075 C050-030X075 rcl 1
C4 100nf C-EU050-030X075 C050-030X075 rcl 1
C5 20pf C-EU025-030X050 C025-030X050 rcl 1
C6 10pf C-EU025-030X050 C025-030X050 rcl 1
C7 47uf CPOL-EUE2,5-6E E2,5-6E rcl 1
C8 100nf C-EU050-030X075 C050-030X075 rcl 1
C9 47uf CPOL-EUE2,5-6E E2,5-6E rcl 1
C10 100nf C-EU050-030X075 C050-030X075 rcl 1
C11 20pf C-EU025-030X050 C025-030X050 rcl 1
C12 10pf C-EU025-030X050 C025-030X050 rcl 1
IC1 OPA627P OPA627P DIL08 burr-brown 1
IC2 OPA627P OPA627P DIL08 burr-brown 1
J1 J7MM J7MM 07 jumper 1
J2 J7MM J7MM 07 jumper 1
JP1 PINHD-1X3 1X03 pinhead 1
JP2 PINHD-1X2 1X02 pinhead 1
JP3 PINHD-1X2 1X02 pinhead 1
JP4 PINHD-1X2 1X02 pinhead 1
JP5 PINHD-1X2 1X02 pinhead 1
R1 4.7K R-EU_0207/10 0207/10 rcl 1
R2 1K R-EU_0207/10 0207/10 rcl 1
R3 1K R-EU_0207/10 0207/10 rcl 1
R4 100K R-EU_0207/10 0207/10 rcl 1
R5 10R R-EU_0207/10 0207/10 rcl 1
R6 1R R-EU_0207/10 0207/10 rcl 1
R7 1K R-EU_0207/10 0207/10 rcl 1
R8 1K R-EU_0207/10 0207/10 rcl 1
R9 100K R-EU_0207/10 0207/10 rcl 1
R10 10R R-EU_0207/10 0207/10 rcl 1
R11 4.7K R-EU_0207/10 0207/10 rcl 1
R12 1R R-EU_0207/10 0207/10 rcl 1

 

[maf_au]

Russ,

Those 627's are like Digikey part# OPA627AP-ND ?

Is there any practical difference between the OPA627AP and OPA627AU opamps? The AU is listed as a SOIC package vs the AP's DIP8, but the schematic and pinouts look the same to my newbie eye...

Michael

 

[DcibeL]

Those 627's are like Digikey part# OPA627AP-ND ?

Those would be the ones.

Is there any practical difference between the OPA627AP and OPA627AU opamps? The AU is listed as a SOIC package vs the AP's DIP8, but the schematic and pinouts look the same to my newbie eye...

I would assume that the different part # is just for the package type. DIPs are always prefered over a surface mount package because if you wreck a dip, it is very easy to take out and replace, especially if it is in a socket. SOIC, not so easy to replace.

 

[Russ White]

Russ,

Those 627's are like Digikey part# OPA627AP-ND ?

Is there any practical difference between the OPA627AP and OPA627AU opamps? The AU is listed as a SOIC package vs the AP's DIP8, but the schematic and pinouts look the same to my newbie eye...

Michael

You should get the DIP package for my boards. It is intended for the DIP package.

You could get the U package (SOIC) but you would have to get an adapter, and the results would not be as good.

Cheers!

P.S. Don't bother spending the extra to get the opa627B it is only better beter than the opa627A in DC, and that serves no purpose here.

 

[maf_au]

Ok, thanks.

I didn't know that a SOIC is surface mount. duh!

What spec do I need on the tranny?

Michael

 

[Russ White]

Ok, thanks.

I didn't know that a SOIC is surface mount. duh!

What spec do I need on the tranny?

Michael

A 24-30VCT trafo good for 250MA is plenty. So anything larger is fine, but larger than an amp or two is really overkill.

I used a 25.5VCT 250MA trafo.

 

[DcibeL]

I'll be using this little torroid, mainly because I already have it. These small Amveco transformers should work very well, and come at a decent price at $20CAD.

 

[maf_au]

And like this one from Jaycar?

 

[DcibeL]

Yes, that one is an excellent choice.

 

[maf_au]

C1 47uf CPOL-EUE2,5-6E E2,5-6E rcl 1
C2 47uf CPOL-EUE2,5-6E E2,5-6E rcl 1

Sorry to be asking all these questions, What do all the CPOL-EU notations mean? Is there a way of telling if it's an electrolytic from that? are they all electros?

What quality and wattage resistors should I get?

Thanks,

Michael

 

[agent.5]

capacitor - polarized - EU(metric) - 2.5mm (distance between leads) 6mm diameter total.

 

[Russ White]

And like this one from Jaycar?

That would work just fine.

 

[maf_au]

Russ, can you explain how you have the internals of your box wired? I've been looking at the photo's and wondering how you have the source and output wired for the firebird and the yardbird.

I don't think they have separate inputs because there is only one volume control. Are they both active all the time and sharing the output from the volume pot? Where does the yardbirds' output terminate?

Michael

 

[Russ White]

Russ, can you explain how you have the internals of your box wired? I've been looking at the photo's and wondering how you have the source and output wired for the firebird and the yardbird.

I don't think they have separate inputs because there is only one volume control. Are they both active all the time and sharing the output from the volume pot? Where does the yardbirds' output terminate?

Michael

Michael, first a little explaination.

The particular preamp in the photo is the one I use with my PC. It takes its input directly from my modded Audigy 4 (AD8620 opamps replaced the JRC parts) via a 3.5mm stero jack at the rear.

That is fed to a single 10K stereo log pot, I then have two wires soldered on each wiper one to go to one channel of the freebird, and one to go to one YardBird.

The outputs of the Freebird go to the 4 RCA jacks in the rear which are connected in pairs in parellel to drive a power amp and an active subwoofer.

The output from the Yardbirds terminates at the 3.5mm stero jack at the center front of the enclosure for headphones. :

This arrangemnet works just great, and everything is very stable, even when either or both the FreeBird and the YardBirds or disconnected from any load.

 

[Russ White]

Sorry to be asking all these questions, What do all the CPOL-EU notations mean? Is there a way of telling if it's an electrolytic from that? are they all electros?

What quality and wattage resistors should I get?

Thanks,

Michael

Yes, those are small electrolytic, Low/Very Low ESR types are best here.

All resistors should be 1/4W 1% metal film.

 

[DcibeL]

Thank you for posting th BOM. Is there a specific capacitor type/manufacturer that you recommend for the other caps (the non-polarized caps)? I am just potting together the parts order now for this board.

This amplifier project of mine keeps getting more expensive every day...

 

[VT67]

This amplifier project of mine keeps getting more expensive every day...

Hhmm..... sounds familiar

 

[Russ White]

Thank you for posting th BOM. Is there a specific capacitor type/manufacturer that you recommend for the other caps (the non-polarized caps)? I am just potting together the parts order now for this board.

This amplifier project of mine keeps getting more expensive every day...

Yes, the parts add up eh, the story of my life.

The 100nf(.1uf) film caps from futurlec are a great choice. And inexpensive. They usally send me Wimas.

Cheers!