Urei MOD-1 OpAmp

Here's another little opamp i've made a self etch layout for. It's the DOA used in the Urei MOD-1 broadcast desk. I'm fascinated with how simple some audio equipment can be. And since this is as simple as it gets for a DOA, i thought i'd give it a whirl. 

First of let me link the thread on GDIY where i first saw this opamp.
 http://www.prodigy-pro.com/diy/index.php?topic=16313.0
Since the schematic, layout and PCB that Peter Purpose (of lazpro.com Check his stuff out!) made for this OpAmp were missing. I thought it might be nice to make my own just to try it out.

So here's the schematic of the original opamp:

and you can download this schematic in HUGE format here.


The original schematic can be found in this .pdf on page 61, along with a host of schematics to build an entire mixing board using this little building block.:
http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-MOD1.pdf

this opamp was used by Peter Purpose as the differential amp on the input on his version of the API 525 compressor. As can be seen here:
http://www.prodigy-pro.com/diy/index.php?topic=22699.msg280210#msg280210
and this is the schematic of that version:

as you can see he substituted the original transistors with commonly found ones and the output pair was replaced with bc550/bc560 instead of the (medium) power transistor types. He used bc550/bc560 on the output because he did not need the load driving capabilities of the original transistors and because he did not have enough room on his pcb.

Since i do not have the same constraints a he had on his 525 pcb. I decided to make my pcb fit the usual 990/2520 pinout/layout and since i DO want the full driving capability i decided on the common BD139/BD140 transistors as the output pair.

So here's my schematic, layout and PCB:

Schematic
Layout
PCB
note: Layout has been tested in the FiveFish Studio Opamp Test Jig found HERE and is confirmed working.

Some notes on this opamp. This is about as basic an opamp can get, so the performance is of course not stellar. It's not gonna win any prices in fidelity and noise but when used wisely it can probably be a great little performer. And maybe another flavour in you arsenal.
Gain is limited to about 27 dB max so when using this in a mic-pre you might wanna use a step-up transformer and an extra opamp for some extra gain. Also there's probably some DC offset on the output so using a DC blocking capacitor is very much needed. This circuit has been verified working as a diffential amp so i believe it should perform just as wel in the 553 layout posted here earlier.

ok i think that's it for now, next up a more elaborate version of this opamp used in Quad Eight equipment.

Greetings,

Thomas

Hybrid Opamp Self Etch

So here's another little project i've made in eagle. It's a single sided PCB of a Class-A only, no servo version of the JLM Audio Hybrid Opamp.

I decided to make my own board, because that's what DIY is all about! I hate having to buy boards for circuits when you can just as easily roll your own. Designing and making boards is a great way to explore a circuit and to understand them better than when you just bought a board/kit and stuffed it. It has you making relavent decisions about what comes where and why. And you can make boards work with what components are available to you.

First off, let's take a look at the original schematic from the JLM Audio website on which i based my schematic/board. Do have a look around at their site if you're not familiar with them, there's a lot info available for Pro Audio DIY and their kits do look the bizz. Anyway, here's the schematic:

http://www.jlmaudio.com/JLM%20Hybrid%20Opamp%20circuit.pdf

on the website they list these specs for this circuit:
Specifications

• 1.1" x 1.1" PCB
• THD = 0.008%
• Min Load = 50ohm
• Maximum power rails = +/-24vdc
• Idle Current in class A/B = 10to 12mA
• Idle Current in class A = 25mA to 30mA

As we can see it's a great simple little circuit that'll drop just right in to almost any circuit requiring a Discrete OpAmp. The circuit can be run on power supply rails ranging from as low as +/-4.5Vdc to as high as +/-24Vdc, the latter giving it great headroom (+/-15Vdc minimum recommended for any serious audio circuits). The circuit can easily drive a step-up transformer on the output and still maintain a low distortion output. Heck you could even drive a pair of headphones with 2 of these. On top of that, it's easily changable from class a to a/b for some different sonic flavor. Pretty good for an opamp, some resistors/capacitors, pair of transistors, 2 diodes and a led.


Now on to my version. There were a few features of the JLM hybrid that i didn't need, like the servo for instance. Most of the circuits i want to use it with, already have DC blocking capacitors installed, so there isn't any need for a servo. The class switching is very nice, but once you've settled on one or the other you just leave the jumper alone, Right?. Since it's just as easy to solder in two diodes as it is to solder in a led i also did not implement it in my version. here's my schematic, layout and pcb:

SCHEMATIC
LAYOUT
PCB

notes on the PCB: i made most of the holes 0.5 mm to make it easier to drill the holes in the middle. C1 and C2 can be ommited if there are already power supply decoupling caps installed in the circuit you're gonna use the Hybrid with. And finally R1 and R2 should be 1/2 watt resistors to ensure they won't burn up when shorting the output.

ok signing of for now.

greetings,

Thomas


Note: Tested and confirmed working with a ne5534 opamp. The opa627 was found oscillating in the fivefish opamp test jig. will investigate and do some listening tests when i'm back from a well deserved holiday! 

API 553

This is one of the projects i'm working on. It's a 3 band swinging input eq from API. On GDIY you can find a kit in 500 series format designed by "PeterC". Since i don't own a lunchbox (YET!) i decided to make a non 500 series PCB for it.

below you will find the original schematic of the 553 eq:


As you might notice the input stage is unbalanced. Since it's nicer to have BOTH the input as the output balanced PeterC on GDIY edited the original schematic with a balanced Differential input stage. See Schematic below.


As you can see from this schematic PeterC added switchable frequencies for all bands. You could calculate your own freqencies. Below at the references you will find a calculator from the opamp labs website to calculate your own frequencies from certain L (inductance) and C (capacitance) values. Note that the hi band only uses a capacitor and no inductor. Do realize that the bands interact with each other so you can't go tottally overboard with the values. Also higher L values mean tighter q. but i'll come back to that in a later post.

The "swinging input" topology is great for making graphic type eq's and various incarnations can be found on the web. A few good ones in particular can be found on the opamp labs website and links to those can be found below at the references.

So on to my version. Below is the schematic, layout and PCB in pdf of my current prototype. Sadly i have not been able to rack it up just yet. so this schematic has not been tested yet. As you can see i omitted the pots and associated components for the eq part and i just made a pcb for the active stuff. Since i wanted to leave this project totally open ended. You could make it fixed band or add switches and make it semi-parametric.

Schematic
Layout
PCB

On the schematic you will see a few changes opa627 instead of opa604 and some resistor value changes. The resistors were changed to compensate for the use of a 1:2 output transformer instead of a 1:3 tranformer to allow for unity gain. Further more i had some 627 opamps and no 604 opamps but pinout is the same so either should work (627 might even need different compensation values). Also eagle doesn't have a footprint for the 604 build in so i used a 627 instead for now.


References:
api 553 500 series kit
http://www.prodigy-pro.com/diy/index.php?topic=12161.0

opamp labs schematics and LC calculator
http://www.opamplabs.com/cfl.htm
http://www.opamplabs.com/325eq.htm
http://headfonz.rutgers.edu/NYDave/opamplabs-109eq.jpg
http://home.mindspring.com/~redbugg/OpampEQ2.jpg
http://headfonz.rutgers.edu/NYDave/opamplabs-325eqapplication.jpg
http://headfonz.rutgers.edu/NYDave/opamplabs-425-eq-app.jpg

discrete swinging input graphic eq QuadEight 712
http://www.prodigy-pro.com/diy/index.php?topic=42413.0

Hello World.txt...... let's introduce myself.........

Hi there and welcome to my blog!

First of let me introduce myself. My name is Thomas Hopman, i live in Amstedam, the Netherlands and i have studied Audio Design at the Highschool of the Arts Utrecht (HKU) in the Netherlands. Since then i have worked as a Live/Studio Sound Engineer for various companies like DeSmet Studios, Paradiso and the Melkweg and as a repair engineer for Backline Rental company Artist on the Road.

Before i discovered music and girls when i was a teenager(these two usually come together when you're a lowlife with no selfconfidence don't they?) , i was always fascinated by electronics. Every piece of gear that i could open up, would get opened up. Usually without getting back together again. I would always look for books at the library about electronics and technical stuff, which i didn't and at the time never could understand.

It wasn't until about 9 years ago at the age of 20 that i started getting back to electronics. I had found a great place called Groupdiy on the interwebs where Gustav from Gyraf audio was offering PCB's for great audio projects. So there i went, never in my life had i built something from scratch that worked, and ordered all the parts for a SSL compressor clone. And because of the great community over there at GDIY, i had a working piece of gear in no time! After that i started building lots and i mean lots of Guitar pedals because as most people know DIY is not about saving money (cos you just don't save any money) and i wasn't that rich to start with. When i made the SSL clone i still had pretty much no clue at all about the workings of electronics apart from the essential basics. So making lots of simple guitar circuits gave me the perfect starting ground to make mistakes and learn a lot in the process.

Since those humble beginnings i've come a long way by teaching myself. Heck i'm even making money fixing stuff. And i'm living my dream of building stuff that doesn't even exist commercially. The purpose of this blog is to showcase some of the stuff i'm doing and to hopefully get some feedback from people doing the same. Heck, some people might actually learn something from this stuff or get inspired to make some DIY gear of their own.

Hope people will enjoy reading this stuff, if you like/hate or find something usefull please feel free to leave a comment.

greetings,

Thomas