opamp construction

Why should I change my opamps
The majority of home electronics appliances are built to a definiate cost , there is little if any margin for the manufacturer to entertain providing esoteric or better specification devices. Yet electronics manufacturers are competing to strive toward the perfect opamp device. There is a branch of manufacture called High end, where performance of electronics is achieved sometimes at very high cost and where the opamp comes under great scrutiny to get the very best result. Both Burr Brown who manufacturer of the opa627 and Analog Devices who manufacture the AD825 , have opamps in high end equipment. An example of this was Audio Synthesis who installed both Burr Brown Digital electronics , and Analog Devices output opamps in their Digital to Analog Conversion models.


An opamp contains a complete amplifier circuit in its basic form it has two inputs , an output and voltage connections for power. There are many common garden variety opamps like TLO71 and TLO72 Dual and NE5534 and NE5532 Dual that have their origins 20 or more years ago. At that time they were regarded as having good audio specification, but now are way behind in terms of their ability to reproduce music compared to modern day devices. The humble opamp can radically change your sound for the better , and at very low cost.

Is it possible to change an opamp myself or should I employ an electronics technician.
This depends on your abilities.If you can follow the images and what is involved - changing opamps really is not too hard. Understanding electronics is a great skill , and spending a bit of time with it can lead you down many different and exciting paths. You will need to spend some time studying components what they do ,and to take the time to understand electrical safety. So yes you can change your opamp but be prepared to learn some new skills. You may also like to employ your local electronics person who might help to show what is involved and in that way you can learn as well as benefit from their expertise.A small outlay of a temperature controlled soldering iron a modest toolkit and a multimeter can provide abilty to fix many electronics items and is lots of fun too.


Instructions for installation - see notes for Quad 405 below

Remove Power to the electrical device , ensuring the power plug itself is removed at all times whilst doing this work. Undo the casework remember to also remove the back screw(s) Locate the Dual opamp device that you need to replace. They should be close to the RCA outlets . If you have ordered the wrong model and you need a Single opamp device DO NOT install a Dual type Opamp where the Single should be.

The importance of getting Pin 1 in the correct location on the circuit board

The opamp Brown Dog adaptor has a square pad indicating Pin 1 – different to the round ones it must match to Pin 1 ie the exact location of Pin 1 in the existing opamp of your player. Take time to make a drawing for your player of how the original opamp is located. Simply note the markings on the opamp relative to other components nearby.




The Square pad on the adaptor shows the location of Pin 1 and little u on the DIP plug indicates the front of the opamp with Pin 1 viewed from the top to the left.





The Single opamp Brown Dog adaptor , note the square pad showing Pin 1 it is wired for single Opamps only


Why use an adaptor?
The adaptor converts a Surface Mount opamp known as SOIC to be suitable for a DIP or DIL ( same thing) 8 Pin installation. There are also DIP size opamps but sadly these are quite expensive. The manufacturers of opamps are moving to SOIC and smaller varietys rather than catering for DIP , DIP however are still available but at much higher cost- its an onwards trend to make opamps smaller. There are a large number of CD players where the opamp is a DIP size. Some CD players have SOIC opamps already. The adaptor provides choice to install the SOIC device in a DIP size plug.

A tall style of DIP plug provides choice for different installations

Technical Information
opa627.pdf

AD825.pdf



The opamp must be installed exactly as stated and get it right the first time. Pin 1 original to Pin 1 new opamp.


If you already have a DIP plug installed
Simply remove the existing opamp. You can either install the supplied DIP Plug placing into the existing DIP Plug ie One on top of each other – noting the exact location of Pin 1 and Matching to Pin 1 , or gently remove the DIP Plug from the adaptor and install it into your existing Plug noting Pin 1 Square pad aligns with Pin 1 of the player. Take care with the Pins of the Adaptor as they are not as strong as a DIP Plug.

Removing the existing opamp(s)
With the opamp(s) located make a drawing of the device and note where its Pin 1 is , relative to other components. There are a few things that help us, firstly the opamp you are removing will have a Dot marking Pin 1 – sometimes its a white dot , other devices its just a black indentation , and with some a white bar across with the black indentation showing us where Pin 1 is located. Make a note where Pin 1 is. Most circuit boards as a fail -safe provide an outline of the opamp showing the small u which is common to the opamp itself too. Remember Pin 1 must match to Pin 1 of the new opamp , and its best to work this out before removing.

With a clean work area ( a piece of A4 paper makes a good temporary work station ) place the parts within easy reach , you might also need a small screwdriver , a temperature controlled soldering iron – or a 20w iron will do. A quick tip is if you use a 12v iron ,is to power it from a car type battery charger Car chargers usually have a switch for Normal or Boost enabling a small adjustment of heat range . I have found irons seem to last longer if used with an AC or part AC supply.

Some manufacturers will use Torq screws ( Marantz ) to screw down the bottom plate of CD players so you will need to get the right Torq bit , or screwdriver with other players to undo the bottom plate.

An upside Down World
You will need to continually reference the location of Pin 1 , particularly when viewing from underneath which might appear a bit different topside and bottom side of the circuit board so get familiar to where Pin 1 actually is, make a drawing to assist if needs be.

Using Solder Wick apply at approx 280- 310 degrees Celsius, apply a very small amount of solder to one side of the Solder Wick , Apply the dry side of the solder wick to one side of the opamp legs that are soldered into the board. Apply heat from the iron to the lightly soldered part of the solder wick – it should fairly quickly start removing any solder near the opamp legs Solder wick acts a bit like a mop to remove the solder from around the opamp pins , OK next apply solder again to one side of solder wick this time try removing solder from the other 4 legs. The Opamp will still be in place but with most of its solder removed its now pretty easy to remove. If its still hard then go over with solder wick again – if you can start seeing a hole you are very close to removing. Gently prise up the existing opamp and check all of the holes to see they are clear – once again solder wick them to see they are clear. Check all opamp circuit traces are clean of solder Once all the 8 pins are clear carefully place the opamp, and observe that the little u on the DIP plug locates Pin 1 to the left when viewed from the top and the Square Pad on the adaptor also matches to Pin 1.

Here are some pictures to assist you that show all the steps in changing NE5532 opamps in a Marantz CD 50 , replaced with the AD825 or opa627 Dual or a combination AD825 and opa627 which ever the case may be.




Carefully solder the DIP plug in exactly the original opamp location . Please note -not all opamps in CD players are orientated the same way as shown in these images, This is a Marantz CD50. You need to copy exactly the way the 8 pin Dip was originally installed for other players.

Solder Solder
If you hold down the opamp from the top this will help to evenly get the pins the same. At approximately 260- 268 degrees Celcius Solder Pin 1 and 5 , then carefully solder the other pins of the DIP Plug. The soldering iron should only connect about 3 seconds at the most to each Pin Good soldering technique can take years to get right – here is a brief lesson Always apply the iron first followed by the solder , The iron should be only on the Pin for about 1 second before solder is applied Apply the solder , then quickly remove the iron away. 2 seconds later. Always ensure the iron is very clean at the right temperature and Tin the iron – which means solder is applied to the iron metal – this needs to be done every 10 minutes if doing large solder jobs.

It is easiest just to solder the DIP plug then carefully install the adaptor , it should then match Pin 1 to the original Pin 1 location .


Check and Double Check your work. Have a rest then come back to check again. Carefully replace the CD players panels and all screws. Connect the audio leads Apply power , put a CD in and audio should appear.With the Dip Plug installed you are now free to try different op-amp models. whilst not strictly fashion items they nevertheless can greatly influence the final sound of your hifi ,and are worth experimenting with.

Notes for installing opa627 / AD825 in a Quad 405 Series 1 or Series 2

Note this is a Single type opamp Turn off the Quad 44 or Quad 33 preamp which powers the 405 , Wait for power to dissipate , Remove Power cord. Undo the two screws attaching the top case.

Undo the 2 side panels with a long Philips head screwdriver , Use the two holes covered by blanks to insert the screwdriver from the rear, carefully put them aside one to the left and one to the right as they are mirror items and not identical.

With Quad 405 Series 1 ,Carefully remove the existing opamp – usually a LM301 or TLO71 in later models. Choose whether the existing opamp holder will adequately hold the adaptor – you may find it better to stack the supplied DIP socket on top of the existing socket. Arrange the new socket and adaptor so that the Square pad on the adaptor is Pin 1 , and the little u of the opamp in the Quad 405 faces inwards to the components
on the board. On series 2 405's the position of the opamp front ( pin 1 to the left ) faces toward the connection terminals . of the amplifier

If you feel the existing socket is just too loose follow the instructions for Series 2 observing the different placement of the opamp on each amplifier.

Series 2
The TLO 71 device in Series 2 was soldered into place by Quad . On the solder side of the board in series 2 there is clear indication of Pin 1 with 1 marked on the board. Carefully desolder using SolderWick clear all socket holes of solder before inserting the DIP socket – as usual observe that Pin 1 is correct on the solder side and upper side of the board. Press the DIP socket gently into place and solder Pin 1 and 5 making sure all pins push through evenly.Solder the remaining pins. Install the Adaptor and opa627/ AD825 observing the cautions of the Square shaped pad is correctly positioned as Pin 1.

Do the same for the other channel

Re-assemble the side panels taking care to insert the blanks back into the rear panel. Re assemble the top cover and screw the panel in place with two small screws you removed earlier.

Connect the loudspeaker cables , and signal cable – making sure the 4 pin Din aligns with the socket correctly – strangely it is possible to get these sitting in the wrong position,or connect the RCA leads. The Din was preferred by Quad as it made the earth connection first but some audiophiles didn't like them. Apply the power cord to the Quad 33 or 44 or other source and switch on the preamp or power. This completes installation in a Quad 405 Series 1 or 2

Power supplies and op amps

The best present ever you can give your op amp is to provide transistors mounted on the DIP adapter and connect the emitter of each transistor directly on to the SOIC pin. pin 7 is positive and pin 4 is negative for a single op amp . With surface mount transistors available this is quite a reality. For the positive supply use a NPN transistor. For the negative supply use a PNP transistor in the same format. You need to bias the transistor using surface mount resistors and 0603 size suits the mounting of the other components. You need to study data sheets and assess the best amount of current to use. Empirically between 2000 ohms and 2800 ohms provides excellent result.

Single ended power supplies
Some headphone amps just use a single voltage supply ie positive and ground- just like a battery. In this case Pin 4 is arranged to be ground rather than as a negative voltage. Single power supplies usually involve some bias across the + input pin in an inverting amp, and also require a DC blocking capacitor.

Listening Tests
The AD825 with transistors enables excellent stereo separation, as a result sounds are located much better spatially, which provides much better detail. Sounds that occupy the left and right are exactly located, this leads to enjoyment of stereo that no other op amp approaches. Without transistors the left and right stereo balance is muddled extending from the center sound stage.
With transistors left and right stereo balance is perfect. On good quality headphones the difference is amazing. The same applies to conventional speakers particularly electrostatics and high quality monitors, however headphones offer exceptional sound - as headphone fanatics already know.

Dual AD825 with pass transistors
Here is the Dual version with transistors, on a single op amp adapter. This adapter is easier to use with pass transistors than the designated dual adapter, Pin 4 is common with each AD825, Pin 7 is common with each AD825. The adapter requires little modification and the wires are quite straightforward to install.Here is the instructions for installing the dual AD825 on to a single adapter for 15 volt dual rail supply.

Cut the track at Pin 7
Cut the track at Pin 4
Mount the Bc856 to have its emitter join to adapter pad 4, its collector join to where Pin 4
came from
its base be joined by 2k4 0603 surface mount resistor to the collector
Mount the bc846 to have its emitter join to pin 7, its collector join to pin 8
and its base to be joined by 2k4 0603 surface mount resistor to the collector
Break Pin 1 and Pin 5 and 8 of both op amps, in this format they are not needed
Join Pin 6 of op amp one to Pad 1 of adapter with enameled wire, taking care to space it
away from pad 6 Join Pin 7 of op amp one to Pad 7
Op amp one, use Pin 2 and 3 and 4 normally, so solder their legs to the adapter tricky as they
are up a bit higher due to transistors below the op amp
Place op amp 2 above op amp 1, solder its Pin 4 and Pin 7 to op amp 1 Pin 4 and 7 - tricky
solder enameled wire from Pad 5 to Pin 3 of op amp 2
solder enameled wire from Pad 6 to Pin 2 of op amp 2
Finally Solder enameled wire from Pin 6 of op amp 2 to Pad 7 of adapter.





Building the Single Op Amp with Pass Transistors.
This image shows the two transistors mounted on the adapter before the bias resistors are added. Pin 4 can be seen to be occupied by the PNP transistors emitter connection. The transistors collector is connected to the voltage input from the track from Pin 4 and the base awaits the connection from the yet to be positioned resistor. This describes the negative voltage rail. The positive is identical however the transistor is instead a NPN device.








This next image shows the bias resistors mounted and connected, note the tiny gap between each transistor, just enough for each wire to not connect the other transistors wire. The wire connects the resistor - the white object that goes on to connect with the transistor base.



At this point a careful check is needed with a multimeter to ensure connectivity from each pin to its designated point, including through the resistor and by measuring with semi conductor resistance a check can be made of the transistor for each polarity. With the checks all finished the AD825 or other op amp is positioned on top requiring a fair bit of skill to solder. Once its soldered, you need to test it in a circuit.



It should look like this.


Retro Fitting... it can be done
Here is suggested layout for single in this case opa 627, where you already have a soldered op amp on a Brown Dog adapter but you want to add pass transistors. In this case cut tracks to Pin 7 and Pin 4 at the very first part of the adapter pad, just before it snakes off as a track to the opamp.

Dealing first with the NPN positive supply, I took the precaution of also cutting track 8 at the first part of the adapter, as the 2k4 resistor is located very close to that Pad ( Pin 8 is normally not used in a single ) So having done that, proceed on and solder the collector of the BC846 to Pad 7, extend 1 strand of wire from pad 7 - now the collector to the 0603 size resistor. I used 2k4 to deliver approximately 6ma to the base, then solder enamel wire from the emitter of the BC846 around to the opamp pin 7. Note there is not a lot of space between Pad 8 and the base connection- but just enough -air is a great insulator.

For the PNP negative solder the collector of the BC856 to Pin 4 extend a 0603 size 2k4 to the base connecting it with 1 strand of wire. Then lighly buzz the track leading to Pin 4 of the op amp with a engraving tool to reveal the copper tin that spot by using a bit more heat than usual then reduce the heat back to 260 degrees and solder the emitter to that tinned track. See the image for detail. Note in the picture the tiny wire extending from the the collector of the NPN to the 0603 resistor and from the resistor to the base for the PNP. I use 1 strand of the shield of a piece of RG58 coax.















Take care when buying
Sadly there are quite a few AD825's and opa627's on the online marketplaces that may not be genuine. Its easy to tell the difference the genuine op amps are black in color. The others are gray and look as if a machine has erased the genuine logo and embossed a new print. Also if you happen to buy one of these report it to Analog Devices or Texas Instruments. If you happen to buy the non genuine marked op amp its easy to tell as they do not sound like a genuine device, the sound is thin and screechy.


spot the genuine here

















Now compare the image above to this image, do you see the difference:















Recording Software
Peter Jodda some years back wrote some really good software called khdrecord that suits many purposes, it has the ability to sense a turn on moment and turn off moment. I have assembled here for everyones benefit all of the dependency files along with some instructions to install. It suits all Debian based Linux operating systems including Debian, AV Linux ,Linux Mint, Ubuntu etc

KHD Record Instructions.pdf
libstdc++5_3.3.6-18_i386.deb
libartsc0_1.5.9-2_i386.deb
libartsc0-dev_1.5.9-2_i386.deb
khdrecord_0.8.0-1_i386.deb