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Soft start, Speaker Protection by Audio Workshop

Soft start. Speaker Protection. Speaker Delay

Soft start. Speaker Protection. Speaker Delay

We have completed this module this week. It is a custom build by order of a customer. The module has many specific functions. It can be used for speaker protection, speaker delay, toroid soft start and others.

Art For Engineers


Well mandala-1we all like and enjoy beautiful things of life. Art is a fine example. Engineers however are a kind of  different animals. They enjoy looking at bizarre things. I do as well. What you see on the right is a fine example. A “painting” made out of electronic elements. Almost every possible type of electronic device is used and I think it’s amazing.

No deep thoughts about this. I’m not an art expert. Some might find it ugly, some might find it strange or whatever. I just wanted to share this with everybody.

If you like this be sure to check out this website.






SSM2017 Line Preamplifier – High Quality Design

This page will show you how to use the SSM2017 as a line preamplifier. With some clever designing a very high quality preamp could be build at affordable price.
For those of you unfamiliar with the chip, here is the datasheet:

Now some few words about this device. It has been designed as a microphone preamp with selectable gain. It requires only one external component – the gain set resistor. As a microphone preamp it was designed to work in harsh environment, long cables, signal pollution, noise etc. Despite that the SSM2017 is able to achieve extremely low noise performance and high gain. This makes it perfect for a normal line preamp with selectable gain.

Now the SSM2017 is obsolete. Few replacements are available from few manufacturers.

AD’s SSM2019:

TI’s INA217

THAT’s THAT1510/THAT1512

THAT’s IC’s have a superior noise performance at low gains so those are preferable. They are a drop in replacement to SSM2017/SSM2019 but a different values of the gain set resistor must be used because of the different input stage of THAT’s IC’s.

Whichever  IC you chose to use, a high quality line preamp is the result. Another interesting thing is the REF pin. It allows us to design a servo. This way we can null all the DC offset at the output and remove any capacitors from the audio path. For this purpose we need a low cost FET input operational amplifier. TL071 is the right choice. The servo is not in the signal path so the servo opmap quality is not critical.

Here is the schematic for this project:

The PSU is pretty straightforward. Two adjustable vregs and filter caps. Nothing fancy here. Use good quality industrial capacitors (Panasonic FC, NCC KY series, Rubycon etc.).

Now for the stage itself. The power supply goes trough an individual RC filtering to each IC. This helps reducing noise even further. Again good quality parts are used. All resistors are metal film to help keeping noise low.

The SSM output is forced into class A operation using a JFET cascodes ad the outputs. This increases the overall performance of the stage. A better sound is the result as well as better driving ability reducing the interconnect cables negative effects.
It is important to match the loading JFET’s so that the two SSM’s work under same conditions. Because the line stage is meant to drive high impedance loads, no high currents are needed. That is why the 2N5484 FET was used. It has a typical Idss of 1-5mA. For our application a value of 2-3mA is more than enough. It is important for the upper JFET to have a higher Idss rating. That is why the 2N5486 JFET was used in this place. It has a typical Idss rating of 8-20mA so no matching is needed here.

The whole project is assembled on a single layer PCB including the rectifier. The original PCB artwork is available for download here: >>> [LINK] <<<

Now some few words about matching JFET’s by Idss. This is actually a very simple job. All you need is a voltage source and a multimeter. Here is the testing schematic:

Simply tie together the gate and the source pins and apply voltage to the drain pin. Connect the  positive node of the ammeter to the gate and the source and the negative node to ground. The JFET will saturate at its own Idss. Please note that the Idss value is temperature dependable. Let the JFET to settle for about 10min and then note its Idss. Repeat the procedure until you find two closely matching devices.

Attention: This design was provided for personal usage only and is FREE for such purpose. Commercial usage is not allowed!


DIY USB Isolator Made Easy

Are you into high quality PC audio? Do you have one of these nice USB DAC’s that pull all the good musical stuff out of your computer? Then you might need to check this article out. You can vary well improve your USB DAC performance by isolating it from all the garbage coming from the noisy(electronically) PC.

What I’m about to show in this article is a way to build you own USB isolator and improve your USB audio. The isolator itsel is build around the ADUM4160 chip from Analog Devices. The complete datasheet is here:

Since the schematic for this project is rather simple, a single layer printed circuit board can be made. Of course a double layer is always better option.

This is how the whole thing looks:

The project also makes use of one high quality LDO regulator. In this case I’m using Linear Technology’s LT1763 fixed voltage (5V). I’ve used this one before in some other projects and I’m quite happy with it. The datasheet is available here:

The board allows you to use external regulated PSU just in case you don’t trust the LT’s chip. This is the complete schematic for this project:

The circuit is pretty straightforward but here is some explanation. JP1 switches the speed – open=low speed(1.5Mbps), close=full speed(12Mbps).

JP2 function is explained here:
The ADuM4160 has an option to delay application of the upstream pull-up under control of the peripheral. This function is controlled by the PIN input. In this application, the PIN input is jumpered high so that the upstream pull-up is applied as soon as peripheral power is applied. In other applications, it can be connected to a GPIO pin of a controller, a fixed delay circuit can be applied, or it can be connected as shown in this circuit. It is the designer’s choice how to use this functionality.

I personally use id closed. JP3 allows you to switch between the power supplies of the second half of the isolator. I recommend using the build in regulator. In this case the board need 10-15VDC. A simple DC adapter will do the job.

The PCB artwork in 1:1 scale pdf file and component placement is available for download HERE.

The PCB can be easily made using a laser printer and an iron. I encourage you to try this simple upgrade, as you won’t be disappointed.

************THANK YOU FOR READING THIS ARTICLE************

Low Jitter Clock For CD Player – Upgrade Module

Do you have one of those expensive CD players that use a simple quartz oscillator to provide the clock? Anyways, the clock upgrade is no doubt the most important upgrade to any CD player. Otherwise you will never hear that nice smooth analog like sounding from your gear.

What you need is a low phase noise clock source to feed the CD player.
Searching the web will come out with many ways to upgrade your CD player. Some of those upgrades come at substantial costs. Many sources simply don’t provide enough data to prove those high costs in my opinion.

So i searched and searched for a nice clock project to upgrade mu trusty Arcam Alpha 5 CD player. This one was already upgraded with a nice new TDA1541A S1 DAC chip so I was impatient to reveal its true potential.

So finally I came across a nice article about The Flea Clock from Pink Fish Media. An very interesting project indeed. What that project aims at is in reality an ultra low noise PSU to power up a Tent Labs oscillator. So my project was based on that one from PFM forum.

I just had to change some things to fit my personal needs.
First – the oscillator was unable to drive any substantial capacitive loads, so I needed to buffer the outputs. Buffering is an easy task. A simple inverter would do the job. In this project I’m using two 74VCH1G04 ic’s to provide me two outputs.
Second – i wanted a oscillator with real measured parameters showing the phase noise and jitter performance since I had no way(equipment) to measure the jitter myself. Few manufacturers that in My opinion are suitable for the task:

Fox Electronics HC-73 series oscillators:

EuroQuartz XO-91 series oscillators:

Silicon Labs Si510 series oscillators:

In my case I’m using 11.2896MHz oscillator to feed the digital filter’s XIN pin(pin 11 on SAA7220 chip). This is the most basic way to feed the new clock to your CD player. Simply remove the quartz form the player and the two caps and the resistor. Here is how I did it:

 A more advanced reclocking to your player can done using a flip-flop to reclock the I2S bus before fitting it to the TDA1541A chip. Here is how its done:
This method has one major disadvantage. It uses one IC to process all three wires of the I2S bus. A better way is to use three IC’s but it’s cost and space consuming.
Possibly the best way is to feed the clock separately to the digital filter(SAA7220) and the DAC chip (TDA1541A). The DAC chip itself requires half the frequency provided to the digital filter. So we need to divide the clock coming from the module. This can be done again using a flip-flop:
In my opinion this is the better sounding reclock. Anyways, a wide field for experiments is available.
So this is the final result. Here is the clock module PCB fitted into my Arcam Alpha 5 CD player
Ultra low jitter clock fitted into Arcam Alpha 5 CD player
The module itself is powered by a preregulated PSU using a LM317 vreg providing 18VDC. I’m using a small transformer to power the whole thing up. This is the better way to do it. One can still use the already available supply rails from the CD player but 18VDC is the minimum voltage required in order the module to work.
A complete schematic for this module is available HERE.
WARNING – This design is provided to the DIY community for free and is intended for personal use only. Therefore the commercial usage is NOT allowed.
*************THANK YOU FOR READING THIS ARTICLE**************

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