Category: NEWS 2019 – 2020

Last year, I started to downsize my recording facility and so a lot of stuff is now up for grabs in my Plasma Music Sale 2020.

It's not just studio gear but drums, cymbals, guitar and keyboard stuff, video  cameras,  computer equipment and live performance gear like complete PA systems, mixing desks, powered monitors, multi-track recorders, amps, radio mics  and so much more.

Some of it's old and some of it is relatively new but either way, it's all been lovingly looked after while I've had it and most of the stuff is in pristine condition and it all works perfectly. Please do check it all out my Plasma Music Sale 2020 here before it all goes on eBay!

If you need more information about a specific item or just not sure about something, then please don't hesitate to contact me.

On the bench today is a Behringer DEQ2496 repair.

This is the third generation of 'Ultracurve' from the well-known German manufacturer. The DEQ8020 and DEQ8024 were both 2U 19-inch rack-mount units but in 2005, Behringer released the super high-specification DEQ2496... in a 1u enclosure.

These extremely high-quality and versatile processors do a lot more than graphic equalisation. Amongst the machine's function is a real time spectrum analyser. You can purchase a Behringer ECM8000 calibration microphone and quickly and easily set up the graphic to 'compensate' for room acoustics, for example.

There's also a myriad of other functions such as parametric eq, dynamic eq, dynamic processing and time delay, to name but a few.

With digital inputs and outputs (S/P DIF on TOSLINK and AES / EBU), the analogue side of the DEQ2496 is balanced and boasts a fantastic dynamic range with its 24-bit / 96 kHz conversion.

Gaining distinction amongst hi-fi enthusiasts and audiophiles, the latest and current Ultracurve is of course, also very popular with theatres, night clubs, PA, recording studios, broadcast and even in musicians' instrument rigs.

So, unreliable power supply, then? No, definitely not! The date code on the one that's on the bench today is July 2006. That makes it almost fourteen years old and quite honestly, it's done bloody well, in my humble opinion.

The power supply isn't actually a Behringer component but is made by a company called Eton, I believe which has an excellent reputation. Generating so much heat in a 1U enclosure however, takes its toll.

Today's power supply took just over an hour to fix. The parts cost about 20 GBP and in no time, the machine's going to hopefully last for another fourteen years. 🙂

Well, not quite. I got lucky with this one. I've seen a lot of these which have required considerably more fault-diagnostics and that isn't easy on switched-mode power supplies. On top of that, some parts are impossible to get hold of now-a-days. There's not always a magic wand fix for these.

Check out the Behringer DEQ2496 Ultracurve here.

UPDATE - 22nd May 2023

Apart from being my gorgeous wife's birthday, I launched a post featuring my Galaxy project. A replacement power supply for the Behringer DEQ2496 Ultracurve, you can read all about here.

Many musicians, engineers and producers appreciate why signals should be kept as 'hot' as possible. High signal levels can reduce your noise floor and of course a lot of professional, studio equipment is designed to run at +4dBu (about 1.25 volts). What many might not appreciate is the virtue of also running balanced signal lines. My unbalanced to balanced converter Transformer Coupled Interface (or TCI) does just that. It converts a +4dBu unbalanced signal to a +4dBu balanced signal (no gain).

SO WHY BOTHER?

So long as the signal level is good, many people would be quite happy to connect an unbalanced output to a balanced input using a cable that connects the pole carrying the 180° out-of-phase signal, to 0V.

Apart from the fact that the balanced version of an otherwise unbalanced signal is 6dB hotter, there’s one big advantage to running balanced signals from your sources to your mixing desk or DAW audio interface and that is, an increased immunity to noise.

Environmental noise exists everywhere all the time. There’s human generated environmental noise such as radio signals, noise generated from switching circuits and so on but there’s also a considerable amount of natural background noise.

To screen signal carrying conductors from noise, cabling comprises a shield which is attached at one end, to the chassis of the source device and at the other, to the chassis of the destination device, thereby ‘extending’ the chassis of each device.

The problem is that screening isn’t 100% effective. We want our cables to be flexible and it’s impossible to achieve a 100% screen, while maintaining a good degree of flexibility.

NOTE for all the would-be rocket scientists out there. YES, I'm quite aware that the output waveform doesn't actually look like that but unfortunately packages like Adobe Illustrator aren't able to display a Fourier combination of what they see as a pair of vector traces. That's why I've blatantly written 'CRUDE REPRESENTATION'. In addition, I personally think this representation makes it easier to 'see' what's going on, particularly for the uninitiated.

So where were we? Ah, yes...

Another approach is that of the balanced line…

Instead of sending a single signal, we send two signals; one being a copy but 180° out-of-phase with the first and then at the receiving end, we put things back to a single in-phase signal.

Noise is in-phase, everywhere. Nothing is producing a 180° out-of-phase load of noise, right? This means that noise is affecting both the in-phase and out-of-phase signals in exactly the same way.

With me so far? Good.

At our receiving end, the (differential) input stage rejects all signals that appear the same on both the in-phase and out-of-phase lines, this being… noise and ‘passes’ everything that is 180° out-of-phase… our signal.

So how cool is that?

I get asked this a lot but after reading all of that, I hope you now understand that balancing the outputs of your equipment will NOT get rid of noise generated by your equipment. It’ll only reduce the effects of noise between your source and destination devices.

A figure known as the Common Mode Rejection Ratio (or CMRR) is the measurement in decibels, of how much signal that's common to both phases is filtered out by a device.

Anyway... unfortunately there's a lot of older gear out there including stuff we all love dearly, which has unbalanced +4dBu outputs. The Marshall JMP-1 that was featured in a recent post, is a prime example. The Roland RSP-550, an excellent nineties multi-effects processor, is another example.

So, the traditional way to convert an unbalanced signal to a balanced signal is to run it into a D.I. box. We're all familiar with those little boxes that cover many a studio and stage floor, right? They work just great but while they balance the signal, they also knock down the level of the signal to a few millivolts which means that you have no option other than to run the other end into a mic. pre-amp, either as a separate unit or built into a desk. That's not always convenient and it seems stupid attenuating a signal, only to amplify it again, anyway!

Have you noticed another downside to trying to use a D.I. box to solve this problem, yet? Earlier I gave the example of the Roland RSP-550. It's an effects unit. It has +4dBm outputs sure but it also has +4dBm inputs! So you ain't easily gonna be able to send signal from your desk to it via a D.I. box! The inputs on the RSP-550 are looking for either -20dBm or +4dBm. The microphone level output from a D.I. box just won't be enough to drive the unit. On top of that, the D.I. box output is balanced. The inputs on the RSP-550 are unbalanced. That's actually two downsides. 🙁

To convert an unbalanced signal to a balanced signal and maintain the level of the original signal was a problem I decided to solve once and for all, many years ago. I developed the transformer coupled interface (TCI) Type 1. It's not rocket science (as they say) but boy, do these things come in handy.

The TCI is a non-powered device (like a passive D.I. box) which basically comprises a single transformer on each channel. For an unbalanced to balanced converter, that's all you need, really.

For those interested, the resistor shown, is reflected in parallel with the winding on the side of the transformer facing the unbalanced input (on the left). It helps maintain a consistent input load as presented to the output of the (unbalanced) source.

Having said that, you of course, want the highest quality transformer you can get. You need a good frequency response but also, good phase coherency. Phase distortion, especially down the bottom end, is characteristic of cheaper transformers and if not addressed, makes bass guitar for example, sound woolly or flabby.

Similar to a passive D.I. box, one hidden benefit to using the TCI, is that it offers something called galvanic isolation which means that there is no physical connection (like a piece of wire for example), between your source and destination equipment. With the ability to easily lift the earth of the source equipment, the TCI Type 1 is just great for helping to get rid of ground loop problems!

Returning to the RSP-550 and similar effects units that have line-level but unbalanced inputs, for a minute, driving an unbalanced input from a balanced source isn't such a big deal. Shorting the out-of-phase signal to ground will be fine for this although I might consider releasing a TCI Type 2. 🙂

IMPEDANCE

All equipment has what’s called an input impedance and an output impedance. Impedance, like resistance is measured in Ohms but differs in that it's frequency dependant. Impedance varies with frequency and so the impedance at say 500Hz will be different to the impedance at 5kHz. Having said that, due to the nature of things, a common resistor is often used on for example, the output of an electronic circuit to provide the output impedance of a system.

Most guitarists will be quite aware that everything to do with guitar electronics is high impedance and that the first thing you plug your guitar into should have a very high input impedance. This reduces the ‘loading’ on the guitar pick-ups and allows for a good frequency response further on down the chain.

Unbalanced outputs like those found on a lot of consumer electronics such as hi-fi gear, have a high impedance, perhaps in the order of thousands of Ohms. Balanced outputs in contrast, are always low impedance; just a couple of hundred Ohms. Again, I won't go into the physics suffice to say that this is why amongst other things, low impedance outputs allow for long cable runs.

There are exceptions however and while unbalanced, a lot of studio gear has low impedance outputs. This makes life a lot easier!

The TCI is classed as a low input impedance device and while it will technically work on something with a high output impedance, you might notice some high-end roll-off. Basically, you’ll need to check the output impedance of your gear before considering a solution like the transformer coupled interface. That’s why D.I. boxes are so popular. D.I. boxes have a high input impedance which means you can plug in just about anything. Like my transformer coupled interface, passive D.I. boxes also have a transformer to convert the input to a balanced line. The turns ratio of the transformer however, is such that while presenting a high impedance at the input and low impedance at the output, the signal voltage is greatly attenuated. Hence, the output of D.I boxes is mic. level.

Housed in an aluminium enclosure, TCI's transformers are individually contained in MU-metal cans, all of which contributes to very high noise immunity.

Here are the specifications of my TCI Type 1:

So, if you've got problems interfacing some of your gear with your mixing desk or DAW and you reckon that an unbalanced to balanced converter might help, please don't hesitate to contact me.

UPDATE - 22nd June 2021

Weeks after launching this post, I received so many inquiries about my TCI unbalanced to balanced converter, that I decided to make a production version. I'm pleased to announce that this amazing little problem solver is now available to buy.

UPDATE - 13th August 2021

Out of the first sixteen TCIs sold, thirteen went to audiophiles, something I really didn’t expect but which I can relate to.

Of course, now-a-days, many powered hi-fi speaker systems, have balanced inputs, especially sub-bass speakers and headphone amps. You’ll be hard pushed however, to find a high-end pre-amp with balanced outputs. Luckily, most have low output impedances and offer very high signal levels, making them ideal for connecting to the balanced inputs of powered speakers, via a passive unbalanced to balanced converter like the TCI Type 1.

TCI Type 1 was designed for studio applications and so has ¼” jack input sockets and not RCA phono sockets, normally found on hi-fi equipment. Short RCA phono to ¼” jack cables are however, easily available and if you really get stuck, I’d be more than happy to make a pair.

The outputs of one customer's pre-amp were on 4-way DIN sockets and again, please just contact me if you need custom cables made.

Like all my stuff, TCI is designed and made by me, here in Hemel Hempstead, UK. I do however, use sub-contractors for making enclosures, PCBs, etc. Unlike many, I only use local companies and here's why...

I'm deeply concerned about the environment and the exploitation of labour and so  I always use local manufacturers in preference to the Far East, with the following in mind:

1. I can be confident that workers are treated fairly and earn a proper wage.
2. I can be confident of the standard of quality of each item that is delivered to me.
3. Communication is important and using local manufacturers, all correspondence is quick and understandable.
4. I believe in supporting the local economy.
5. I can be confident that the disposal of manufacturing waste is managed properly and in accordance with national and EU law.

Using local manufacturers isn’t the cheapest option but the above points are important to me. I hope that they’re important to you too.

Over the past couple of weeks, I’ve been designing an audio triggered power switch; a gadget to switch on a power amp when an audio signal is detected and to wait a few minutes to switch off the power amp when no signal is present on the input.

The audio signal comes straight from the sub bass output of an A/V receiver amp and is therefore about -10dBV (approximately 310 mV) unbalanced. So apart from auto switch-on / switch-off, the circuit also amplifies the input signal to +4dBu (about 1.25 V) balanced which is whet the power amp wants to see on its inputs.

After testing a prototype for several months, this evening I ordered the PCB (the  design of which is pictured above) for the final version.

SO WHAT'S THIS ACTUALLY USED FOR?

Well, the power amp in question, drives a sub-bass system on a home cinema. It's a big, professional amp and definitely wouldn't come with auto power-on / power-off or standby, which of course, the main (consumer) A/V receiver amp does have and which 99.9% of consumer sub-bass units have built-in.

The idea is that when the home cinema system is switched on, the power amp comes on when it detects a signal. When the system is switched off, the power amp switches off a few minutes later... PERFECT!

I wanted a minimal signal path for the audio that's being sent from the A/V receiver to the power amp, with just a little gain (-10dBm to +4dBm) and unbalanced to balanced conversion and I also wanted bags of headroom so the whole thing runs at +/-15V.

CREDITS

I don't see the point of reinventing the wheel, especially if someone has already designed something really good that works. Hence, the switching circuitry of this gadget is based on a design by Rod Elliot of Elliot Sound Products (see project 38). Rod puts up some fantastic, in-depth explanation into how the circuit works and how it can be tweaked to your specific requirements.

UPDATE - 18th February 2020

This morning, my PCBs arrived. I couldn't wait and quickly got down to populating one of them ready to test later in the afternoon.

Well, I'm pleased to report that all worked well. With a 1kHz sine wave, the sensitivity of the circuit is about 4.5mV and the delay to switch-off time is about ten minutes.

Unfortunately, the case I'll be using for this, is currently out of stock 'till 17th March, so  it looks like this is going to sit on the shelf for a few weeks 🙁

UPDATE - 18th March 2020

Today I went over to RS Components in Watford to collect the enclosure that I'd planned to use for this project and the dimensions of which were part of the design of the PCB. Well, I couldn't believe what I was told; the boxes remain on back-order 'till, wait for it... 31st July. Seriously?!?!? I checked last night and there was no change in status. What the hell are you playing at?

This Roland VK-7 power supply rebuild started with my friend, Alex Richards bringing me his broken machine. The transformer is mounted upside-down on the inside of the top chassis. Guess what? It fell off! The machine  was plugged in at the time so the accident caused considerable damage but luckily no one was injured.

To avoid this happening again, I mounted this heavy little component to the bottom (steel) chassis and laid new connections to the power supply board. Mounting the transformer to the chassis required some hole drilling but at least the transformer was undamaged. I don't think I would have been able to source a replacement if it wasn't.

Twenty years old, has taken quite a few knocks but it plays and sounds great. Check out more on the Roland VK-7 here.

If you have one of these and there's no power, perhaps you can hear or feel something loose inside, then contact me for a Roland VK-7 power supply rebuild.