RIAA Preamplifiers on a Budget

Pre-amp Circuits for turntable MM or MC reproduction

Apologies for the lack of updates over the last few weeks, our scribe has been off ill for a few weeks. Here’s to a new session of articles and hopefully a little bit of invigoration to our framework.

The true value of Vinyl

It’s amazing how times change – I was recently given a treasure chest of CDs, DVDs and records (vinyl) from my brother whom has left our shores for the UK and guess which media carries the most value?

In line with this and the comparative interest from local folk to listen to vinyl (read: huge interest) we thought it relevant to add some words on the subject. Continue reading “RIAA Preamplifiers on a Budget”

Focusrite 18i20 Revision One

Focusrite 18i20 Release One

As an avid user and lover of the Focusrite mic preamps I recently found my preamp had a broken button for the +48V phantom supply.  As one part of the button had broken off I tried to find the missing part and try a quick fix. Since I had to open the unit I’ll share some thoughts.

The 18i20 uses Cirrus Logic CS4272 114 dB, 24-Bit, 192 kHz Stereo Codec A/D DACs, JRC4565 (New Japanese Radio Company) and HEF4053 triple single pole double throw analogue switches.

Although I paid way over market RRP for the unit they were in scarce local supply when ordered so I wasn’t too surprised. As a DAC it’s absolutely incredible and although giving spec lower than some of the others giving a more optimistic SNR there is absolutely no audible noise.  I use Eltax Millenium 500 speakers in the sound system as the main drivers along with some cheap arsed Sansui’s and although the Eltax speakers are supposedly entry level and bass heavy I have not found this to be the case. As a rule this website is not critical of other products, we aren’t a Phile Critics Zine Zone, the Eltax 500s perform very well on higher powered amplifiers. I also use RCF Ayra 8 monitors for mixing.  The Focusrite – Behringer NU6000 mix makes for good listening and although the Golden Eared fraternity may cringe I think the match is pretty good. The Eltax btw handle an input power of about 400W admirably with absolutely no audible distortion.


The first revision 18i20 may not have the newer GUI of the newer version, neither the latency but it doesn’t really make a difference in the grand scheme of things. But you should be able to pick up the older version now quite cheaply which makes it a very attractive purchase. I have read a lot about out of box failures etc but if you are on the lookout for an 8 input mixer I cannot think of one thing which is against the Focusrite.  Oh, I wish they had used alloy knobs and buttons, plastic doesn’t do this product justice. Let ist cost more, this is a beautiful product.

Focusrite 18i20 1st Edition top cover removed
Focusrite 18i20 1st Edition top cover removed

As far as DACs go, I cannot fault the unit. I don’t particularly like the mixing software, more to get the hang of  the I/O but it’s not a difficult learning curve. I believe Numero Dos (and no, not the “gonna have a number two” kind) has what I would term more efficient software, shorter and more understandable mixing software.

If you are planning to purchase a digital mixer in the near future to do recording/mixing through USB, give it a try. All of the models are similar except of course for the amount of available channels.

More info coming up in a future column.

DIY DAC for Audio

Bits, Bytes and Sampling – DIY DAC

To kick off we need to piss of a couple of people, one being the high end user wanting the fastest sampling rate possible and the second, that cheap means nasty. A DIY DAC may mean a purchase and mod with better supply or even a build from loose components up.

Some Capable DACs - purchased but not a DIY DAC
Some Capable DACs


When we went into the Philips Hi-Fi arena 50 years back the CD disk was supposedly going to be the end of our woes, high definition audio at a sampling rate of 44.1kHz and in total using 16 bits to reproduce simply put pitch, loudness and quality.   16 bits of binary, looking at the analogue breakdown would equal to over 65 000 variants of a signal at 44.1kHz sampling.

For a stereo system we calculate the bitrate as being 2 x 44100 x 16 or 1411 kb/s or 1.411 Mb/s. Continue reading “DIY DAC for Audio”

Transistor Equivalents – old equipment restoration

Where to find transistor equivalents?

Restoring old gear can be a nightmare when it comes to some of the more obscure transistor types, and a pretty expensive exercise as well. Transistor equivalents for substitution is often a necessity when repairing vintage gear. This applies equally well to silicon devices and not just Germanium.

Years back we were confined to telephonic conversations or writing letters to the supplier, the snail mail variety.  In South Africa we are fortunate enough to have proactive suppliers in the electronics industry, unlike in the motor or metal industries where staff are still learning how to send emails, except if they see a big sale pending. Continue reading “Transistor Equivalents – old equipment restoration”

Vintage Audio Vs Modern Technology

Is vintage audio better than modern releases?  (post 2000)

This reminds me of the first argument I had regarding the merits of mechanical VU meters over LED.

Yeah, we like vintage stuff, especially with those big VU meters. Hell, I was looking at the specs of the Pioneer SX-1980 the other evening and thought  what a beast this must have been in the 1980s. At 270W this is certainly by no stretch of the imagination much in modern times thanks to PWM, Class D and mounted on a one inch square heatsink.

McIntosh MA6800

en:McIntosh Labs MA6800 amplifier. *Source:  *Credit: [http://www.flickr.com/people/ux/ Akira Kamikura] *License: cc-by-2.0 {{cc-by-2.0}}

Continue reading “Vintage Audio Vs Modern Technology”

Line and Microphone inputs

What is the difference between Line and Microphone Inputs

This is a question often asked in the forums, not necessarily as simplified as this but there is often ambiguity in the replies. So here we will look at what not to do and hopefully this will prevent mishaps in the interwiring of consumer and professional audio goods.

Behringer DI-Box DI100
Behringer DI-Box DI100  (Sweetwater)

Firstly, the tried and trusted Decibel (dB) Continue reading “Line and Microphone inputs”

“Sound City” – A forgotten Art

Sound City and analogue mixers

I watched this movie a few weeks back and it had me intrigued on many levels.  Not just the snippets of famous and much loved musical genius but the mere fact that one went to Sound City Studios to make music first and secondly to become famous.

Neve 8078
The legendary Neve 8078 in The Way Recording Studio, London.  (Wiki )

You had one take.  Now with our DAW, digital mixer and a host of plug ins one can become famous from your bedroom. And it happens. It just so also happens, and not because of my age, that much of the music made then rather than now is timeless.  Here I’ll single out Fleetwood Mac.  Who didn’t have a crush on Stevie Nicks in the 70s, girls and guys.  But we must stop and consider the impact that the aristocratic Michael Fleetwood had on this group. Co-founder and driving force,  I always visualise this goliath behind a drum set and mixed through a Neve 8028.

David Grohl really does a fantastic job in this documentary, a must see for not only 70s music and audio enthusiasts but budding sound engineers as well. Continue reading ““Sound City” – A forgotten Art”

Multiplexer and Demultiplexer switching (follow up)

Using Electronic switching to route signals

As a follow up to our article on multiplexing (and demultiplexing) or MUX/DEMUX and running my own experimentation with a CD4051 it comes as no surprise that this chip works well but there are limitations.

As I am no expert in this field I must confess that the biggest obstacle IMO when switching or routing signals is not the degrading of signal quality necessarily but the dangers of phantom power.  As most microphone preamplifiers use an XLR plug or TRS combo, the TRS does not pass the +48V but the XLR does.  Now if someone unwittingly connected his expensive tape deck to XLR outputs and then into an XLR mic preamp there is a chance that they would end up with a toasted front end to the deck. Yes, we all like XLR plugs but this can be a problem. How to eliminate this problem? Continue reading “Multiplexer and Demultiplexer switching (follow up)”

Upgrading to the new Mixer or Mic-preamplifier

Scarlett 18i20 Gen 1

To upgrade or not to upgrade is the question

So last year Focusrite decided to change their range of 1st gen Scarlett series to 2nd generation and I found myself looking at my older 18i20 unit which had just lost a couple of bucks in value.

Scary stuff, but not as scary as vehicle depreciation.  So the question that arises is does one sell now, get new or hang on?  This is a dilemma which we all face at some time or another.  The solution is usually to use common sense and logic. Team marketing hope that you have neither. Continue reading “Upgrading to the new Mixer or Mic-preamplifier”

Hybrid Amps

Hybrid Amps: Some more circuits

Using the first article to get our creative juices flowing I found some more well written well designed amplifiers using tubes and semiconductors.

Nobsound MS-10D MKII
Nobsound MS-10D MKII – 2 x 25W 2 x dual Triode 6N1(P) and 2 x 6P1(P) beam tetrode. (the code without (P) is Asian, with (P) Russian.

The design link below shows various permutations to feed a high voltage swing with little distortion to an emitter follower output stage.  This circuit, titled Hi-End Hybrid Amplifier 100W uses a high end K&K solid state current generator (source) in series with a pentode voltage amplifier. The tube in this case can be a Siemens D3A or Russian 6C45.

OK, so what is our pitch here?

High safety margin, for a 100W amplifier using 4 x MJE15032 and 4 x MJE15033 output transistors in the output, the input to the current amplification circuit is through a capacitor (DC block) from the voltage amplifying pentode and an LM308 op amp for stabilising the DC offset at the output, removing the need to apply manual adjustment.

The MJE15032/MJE15033 can be obtained at a good price from Mantech (Communica advertise only the PNP at R17 each excl).

The K&K current source can be found under the two terminal current source on the K&K website. The source is a design around the depletion mode IXYS IXTP08N100D2. As these are not locally available I’d advise the reader to first open the Two TerminalCurrent Source Kit pdf file from K&K – Microsoft Word then get your nose into Rod Elliot’s article on sinks, sources and mirrors. A few minutes read up on current sources should throw some light on the subject and have you amped for your next journey.

An auto-bias heater filament Mosfet load headphone amplifier

Quite a mouthful but nice clean design pulls all the stops in hybrid design. Design found here.

Hybrid vacuum tube/solid-state audio power amplifier

Nice design which will break the bank amplifier found here – this amplifier uses an 6AN8, a pentode-triode combo. The output devices are BUZ900 and BUZ905.  The 6AN8 may not be that easily available in South Africa but the good news is that Mr. Valve lists this valve for R150.00.    Based in Pretoria, excellent service.

The BUZ900 and 905 are expensive, TO3 equivalents include the Hitachi 2SK134 and 2SJ49.  Available (no price given) at Mantech otherwise Yebo listed as ECF20N20 and ECF20P20 going for over R300 per pop. Ouch! Note that these are lateral type MOS devices and because of the TO3 can this amplifier is ideal for experimenters wishing to modify the output stage with cheaper alternatives. After all, we are looking at the voltage gain devices, chiefly pentodes driving Mosfets.