Audio DIY

Audio Note Kondo M77 Tube Pre-amplifier Clone DIY

Audio Note Kondo M77 Tube Pre-amplifier

I have just converted my 12B4 tube pre-amp to this Audio Note M77 Clone. The 12B4 / 12B4A circuit was my reference bettering all other tube pre-amps I have owned in the past but this just betters it in so many ways. The circuit was linked from another overseas forum over at DiyAudio. Someone had opened up a real Kondo M77, took photos and traced the circuit plus measuring all voltages sketching this onto lined paper. I have re-drawn the original circuit in X-Circuit and the supply I used.

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MegaClamp Clone DIY Mains Filter

MegaClamp Clone

It is possible to make something similar to a Russ Andrews Mega Clamp or the Super Clamp at a lower cost. The purpose of any clamping device such as this is to clamp very high voltage spikes on the mains to limit them entering equipment. A typical spike protector power strip or plug in box is built using Metal Oxide Varistor's (MOV). The cheapest kind use just one clamping device, usually a single varistor between L-N. A better protector will use at least three MOV's, between L-N, L-E and N-E.

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Nelson Pass B1 Buffer Pre-Amplifier DIY

Nelson Pass B1 Buffer Pre-Amplifier

I decided to make a B1 buffer for my Nelson Pass F5 power amp after listening to a friends version. The B1 is a no feedback JFet buffer that offers low distortion and noise with a very wide bandwidth. Being a buffer it has no gain and just acts as an impedance matching device with a volume control. It is really a source follower and outputs less than its input at less than full volume. It can be used between any source component and power amplifier and even used with another active stage.

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Diy HiFi Supply EZ Preamp Kit

Diy HiFi Supply EZ Preamp Kit

The EZ kit from Diy HiFi Supply is a a linestage pre-amp with an adjustable gain from 6, 12, 18, 22 and 30db. Input impedance is 400k+ depending on the gain setting chosen and consequently measurements vary with different tubes fitted. This is not my own unit but for Val I know who asked me to build this pre-amp with some special custom modifications.

Upgrades :-

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Nelson Pass F3 Class A Single Ended Amplifer DIY

Nelson Pass F3 Class A

When I was building my Nelson Pass F5 power amplifier, a Friend (Dave H) was building his F3 at the same time. This is the result, using the same Italian Made case as the F5. The F3 is again a class A design like the F5 but that is where the similarity ends, the F3 being 15W single ended were-as the F5 is 25W push pull. The F3 output is Capacitor coupled since it uses a single rail power supply were-as the F5 needs a split rail supply. Also due to the F3 lower power output it better suits an easier load were-as the F5 is a little more forgiving.

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Havana PCM56P DAC Upgrade DIY

Havana PCM56P DAC

I was asked by a friend to upgrade his Havana DAC with some better capacitors and non magnetic resistors in key locations which he supplied. This is the result and these are Val's ideas for upgrades. Output coupling is now by Clarity caps with Glass based Russian silver mica and BlackGate caps used elsewhere except the power supply which keep the original Gold Muse caps. This DAC uses a classic Bur Brown PCM56P chip with a simple form of conversion using matched resistors in a ladder configuration. This results in less signal manipulation during the conversion process.

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Nelson Pass F5 Class A Power Amplifier DIY

Nelson Pass F5 Class A Power Amplifier

Recently I have been moving away from vacuum tube power amplifiers and more towards solid state amps capable of driving a pair of Electrostatics, namely an older pair of Martin Logan made around 1995. These speakers have newish panels and rebuilt cross-overs with brand new film caps. However these speakers are a difficult load and quite current hungry. I have also tried these speakers with other power amps, namely a Korsun / Dussun v6i in power amp mode capable of 400W into 4R, an Accuphase P180, a Crown Pro Audio, a few tube amps and finally this F5 which is my main amp at present.

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12B4A Tube Pre-amplifier DIY

12B4A Tube Pre-amplifier

If you do a quick search though the diyaudio.com forum you will come across an old thread that was once very active. It is based around building a 12B4A based pre-amplifier. The circuit given uses a regulator in the cathode for a constant current design but a resistor can be substituted in its place. The main circuit is very simple, easy to make which I always like. It was also getting quite favourable reviews from those who had built it so I decided to have a go myself.

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Martin Logan Crossover Upgrade DIY

Martin Logan Crossover Upgrade

My Martin Logan Aerius speakers had been fitted with new panels but the cross-overs had never been touched in 15 years. I replaced the most important original panel capacitors which consisted of 1x10uF Solen film wired in parallel with 1x20uF Non-Polar electrolytic with 1 single large 30uF film cap. I also replaced another 10uF electrolytic with a single film cap. Other caps are a little too large in capacitance for a film cap and they are only used on the Bass unit anyway to shunt high frequencies to ground so less important as no audio passes through that ends up at the panel.

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Bucking Transformer DIY (Drop 240V to 220V)

Bucking Transformer Circuit

The problem with many china made tube amplifiers from the likes of eBay is the voltage requirement being 220V. Do not believe the voltage written on the back of most china HiFi. My now sold Mr Liang 845 SET amp was marked as a 240V unit but checking the 6.3V heaters showed them to be running high at 6.85V and the 845 heaters at 11V. This means all the voltages can be 10% higher including that HT !! A problem waiting to happen. A higher voltage may not be an issue for a transistor amplifier or CD player that is well made with over rated components.

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