Havana PCM56P DAC Upgrade DIY

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. Those clarity caps are huge and only just fit in the case and I had to fit them rotated 90 degrees compared to the originals. These would not be my choice for practical reasons of fitting as the unit is very compact.

Havana PCM56P DAC

Nelson Pass F5 Class A Power Amplifier DIY

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. This amp was a scratch build using PCB's bought via a group buy. Case is from Italy and other parts from RS and CPC. I used premium parts when available and later upgraded to Aerovox caps for the PSU.

Nelson Pass F5 Class A Power Amplifier

12B4A Tube Pre-amplifier DIY

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. I wanted a pre-amp at the time to test with a 20W Mr Liang 845 SET, which although is an integrated, sometime needs a good pre-amp for a little more gain. I also later tested this pre-amp with the large Korsun (Dussun) V6i transistor power amp from China and a DIY 25W Nelson Pass F5 Class A power amp.

12B4A Tube Pre-amplifier

Martin Logan Crossover Upgrade DIY

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.

Martin Logan Crossover Upgrade

Bucking Transformer DIY (Drop 240V to 220V)

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. However with vacuum tube amps the heater voltage can be a problem in that it will shorten the tube life if they are running hot. Also the heat output can be an issue and the HT being higher may stress other parts.

Bucking Transformer Circuit

Mr Liang 845 SET Tube Amplifier Driver Modification

Before I got back into using Solid State Amplifiers I had already gone through many tube amp kits, various KT style push-pull builds, 2A3 and a 300B Mono-Block SET for example. I eventually got talked into buying a 845 SET. This was my last tube amp before switching to a Nelson Pass F5 Class A. The build quality for a china made amplifer was high and this thing weighed a ton, far better than some of the typical China tube amp junk floating about on eBay. It really is a two man lift.. it is that heavy.

However, as good as the sound was on first use it soon became obvious that it could be easily improved and it had a few flaws, namely being a little rough around the edges.


NOS Tube Changes

Mr Liang 845 SET Tube Amplifier

Korsun Dussun V6i Integrated Amplifier Review

The korsun / dussun v6i is a monster of a power amp from china costing around 800 usd. It really is a poor man's krell or Mark Levinson that is built like a tank with dual mono construction in 1 stunning but large aluminium chassis. It is kind of a class A build in that the first few watts are class A were then it slides into class AB mode as it is driven harder; with output powers of 2x300 W into 4Ω and 2x150 W into 8Ω.

Korsun Dussun V6i Integrated Amplifier

Aikido Tube Pre-amp DIY

This was the third and final incarnation of the Basie Vacuum Tube Pre-amplifier from Diy HiFi Supply and it went through a complete re-design both in looks and the circuit it uses. The new circuit was based on John Broskie's famous Aikido design of TubeCAD fame. John kindly gave permission for his circuit to be used in this new kit. John is clearly a talented tube circuit designer, there are not many these days. I certainly don't claim to be. I just build kits and other peoples ideas :)


Design Changes

Aikido Tube Pre-amp

Vintage Trio KA Series Amplifier Repair and Re-Cap

I picked up this vintage Trio KA-4000A amplifier to use on my Desktop PC (DAW) to drive a small pair of book shelf speakers. However, the amp had a fault on testing so out came the iron and a box of spares. The fault was noise (hiss) and crackling on one channel. This turned out to be a faulty transistor, namely a 2SC458. This particular transistor is quite well known for failing and is a common part in many amplifiers and other audio equipment of this era. Therefore changing these is a must. If you have a vintage solid state Trio amp with a noise problem and it is not just a simple volume pot cleaning process then check for any of these 2SC458 transistors.

Trio KA-4000A

Joplin 2A3 DHT Push Pull Tube Amplifier DIY

The Joplin tube amplifier was a 2A3 or 45 based unit using 2 DHT power tubes per channel in push-pull configuration from Diy HiFi Supply. The unit featured a pre-amplifier stage and a volume control allowing it to be driven directly from a line level source negating the need for a separate pre-amplifier. I eventually rebuilt my unit to replace the pcb, making it all hardwired to create some space for larger Teflon caps. Below is the original build review in pdf format.

** I have included the circuits which would allow you to build this amp from scratch build as the kit is no longer available **


Joplin 2A3 DHT


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