Audio HiFi

Vintage Trio KA Series Amplifier Repair and Re-Cap

Trio KA-4000A

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.

Joplin 2A3 DHT Push Pull Tube Amplifier DIY

Joplin 2A3 DHT

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 **

 

Basie SRPP And Basie Mk2 Tube Pre-Amplifier DIY

Basie SRPP And Basie Mk2 Preamp

The Consonance Basie Pre-amplifier kits were originally available from Diy HiFi Supply. The Mk1 was a SRPP based unit with a cathode follower output stage that could be modified to use other tubes. In my original build I eventually by-passed the cathode follower and used 2 x Mullard E80CC driver tubes making it an Anode follower.

Billie Ladyday 300B SET Power Amplifier DIY

Billie Ladyday 300B SET Power Amplifier

The Consonance Billie 300B SET amplifier kit was originally available from Diy HiFi Supply. This was a dual mono 300B single ended tube power amplifer with many upgrades and possibilities.

I upgraded this unit over a period of 5 years to incorporate the newer Ladyday 300B features such as the WE91 power supply, Ultrapath caps, MU driver stage and grid chokes. Below are the original various pdf files such as build reviews, tweaks and upgrades.

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

 

Simple Clamp Filter DIY

Easy Super Clamp Mains Filter

It is possible to make a SuperClamp plug using a standard UK mains plug and a few parts. Total cost is a few pounds. Simply take any UK mains plug, the MK ones are better since they have more space inside them but I managed with a cheap one. Inside the plug you need to connect a varistor across Live and Neutral. If there is enough space you should use 2 in parallel. That is it !! You can take this a step further and connect a varistor across Live and Earth and one between Neutral and Earth. They are very low capacitance like a typical Y-Class Cap and act as such here until clamping a spike. Blank the cable entry with a rubber grommet or some sealant if you wish.

 

In Use

Audio HiFi Chassis Mains Filter DIY

Audio HiFi Mains Filter

An alternative to the full DIY mains filter build in the previous article is to use a standard chassis filter make by either Roxberg or Schaffner. These are off the shelf parts that come assembled in a metal box with input and output tags for L, N,E. They can be selected based on the current rating you require and have various choke sizes.

Choose a filter with a large inductance choke (10mH) for a source component filter like CD players, DAC, pre-amp or small integrated amplifiers for example. Use a smaller inductance (higher current rating such as 10A) for large dedicated power amp filtering. A mid range inductance (5mH) is fine for a computer based filter or more general audio use. The chassis filters can be bought from RS components, CPC and even on ebay occasionally.

Audio Hi-Fi Mains Filter DIY

Audio Hi-Fi Mains Filter

This is a full mains filter build that can be made with or without the chokes if you wish. The first picture shows the unit I made in a simple ABS case. This filter is a complete DIY solution where you make the circuit yourself, either on a PCB, vero-board or tag strip.

The sonic benefits of any mains filter is subjective at the best of times. Some people swear by them and others dislike them. I have always preferred my system with some kind of filtering and cannot see the purpose of using high grade audio mains leads without a filter circuit before them. The filter isolates the audio grade mains lead from the yards of twin and earth grey cable under the plaster and the miles of cable to the local sub station on your phase.

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