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alexcp alexcp is offline

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  • About alexcp
    United States


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Blog - My DIY projects
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  • Last Activity: Today 01:22 AM
  • Join Date: 9th June 2009


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Posted 7th March 2017 at 03:00 PM by alexcp Comments 0
Posted in Preamps
I purchased an Aikido Cathode Follower 2 (ACF-2) All-in-One 9-Pin PCB from The PCB is designed by John Broskie, the editor of Tube Cad Journal (, and the flexibility that he designed in is quite remarkable. The PCB allows to test various configurations, which is often not a feature of a design committed to a PCB. The quality of the PCB is outstanding; it withstands multiple soldering and desoldering without complaint. It is an outstanding product IMHO.

The schematic seems to be simple, with a cathode follower loaded by a triode current source. JJ E88CC with 221ohm cathode resistors shows 0.003% THD with pure 2nd harmonic, and select 6N1P-VI achieve 0.005%. (My 6N1Ps are hit or miss; some of them have much higher 2nd harmonic, and some of them have a mix of 2nd and 3rd at Ia=6ma and Ua=140V).

As I tested my ACF, I noticed excessive hum at its outputs - audible buzz in the speakers and 0.15% THD+N, well above the THD.

Posted 9th April 2016 at 01:51 PM by alexcp Comments 0
The designer of Cambridge Audio A3i had talked about the amp in this forum and suggested some changes to the components that bring the performance of the amp to a new level.

When I saw a cheap A3i on eBay, I decided to try it out. One channel was DOA, but it did not matter as I was about to mod it anyway.

Here is what I've done:
  1. Replaced all rectifiers (D201-D206 on the schematic) with soft recovery diodes and removed the capacitors in paralell with the diodes;
  2. Changed the grounding scheme so that the protection circuit and the relay driver are connected directly to the star ground;
  3. Added a 30ohm resistor in series with the rectifiers of the protection circuit;
  4. Replaced the electrolytic capacitors in the amplifier (but not the protection circuit) with Nichicon KA and replaced the two large power supply capacitors with Nichicon LLS;
  5. Replaced all film capacitors with Kemet PHE426 or, where PHE426 wouldn't fit, with Kemet SMR;
  6. Replaced the rectifiers

Posted 9th April 2016 at 01:27 PM by alexcp Comments 2
When I saw the discussions of KSA-5 headphone amplifier on and on this forum, I thought it may be a nice use for the bag of 1000uF capacitors I had at the time. This was the main motivation for putting this Krell KSA-5 clone together.

The main challenge was to drill the front panel. The 10mm aluminum panel that came with the enclosure is easy to work with, but I wanted it to be pretty and asked the people at Modushop to CNC it for me.

Although it works ok, I think it is not a very good power amplifier for loudspeakers. As a headphone amplifier, it is no match for my Musical Fidelity X-CANv8.

Posted 9th April 2016 at 01:20 PM by alexcp Comments 0
Ever since I heard about the Hypex NCore technology, I have wanted to build a power amplifier based on Hypex NC400 modules. Here is what I got. It works very well with the preamplifier from the previous post.

I used a spare Arduino to control the SMPSes. For now, it simply allows to use a momentary push button on the front panel. I may add remote control (12V trigger or similar) later.

Posted 9th April 2016 at 01:14 PM by alexcp Comments 0
Posted in Preamps
In April 2013, Linear Audio published in Vol.5 Bruno Putzeys' article "The G Word, or How to Get Your Audio off the Ground". Linear Audio included a free PCB for the demo project from the article: a balanced volume controller, or rather a minimalist balanced preamp with two pairs of balanced inputs.

I have been looking at balanced interconnects for some time and decided to use the free PCB and build the preamp. Here is what I built.

The enclosure used is Galaxy GX247 with front and back panels custom made by Front Panel Express. It was difficult to place a C14 power inlet on the back panel, as the space is quite limited due to the central placement of the six XLR connectors. An easy solution would be to fix the power cord permanently to the preamp, but I found a compact snap-in connector that fits the 3mm back panel of the enclosure.

I understand the article is available for download at the Hypex web site, and the PCB gerbers and a...
Recent Comments
KSA-5 is a power amplifier...
Posted 26th February 2017 at 07:48 AM by alexcp alexcp is offline
I wonder how it will...
Posted 24th February 2017 at 01:35 PM by idir idir is offline
Marc, apologies again...
Posted 11th February 2017 at 02:14 PM by alexcp alexcp is offline
Do you happen to have...
Posted 25th October 2016 at 07:49 PM by marc brown marc brown is offline
Hi Marc, sorry I was...
Posted 30th July 2016 at 02:43 AM by alexcp alexcp is offline
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