Posted 9th April 2016 at 01:27 PM byalexcp (My DIY projects)
Updated 11th April 2016 at 08:14 PM byalexcp
When I saw the discussions of KSA-5 headphone amplifier on head-case.org 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 byalexcp (My DIY projects)
Updated 9th April 2016 at 07:46 PM byalexcp
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 byalexcp (My DIY projects)
Updated 11th April 2016 at 08:21 PM byalexcp
In April 2013, Linear Audiopublished in Vol.5Bruno 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...
1. You have a schematic in PDF format, but it's hard to read when printed on A4
2. Only A4 printer available
3. Printer drivers can't solve the problem
4. A3 size wanted (ie two sheets A4, with some overlap for taping together)
5. Following (free/OSS) programs are available:
To illustrate point 3: my printer will print multiple pages per sheet ("2 in 1" - ie reduce), or print an A4 page on (n x n) sheets (A2 - four times the area), but there's no option to double the size to A3. A4 too small; A2 too big
About GIMP - https://www.gimp.org/
Open source image manipulation program - sort of free Photoshop, plenty of info around.
About PosteRazor - PosteRazor - Make your own poster!
PosteRazor is designed to split image files into [n by m] individual pages in a single PDF file, on whatever page size...
I was going to call this amp 'fleapowered' but after doing some searching online I found fleapowered amps in general were much higher output power than this - single digit Watts typically. Whereas this one is more than a couple of orders of magnitude lower than that (under 10mW) so deserved a different moniker. Seeing as a mite is smaller than a flea, 'mighty mite' seemed to me as good as any descriptor for it.
The mighty mite started life in my imagination after I walked into a local headphones shop and tried out some cans that the shop assistant recommended to me - AT MSR7s. I'd brought my 'Buffalito' headphone buffer with me and some step down transformers for its output - fed from my mobile phone its way too loud for my AKGs and Superluxes. However the MSR7s were too loud even with the 2:1 step down trafo so I told the assistant I'd come back and listen again once I had a more suitable trafo. I figured it needed to be 4:1 step down, so I built a pair of those (PQ32/20)...
Posted 29th March 2016 at 05:10 AM byrjm (RJM Audio Blog)
Updated 18th April 2016 at 11:52 PM byrjm
Truth be told, for a self-biased jfet audio circuit like the CrystalFET the main reason we need to used matched jfets is to ensure that the signal gain is the same in both channels. The operating point of the amplifier stage (the voltages and currents) can be allowed to vary a little so long as the transconductance, g_m is the same, as this is directly proportional to the open loop voltage gain, A, as
A = g_m R_l (transconductance x load resistance)
Now, yes, ideally you would find two jfets with identical saturation current and pinch off voltages, ensuring not just the same gain but also the same operating point. In practice though you are usually binning parts that are close to each other based on some reference parameter like the pinch off voltage (V_gs0) that you hope closely correlates with the signal gain. This is not quite as good though as the calculating the actual transconductance of the particular device in the circuit it is to be used in. And since...
Seems I got a bit carried away with listening to my heavily modded XuanZu amp in the last-to-one blog post. I even considered it was superior to my current headphones - that would mean shelling out on some new ones. Before I went shopping though I did try it into my DT880s, which are 600ohms (hence I usually only use them for special occasions) - they sounded cleaner, although considerably quieter. This amp doesn't have enough voltage swing available to deliver the SPLs into such a high impedance. So was the cleanliness of these phones due to their being higher quality (they're at least 4* the cost of the others)? Or just because of listening at a lower level?
When my over-enthuasiasm for the amp had subsided a bit I decided to consider a way to answer these questions. If the amp was indeed not producing the artifacts which I was hearing on piano into the low-Z cans, then putting a 2:1 step-down transformer on its output would make no difference at all. The amp has plenty...