This is a great new arm board made by Carl to fit my Lenco plinth. I’m planning to add a second plater so needed to raise the tonearm and therefore a new board was required. Carl can make this arm board to fit any requirements. Just get in touch with Carl if you need a special arm board for your plinth.
Author: Ale Moglia
"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)
Trane’s Psalm hipnotism
I normally will write about the sound of Coltrane’s music in a sweet class A amplifier, but not this time. Of course I was listening to trane’s music in my 4-65a SE amplifier when I got tele-transported back in time. The 4-65a SE output valves are really setled in and the amp is playing at its glorious sonority capability. I’m afraid of touching it as it sounds good.
Anyway, if you haven’t listened “A love Supreme” by Coltrane, then you’re definitely missing a master piece of the jazz music. In fact, I recall playing this record back in the early 90s to a friend who was very fond of 60s rock and some of the 90s electronic music. The monocorde progression of trane’s scales with Elvin Jones and the rest of the Quartet creating the most incredible mood is magnetic, or hypnotic. I’m not looking to review one of the greatest records of all. Simply, Psalm (Part 4) is one of those tunes that gives me goose bumps. Every time I play it, is unique and that is the lovely thing about music. When I played music before, I was really into bebop but then discovered how beautiful was to express with fewer notes and slowly. Is like when I draw cartoons. You can express a lot with fewer traces and just plain indian ink. But a very small number of people have mastered the art of reflecting the most incredible things and experiences through fewer notes.
That Quartet was unique and I’m sure they were in trance when they played Psalm. They were taken to another dimension. We can enjoy their music still, but only God knows what they felt as part of that collective experience.
Anyhow, I’m still sitting here with my Single Malt in one hand and just decided that these lines were enough (hopefully) to reflect what I experience every time I listen to this record.
Cheers
Ale
JFET RIAA Preamp Build (Part II)
I made the following changes to the RIAA stage to improve its accuracy:
- Measured all caps
- Adjusted 75uS network to compensate for the capacitor variance and the cascode output impedance
- Adjusted 318uS and 3180uS networks to compensate for the capacitor variance
All resistors were adjusted with a pair of 0.1% SMD resistors to avoid series connection to reduce noise level.
As shown below, the response is really good matching at less than 1% for frequencies above 50Hz. the error at low frequency is due to the rumble low pass filter, the hum and the soundcard LF response which introduce a slight distortion at very low frequency in the MLS measurement:
| Frequency (Hz) | Test (dB) | RIAA (dB) | Error |
| 20 | 18.80 | 19.27 | 2.44% |
| 100 | 13.00 | 13.09 | 0.69% |
| 1,000 | 0.00 | 0.00 | 0.00% |
| 10,000 | -13.70 | -13.73 | 0.22% |
JFET RIAA preamp build
Last week I started with my JFET RIAA stage. This stage is designed for my current MM cartridge (Ortofon 3e) which has a relatively high output at about 4mV. The stage is a variation of the Werner Ogiers’ circuit, inspired by the John Curl Vendetta. Rod Coleman helped me out here to get this design optimised, so thanks Rod again for the contribution.
A two stage RIAA stage with only about 42dB gain is not ideal. I’m looking at replacing my cartridge soon and hopefully buying an DL-103 MC cartridge. I will then easily tweak the gain and RIAA network to use the Denon one instead.
I built a breadboard of one channel and tested it:
Here is a first test of the RIAA response: Continue reading “JFET RIAA preamp build”
JFET RIAA preamp project started
Now is the time to upgrade my current RIAA stage. A bit unorthodox approach for a valve enthusiastic but you will see me now with my hands on sand. A very simple JFET input stage with a shunt cascode pair to drive the passive RIAA network. The final gain stage is an OPA604 with remaining part of the RIAA network. The Op Amp is forced into class A by a nice pair of BC847C forming a CCS.
Given the shunt cascode bipolar is an PNP Darlington formed by 2 BC860C low noise and the CCS has also SMD devices, I started by soldering these into 4 PCB adapters for SOT-23 devices
More to follow…(just a start)
SX-201a Sylvania
Upgrading the DHT filament regulators
I upgraded the DHT filament regulators to version 4. Rod has released a new kit which introduces temperature compensation for high current filaments. This is a key feature in my 4-65a design and I shall explain why:
Valve Tracing & Testing Service
If you are looking to test your precious valves and you don’t have the equipment, I can now offer this service for you which includes:
- Valve health check
- Valve bias point measurement (Ia, Is @ Va, Vs)
- Transfer curves
- Characteristic curves
- Microphony (optional)
- Distortion – THD (optional)
- SPICE model for triodes (optional)
Some examples of a lovely EL34 Mullard tested on request:
My fees are very competitive and this service is worth if you are looking to sell your valves or match them.
Terms and conditions:
- Price varies on level of testing and amount of valves
- Postage is not included and depend on your location. I’m in London, UK so you can easily estimate the costs beforehand.
Update – August 2021
My apologies but due to pandemic and lack of free time, I’m not offering this service anymore.
4P1L model improved
Improving the DHT model in A2
After playing for some time with the uTracer, I found that the tracer wasn’t measuring accurately A2 curves. Ronald clearly advised me (as explained on his site) that uTracer wasn’t designed for this purpose although there was a great trick to use the screen driver to generate the A2 curves and also measure grid current. Measuring grid current is key in A2 mode so a better grid current model can be derived to better simulate the non-linear and low impedance behavior of the grid in positive bias.
My incarnation of the uTracer is not neat. I’m using my existing analogue curve tracer. As shown in the pictures below, my current tracer have a plethora of sockets and just adding right jumper cables for anode, cathode, screen and grid connectors will still give me the flexibility I had with my analogue tracer
Additional 3,300uF capacitor across C13 to help A2 traces
My version of the uTracer
uTracer using my analogue tracer sockets 🙂
The process of generating the A2 curves (and SPICE model) starts by plotting the normal curves. The uTracer is great for this. Then you have to overlay the A2 curves in Excel (or whatever tool you prefer) to combine both set of curves.
4P1L: Tracing A2 curves (first test)
Just finished the digital tracer project uTracer V3. Did some further tests this morning, now with my favourite DHT: 4P1L.
Started with a well known bias point for triode-strapped operation:
