Resistor ladder soldered. Now it’s time
For the Logic ICs….
Mood
It’s been a long and wet winter. I barely gone out as it was always pouring down buckets of water. Spring is coming, and with that the mood of everyone is changing. A time to enjoy the open air and play music that cheers us up. New project and challenges. but for whatever reason is, I tend to play a different set of records when the weather is good. Can the british weather affect us so much?
I’m really looking forward to the good weather and for the summer to come, oh yes…
The least we can do…
I recently found a pristine copy of a great record from Van Der Graaf Generator: ” the least we can do is wave to each other”. If you don’t have a copy, I urge you to explore VDGG’s repertoire. Impressive stuff. I was a big fan on my early days of playing saxophone. I was blown away by Jackson, but it was Peter Hammill’s lyrics and music that grabbed all my attention. Still today it does.
And so I did have the great opportunity recently to say hi and exchange some words with Peter when he presented his latest work with Gary Lucas.
Fixed bias regulator
Testing the Rod Coleman Fixed Regulator
As part of my 300B SE project design, I looked into various fixed bias arrangements and regulators. Rod Coleman has developed another fantastic circuit after the success of his DHT filament regulator which is now the preferred filament supply kit within the DIY audio community. After many years of refining the DC filament regulator, Rod came up with a clever design for fixed bias using the same concept: a gyrator and a temperature-compensated CCS. Instead of feeding a current through the DHT filaments, in this case the current is used to generate a clean bias voltage across a “bias resistor”. The bias resistor is bypassed by a capacitor as the high impedance loop formed by the regulator and the bias resistor is sensitive to pick up HF noise which could be amplified by our system.
The kit is of the same quality you would expect from Rod’s boards and very easy to build. It takes less than an hour to build the boards:
London Audio Circle meeting March 2014
We had a terrific day at George’s on Saturday. Weather played in our favour and barbecue was on the agenda. I’m not looking to review a fantastic day with the circle members on this post, but just to capture a moment of this day with Susan Parker fitting her new cartridge on George’s Audiomods arm. I contributed with my Phono RIAA stage which was very well received (I think) despite the hum picked up by George’s system unfortunately. Great records played though…
Thanks George for the hospitality and a great day with friends.
Susan’s cartridge grabbed all the attention this day. I wish I could afford it!
Cheers
Ale
Refurbishing an LCR bridge
Recently I acquired a second-hand and untested TF2700 LCR bridge from Marconi. This is a fantastic piece of engineering and a superb LCR bridge that can only be beaten by an expensive impedance analyser, something I can clearly not afford.
This bridge is perfect for selecting accurately capacitors for a RIAA network with extreme accuracy. In fact, the 1% precision can be improved down to 0.25% by replacing the main bridge 0.5% resistors with 0.1% ones as suggested by Morgan Jones in his “Building Valve Amplifiers” (Second Edition) page 330 and 331.
Customised Potentiometers
I was looking to repair my LCR bridge and found that a 2k5/25k ganged potentiometer was needed. I found this great supplier of potentiometer that can provide you with a customised ganged potentiometer at a very competitive cost. Worth considering this great Welsh company!
Ale
Vinyl hunting in NYC
Last Sunday had the great opportunity to spend a day out in New York prior to a hectic work week ahead. Obviously record hunting was on my list of things to do. It’s been a long time since I last went to NYC and can say that the record scene has changed a lot. I’d like to highlight this great place owned by Jonathan Sklute. A passionate guy that loves vinyl records so much that has this cool small shop located in 218 East 5th Street, right in the East Village. The record store is called “Good Records NYC” and the owner proudly curates a selection of Jazz, Rock, Blues and other genres. Each record is carefully clean using a nice RCM (which I didn’t manage to capture model as it was placed on the back).
I came out with four gems from the Rolling Stones, The Kinks, Eric Dolphy and Little Sonny.
Highly recommended if you are around New York 🙂
Ale
4P1L driver – LL7903+LL1671 tests
Last week I did some preliminar tests with the LL2746 in 1:2 step-up mode. Despite having measured good results with it, it will be a challenge to drive grid current given that the output impedance of the 4P1L will be multiplied by 4 so about 5KΩ.
Before looking at the LL1671/20mA which is suitable for multiple driver valves, let’s see how the LL2746 driver performs with the addition of the input step-up microphone transformer LL7903. I’m currently using the LL7903 in my 814 SE A2 amplifier and sounds really nice. The LL7903 was wired up in 1:4 setup so gain can get about 63:
6e5p beam tetrode SPICE model
Thanks to the great work that Derk put into his great Extract Model tool, I helped him to refine and debug the application by tracing the challenging 6e5p beam tetrode. After 4 versions we managed to optimise the model:
The model fits really well including the kink section but given the saturation of the 6e5p tetrode at currents above 50mA there is a slight divergence as the valve cannot reach the same anode current at higher voltages.