All about electronic valves and hi-fi
Over the past 5-years I have received several queries about the current limiter resistor and LED additions to the hybrid mu-follower PCB. Although these are explained, clearly not well enough from my side. So I decided to document this a bit more to help out everyone working with this board:
Watch the video here.
This is my first ever recorded video and hopefully there is interest in this format to share some content.
I’ve been using these boards for many years now. Haven’t offered them as is required for anyone to be experienced well enough in SMD soldering to get these done effectively. I have a reflow oven so work at scale is easier this way. I’ve been doing a lot of SMD board design and building over the past few years though.
On a busy time regardless, I found the space to build these four commissioned boards for D3a drivers like the ones I used on my 300B amplifier. There seems to be a lot of interest and build work done around this design, so happy to see this happening.
I’ve used the LR8 reg a few times here and there, always with satisfactory results. Yet, I’ve never spent time looking into it with more detail, always helped me to fix a voltage reference needed. Over time, I shifted towards the gas regulators and MOSFET-based voltage regulators where needed.
I also wrote extensively about the “sound” of regulators and why I’m reluctant (as many out there) to include closed loop regulators in my HT supplies. Having said that, having a tight closed loop reg to generate a reference and use a cap multiplier is a great alternative to provide a very clean supply.
The LR8 can do a great job here for voltages below 430V-ish if you marry him with a nice MOSFET like this:
The LR8 needs a 1.2V reference across the ADJ and output pins. R1 and Rtrim+R3 provide the adjusting network to dial the output voltage. See the datasheet for more info. R3 sets the minimum voltage and Rtrim provides the range needed for adjustment. Of course you can tweak this network for your needed voltage. I just simply worked this out to provide a 90V reference. RLPF and CLPF are the low pass network feeding the pass MOSFET. The LR8 has some BW noise like every reg which spreads into HF. Although there is no info on the datasheet, I remember measuring this but can’t find the data at hand. The 220K+47uF combination on the LPF network seem to provide a good balance on the rejection at 50Hz as well as the transition response to slowly rise the output in about 45sec.
The spice model I use isn’t trustworthy as is not official. It shows a notch which can be moved to about 100Hz with the above RC network values chosen. Proof is in the pudding and have to measure this to see if it’s somewhere near this simulation. Either way, the rejection is over 80dB across the band and if it measures as good as this, then we are all happy.
I’ll do a small PCB for this so if there are interested on it, just let me know.
The use of CCS in HT power supplies is well known, however generally misunderstood why it can be a good addition to some circuits. There is an excellent article from Gary Pimm which has been lost and luckily I found it on my archive. Here it is in case you haven’t read it. Worth it as a refresher or for anyone who is new to the subject:
Continue reading “CCS in power supplies”Finally after many years, I managed to document this great PCB. If you already have this PCB and want the build guide and BOM please let me know.
Here is an extract of the build guide for the ones who are interested in this circuit:
Continue reading “Cap Multiplier PCB: build guide and BOM”It’s been a long while, yes, I know. Life goes in particular ways, you can help that. Having said that, I’m now back after a long absence.
Life has changed for me and have some more free time for a while so will crack on some project. There’s plenty I want to work on and we always fall on the same trap: there’s not enough time. I’ve been very much involved on music and synthesisers. That’s where all my free time and design/build effort has gone into over the last few years.
However, I have some RIAA project, 845/211/GM70 amp, second turntable and probably an RL12P35 Amp I want to get working on, hopefully all soon
In the meantime, a lot of people are writing to me for advice. I sometimes get frustrated as people seem to try a shortcut and not do any homework before they ask for help. When I’m short of time, this kind of frustrates me. Anyhow, there is a big up tick on building a lot of my designs which is very rewarding.
The lovely look of the 46 drivers into 814s which I won’t forget.
Thank you for holding on out there. I hope I’ll post back soon
Firstly, my apologies. It’s been long overdue to get back on this blog. I receive several emails from people asking me to share more. I hope I will, when I get the time and energy to get back on hi-fi audio projects. I still work a lot on synthesisers which keeps me very busy when I catch a glimpse of free time from my hectic day life.
We’ve all been hit by the short of semiconductors. Yet, the HV precious parts are in shortage as well. Luckily some of the key parts like LDN150 and IXTP08N100D2 are back in stock, not sure for how long. These are key parts for building any CCS or hybrid mu-followers for audio circuits.
Continue reading “Short of sand”It’s been a while indeed. Mostly busy with my day job and family. However, spare time is dedicated to synthesisers – I’m designing and building modules for Eurorack – and playing and listening to music.
I’ve been asked about the GU-50 triode curves. I have misplaced them, however I have something even better to share which is the accurate model created for this great valve.
Ok, title isn’t very appealing. I know, however it truly reflects what I experienced over the past few days. Let me clarify before I start: a gassy tube developed a nice fault-finding journey. You always learn a lot from all this, for sure. Luckily, due to the holiday season, I had the time to work on this. I’d rather have spent it otherwise, but my 300B amplifier was dead.
I had a gassy 6BY5-GA damper rectifier tube. I should have changed it, but I was lazy and I paid the price for it. When turned on the 300B HT power supply, it will flash blue for a sec or two and the gas ionisation will disappear after a minute or two when tube was warm enough and operated as expected. Problem was that my stash of these damper tubes was up in the storage, who knows where.
Continue reading “Gassy nightmare”It’s been long overdue, I know. At least we are here. Another Christmas to celebrate in a good way. A couple of days late this post, but hey at least I’m writing this entry 🙂
