Sunday 15 December 2013

Coleman Regulators - GM70

 
Heating of directly heated filaments is a much discussed subject. Unlike indirectly heated valves directly heated filaments are a whole lot more picky about how they're warmed up as they are directly in the signal path. And they have a tendency to hum (and the more power they consume the more they want to hum).

Many swear by AC believing it's more natural; there's less circuitry in the signal path, and it's cheaper on hardware too. Others believe that DC is the only way to go - not only should it remove any hum but it's cleaner too removing the harmonic fringes of the 50Hz AC (or 60Hz depending on where you live).

But even in the DC camp there are different ways to go. You could try passive DC with lots of high current chokes and big capacitors, and LCL is said to sound the best and means there isn't a whacking great electrolytic cap strapped across the filament. It's not so easy to set the voltage though.

Or you could try a current source (leave the voltage sources for your indirectly heated valves). These can be fairly simple, or fairly complicated. Fortunately there are some options available if you want to have a go but don't know how to design a good one. If you want a ready made option then the Tentlabs modules will do the job admirably. DIY Hi Fi Supply used to have their own modules too, but they look to have stopped making them. Anyway, just wire 'em up, set the voltage by twiddling a screwdriver and away you go.

Or if you like to build stuff (and save a few quid) then another option is Rod Coleman's regulators. Rod has been developing his modules for the best part of a decade now I'd guess and has been supplying them for maybe three years. Send him some money and you'll get a compact PCB and all the components to populate it, plus instructions to build and test them. You just need to supply a raw DC power supply, and advice is given in the instructions. Rod is contactable by PM on the DIYAudio forum.

I've built three pairs of Rod's modules before for my 26-10Y-300BXLS monster and each one improved the sound over the passive DC I was using before. So when I finally started the GM70 amp I'd been meaning to build for about three years it was an obvious "fit and forget" choice to build a pair of Rod's modules again. And here's a series of photos of the build sequence.

First I like to lay out all the bits, check them off, and mark them up with which component they are



So start with the bare board



And then the smallest components first - the resistors. And then the first capacitor.


Then the variable resistor used to set the voltage


Then the first two transistors, to the same height as the variable resistor


Next the second capacitor


Then the third of the transistors, again to the height of the variable resistor and adjacent capacitor
 

Next the thermister which stabilises the current temperature (in position R11) (note that only the higher current GM70-type modules use these)


Then I add the sense resistors as I prefer to mount the two 3 legged chips when I assemble the heatsink. I find this the best way for me to get a good job, but it is a bit fiddly soldering the chips as access is a bit tight. Note that the resistors need to be stood off the board by at least 14mm as they get very hot.


So here's the module mounted on the heatsink - a piece of aluminium angle with the PCB connected by standoffs. Note the use of mica insulators as the higher current regulators need insulating. Make sure you use some thermal paste on both sides of the micas - I didn't have any to hand at the time but retrofitted later. Note also a zener fitted across the chip pins, a little fiddly to solder. This is some added protection in case the valve isn't plugged in when the power is turned on.


And here's the finished module with additional heatsink. As I breadboard I like to use them as self contained modules, which is why I mount them on the aluminium angle. If I ever do get around to putting them in a box they can then be mounted to the metal chassis for additional heatsinking. The finned heatsink does a very good job of taking the heat away from the regs and I intend to mount the heatsink above the chassis eventually. (The heatsinks I bought in Japan for about a quid each...)


Here are the two regs in service. Rod supplies instructions on how to test and commission the regs, and as you can see from the DMM it's easy enough to set the voltage. I like to set it just under the nominal voltage and backed it off just a little from the voltage shown.

You might just be able make out the additional capacitor across the raw DC supply - this is a 1000uF cap that decouples the reg from its power supply when connected by longer wires, if it's in a separate chassis for instance. This is a rather nice amp I have to say, one I should write about some time.




Tuesday 10 December 2013

Quasars - Open Baffles Par Excellence


Okay, okay, it's time I wrote about some proper DIY audio, enough shirking and flattering to deceive. And if you're thinking "he's a bit full of himself - first blog about DIY and he's telling us how wonderful his stuff is" then you'll be relieved/disappointed to know that I make no claims to progeny of these speakers at all. No, speakers are not my "thing". These open baffles are the design of James Doddington and we are fortunate as a community that he has been happy to share his design. Mine are fairly rough prototypes, but these are James' own speakers



The drivers are fullrange AER Mk 1s which cross over around 150Hz to Supravox 285GMF bass helpers. Both are very nice drivers and not cheap either, though the AERs are no longer available.

James has spent a long time fine tuning the shape of the baffles. By their nature baffles need a large surface area for low bass notes, even allowing for the pi/2 effect of using the floor. The shape of James' baffles use the cardiod effect to improve bass response for the given size, down to 40Hz. Nevertheless these are still large speakers at 1350mm high and 420mm wide. The size is the downside of baffles, but the upside is the lack of boxy honky colourations that cabinets usually have, and well built baffles shouldn't.

Whereas I used yucky 18mm thick MDF for my prototype build James' finished articles use 20mm thick perspex which being see through minimises the visual intrusion compared to wood. The front baffle is shaped, the sides of varying depth and the base profiled as they all enhance the sonics. There's some discussion too as to whether the perspex enhances the sound too. Here's the dimensions of James' Quasars.



In comparison my prototypes are an easy build. The front baffle is flat and 450mm wide x 1350mm tall sloped back at 5 degrees, the base is 500mm deep, and the sides are a simple triangle. It's important that the joins are all air tight. Sadly two baffles won't come out of a single sheet 2400mm x 1200mm, but spare MDF is always handy. The bass helper is mounted approximately 100mm above the base, and the full range driver at 750mm.

The crossover is usually a series one as this offers benefits over parallel. It's fairly simple, or rather there are few components: an inductor, a large polypropylene capacitor, a much smaller paper in oil capacitor to bypass the PP and bring back a little tone, and likely a resistor to balance the relative efficiencies of the two drivers. The inductor wire benefits from a cross sectional area of 2.5mm^2 as this minimises the DCR of the coil, though smaller diameters will work.

Currently I have a pair of Alpair 12Ps mounted as they're new and I thought I might as well run them in in the new baffles. My intention is to make some MLTLs for the 12Ps and use my Fostex FE208E sigmas and T90A supertweeters in the baffles, but one job at a time. I'm waiting for the crossover components to arrive, it'll probably be in the new year now unfortunately.

According to the Mark Audio datasheet for the 12P the drivers should be treated gently for the first 100 hours, then slowly increase volume and bass content and the drivers will improve for up to 800 hours! So at the moment I'm trying to resist the temptation and turn the wick up and listen gently. But the speakers already show tremendous potential.

I wasn't expecting much soundwise as the 12Ps are new and I don't have any crossovers yet but even now they're really very nice, albeit quiet. The pedigree of the 285GMF is clearly evident; it's a wonderful driver - clean, fast and tuneful. A number of James' Quasar designs have used 15" Eminence Beta drivers to excellent effect and are substantially cheaper, but the Supravox are really nice. It's early days with the Alpairs, but initial signs are good; they sound a sweet driver and very capable.

So only another 95 hours to go and I can turn the volume up a bit :-). It will be interesting to compare the 12Ps with the 208s in the fullness of time.

Sunday 8 December 2013

Record Players and Flamenco



Oh come on, he's having a laugh now surely?! This is his fourth blog and he finally mentions record players, but he's going to talk about Flamenco! And they're not record players, they're gramophones. What does he know about Flamenco anyway?

Well truth be told not a lot. But the more I experience it (and I think you do experience Flamenco) the more fascinating I find it. Until my last couple of trips to Andalucia the little I knew of Flamenco came from TV and according to telly it's not easy to see the real deal y'know, most of it is for the tourists de diddly dee. Real Flamenco is squirrelled away behind closed doors. Now I don't know how "real" it is but Flamenco is pretty easy to find on the streets, bars and restaurants of Malaga and Cordoba.

Whilst walking into Plaza Constitution in Malaga a couple of weeks ago there was some live Flamenco mid-afternoon which the locals and a few tourists were enjoying.

 

And then a chap in the audience fancied an impromptu dance and joined in. Clearly Flamenco was in his blood. As it was the locals watching.

 
 
 
 
 
 
 
 

I saw him walking away down Calle Marques de Larios afterwards breathing a little heavily and drawing hard on a fag. And looking rather content.

Malaga is an interesting and vibrant city and as we had an evening flight home the following day we had plenty of time to take in the Flamenco Art Museum. But first breakfast and as a last-day treat it had to be churros con chocolate y cafe doble. General I find that food which is brown is unhealthy. And rather yummy. You really couldn't eat churros every day and live a long life, but as a treat it's fabulous! And I don't drink coffee so you can imagine what a double hit does to me...


Now buzzing from caffeine, sugar and fat it was off to find the Museum of Flamenco Art.


It's a relatively small museum in a couple of rooms above a bar on the ground floor, but has a number of old wind up gramaphones which were interesting. Flash wasn't allowed so the exposure isn't ideal in some of the photos.




This is Carmen Amaya. I'd never heard of her until a few days earlier when I saw an old film of her in the super Flamenco Centre in Cordoba.



This is a clip from the film Los Tarantos, shot in 1963, the year she died. I think it's extraordinary and compelling, and unlike any of the Flamenco I've seen myself. Perhaps because they can't match her speed? See what you think.


There's a colour version out there too but I prefer the black and white version, perhaps because it's grainy, perhaps because it's the first version I saw.



Back to the gramophones






Close up of the horn





And finally The Graphophone with presumably wax cylinders







Sunday 1 December 2013

Audio Meet - Owston 9th and 10th November 2013

Well, not much of a blog this is it? A couple of posts barely relevant to hi fi then silence for four months. I have no excuse but overwork. And whooping cough.

Yes, whooping cough. Isn't that something kids get? That's what I thought too, but it's more common in adults than children these days apparently as vaccination is so successful. But the efficacy wears off with age, so more adults contract it than the young.

I've had it for about four months now and although I'm in the recovery phase I'm still not on top form yet. I definitely can't recommend it and I understand why babies and young children can be hospitalised. Anyway, you didn't come here to hear me moan so let's get on with some photos :-).

Owston Park Lodge


Every six months or so a number of us meet up to "show and tell" with our latest kit. As we predominantly inhabit the Audio Talk forum most of us are DIYers, and most of us prefer valve amplifiers. After that things splinter a little - some like SE some like PP, some like open baffles some like boxes, some like vinyl some like digital, and most of us like most of them. We're a pretty broad church and some of the attendees are commercial, some have become commercial over the years we've been meeting.

The usual venue is the function room of a pub to the north of Doncaster, so unlike some dos in hotels we're all in one room albeit rather large. Acoustics can be a bit tricky but it suits our ethos as we're all together and meeting up is as much social (and alcoholic) as about audio.

Saturday was a rather grey and at times damp day, a good day to be inside really.

The regulars meets up on the Friday night for a good drink and discussion about various things. The later it gets the more compelling the discussion! Further catching up is done on the Saturday morning whilst everyone assembles their kit. Some have been known to shake their head wondering why it doesn't sound as good as it does at home. Yes, the room can be a killer, but at least it can be blamed.

And then our "host" and organiser Steve S calls us to order, welcomes all, and provides the important information - like what time the buffet lunch will be.


Kicking us off this time was Dom and Natalie from Northwest Analogue. Dom's a nice guy and really knows his stuff with vinyl. Not sure about his choice of handbags though. At least I think it's his... Maybe not.


They used a Garrard 401 in one of Dom's custom made slate plinths



They were also using the protoype of a new cartridge Dom has built. Nat was a bit concerned about photos showing the unfinished state so I've respectfully and if I may say so rather skillfully photoshopped it out in this photo. Okay, I lied, it wasn't very skillfully done, but then I lied about using Photoshop too!


They used a 5881 SET with 274 rectifier, but I didn't catch what the driver was


They were using Colin Topps' new Jenna speaker. This is another design from Scott and very nice they were too. They'd walk out of any hi fi shop and would retail for a good sum. They're named after Scott's favourite fiddle player.



Following Don and Natalie was Ed with the first of his two systems. It was Ed that inspired me to create this blog so I could record our meets for posterity, since I lost access to my old Simon's New Adventures In Hi Fi site. Assuming Google doesn't go belly up or start charging for the privilege anyway. Ed also shares my bemusement about the whole concept of golf and golfists.

Ed has struggled for some time to fettle his Coleman regs he uses for SV572 filaments but has now found success by using a couple of cheap ebay SMPS for the raw DC supply.

Using his "vintage" Squeezebox Ed demonstrated with his kit that he certainly has plenty of know-how


I love valves that glow!



The cheap ebay SMPS

And Ed's own design and constructed VoFo speakers with Fostex 207s (I think)


Next, going round the room was Mike with Scott's latest design, a double bass reflex with Mark Audio Alpair 10P (I think). Here Scott introduces the concept of the speakers.

And Mike talks about his solid state amp with germanium transistors


Having used a phone before here myself Mike's a man after my own heart using his iPhone as source. Of course I use Android (this was kindly brought to you by our host and sponsor Google!)





Having lived with Fostex 208E sigmas for about 10 years I'm always intrigued when I see a cone with a lot of movement , and the Alpair 10P has quite a bit

And then it was the turn of our host Steve. I like Steve's kit a lot, he ploughs a slightly lonely furrow in the way he does things, but then he has one of the largest collections of early British valves :-). Steve thinks of Second World War era valves as new fangled inferior mass produced jobs.

Steve brought his new amp finished late the night before (or was that early the same day?) He was a bit concerned about it as he thought it might need a bit of fettling, but it was fine :-). The interstages and output transformers were fresh from Pieter at Tribute, some fancy amorphous type material apparently. So whilst the valves were probably the oldest things in the room the iron was probably the newest.

PX25 globes

Source was his trusty DVD player and TeraDAC

Several pages could be written about Steve's speakers. They're the culmination of many years of experimenting with open baffles. Yep they're baffles, not boxes.

I'm not sure what this incarnation uses but there's a couple of Fane bass drivers, possibly a 15" and an 18", teamed with a nice Beyma TPL150

Next around the room was Graeme who hasn't been for a little while so it was good to see him back again

Graeme brought his very much DIYed turntable - originally a Lenco GL75 I think? with air bearing parallel tracking arm, and cartridge built by his wife. That's pretty DIY :-).




Graeme's using his WAD KEL84 PP amp to bi-amp with a Quad 405 to power his Tannoys



Then we came to Steve (the Shadow) with his balanced KT120 PP amp and Colin's Jenna speakers

Steve was using his Apple front end



Following Steve was David from Mains Cables R Us with a selection of gear.


The turntable was a well-specced Technics. A bit of leg pulling in the room suggested it might be trying to make a silk purse from a sows ear!

Phono stage was Nick's

The preamplifier Nick had "knocked up in his shed the night before" according to David. Which might have a grain of truth perhaps, but was a little more leg pulling.

Dave was using some interesting concrete speakers. A three way design, the fascination for me was the construction of the cabinets. I've long held reservations about using concrete for speakers - when hit with a hammer well compacted concrete rings. I can't help thinking this must affect the resonance of the speaker but as I've never tried it I don't know if that's actually the case. These speakers didn't ring as far as I could hear, and the designer confirmed that he'd added some kind of rubber pellets to his mix which I think may well have been a master stroke. Construction was very good and they sounded like good box speakers to me.




Meanwhile Andrew was testing various people's amps for them with his super-improved lightweight testing rig, no one a laptop rather needing to lug a desktop down from Scotland. The testing process has proven valuable to a number of people helping them to focus on areas to improve.

Back to the systems, and following David was Ali who was very excited as he heard his Garrard 401 for the first time after it had been living on top of his wardrobe in storage for a few years. A little fettle by Dom and it made sweet music with his active solid state amps and baffles with Visaton and Eminence Alpha drivers. The pre amp might have been borrowed from Nick?




Next was Steve again, this time introducing Ant's system (who was outside taking a breath of fresh air)



Then Ed went again with his second system. Ed was valiantly trying to demonstrate the weaknesses of the speakers and that he'd had to heavily damp them, but they sounded okay to me. He used his F2 this time.




And then we came to Mark with this Owston's award for most hardcore DIY effort with his multi way horns. Mark asked for feedback from the floor and was promptly told he was a nutter. Not quite the sort of feedback Mark was looking for! Source was James' super Kenwood direct drive turntable, amp was Mark's 4P1L-6B4G (I think) with shunt reg power supply.









Then a mix of kit was put together so we could hear Mark's 5687 Aikido pre amp. This was Mark's first DIY build and he was understandably very proud of it. The chassis was built by Ant, turntable was Dom's NWA 401 with the concrete speakers again.


Nick had a go next, with an active crossover using a DSP board to compare against the passive crossover in Colin's Jennas.

Greg was next with his WAS 2A3PSE and WAD PREII converted to cathode follower.


Poor old Dave had been trying to have a go for a while but kept missing out. But we couldn't put him off forever and eventually had to let him have a go. Dave had brought a 300B amp with four separate regulated bench supplies for the HT. On the Sunday we compared the AC heating of the 300Bs with some DC modules Andrew has designed. There was a subtle difference between the two, and the preference was universal. This says a great deal for how well Dave had implemented the AC heaters, indeed this is a very fine amp indeed.




Last but by no means least was Thomas with his TV trolley masterpiece. This time it was sporting 6SN7-46-300B with Coleman regs for the 46 and 300B filaments and series reg HT. Jolly nice indeed. The first photo is perhaps a little unfortunate, but as Thomas was insistent on assaulting us with Henry Rollins it seems rather appropriate! Sorry Thomas!



Another great meet with some really good sounds. The standard of our meets is so very high these days. Roll on the next one.