KT88 conversion to integrated

[bikerhifinut]

I had a notion to convert my WD 88 amp to the integrated version some time ago, the purchase of a front panel on eBay finally resulted in my doing this. I initially dug out of the toybox the original Alps RK27 potentiometer and fitted a full set of input sockets. I simply made a harness of thin screened cable to take each input to a 6 way rotary switch.
It was bulky, it was messy, but it gave me enough to realise it was worth doing the job with the relay board.
So I bought one off Matthew. I should point out here that if you use thin screened cables and secure them neatly, you can make a decent looking but I couldn't resist the relay board especially as I have been thinking of moving this amp on and if its got the pukka WD bits in ……..

Anyway initially I had an issue with just about every aspect of retrofitting the input board, theres not a lot of room there for it. I had to move the HT rectifier tagboard towards the HT capacitors just to be able to squeeze the relay board in. Then it was a frustrating experience to find one of the relay wasn't energising on the CD input. Meter testing indicated the coil was ok and the circuit was good but somehow it wasn't clicking in.
I lashed up a PP3 battery to the power input and ran it through.
I couldn't find a wiring fault so assumed the relay was duff.
At this point I realised unsoldering the centre pins of 12 phono sockets wasn't going to be easy, even considering I'd used the smallest dab of solder to connect them.
suffice to say it all came out after a lot of swearing and use of various solder vacuuming and wicking aids. But not before discovering I'd trashed a 1N4148 on one of the relay coils, I ended up breaking it off with thin nose pliers and soldering a replacement of the "wrong" side of the PCB as an easy if untidy option.
I tested the board out of the chassis and all worked including the dud relay...……… hmmmmmm I wonder if a slight distortion on the PCB somehow prevented the solenoid moving?
So to put it back and I had a thought, what if I opened out the centre holes so they were a slacker fit? This wouldmean a simple dab of solder wouldn't be practical but I figured an ultra short wire link would have no effect on the performance so I opened the holes out by about 1mm with a drill. and the board slotted in nicely over the tightened down phono sockets and the use of a short wire link (3mm or less) did the rest.
So to do an operational test and thankfully it worked flawlessly, no background hum and all relays operating.
The real surprise has been the sound quality. No longer using any sort of active preamplification, just feeding the signal to the grid of the first stage off the wiper of the Volume pot but by a very short piece of wire and I was taken by how "together" it all sounded, including a very deep and tight bass on all sources.
I'm beginning to have second thoughts here about moving it on and am now looking to retrofit a remote volume control.
I tried a cheapo eBay board with onboard ALPS pot, the sound quality was fine but the control side was pretty awful, I suspect because it uses a simple halfwave rectifier and off 6.3V AC theres just not quite enough volts to get the onboard 7805 SM reg to stay in regulation.
However there's plenty of room on the LH side to slot in a Hi Fi Collective PCB and as I have a selection of motorised pots, this will likely be the route I take. It works as a few here know but I think its horribly overpriced at nearly £50 with vat and postage for what it is. That said it looks like the only show in town and I figure if Matthew could get a board out for half that price, maybe as a DIY kit to solder up he'd get lots of custom as it will fit neatly in a Pre3 too and for me its no big deal to get up and manually switch an input but it's so handy to be able to fine adjust the volume from one's armchair.
There's another issue with the WD Power amps and that's space to fit the ALPS "blue" RK271 motorised jobs without fouling but there are other Alps motorised pots out there such as the RK168 which does fit quite well. I won't argue the toss about perceptions of sound quality, suffice to say I can't tell the difference and if that means I have cloth ears so be it. I'll go on record here as being one of those who thinks the shunt mod is a retrograde step and it doesn't work for me at all, in particular the way it seems to alter the "Log law" when adjusting levels. As well as altering the input impedance with rotation.
Ok a lot to take in folks, and when I get the remote board delivered in the New year i'll report back. I will remove the power LED and use the hole for the sensor.

Andy.

[bob orbell]

Interesting Andy, I can concur with the Hi-Fi collective motorized kit from Nick Lucas, I have that in my Akidio CF, it works on 9volt DC or 6volt AC, so you will use 6v AC, I use a tap off the 9 volt after the rec. in PSU III, due to my high mains I have a small dropper resistor and a 9.1 volt, 5 watt Zener diode to supply the circuit, works good. I also agree with your comment about the shunt pot did not like it at all. Will you be giving up on a Pre ? if you do and wish to sell your J B power supply, give me first refusal. Bob

[bikerhifinut]

Originally Posted by bob orbell

Interesting Andy, I can concur with the Hi-Fi collective motorized kit from Nick Lucas, I have that in my Akidio CF, it works on 9volt DC or 6volt AC, so you will use 6v AC, I use a tap off the 9 volt after the rec. in PSU III, due to my high mains I have a small dropper resistor and a 9.1 volt, 5 watt Zener diode to supply the circuit, works good. I also agree with your comment about the shunt pot did not like it at all. Will you be giving up on a Pre ? if you do and wish to sell your J B power supply, give me first refusal. Bob

Yep Bob, I've got one of the Hi Fi collective boards in my Aikido CF in pre3 case. Does the job well. And using the Phillips RC5 code means the remote control for my rega CD player and Silicon preamp works, which is handy and saves having myriads of remotes on the coffee table.
I didn't prat about with the input volts, it works just fine off the 6.3V DC, I simply bypassed the rectifier and that feeds straight onto the onboard 7805 regulator. You don't need to mess about dropping the volts down to 9V either Bob, that's what the onboard 5V reg is for, it'll work well with 12.6 V AC across it.
No plans to get rid of preamps yet as I also use the homebrew EL34 power amp and often dig the old Leak Stereo20 out too for a session and keep its electrolytics formed. And of course the main reason I built the regulated supply was to run the Phono3 with nice steady clean power.
I've unfortunately mislaid the paperwork for the JB regulated supply as it comes with a circuit diagram and a nice table of resistor values for adjusting the output. I set mine at 270V and use a resistor to drop the volts to the phono and preamps, works a treat and the voltage stays rock steady. It was worth every penny Bob.
If you still have that over voltage toroid what's the raw AC on the HT? I may be interested as I'm looking at a circuit that will need 300+ V ideally on the HT. I have a trick up my sleeve which would be to use an EZ81 rectifier or similar which would reduce the available HT due to the drop across the valve rect. I have a 1A heater transformer looking for a purpose in life! This PSU will initially be a simple CLC smoothed job with further RC filtering to adjust the HT. My mains also hovers around the legal maximum for the UK grid at just over 250V, we're close to the local distribution transformer which may explain it, as the overhead power lines go up the fell a bit to supply several more remote farms and I figure the power distribution people deliberately run the grid high to alleviate the voltage drop at the end of the line. I reckon I can tell when they switch the big ovens on at the commercial bakery in the village as the lights dim momentarily and the run of mr Kiplings exceedingly calorific confections commences.

[bikerhifinut]

I've just wired up a Hi Fi Collective remote volume control board into the WD KT88 Amp.
I had to drill a 3mm hole in the top panel for a stand off and now its all tested I'll drill another to get the board on a couple of standoffs for a bit better mounting. It fits snugly but not cramped just behind the Left hand Front panel. I positioned the board so that the IR sensor can be lined up with the hole for the Power LED, I had to bend the legs a bit, carefully, but its lined up and no desoldering or extended wires needed to get the Sensor in a convenient place. Power is taken from the KT88 heater pins of the nearest valve base, the one with the power LED feed. Nice short run of AC heater wire twisted tight and its nicely away from the low level signal circuitry around V1. I fitted PCB "veropins" in the relevant holes for AC in, power out and mute so that it will be easy to remove/replace.
The motor supply was routed in the bottom corner of the chassis and brought out by the Pot, I used my usual 0.6mm solid core insulated copper that I use for small signal valve heaters, twisted tightly using the drill to get a nice even twist. I like solid core wire for these hook up jobs as it stays in shape when bent, just remember not to keep bending it to prevent fatigue fractures.
I was scratching the old head as to whether to wire up the muting facility on the board until the 15watt bulb went on above my nut. You can wire the mute relay as either normally open or normally closed so instead of the normally open option and using the mute to short out the signal wires as I really didn't want a run of wire carrying the input signal running across the front of the amp, I realised that as I was using a relay board I could use the normally closed option and wire one side in series with the supply wire from the relay board (black) this was done quite neatly by using the redundant side of the selector switch as an anchor point for the supply in which was then led with another length of twisted wire to the board and then back onto the "wiper" tag of the rotary switch. And it works a treat, using the relay boards own mute facility and I can remotely mute as well as manually. Plus I get all the nice things like the wind down of the volume pot on switch on and a 30 second muting period as the amp warms up. I like the idea of the amplifier never being at any serious volume setting on switch on.
Anyway so far so good, I will do a "dry run" with an Alps blue RK271 pot to see how much clearance there is from the adjacent KT88 valve base and if it fits then a call to matthew for the nifty PCB for alps pots is in order. I'm using an Alps RK168 which is the current production Alps motorised pot. It works fine of course and the sound quality seems no worse than the Blue. its got slightly worse channel matching, his one is a quad pot job and one pair is definitely not as well matched on attenuation as the other when I measured it. The RK271 I find usually has very good balance between channels right round its travel. I put that down to the difference between a 27 mm diameter track and a 16mm track. And where I feel much of the criticism of carbon track pots (or even plastic film) comes from against switched attenuators. The other issue with the newer RK168 jobs is that the solder pins on them are tightly spaced and in a single line, and there's a common ground pin so anybody wanting to try out the shunt mod is banjaxed. So it looks like a right rats nest there just now.
Anyway it's getting a soak test and I will have a good listen over the next few days, but so far I am liking what its doing.
Anyone who uses the integrated version of the WD amps could do a lot worse than invest £50 plus the cost of a motorised pot of choice (and shop around for those although Matthews prices are reasonable) and it gives the amps an extra level of ease of use with no adverse effect on the sound.

Andy

[bikerhifinut]

Has anyone knowledge of the TKD potentiometers sold by Hi Fi collective? They do a motorised version and the specs suggest a tighter tolerance item than the Alps RK271. They are also Conductive Plastic Film which as far as I know makes it easier to make a well matched pair of pots on the one spindle?
They are rather expensive at around £100 as opposed to the Alps Blue RK271 at £20 or so from RS, I haven't found any other suppliers of the TKD so Hi Fi collective it would have to be.

I don't know of any other motorised pots on the market as Panasonic have discontinued theirs.
Andy.

[bob orbell]

Andy, I have a used 271 in good order, apart from iron burn marks at the pins, it is yours for the asking if it helps. Bob

[bikerhifinut]

Thanks Bob generous as ever and a gent to boot. I might drop you a PM, I do like the Alps RK271 "Blue" motorised as mine have all measured very well on the all important channel balance.
I just wondered if anyone had any critique of the TKD pot as its roughly 5x the price of the excellent Value Blue alps.
Whilst accepting the law of diminishing returns I'd be interested as to how others think it performs, Given that I reckon I can hear a subtle difference between the 16mm motorised Alps and the 27 mm. It's a shame that the Black Alps is gone as a motorised version of that would have been interesting. I am led to believe the Black pot was even larger in diameter of its track which would suggest it could have had better matching round its travel?
I have a feeling the RK271s days are numbered so if anyone thinks they have a use in future, get one in whilest stocks exist. The later RK168 stuff is 16mm diameter track. They aint bad and I have had a couple or 3 through my hands but I figured the balance between gangs/channels wasn't a patch on the 27mm Blue.

Andy.

[Greg.]

Andy, within the diy circles I inhabit, I have not heard anyone discussing the TKD pots. I have however heard/read many tributes for the Tocos pots. Unfortunately, these don’t seem to have a remote control option. Just trying to help your perspective.

[bikerhifinut]

Ta Greg,
It looks like HFC are not restocking their Tocos stock due to issues with channel matching.
As you say, I'm more concerned with the motorised types.
If I were to use a "manual" attenuator it's a no brainer for me, I'd go straight for a nice switched attenuator and let's not argue about whose resistors we'd use, that's about as much use as saying my preference for Kenya coffee is better than yours for Colombian if that's a suitable analogy?
Ta Greg, might see you at Tonbridge, weather and other factors permitting.
A.

[Greg.]

Sorry, won’t be a Tonridge this year. Nigel’s passenger seat and space on the table is taken. It’ll be another time.