The next phase:

[bikerhifinut]

Now then gents.
In the wake of the power amp developments my thoughts turn to the preamps again.
I know I have an excellent Pre in the form of a unity gain Aikido CF, complete with remote volume control and I really should be content with that.
Anyway I found myself in possession of a set of Pre3 transformers and a PSU3 mains transformer and choke complete with PCBs for pre3 and PSU3 thanks to an ad on this forum.
I was thinking of building up a standard Pre3 in the WD case, but I really don't like having to work in such a cramped space and in any case I would like to have less boxes.
So I am thinking of a Pre3 "type" design as a "one box" solution. Unlike a Phono amp I am not dealing with signals measured in Microvolts and therefore I feel that with due regard made to layout I should be able to build a nice quiet preamp complete with PSU combined.
Advantages to me are a the direct link from PSU rather than a fiddly umbilical. And it's own dedicated supply too.
With a larger case I can incorporate remote Volume control, and if I get ambitious, remote source selection. This is not very high on my list of priorities as I really only need 3 inputs these days. That is, Phono stage, DAC, and analogue tuner cos I still really prefer good old FM radio off the troughline even in glorious mono.
So the choice of casework is the dilemma.
I want something that looks at least as good as the WD stuff.
It has to be big enough to accomodate the mains transformer and output transformers and allow space to shield the mains tx and raw PSU from the signal circuits and OPTs.
The case that springs to mind is obviously the HD3 one.
So has anyone here got "hands on" knowledge of the HD3S case and if so am I on the right track to getting a "one box" solution this way?
There will be other things to consider, not least the front panel but I guess I could adapt the HD3S one to suit, all I'll need is an extra hole for the selector switch. I am minded to keep the headphone socket for future development. And I'll bet the Pre3 could drive headphones..............thats a side issue though.
The outputs will be single ended but with a choice of balanced also as I have plans in the long term to build a totally balanced push-pull power amplifier. I have to say that I think the idea of having a fully balanced output from a preamp is wasted if all you do is unbalance it at the input of a power amp only to split the signal in a valve later on. Why not take it all the way to the output transformer.
Finally I don't feel a "Traitor to the cause" by this as I would be building what is basically a WD amp in WD metalwork, Just not as we know it............

Andy.

[bob orbell]

Hi Andy, the case you refer to will easily accommodate all the pre III parts, and more, in fact this case was used as a pre with remote volume and electronic source selection as a prototype, I have seen it, sadly it was scraped. The front panel will need to be drilled and counter bored to accept the source control and you will need to make more holes in the back of the case for your RCA sockets, (there are only four) you said in another post that your metal working skills are poor, if you decide to go this route, I can and will machine the front panel for you, to accept the source knob, and if you also find making the extra holes in the case a problem, I can also help with that. BOB

[bikerhifinut]

Originally Posted by bob orbell

Hi Andy, the case you refer to will easily accommodate all the pre III parts, and more, in fact this case was used as a pre with remote volume and electronic source selection as a prototype, I have seen it, sadly it was scraped. The front panel will need to be drilled and counter bored to accept the source control and you will need to make more holes in the back of the case for your RCA sockets, (there are only four) you said in another post that your metal working skills are poor, if you decide to go this route, I can and will machine the front panel for you, to accept the source knob, and if you also find making the extra holes in the case a problem, I can also help with that. BOB

Bob,
Thats extremely generous and kind of you.
I will definitely bear that in mind.
I am ok drilling holes in the back of things, I do have a useable bench drill that I can accurately bore holes with. But stuff like the front panel that will need milled to match is a different animal.
The Source Knob will be the only Extra for the front panel. I'm minded to keep the headphone socket as I have a transformer option that has an extra winding that could easily drive a small chip based headphone driver. And as previously noted, I strongly suspect I could get away with driving Phones direct from the output transformers.
This sounds promising. I remember well the HFW article describing the RC WD Pre and that's what got me on my train of thought.
I feel a phone call to Matthew coming on.
I reckon there's scope for an option in the WD range for a self contained pre3, It wouldn't take an awful lot of extra bits, the hardest bit would be an extra front panel, and include an optional PSU out for a Phono3, and bobs yer uncle!
I will keep you in the loop, my projects have tendency to have long gestation periods but I'll get there in the end.

Andy.

[bob orbell]

Message received and understood, over and out. PS, be very careful when drilling the holes in aluminium, which the cases are, I use a small pilot drill and a tapered machine reamer, gives a very nice finish. BOB

[bikerhifinut]

As an additional, I haven't got to the circuit stage yet. I have many options.
I can use the WD PCB and build the standard 12AU7 amp. I noticed the board seems designed to be capable of being separated into 2 separate mono boards, which may well help with layouts inside.
Sticking with B9A Valves I can also investigate alternative Toobs. I have some 6CG7 which would likely work with no resistor changes, being small envelope 6SN7.
And that brings me neatly to the MAD option of using a pair of Octal Valves, probably 6SN7. I just like the butch look of them and they are so much easier to solder onto when hard wiring, I find B9A bases oh so fiddly.
My liking for tagboard/hardwire has it's roots in the easier substitution of components when developing a prototype circuit. PCB's are great for preamps but I consider a PCB as a single use part. Although I tend to use veropins in locations where I may be experimenting with resistor values and types and crucial coupling capacitors. Pins are great for replacing bits on PCBs as you can leave the board in situ if the part is accessible.
Bob would it be ok if I pm'd you with a discussion on machining panels etc?

Andy.

[bob orbell]

Yes Andy, no problem I think the 6SN7 with valve base will be too high for the case in question, unless they will work OK on there side, you need to look at the valve data. BOB

[vinylspinner]

Hello Andy,

I have sent you a pm ref: chassis and faceplate.

Nigel

[bikerhifinut]

Originally Posted by vinylspinner

Hello Andy,

I have sent you a pm ref: chassis and faceplate.

Nigel

Reply sent

[bikerhifinut]

Ok folks.

I will be on the R & D phase after next week. This I think will take a bit of time. I have a habit of not diving straight into a scratch project. I will likely spend time with "Dry positioning" of Transformers, chokes, and circuit boards etc before metalwork and also mull over alternative circuits to drive the transformers. But for now It will be the WD ECC82 design as a known quantity, and I have a full suite of genuine WD parts and boards which is part of the philosophy behind this, If I can prove it's possible to build a successful remote volume control "all in one box" WD pre3 then It might be a template for others and put some businesss Matthews way. This before investigating any differences, eg use of a pair of 6CG7 which I feel are a superior audio valve to the ECC82 which was originally a TV valve. As far as I know anyway.
Strange that I like the ECC82 as a cathode follower but not as a common cathode amp. But they are different applications so maybe not so strange.

Cheers guys.

A.

[Richard]

Hi Andy, we're following with interest, please post pics if poss

Re the valves, ECC81 and 88 were Radio/TV types, and 82 and 83 were low and high mu audio amplifiers. 6CG7 is similar to ECC82 but has a different heater arrangement, 6.3V only for controlled warm up when series wired, and uses twice the current (you probably know that but it may affect psu arrangements). I've not used it but do like ECC82 which has many plug'n play varieties such as 5814, 6189, CV4003 etc which vary in tonal quality but most sound good