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A valve line pre amp for the DIY fishy

I've got one of Audioflat's shoeboxes, I'm tempted build one of these into it and see how badly it slaughters my Audio Research SP9/III. I've got a reasonable supply of old Amperex/Philips ECC88s.
 
Better late than never, I finished building this pre-amp today after a couple of weeks. First impressions are extremely enjoyable with a really open and natural soundstage and tight, controlled, bass.
It's currently running with a NOS Sovtech ECC88 equivalent. It biases up perfectly and worked first time. I bought an old power supply off ebay for £15 that had the correct transformer, centre tapped heater windings and a valve rectifier. Great fun. Now, where's the phono stage...?
 
Arkless Electronics said:
You know what Barry, I was just thinking that myself when I saw that a new post had been made here....

At the end of the day there would have to be enough interest to make it worth my while financially, and what have we seen so far.... 3 building one and about the same again expressing interest in maybe building one in the future...

If a dozen or more people come forward and say that it's the lack of a kit of parts that's putting them off then I will consider acting on that...
I could even make a PCB available, or a kit for point to point wiring with a sort of "idiots guide" on how to make one with diagrams , photos etc.. if there was the demand. I'm not going to do this first and then see if the demand follows though! It would be far too labour and time intensive to risk doing it and then finding only 3 more people want one...

Interesting to see that Snowman Al rates it as much better than the AudioNote pre amp kit which is I believe something like £1K....
Click to expand...

I'd probably be interested at some point in the future depending on cost. It's forever since I have built anything, I'd like to get back into it, I was actually looking at trash £10 Chinese two valve pre-kits with a wall wart on eBay earlier as I quite like the idea of something that comes with everything and easing myself in with something I won't be too upset if I destroy first! I might even buy two anticipating said destruction :D But if I regain some competence and confidence I'd like to try something like this that might find a place in my main system.

Case not so much, there are many different affordable options there and buyers can choose according to budget and taste or lack thereof. A friend has something along these lines, (quite possibly based on this, I think he "lurks" here but doesn't post) in an old Creek (I think) case with holes drilled for the valves to stick out the top and the volume know sticking out of the back :D He also used to have chipamp.com amps just screwed to a piece of wood for about two years so he could swap components easily until he decided he was happy and put them in cases.

His does indeed sound better (according to him, I haven't compared directly) than his AudioNote Pre which IIRC he sniped on eBay as spares or repair, and repaired.
 
I'd forgotten all about this preamp...and my thanks to Mark for being so generous with his time to build me a bracket and supply a transformer and valve...I must look them out and get this built.

I've never built tag board before, veroboard yep,but not tag board.

Pulling my finger out...

I'll be back to ask some bone questions. :)
 
Very nice work.
You could extend it a little and use the same PSU to feed a phono valve preamp too.
I don’t use 6922 valves any longer, I went back to ECC83 double triodes some time ago.
 
IIRC I went through this up thread but for anyone planning on building one of these be sure to use a valve rectifier as if you use SS the HT comes on instantly and can shove a 100V whump into the power amp! Mine has SS rectifiers but also has a relay delay circuit which shorts the output until the valve has warmed up and then releases the relay instantly on power off. This works so well you can switch on or off the pre with the power still on.

I discovered a few months back that the Croft 25 line pre is virtually the same as this but uses the much less suitable ECC83 valve and so mine whoops it's arse on all measured parameters and drives much lower impedance. I've no idea how they compare subjectively. I believe the Croft also has a relay delay to allow it's use of SS rectifiers but haven't been able to study the small PCB which likely is said circuitry.
 
MJS said:
Better late than never, I finished building this pre-amp today after a couple of weeks. First impressions are extremely enjoyable with a really open and natural soundstage and tight, controlled, bass.
It's currently running with a NOS Sovtech ECC88 equivalent. It biases up perfectly and worked first time. I bought an old power supply off ebay for £15 that had the correct transformer, centre tapped heater windings and a valve rectifier. Great fun. Now, where's the phono stage...?
Click to expand...


I have done pcbs for the hifi world valve phono stage, you can have the kicad files if you want.
 
Reminds me that I started a build when I made the brackets for Chilly and Dowser; may just venture into the garage to pickup where I left off.
 
mark121211 said:
Reminds me that I started a build when I made the brackets for Chilly and Dowser; may just venture into the garage to pickup where I left off.
Click to expand...
It was discovering the Tx, valve and mounting bracket in a box upstairs that jogged my memory about this thread and Mark's generosity. Thank you again Mark.

Now I'm a little more familiar with valves I thought I might have a go at building this pre amp, with a valve rectifier and tag board.

Second time at this I notice...
 
A little bit of progress.

2023-06-02_05-06-16 by Garf Arf, on Flickr

I'm not good at metalworking at all...that bracket for the valve rectifier and ECC88 took me ages.

The layout is stolen from Al's build above (I've not seen him around in a while, I do hope he's okay). The pot is a 50k Noble I bought from Les moons ago and has been in every preamp I've built so far.

I'm thinking to mount the actual input selection switch at the back of the case, by the inputs, running the shaft through the centre of the valve bracket...another hole to drill :). I have all the parts attached to a Starfish preamp I built, oh a long time ago.

687 by Garf Arf, on Flickr

Going to start marking out where things are going to be. And build my first bit of tag board from a cct diagram.

Shame Jez is here to see his design being built. I hear he is not very well atm.
 
It lives...

PXL_20230617_185428503 by Garf Arf, on Flickr

PXL_20230617_185433462 by Garf Arf, on Flickr

Having a bit of a soak test atm.

Anodes are at 65V, cathodes at 1.3V. Looking forward to giving it a good listen to.

I should say that the first time I turned it on the recitifier didn't work. I was getting 110VAC on one and 30vAC on the other. Only then did I realised that there wasn't a CT on the HT transformer, DOH. So a couple of diodes later and a link to the earth and we had HT!
 
Fabulous!

Interesting to see your lovely clean build - how there is so.little, to it based on tagstrip and little more.
Looking forward to future comments on how you find this / how it suits your requirements, tastes, etc.
ATB.
 
Thank you Martin. It is all in a surprisingly small box. You'll notice that I had to slightly rotate the choke as the chunky on/off switch case fouled the choke's body. There's bits of it that could have been a little tidier, but on the whole I'm pleased with the way it has turned out.

I did I bit of measuring this morning the THD+N comes in at about 0.09% @ 1kHz, averaging 0.1% across 5Hz to 20kHz. FR is -3dB down at 4Hz and flat out to 22kHz.

The two things I've left to do is to replace the wire between the chassis gnd and the audio gnd with a 10R resistor, but I'll see if there is any audible hum before I do that. And consider where to attach the HT Tx's centre tap to, the PSU gnd or the chassis earth. I have is attached to the chassis earth atm.
 
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