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View Full Version : Turning a valve preamp into a phono stage?



HighFidelityGuy
30-12-2009, 18:28
Hi,

A few months ago I purchased a valve preamp off ebay to have a play with.
Since then my plans have changed a bit and I don't really have a specific use for it any more. However I do need a phono stage. So I was wondering if it was possible to modify the preamp to make a valve phono stage of some sort. I understand I'd need to somehow add in an RIAA equalisation circuit but other than that I'm unsure what would be required or if this is even worth considering at all.

Here's a photo of the preamp circuit board (click to enlarge):

http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/th_CIMG2169.jpg (http://s2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/?action=view&current=CIMG2169.jpg)

If I remember correctly the circuit uses one 12AU7 valve and two 12AX7 valves along with an odd Chinese rectifier valve.

I'd like to end up with a phono stage that could be used with MM or MC cartridges and had plenty of flexibility for changing load impedance etc so I've got flexibility for the future.

Do you think there's any hope or point in attempting this?
I'd be grateful of any advice on what I'd need to do to get this working.

Cheers.

Rare Bird
31-12-2009, 04:13
Too much pain Dave.

Just build a fresh like this

http://www.dddac.de/tp07.htm

alb
31-12-2009, 07:39
I agree with Andre.

John
31-12-2009, 08:47
You can get the WAD phonostage in KIT form and it sounds fantastic

DSJR
31-12-2009, 10:33
You can also get Crofty's "R" grade phono stage for £500 I believe ready made and with warranty (the WD is getting pricey now) and a good few of us know what Glenn can do with a phono stage from all his "era's."

theoldtrout
31-12-2009, 19:40
Forgive my butting in on this as my first post but I agree that converting your amp to a phono stage is probably not worth the effort.

I’ve designed and built various phono stages [not easy] but I’m currently using a version of the Phonodude as mentioned by Andre. You may want to look at John Broskie’s Aikido http://www.tubecad.com/

Layout and earthing are critical to avoid hum, you also need a quiet PSU; and if you want to use an MC cartridge then put a transformer up front as it is a lot easier than try to make a quiet MC input stage.

Ali Tait
31-12-2009, 20:37
Yep,agreed too much hassle.Valve phonos are not easy to do,but can be worth the effort from what I've heard.

HighFidelityGuy
02-01-2010, 16:06
Thanks for all the replies. I had a feeling this wouldn't be worth the hassle. I'll check out all your suggestions and weigh up all my options. I like the idea of building a kit, so I think I'll concentrate on that option first.

Cheers.

Mike
02-01-2010, 17:32
You can get the WAD phonostage in KIT form and it sounds fantastic

Wot he said!

Or, you could do THIS! (http://theartofsound.net/forum/showthread.php?t=360) :)

HighFidelityGuy
03-01-2010, 16:36
The WAD looks very nice and is the sort of kit I'd feel comfortable building but it unfortunately adds up to more than I'd like to spend right now. I could handle the price of the phono stage it's self but the fact that the PSU more than double the price kills it for me. I think my limited budget is going to kill my overall idea of going the valve route. That's why I was hoping I could use my existing valve preamp as a starting point to save money so that I wouldn't have to buy the PSU and valves etc all over again.

My current thinking is to just build/buy a solid state phono stage for around £100-200 to get me started. I like the idea of building one as it will give me some good practice at the diy aspects and hopefully allow me to get something that's better value for money. Along with the sense of achievement that comes with making things your self.

My current favourite idea is to use this design: LINK (http://sound.westhost.com/project06.htm)
I can get the relevant PCB's from them for a few quid. Then I'd just need to source the components, build it up and put it in a case. Unfortunately I lack the skills to design my own or do anything much more than follow instructions.

Out of interest, roughly how much did it cost you to build yours? If it was less than £200 and there were some easy to follow instructions I'd certainly consider giving it a go.

Cheers.

John
03-01-2010, 18:43
Dave the WAD sounds pretty good it might be worth holding onto funds allow The other route would be the Croft. Glen has always known how to build a good phono stage.
With the WAD you have to spend a lot of money to get something better

Mike
03-01-2010, 21:16
Out of interest, roughly how much did it cost you to build yours? If it was less than £200 and there were some easy to follow instructions I'd certainly consider giving it a go.

About £150 not including the step-up transformers. That's for the phono stage AND psu...

HighFidelityGuy
04-01-2010, 19:25
EDIT: Oops I did't read your post properly, original reply deleted. :doh:


About £150 not including the step-up transformers. That's for the phono stage AND psu...

Thanks for the details.

HighFidelityGuy
04-01-2010, 19:34
EDIT: Oops I did't read your post properly, original reply deleted. :doh:

Mike
04-01-2010, 19:38
Which one are you talking about?

The Phono 3 that I 'cloned'! :)

It could be done for a lot less than £150 if you're not fussy about the cases.

HighFidelityGuy
04-01-2010, 19:40
Sorry for the confusion Mike, I read John's reply about the WAD and then read your's and for some reason thought you were talking about the same thing. I've edited my replies accordingly. Cheers. :)

HighFidelityGuy
04-01-2010, 19:44
I had a quick read through your post about building your phono stage but I must admit I got a bit lost at times. Is it possible to just buy the PCB's and then source the components etc separately? I don't have the necessary skills to design anything my self but I could easily solder everything together.

Cheers.

Mike
04-01-2010, 19:47
I had a quick read through your post about building your phono stage but I must admit I got a bit lost at times. Is it possible to just buy the PCB's and then source the components etc separately? I don't have the necessary skills to design anything my self but I could easily solder everything together.

Cheers.

Indeed it is!

That's how the whole thing came about!... Several people have heard it, and not one has had a bad word to say! :)

Cheers...

HighFidelityGuy
04-01-2010, 19:57
Awesome, can I ask where the PCB's can be purchased from as I can't find them on the World Designs website?

Also are the PCB's nicely labelled up with component ratings etc so I know what goes where etc?

Cheers.

Mike
04-01-2010, 20:09
Awesome, can I ask where the PCB's can be purchased from as I can't find them on the World Designs website?

Also are the PCB's nicely labelled up with component ratings etc so I know what goes where etc?

Cheers.

Hi Dave,

I've just had a look and can't see the relevant PCB either, odd!.... However, give them a call and ask for a 'Phono2 PCB' (the boards are the same for the 2 & 3) and I'm sure you'll find them more than happy to sell you one. IIRC they're about fifteen quid. I can easily talk you through the rest.

The complicated bit might be the PSU. If you can stretch to it, then buy the WD PSU3. If not, the NickG PSU I built isn't difficult, I can help there too...

Cheers...

HighFidelityGuy
05-01-2010, 13:06
Thanks for the offer of assistance Mike, that's very good of you. :)
I'll get in touch with with WD to see if they can still supply PCB's.

You may also be able to help with another related problem I found out about yesterday.
The problem I have is that I have a passive preamp and I didn't realise how low the output voltage was from most phono stages was. So I will probably have a problem getting a phono stage to drive my power amps correctly. Can you think of any way round this, short of buying an active preamp?

Thanks. :)

Mike
05-01-2010, 14:48
I'd try it first and see what happens...

My WD clone happily drives my own passive pre! :)

HighFidelityGuy
05-01-2010, 15:22
Awesome, this is sounding very promising.
I'll get in touch with WD asap.

I've just got a couple of quick questions about valves for you:

I notice the phono stage needs 3x ECC83 valves. I'm guessing two are for the left and right stereo signal but what's the third for? Would it matter if this one was a lower quality Chinese version? The reason I ask is that I have a couple of nice Mullards and a couple of Chinese ones already. I also have a Mullard ECC82 but I don't know if that's of any use.

Also, what valves does the PSU need?

Cheers.

Mike
05-01-2010, 18:15
ECC83's are double triodes, the phono stage uses one half for left and the other for right. All three valves are used for both channels with the RIAA equalisation in between the amplification sections. You could use pretty much any make to get you started and upgrade at a later date. 5751 valves also work particularly well but have slightly lower gain.

PM me with your email address please, it's easier to explain with pictures! :)

The PSU uses a 0A2 (http://www.r-type.org/exhib/aaa0696.htm) and a 0B2 (http://www.r-type.org/exhib/aaa0357.htm) (gas voltages stabilisers) which are connected in series to give 250V regulation.

HighFidelityGuy
05-01-2010, 21:30
Thanks Mike. I've emailed WD, so hopefully they'll get back to me soon. I guess I can't really do much until then as I don't want to start ordering parts if I can't get the PCB's any more. Not to worry, I'll concentrate on my valve preamp project until then.

Cheers. :)

HighFidelityGuy
11-01-2010, 10:00
WD got back to me today. They can supply PCB's for their phono stage and the matching PSU. Prices are as follows:

WD Phono3 £15.90

WD PSU3 issue 3.1 £21.55

WD Phono3S (our switchable version) £24.33

I'm going to go for the Phono3S as it will give me more flexibility for the future. I've also decided to get the PSU PCB from them as well to keep things simple. I'll hopefully get these ordered later today. :)

HighFidelityGuy
11-01-2010, 17:09
I didn't managed to get the PCB's ordered today as I decided I ought to find out what other components were needed just in case there was something else that I couldn't get from my usual supplier that WD might stock. As it turns out I need a choke that Farnell don't stock. RS have one but it looks rusty in all the pictures so that doesn't fill me with confidence. So I've asked WD if they can supply this. I've also asked if they can supply the transformer as I can't be bothered to hunt round for that.

So hopefully they'll get back to me with prices for all that lot tomorrow.

Ali Tait
11-01-2010, 17:34
That'll bump the price up a bit!

Mike
11-01-2010, 17:37
WD got back to me today. They can supply PCB's for their phono stage and the matching PSU. Prices are as follows:

WD Phono3 £15.90

WD PSU3 issue 3.1 £21.55

WD Phono3S (our switchable version) £24.33

I'm going to go for the Phono3S as it will give me more flexibility for the future. I've also decided to get the PSU PCB from them as well to keep things simple. I'll hopefully get these ordered later today. :)

Make sure you can get a suitable transformer, or the PCB will be of little use! You need secondaries of 270V for the HT and 9V for the heater supply. You could always use a separate tranny for the 9V though...

Mike
11-01-2010, 17:38
Actually... don't worry too much about 270V either... There are 'ways and means'! ;)

Mike
11-01-2010, 17:48
Chokes 'n stuff here... http://livinginthepast-audioweb.co.uk/xfrmrchokes.php

:)

HighFidelityGuy
11-01-2010, 18:57
Thanks for the info. That's another useful site to add to my favourites.
I'll see what price WD come back with and if that seems reasonable I'll go with that, if not I'll look elsewhere.

Cheers.

Ali Tait
11-01-2010, 19:31
Should be pretty reasonable,and it's good quality iron too.

HighFidelityGuy
12-01-2010, 11:33
Well I've got good news and bad news. The bad news is that WD don't have the transformer or choke in stock as the original manufacturer went bust and they're part way through getting a new manufacturer to supply them. :(
The good news is that I've ordered the PCB's anyway so I can get started.
I'm going to order all the other parts asap and leave the transformer and choke until later.

I'll now stop posting in this thread and start a new one about building the WD phono stage once I've got something to get started with.

Many thanks to everyone who contributed to this thread, you've all been very helpful. :)

Cheers.