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Raj1 7th September 2003 11:42 AM

tube cd output advice
Hi people,

Here's a link to a tube stage I intend to build for my pioneer pd-s 703,

Here's the schematic,

I live in the UK and on some investigation, I have managed to find stockists of the tubes, and output transformers (sowter).
However I can not seem to find a required mains transformer to provide the exact 100v outputs for the circuit. I do know that maplins do have mains isolation transformers which provide around 115v, perhaps I could use one of these instead, and drop the voltage with a resistor???

Or does anyone know of an off the shelf type which is suitable?

I ask this as it may be cheaper than having a custom tranny wound for me.

Also the 4H choke, does anyone know of a stockist in the UK, Sowter does have them but not at this value which means I need a custom one, this might be expensive?????

I do know that Maplins have a 10H choke which is quite cheap, and if possible I would like to use this.

Just thought I would ask more experienced people before making assumptions on how to get the correct rail voltages and filtering by using substitute parts.

I am reasonably confident I can do this, I have built SS kits before, and can now read schematics well enough to understand how this links together.


fdegrove 7th September 2003 03:31 PM


I don't see much of a problem with the powerxformers being a little hotter than needed.

Prior to buying the chokes have a look at their DC resistance, 10H choke normally have higher DCR than say, a 4H choke.

BTW, Ultranolg is a member here although it's been quite awhile since he last posted.

Maybe you could buy all the iron where he had it made?

AE is contactable here:

Automatic Electric Europe.

Mr. Wil Blauw is the man behind the iron.


Raj1 7th September 2003 03:39 PM

Tried contacting ultranalogue, but he's knda reluctant to tell too much (for the simple reason of not having anyone blaming him for mishaps I suppose!), didn't manage to get past him telling me to buy a scope - fair play to him!!!!

Yeah I suppose I could always use the 115v isolation transfo, and tthe 10H choke and measure the rail once it's up and running, I don't suppose say 2-5v either way should result in catastrophe???

Thanks once again for your kind help,


fdegrove 7th September 2003 03:55 PM



didn't manage to get past him telling me to buy a scope - fair play to him!!!!
Ah...that was you?

Nah, Remco (Ultranalog) is a busy fellow...he just doesn't have the time to help everyone out.


I don't suppose say 2-5v either way should result in catastrophe???
It often doesn't matter that much.
I'd pay more attention to the OPTs which are the most important components, i.e. quality is usually linear to what is paid for those OPTs.

Are you planning to use the 3A5?


Raj1 7th September 2003 04:04 PM

3A5 = yes
Hi mate,

3a5 is the one that I would like to build, I think the review of this given on the website tickles my interest. I will cost cut though and use the sowter output transformers, which seem to be more than adequate. Really looking forwards to getting this together, to provide that musical magic:bigeyes:


ultranalog 7th September 2003 04:38 PM

I'm afraid I have to advise you NOT to use the AE trannies. Their amorphous cores did not reach my specified impedance and regular C-cores turned out to be 10x under impedance. This led to unacceptable phase shift in the bass department.

For more info, read
AE impedance measurement

The amorphous core is useable for the stage, but too expensive by far.

Instead, I recommend the Sowter 8650. Whilst being much smaller, it has always performed excellent given it's modest price. Also, the Sowter service is much better. I haven't heard from AE after their promise to take my trannies back.

On another note:

I did not go into DAC details not because of protectionism or arrogance but since Raja refuses to buy a scope. This is DANGEROUS! He found a scope too expensive. It may one day save your life, which cannot be expressed in money.

Raj1 7th September 2003 05:40 PM


Sorry Remco, I did have a look at scope prices and they seemed to cost from say 300 to over 1000, and this put me off, although you are correct, the cost of life is far more valuable.

You see I have a DMM and I thought that this was adequate for diy that I undertake.

In this instance I wrongly thought you were only suggesting a scope to find the audio pinouts (sine) on the dac, and I thought I could get this info via yourself or via a forum, as proved to be the case.

As such no-one had ever really recommended me to buy an oscilloscope before, and I had only deemed them useful for measuring distortion etc.


Raj1 29th September 2003 05:50 AM

It's working
HI Guys,

Well thanks to the people on this forum, I got the output stage up and running, everything works just fine!!!!:)

Frank, I connected the B+ to the 3a5's and the voltage dropped to around 105-110v (have given time for warmup).

I've listened to some tunes on my senn hd580 'phones, and I must say that this is a very good ouput stage.

Getting a bit of hum thru the phones - heater tranny is noisy and mounted on top cover, and I still need to star eart both ouputs properly...... will investigate..........

The sound is much smoother than I'm used to with solid state...... The tone and timbre of the sound is what this stage excels at...........

Bass isn't as powerful, but maybe bass was overblown before---- listening will tell.......

A far more musical experience than the solid state device that was in the stock player (pd-s703)..........

If you have a voltage output dac this is a must consideration................

I'll see if I can post pics soon.............

My thanks go out to Fdegrove, Dhaen, Paul Barker and all other who helped me thru building this thing, sorry for the stress you guys........

Also thanks to Ultranalog for the design..............


Brian Guralnick 29th September 2003 11:37 AM

I've also been looking into what's the best way to get sound from a current output dac. Im designing a mono AD1955 based DAC unit.

I was thinking along the line of using a Sowter 9545 transformer right at the DAC as an IV stage, and a basic triode line stage buffer.

How would this compare?

I'm beginning to think around the lines of killing the line stage buffer & driving my tube power amp directly from the transformer, however, as I change volume, there is a small difference in input load & capacitance which may alter the sound.

(sowter transformer specs: )

Raj1 29th September 2003 08:40 PM

Hi all,

Brian you may want ask ultranalog your questions directly, as he'd probably have some good answers for you.....

Can't seem to get rid of the hum,

I have tried earthing the outputs, moving the choke, output transformers, twisting cables etc.........

Interestingly enough the hum gets real loud if I touch the chassis of either the cd player or preamp (being used with headphones)

Out of interest how close should R7 be to the socket pins, at present I habe a long length (20-30 cms) of cable running into pcb mounted terminal block which is then connected to R7.?????


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