• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube Phono stage dilema

HI, having recently redescovered the delights of vinyl I am looking to build a moving coil compatible tube phono stage, for a low to medium output mc cartridge, 0.3mV output.

Previously i have used the first version of the Curcio Daniel, set up in the higher gain option, this comprised a single ECC88 cascode with 100R cathode, and 20K plate load, Passive eq and a further Parallel ECC88 Common Cathode with 392R on each sections cathode and a
20K plate load.

Great sounding, but I found the noise levels not really acceptable for a 0.3mv output moving coil. Not in the long term anyway.

So what to build?

I would prefer a zero feedback topology, all tube if possible. with minimum number off stages

I have considered a hybrid similar to the Daniel, only with a Jfet as the first input device aka Allen Wright, Erno Borbelly amongst others. I guess this would solve the noise and gain issues, but i would still prefer an all tube design

Or perhaps a parrallel input tube like the Steve Bench or Toccata Loesch preamp, or the later Curcio Sarah would just be quiet enough.

Would it be better to build a 2 stage low gain moving magnet RIAA equaliser and build an extra moving coil stage such as the Hampton or MC Hammer , trouble is 3 stages off amplification.

Has anyone tried a cascode with multiple tubes on the bottom section, operating with near zero grid bias?

Any sugestions or ideas welcome
 
velvetsunrise said:

I have considered a hybrid similar to the Daniel, only with a Jfet as the first input device aka Allen Wright, Erno Borbelly amongst others. I guess this would solve the noise and gain issues, but i would still prefer an all tube design

Or perhaps a parrallel input tube like the Steve Bench or Toccata Loesch preamp, or the later Curcio Sarah would just be quiet enough.

It's going to be tough to get reasonable noise performance without a step up transformer or jfet input. You could the replace the input tube with a jfet in the Bench design. I built a variation of his design, but used a transformer step up. If you use one of the Jensen transformers, you can get more than 25-30dB of gain, depending on how you load it: http://www.jensen-transformers.com/datashts/34kdx.pdf

Sheldon
 
I'd second that. You have a nice, low input capacitance, just perfect for a good step-up transformer. A nice 1:10 from someone like Jensen or Sowter, and you're good to go. The step-up also allows you to run your cartridge and interconnect balanced, which can be a big advantage with regards to noise pickup.
 
Hi, Chris

Thanks for your suggestion.

I have tried a couple off vintage transformers from neve and utu, nice, but sounded a just a tiny bit bandwidth limited at the low end. I guess the modern ones now available have greater bandwidth.

I was hoping to avoid transformers if at all possible, just to create something a little bit different i suppose.

Though, if it sounds good, it is good.

Thanks Chris.
 
Hi, Sheldon.

Hi, Sy.

I have enjoyed reading all you posts. You obviously have a lot off experience of RIAA preamps.

Seems the Transformers have it. Unanimously!

I guess it would be easier and cheaper to just add a transformer than build a new phono preamp from scratch, though i was looking forward to starting a new project. I have been collecting a few choice parts for a while.

I will investigate your transformer options.

Thanks.
 
I built an MC pre-preamplifier with E88CC. It was running from about 50V. The two halves of the tube are connected parallel. The cathod is directly grounded, the grid resistor is what the cartridge needs (100 ohm in my case), the plate resistor is 10 kohm. Important is the good plate and heater voltage filtering. The noise level was about -60 dBA @ 5mV output, the gain was about 20 dB. Not very impressive figures, but it had good sound. It is easier to get similar quality (and far lower noise) with a transformer, although more expensive...
 
Hello Velvetsunrise ,
I have built 4 or 5 "Daniels" for me and for my friends .

http://www.ak-tubes.de/Vorverstaerker/Daniel/daniel.htm

I use this preamp with different input transformers with good results , some vintage from old german studio equipment , some new like the Lundahl 1681 .
The noise floor in the high gain version of the Daniel was too big for my ears .
I have tried many , many tube circuits as MC - preamp with nuvistors ( the Conrad-Johnson circuit ) , 8 or more tubes parallel or cascoded designs .
They all had the problem with noise , no hum but hiss .

In the last years , I use only my own design with D3a tubes , I like this a little bit more than the Daniel :) .

http://www.ak-tubes.de/Vorverstaerker/D3a RIAA/riaa.htm

But also in this preamp , I use a step-up transformer for my DL 103 and my Lyra Argo .
Regards , Alexander .
 
MC head amp

I like you dont like the sound of Step up treanformers. I tried a great design from here using a 6dj8 with 24 V plate supply which some of my friends liked but I sadly didnt. That is not to say that you wont like it, I wan to make that clear. I settled on a Neville roberts design which is based on the bc 214 transistor.. I really like that one
Here is the link http://homepages.tcp.co.uk/~nroberts/article64b.pdf.
Good luck with your quest and just remember once you find the design you like, it will have been worth it.
Nick
 
Hello RE-604.

Some very nice builds you have there, your D3a preamp looks very interesting, do you have a circuit diagram?

It would seem moving coil amplification with tubes is perhaps unobtainable unless some noise is tolerated. I think i will add a transformer, and perhaps build the MC Hammer head amp too, as i have some spare ECC88s.

Thanks.
 
Re: MC head amp

duderduderini said:
I like you dont like the sound of Step up treanformers. I tried a great design from here using a 6dj8 with 24 V plate supply
Blaming the Tx's when you could have done a lot more to optimise the ECC88 part seems a bit wrong. Though an ECC88 can be operated this low, I never would if looking for highest SQ.

Morgan Jones and Allen Wright (earlier non-hybrid cascodes) come to mind as good examples as does the Curcio from memory.
 
Subjective

Hi Brett.
The design using parallel 6dj8;s is from a diy member and it as I said was liked by my friends, I however dont like the generic 6dj8 sound... let the debate begin.. I also tried transformers and didnt like them either.. and goodness knows I tried all the loading and capacitance till the cows came home.
I have built probably 7 different phono stages and 3 or 4 head amp species and essenitally settled on one that I like. Using Neville Roberts Head amp which runs on a 9V battery complemented it. Subjectively speaking its what I have found to be most pleasing to me.
One thing is for sure though and that is Moving coils are just better (to me) than MM.
It is woirth the bother I found
Nick