MONOphono preamplifier by enjoythemusic.it

[HMV130]

Hello to everyone,
some months ago one user of this forum suggested me to look at the MONOphono preamplifier illustrated on enjoythemusic.it (click here for the article).

I decided to start building it however I do not clearly focused how to do it specifically regarding the powering.

In the attached schematic is shown that the all the circuit needs 320-350V DC so can someone provide me a solution to power it as an independent unit? Is advisable use a 5Y3 tube? If yes can someone provide a little schematic and tell me where to find a suitable power transformer (I live in Italy, so the power transformer needs to work with 220-230V AC)?

 

[kevinkr]

There should be a recommended PSU design for this design, I recall seeing it in the past.. If not you need very well filtered supply in the recommended voltage range. A 5Y3 will be fine into a CLC filter on the supply, additional filtering on unit as shown.

Most phono stages (including tube based) are in analogue source, which is where most of the phono-centric crowd hang out. So I will move it.

moved to analogue source

 

[kevinkr]

Use PSUD to design the required PSU if you cannot locate a schematic for a recommended supply. Since this is a phono stage separate chassis for the PSU and a really well filtered supply is NOT overkill. I would aim for way less than 1mV of ripple on the output of the supply under load, and the additional LC on the pre-amp chassis should take care of the rest.

I used regulated supplies in all of my designs which you will find on this forum. (My designs have zip for PSRR)

Take some care choosing 6SL7 for this design as they can be quite microphonic. Built with a little care this is a great device for playing mono recordings of all sorts. And, umm resist the urge to "improve" the design, build as intended some thought went into the original.

 

[Bigun]

Since this is a phono stage separate chassis for the PSU and a really well filtered supply is NOT overkill.

+1

A friend of mine just spent a lot of effort and some heartache debugging the 'hum' in his phono because he tried to put the power supply on the same chassis as the phono. He's now making them separate.

 

[HMV130]

There should be a recommended PSU design for this design, I recall seeing it in the past.. If not you need very well filtered supply in the recommended voltage range. A 5Y3 will be fine into a CLC filter on the supply, additional filtering on unit as shown.

Most phono stages (including tube based) are in analogue source, which is where most of the phono-centric crowd hang out. So I will move it.

moved to analogue source

First of all thank you for the reply.

Second, I have a General Electric 5y3-GT tube of which I found copy of the original specification sheet (please see the related attachment).

It is clearly shown that using the tube as Full-Wave rectifier with a apacitor Input filter (respectively - 20uF and 100ohm) and powering its plates with a total of (350*2)V AC it is possible obtain a 360V DC ready to use.

Performing some calculations I obtain that the minimum voltage required to power the tube in order to obtain 320V DC (minimum required by the MONOphono preamplifier) is 622V AC.

So using a 325-0-325 power transformer I can power the tube with a total of 650V AC obtaining circa 334V DC (less than 350V DC which is the maximum voltage usable by MONOphono preamplifier).

Please see the schematic of the PSU (calculations are included).

Do I have to scale the capacitor and the resistor values too? (I think no) Do I still have to use the indicated filter choke (please see the schematic of the top first post) after the capacitor filter input?

If all this is correct can you please provide me a brand and the model of the needed power transformer (it should work whit primary of 230V AC - and what about the mA?; I saw online many 325-0-325 that provides different currents)?

P.S: Should this topic be in the analog line level section?

 

[kevinkr]

You still need the CLC filter I mentioned in one of my earlier posts, you need to knock the ripple down to very low levels unless you want a lot of buzz.

Don't exceed the maximum input capacitance value for the 5Y3, use something on the order of 15 - 20H with a DCR of a few hundred ohms, and a large electrolytic on the output, perhaps 100uF or more.

Use PSUD to design a supply with well behaved supply voltage ramp up and low ripple.

I'd aim for the middle of the recommended voltage range at a nominal mains supply of 230V.

I can't make specific recommendations on chokes or transformers given you are in Italy and I am in the U.S. There must be local vendors. Look at Lundahl, and perhaps some German or French makers.

 

[HMV130]

You still need the CLC filter I mentioned in one of my earlier posts, you need to knock the ripple down to very low levels unless you want a lot of buzz.

Don't exceed the maximum input capacitance value for the 5Y3, use something on the order of 15 - 20H with a DCR of a few hundred ohms, and a large electrolytic on the output, perhaps 100uF or more.

Use PSUD to design a supply with well behaved supply voltage ramp up and low ripple.

I'd aim for the middle of the recommended voltage range at a nominal mains supply of 230V.

I can't make specific recommendations on chokes or transformers given you are in Italy and I am in the U.S. There must be local vendors. Look at Lundahl, and perhaps some German or French makers.

Thanks for the reply. See, I'm a novice in the "diy tube amplifiers and preamplifiers" field. Please be patient because I never used PSUD before .

Please see the attached result. I obtain a 326V DC but I have doubts about the "source res" value (30ohm) of the power transformer and about the "load amperage" value (100mA). Did I have to change them with other values? If yes which? If this is correct, which amperage value should have the power transformer (a 325-0-325 transformer seems to be right for the purpose but there are many with different amperages)?

 

[Carter]

Hello to everyone,
some months ago one user of this forum suggested me to look at the MONOphono preamplifier illustrated on enjoythemusic.it (click here for the article).

I decided to start building it however I do not clearly focused how to do it specifically regarding the powering.

In the attached schematic is shown that the all the circuit needs 320-350V DC so can someone provide me a solution to power it as an independent unit? Is advisable use a 5Y3 tube? If yes can someone provide a little schematic and tell me where to find a suitable power transformer (I live in Italy, so the power transformer needs to work with 220-230V AC)?

If you wish to build it just as Diego Nardi designed it, the MONOphono EQ amp was intended to use the same power supply as the phi-42 phono preamp. Diego used a 6X5GT rectifier. It is a nice enough power supply and is designed to provide the high voltage referenced heater supply very necessary for the elevated voltage direct connected 6SN7/6J5. The phi-42 was in Sound Practices issue 14--the whole set is available from Joe on Ebay. Then you can build the stereo RIAA EQ amp, too!

--Carter

 

[HMV130]

Hi Carter, thank you so much for the reply. Finally I figured out all the needed parts and how to built a suitable PSU for the MONOphono preamplifier.

I'll start to buy the components soon. I was wondering if you have any suggestion for the construction such as if screen or not the 6SL7GT valves or where to use shielded cable (only from the input RCA sockets to the first valve or thought each valve up to the output RCA sockets?).

Moreover does anyone know where to find decent "all metal" rotary switches with a medium shaft? (I found on eBay and amazon only cheap "plastic" ones).

 

[Carter]

Hi Carter, thank you so much for the reply. Finally I figured out all the needed parts and how to built a suitable PSU for the MONOphono preamplifier.
.

Be sure to build a separate, raised heater supply for the 6SN7
so that you do not exceed heater/cathode voltage limits!

--Carter

 

[HMV130]

Hello Carter,

following the Diego Nardi's schematic of the PSU for the Phi 42 Phono Preamp (click here) I extract this PSU schematic. Is it adequate for the Monophonic preamp? What do you mean exactly with "a separate, raised heater supply for the 6SL7"?

N.B - I will use all GE tubes. GE 6X5-GT has a separate heater/cathode.

 

[HMV130]

Now I should have figured what you meant thanks to this article. First of all I have to specify that the transformer that I own has also a 5V @ 2A secondary. Second, considering the schematic that I drew, it will be sufficient to create an "artificial center tap" (please read the article) just before the heater of the 6SL7-GT to minimize the any possible hum?

 

[Carter]

The direct coupled cathode follower output tube is a 6J5, which is half of a 6SN7. The circuit raises the cathode voltage. The peak voltage difference allowed between the heater and the cathode of a 6J5 is 90V. That voltage difference is a source of noise. So Diego uses a separate supply for the 6J5 heater. That supply can be allowed to float or can be raised to a value within the tube limits. The 6X5 allows 450 volts heater/cathode, so it will be ok. Diego also used DC supplies, which are quieter, especially in a low level phono amp. It's all in Issue 14!

--Carter

 

[HMV130]

Hello Carte, sorry for the delay in reply. Now I understand what you mean. I will keep updated this topic as soon as I will start to built it.

 

[anystereo]

The pdf of the schematic is difficult to read. Can anyone tell me the values of the 2 resistors one switched on the 2nd grid and the cathode caps? Best guess?