I'm looking for a small sized and low voltage phono cartridge pre amplifier to be placed inside a Numark DJ turntable. I thought of ssubminiature tubes such as 6N16B or 6N28B, and would like sugestions of schematics of RIAA circuits based on those tubes or other subminiatures, prefrebly with 2 stages.
Stevie Bench's 6088 sub-mini phono preamp sounds good. I have no idea if you can build it small enough for the space you imagine.
Matt
<https://diyaudioprojects.com/mirror/members.aol.com/sbench/6088pre2.html>
Matt
<https://diyaudioprojects.com/mirror/members.aol.com/sbench/6088pre2.html>
6CW4 ( nuvistor triode ) might be what you are looking for.
conrad johnson made one http://www.vintagehificlub.com/reviews-articoli/conrad-johnson-premier-seven-tube-premplifier/
Bo hansson in sweden made a small series of 6CW4 equipped riaa stages,
conrad johnson made one http://www.vintagehificlub.com/reviews-articoli/conrad-johnson-premier-seven-tube-premplifier/
Bo hansson in sweden made a small series of 6CW4 equipped riaa stages,
Since these are low gain, probably would need a circuit that does not use overall feedback:
common cathode -> passive RIAA -> common cathode.
common cathode -> passive RIAA -> common cathode.
Probably the line preamp section is not needed as it first attenuates, then amplifies (not many need gain for line inputs) and the output impedance is way higher than that of the source driving it.
BTW 272V is not low voltage if OP means safe voltages. Safe voltages are till about 50V.
BTW 272V is not low voltage if OP means safe voltages. Safe voltages are till about 50V.
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Yes - it is an estimate based on comparing it with other phono stages with 40dB gain & 46dB gain + 36dB one ( measured ).
Overall phono & line together have gain around 48 dB, without Pot between them ( having built before the one with aprox. same gain, same tubes, just little different gain disribution between the stages ).
Tried only phono, then phono+ line without pot and then with the pot. With original passive PSU & regulated afterwards ( not really needed ).
Please keep in mind it just an estimate, not measured.
P.S. For MM carts general practice is to make phono stage with the gain from 36dB-38dB ( low & rare today for separate units ) to 40-42 dB.
For MC carts higher gain may be preferable, even with SUT or pre-pre / Head-Amp for MC cart.
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Maybe something like this, I assume the price is in AUD.
https://oatleyelectronics.com/product_info.php?products_id=936&osCsid=5pqtpou4rc3e31ntc2ioo5l493
https://oatleyelectronics.com/product_info.php?products_id=936&osCsid=5pqtpou4rc3e31ntc2ioo5l493
If you are going to use only two tube stages, I would recommend using a FET source follower on the output as a buffer.
Good to know, and thanks for the sugestion. Do you think it would work on lower voltages? Have you tried it?
For Lower voltages there is another phono here, search for 6N16 Mini Me, but that one is exclusively phono with three stages + CF so the gain is 48 dB or little over. These are still in the range 170-150 Vdc.
Did not try to do posted schematic with lower volatages, this is not just a matter of lowering voltage it would be a new design + also did not have a need for low voltage.
You can try but the RIAA network is partially dependant on the tube charateristics - so for lowering the voltages significantly these could change or maybe You could try to design the gain stages with low voltage but aproxximately the same characteristics - talking out of head, don't know if that is really 100% possible.
For this You would need 6N16 Spice model or to work in old way with paper and pen on the static diagram from the datasheet.
The only other thing of value that i can say is that everything could be built on Euro format board ( 100x160mm ) and that You should include some kind of Cathode Follower if the following piece of equipment is working with lower than 100K pot at input.
6n16b:
If you take a look at the curves, then we need about 40V on the plate to get one single mA thru the tube with -1V on the grid. I would not go any lower to avoid grid current to spoil the RIAA network.
Maybe 60-75V B+ min required.
Gain could be kept up with FET CCS as plate load instead of resistor.
7895 Nuvistor:
Even worse, needs 50V to pass 1 mA.
6n28b:
Better chance here. We get 2 mA at -1V and 30 V on the plate.
50V B+ might work with CCS load.
Maybe I will try a sim ... have to do the spice model first tho.
Anyway, why a tube based solution when space is crucial ?
A single dual opamp can do the job for both channels.
Easily fits on a 5 x 5 cm pcb, not to mention the ps which is a piece of cake.
And no hussle with hum, noise, heat etc. Even a vintage NE5532 might do the job well.
( That' s what I did in a similar situaltion)
If you take a look at the curves, then we need about 40V on the plate to get one single mA thru the tube with -1V on the grid. I would not go any lower to avoid grid current to spoil the RIAA network.
Maybe 60-75V B+ min required.
Gain could be kept up with FET CCS as plate load instead of resistor.
7895 Nuvistor:
Even worse, needs 50V to pass 1 mA.
6n28b:
Better chance here. We get 2 mA at -1V and 30 V on the plate.
50V B+ might work with CCS load.
Maybe I will try a sim ... have to do the spice model first tho.
Anyway, why a tube based solution when space is crucial ?
A single dual opamp can do the job for both channels.
Easily fits on a 5 x 5 cm pcb, not to mention the ps which is a piece of cake.
And no hussle with hum, noise, heat etc. Even a vintage NE5532 might do the job well.
( That' s what I did in a similar situaltion)
My serviceman gave me the phono he made - just said "a proven circuit with NE5534" - the box was like a pack of cigarettes with the PSU inside and transformer was Peaktech AC-AC 230-24 Volts ready made solution. It worked extremly well.
Puting something like that in the turntable would be much easier and additionally there is no possible problems from heat generated by the tubes if the space is closed.
Puting something like that in the turntable would be much easier and additionally there is no possible problems from heat generated by the tubes if the space is closed.
Two stage phono pre with 6N16B has no more than 29...30 dB overall gain.
Gain per stage = ~26 dB, loss at RIAA network 22...23 dB (at 1 kHz).
Gain per stage = ~26 dB, loss at RIAA network 22...23 dB (at 1 kHz).
My sim of krca45's circuit gave 33dB at 1kHz. Reality could be less.
So a max 5 mV output from a mm cartridge would result in 200mV output from this 2 stage phono at best with 6n16b.
A quick sim with 6n28b CCS loaded for max gain and 50V B+ / 35 V plates barely shows 27dB, another 6dB down. So phono output no more than 100mV.
That's only 1/10 of what a typical line output should have.
You either need a 3rd stage or a power amp with a very sensitive input (many vintage tube amps had 100mV sensitivity for crystal pickups) or an amp with integrated pre.
So a max 5 mV output from a mm cartridge would result in 200mV output from this 2 stage phono at best with 6n16b.
A quick sim with 6n28b CCS loaded for max gain and 50V B+ / 35 V plates barely shows 27dB, another 6dB down. So phono output no more than 100mV.
That's only 1/10 of what a typical line output should have.
You either need a 3rd stage or a power amp with a very sensitive input (many vintage tube amps had 100mV sensitivity for crystal pickups) or an amp with integrated pre.
Or keep the line preamp only for higher line level. The volume potentiometer would then be "output level".
Said "estimate is 34-36dB with line 12-14 dB" additionally i would say that estimate should be lower than 36dB - only phono for sure has little less gain based on comapring it with another phono with 36dB gain measured - not much but probably 33-34dB maximum would be the final estimate ( this when i think back when i did this ).
36dB phono is low for my system at that time - this posted schematic, only phono section had little less gain so by itself to low for me and with the line stage way to much - the reason i had to go on.
Also i am prety sure when i say that estimate for phono + line is cca. 48 dB - this was too much comparing it with 46dB phono ( measured gain ) - if the gain was around 44-45 dB i could live with that and this would be boxed unit by now - i have made a prototype and then made a new layout on paper 1:1, bought new parts but by that time six months had passed and when i had to make a final decision - it was just too much gain so i gave up and dismantled the unit.
Optimaly in theory You should find or make a phono with first gain stage with different sub-mini tube with more gain and then the second can be 6N16 for second stage & cathode follower duty ( if You need one or sections could be in parallel ).
Maybe exploring what cascode type circuit can give in terms of gain, or with CCS...?
The Soviets made a sub-mini tube 6x31 i think, with much larger gain but finding that one now.... well i haven't seen it anywhere ( if i got the last two numbers remebered right ).
Regards, Krca
The 6S31 has a gain around 20
Some higher Mu Russian miniature single triode tubes are,
6S7B (6C7Б) around 65
6S27B Mu 70 (6C27Б-K version is quiet)
6S32B Mu 80
6S35A 85
Twin triodes
6N17B around 70
6N21B around 80
6N33B around 70
6S52N (nuvister with flying leads) 60
Some of the tiny ceramic planer triodes have been used in phono amps like the 6S17K (6C17K), soldering directly to the tube has always worked for me.
Data is found at <https://next-tube.com/datasheets.php> <http://www.russiantubes.ru> and many other places.
I've built a variety of phono amps around the triodes above. But Stephie Bench's mini-tube 6088 phono referenced above is the best sounding of the bunch.
Matt
Some higher Mu Russian miniature single triode tubes are,
6S7B (6C7Б) around 65
6S27B Mu 70 (6C27Б-K version is quiet)
6S32B Mu 80
6S35A 85
Twin triodes
6N17B around 70
6N21B around 80
6N33B around 70
6S52N (nuvister with flying leads) 60
Some of the tiny ceramic planer triodes have been used in phono amps like the 6S17K (6C17K), soldering directly to the tube has always worked for me.
Data is found at <https://next-tube.com/datasheets.php> <http://www.russiantubes.ru> and many other places.
I've built a variety of phono amps around the triodes above. But Stephie Bench's mini-tube 6088 phono referenced above is the best sounding of the bunch.
Matt
My mistake - probably some of these tubes, but can't be sure. The first one maybe, something that NAT Audio used in their commercial offering a few years ago - when i tried to find it, out of cuirosity, there was nothing.
Valuable experience. Thanks.
Regards, Krca