Concerning the previously mentioned Raysonic SP120 Mk I : (recapped, RC filtering changed to choke + Cap type, coupling caps to Clarity Cap ESA, etc.)
It has enormous drive capabilities, an almost incredible "bottom" end, glorious midrange and spatial presentation (6SN7-KT120), but lacks a bit of transparency in the upper range. Based on my earlier experience I think the culprit is the front end, which is Russian made 12AX7-s (Voshod 6N2P). That tube is not the last word in transparency....
Can anyone recommend a little bit livelier 12AX7 type that can match the rest?
It has enormous drive capabilities, an almost incredible "bottom" end, glorious midrange and spatial presentation (6SN7-KT120), but lacks a bit of transparency in the upper range. Based on my earlier experience I think the culprit is the front end, which is Russian made 12AX7-s (Voshod 6N2P). That tube is not the last word in transparency....
Can anyone recommend a little bit livelier 12AX7 type that can match the rest?
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The 6H2Π (6n2p) pins out differently than the 12AX7. This is not a "plug and play" situation.
Fortunately, only pins 4, 5, & 9 (heater connections) need re-configuring. If this can be done without cutting/bridging PCB traces, you can try OS RCA or OS TungSol stock, which are noted for their "chime". In current production, New Sensor's "reissue" TungSol 12AX7 has hints of OS "chime".
BTW, simply installing 6H2Π-EB (6n2p-ev) specimens may give you what you want. The suffixed variant is manufactured to a higher standard. Look here for some "EBone" listings.
Fortunately, only pins 4, 5, & 9 (heater connections) need re-configuring. If this can be done without cutting/bridging PCB traces, you can try OS RCA or OS TungSol stock, which are noted for their "chime". In current production, New Sensor's "reissue" TungSol 12AX7 has hints of OS "chime".
BTW, simply installing 6H2Π-EB (6n2p-ev) specimens may give you what you want. The suffixed variant is manufactured to a higher standard. Look here for some "EBone" listings.
a small modification with a switch will allow him to go from 6n2 to 12ax7.
for a 12ax7 "shinier" = JJ ecc803s, ecc83 Mazda flat chrome, gold ecc83 CIFTE 5 stars triple micas.
But the Russian 6n2-ev has already tended to be a little bright for my ears and maybe it would be necessary to start by controlling the point of operation of yours before making changes.
I had this problem with a very well known amp in France and reputed to work very well across the spectrum, I ended up finding that a small capacitor (3pF) between grid and plate of two of my ECC83 had changed value and made the sound darker but with a huge bass.
for a 12ax7 "shinier" = JJ ecc803s, ecc83 Mazda flat chrome, gold ecc83 CIFTE 5 stars triple micas.
But the Russian 6n2-ev has already tended to be a little bright for my ears and maybe it would be necessary to start by controlling the point of operation of yours before making changes.
I had this problem with a very well known amp in France and reputed to work very well across the spectrum, I ended up finding that a small capacitor (3pF) between grid and plate of two of my ECC83 had changed value and made the sound darker but with a huge bass.
Unfortunately there is no schematic exists for this amp (at least I couldn't find one despite asking for it earlier here). I tried to retrace -and draw- the double sided PCB but got confused after a while. Not an overly simplistic circuit.... Another possibility (for the dark sound) I thought of is the OPT, but according to specs and measurements it is quite linear up to 35k. The gain of 12AU7-s is too low for this amp I am afraid.... Thanks for the suggestions anyway.
Yes there are (cathode caps), I've already replaced them with Silmic II-s bypassed.
Well I think the problem is found.... The volume pot is 100k, wiper feeding the grid directly where there is a 220 pF poly cap connected between grid and ground.
At low volumes therefore the source impedance rather high, and this combined with the mentioned 220 pF + the Miller capacitance (calculated cca. 150pF) results in a rolloff at around 13-15 kHz.
At low volumes therefore the source impedance rather high, and this combined with the mentioned 220 pF + the Miller capacitance (calculated cca. 150pF) results in a rolloff at around 13-15 kHz
.My sources would allow much lower input resistance,(even 20k) but there is no way of replacing the volume pot (it is a double sided PCB mounted 4x100k motorized Alps) without loosing the remote possibility.... Not to mention the fact, that to "free" the board to work on it is a real nightmare. Any solutions?....
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Maybe it is so.... I paid the equivalent of 380 USD, I think it is reasonable... But as I mentioned earlier, besides this problem the sound is marvelous. I don't really understand why they've used 100k volume pot, most of contemporary sources can handle much lower values.
Thanks for the suggestion, I will try the 5751 (I have only one, but at least I can check the difference...
Can you trace out the values of resistors, etc. around that 12AX7 stage?
Do you need all the gain that 12AX7 provides?
In many cases you can simply swap in a 12AY7 in place of 12AX7, but not always.
12AY7 has lower gain, lower input capacitance, was designed to be a low noise input triode.
It does bias up differently than a 12AX7, so it might not be a drop-in swap in your particular circuit.
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Do you need all the gain that 12AX7 provides?
In many cases you can simply swap in a 12AY7 in place of 12AX7, but not always.
12AY7 has lower gain, lower input capacitance, was designed to be a low noise input triode.
It does bias up differently than a 12AX7, so it might not be a drop-in swap in your particular circuit.
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12ax7 is incredibly linear. You will not find a "brighter" variant.
My current favorite are thick glass china 12ax7's from the late 90's onwards. Super cheap and shunned by most. Modest selection is required as per all 12ax7's. They sound every bit as good as revered <> diamond based german telefunken..
My current favorite are thick glass china 12ax7's from the late 90's onwards. Super cheap and shunned by most. Modest selection is required as per all 12ax7's. They sound every bit as good as revered <> diamond based german telefunken..
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