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Psilonaught

6SN7 own goal :(

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I eventually received my 6922/ 6SN7 adapters and so I was able to install a quad of Sylvania GTA NOS in my Musical Paradise MP-D2 dac.

They replaced a quad of eh 6h30 gold pin.

Well all I can say is massive disappointment. It was like putting beach towels over my speakers. An immediate loss of sparkle and top end resolution.

Can I expect these 70 odd year old tubes to improve over a few 10s is hours? They came from Langrex so are genuinely unused stock.

I was under the impression that the 6SN7 is the best output tube for preamps (and analogue DACs)...

I could try the CV181 tube but they are very fat and my sockets are quite close together. 

:/

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They look nice however!?

IMG_20200910_214915_resize_92.jpg

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31 minutes ago, Psilonaught said:

I was under the impression that the 6SN7 is the best output tube for preamps (and analogue DACs)...

Those tubes are not that similar. It is a bit like swapping an ECC82 for an ECC88 (please correct me if that is a wrong analogy). In anything other than a really simple circuit I would expect some circuit redesign to be required to optimise for the different characteristics.

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Super Wammer

I’ve been reading up a lot on this sort of stuff recently and the application in theory is sound but from what I have read, sonically this may bring unsatisfactory audio results. This tube rolling malarkey can be fun but expensive and no guarantees of improvement. Having had a small amount of experience with the 6922 valves on my pathos amp, it’s clear to me that those Electro Harmonix gold pin valves are quite special for a small outlay.

The standard EH valves I have and imo are an improvement over the Jan Phillips valves that also came with my amp. Not knowing the hours on either valve, it does draw me to want to start afresh as I have no means of testing the valves. 

I will say however, Your DAC does look impressive 😊 
 

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Did you modify the circuit to optimise the 6SN7s? If not you're just asking for trouble. They're very different valves. The 6SN7 has a higher anode resistance and would require different loading to make it sound right, probably also a different operating point. You can't just say "the 6SN7 is good so it should sound better" - that only works if you design for it. I'm not a huge fan of either the 6SN7 or the 6N30 but at least they will work best in a circuit specifically designed for them. You can run into all kinds of issues when you go outside the design, like even the heater current. The 6SN7 is 600mA, the 6N30 is 830mA. Luckily you're going in the right direction in this case, but you see the point. 

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13 minutes ago, pmcuk said:

Did you modify the circuit to optimise the 6SN7s? If not you're just asking for trouble. They're very different valves. The 6SN7 has a higher anode resistance and would require different loading to make it sound right, probably also a different operating point. You can't just say "the 6SN7 is good so it should sound better" - that only works if you design for it. I'm not a huge fan of either the 6SN7 or the 6N30 but at least they will work best in a circuit specifically designed for them. You can run into all kinds of issues when you go outside the design, like even the heater current. The 6SN7 is 600mA, the 6N30 is 830mA. Luckily you're going in the right direction in this case, but you see the point. 

the dac circuit is designed to take a range of output valves and has a 6.3v and 12.6v switch. Having said that, the dac ships with 6H6N and therefore one would assume that the dac was designed around that type of tube. Might explain why the eh 6h30 sounds so damn good.

I totally see your point about circuit design, and that could well be why in this situation the 6SN7 sounds worse.

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36 minutes ago, Psilonaught said:

I totally see your point about circuit design, and that could well be why in this situation the 6SN7 sounds worse.

The 6SN7 is a totally different valve to the 6H30. The 6H30 is a high current triode with a low anode resistance of around 840 ohms, the anode current may be 20 to 30 mA for the 6H30 in that circuit with an anode load resistance to suit.

The 6SN7 is a small signal triode with an anode resistance of 7700 ohms, when run as a class A amplifier the anode current would be around 5mA. The Anode load resistance would need to be much higher for a 6SN7. Goodness only knows what anode current is flowing through a 6SN7 in that circuit. I'd take them out right away.

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I wonder what's in the adapters other than the pin arrangements to allow the swap?

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there is a circuit board inside I noticed, so some form of conversion is going on. I have been specifically told by the designer of the dac that this adapter works, and i know of another guy on headfi using 6SN7 with this dac, so that isn't an issue.

I've got them running all day and i'll listen again this evening to see if i can hear an improvement. 

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15 minutes ago, mr.me said:

I wonder what's in the adapters other than the pin arrangements to allow the swap?

I doubt if there's much you could put in the adaptor that would do much good. EG the anode pin: if the new valve needed a higher value anode resistor you couldn't put one in the adaptor because the surrounding circuitry would assume the audio o/p is coming straight from the pin, not via a resistance added in series with the existing anode resistor to make the valve think it had the correct anode load resistance. I'd also suggest that grid or cathode bias circuitry can only be adjusted outside the adaptor not inside it.

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Moderator

Valve socket adaptors are the spawn of the devil, as they just encourage people to stick valves in places they weren't intended to go.

Sorry James, I didn't really look at the original thread, but I'm equally never particularly impressed by equipment that ships with instructions saying the vast range of valves that can be used. Valves have different designations for a very simple reason. They are different. Different pin connections and heater voltages are just the basics, but there are countless electrical properties that matter if you're designign  a circuit. Just saying a range of valves can be used is crazy, because the circuit should be optimised for a particular operating point. Anything else, and the valve will not be running at its best in one way or another.

The main reason a lot of things have a 'valve sound' is because there's distortion or non-linearity that wouldn't be there if the valve was running as it ought to.

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2 minutes ago, rabski said:

The main reason a lot of things have a 'valve sound' is because there's distortion or non-linearity that wouldn't be there if the valve was running as it ought to.

that makes sense. The dac with eh 6h30 gold pin sounds very precise and almost "clinical", and the adapter/6SN7 sounds "clouded" and "coloured". 

Sounds like this is a lost cause. I'll give it another go tonight but I guess I just need accept this isn't going to work 

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Super Wammer
5 minutes ago, rabski said:

Valve socket adaptors are the spawn of the devil, as they just encourage people to stick valves in places they weren't intended to go.

Sorry James, I didn't really look at the original thread, but I'm equally never particularly impressed by equipment that ships with instructions saying the vast range of valves that can be used. Valves have different designations for a very simple reason. They are different. Different pin connections and heater voltages are just the basics, but there are countless electrical properties that matter if you're designign  a circuit. Just saying a range of valves can be used is crazy, because the circuit should be optimised for a particular operating point. Anything else, and the valve will not be running at its best in one way or another.

The main reason a lot of things have a 'valve sound' is because there's distortion or non-linearity that wouldn't be there if the valve was running as it ought to.

:goodone:

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If you want to tube roll, look for a tube that is or closely resembles a 6N6P,  if that's what it ships with. Check this page out - it describes the 6N30P as "hard and glassy":

http://www.lampizator.eu/UPGRADE/upgrade noval tubes to 6H6P.html

But watch the pinout. 6N6P has pin 9 as screen, like 6N30P, so same socket connections.

ECC99, a close relative, has pin 9 as heater centre tap. So it depends how pin 9 is connected in the equipment. You'd need to ask the designer how the sockets are wired, you can NOT assume it's a substitute. E182CC is sometimes called an "equivalent" but it has a different pinout and can NOT be directly substituted. 

So have you tried a quad of 6N6P?

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4 hours ago, Psilonaught said:

I could try the CV181 tube but they are very fat and my sockets are quite close together. 

:/

CV181s are different again, particularly the 900mA heater current, where 6SN7s are 600mA.  Assuming valves marked CV181 are really that; the Shuguang ones in my amp are actually 6SN7s.  I measured the heater current.

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