[baronbeehive]

Following on from the previous discussion where it was stated that there could be many tube bias points that need to be listened to, not just drawn on the graph. I've got together my final say on the points that could be tried, because I don't really want to bother plotting any more load lines for the moment. These are points that I would have tried had it not been for the fact that I've finished experimenting, so I've go this together for others who might like to try. Hopefully it can be understood what to do now!!

This is for 6SL7 tubes:

The brown load line is the one drawn by sonic, red by Maxx, and the black is the stock line. On the brown, red and green lines I have already tried 3 different cathodes and have picked my best ones. The remaining points - 1, 2, 3 and 4 I have added to try now if anyone wants. They represent the extremes of values and also a good spread of values.

All that remains to say about these new points is that 2 of the points, that is points 3 and 4 are extreme values going into non linear regions where compression or distortion should be heard which may or may not be pleasant, for people that like tubey sounds for example.

The values are in red top right of page, Ra is the anode, Rk is the cathode.

If anyone wanted to try intermediate values you could do that, for example, the Rk at point 1 is 1K and the Rk at point 3 on the black line is 5K so any intermediate value between these could be tried if that is what you want. I haven't bothered to plot these intermediate points.

Edit: It doesn't matter if the values you choose are not exact or if you can't get the exact resistor, near as dammit will do.

 

[baronbeehive]

This is for 6SN7 tubes:

Again the values are in red top right of page, Ra is the anode, Rk is the cathode.

I've drawn 2 load lines, line 1 and line 2 each with 4 bias points along the line, the points represent a good spread of values and go from extremes left to right meaning that pretty well all relevant values have been drawn, but if anyone wanted to try intermediate values you could do that, for example, the Rk at point 8, line 2 is 250R and the Rk at point 7 is 5K so any intermediate value between these could be tried if that is what you want. I haven't bothered to plot all possible intermediate points.

On the extreme top right are some other points I have calculated without bothering to draw the load lines, for example at top right I have given the values for Rk of 166R and 5K3. These are values that would lie on a line half way between line 1 and line 2 with a current of 10mA. Any value between 166R and 5K3 could be tried for any points that you would like to try along that load line.

The values of Rk of 1K and 16K are along the black line which is the stock load line. Again any values between these extremes could be tried.

Again the values at the extremes are values which could sound compressed or distorted which tubey sound lovers might actually like.. maybe a lot!

Edit: As before, doesn't matter if the values you choose are not exact or if you can't get the exact resistor, near as dammit will do as it won't affect the bias point much.

This graph might explain why some people picked up differences between, say TS6SL7 and TS6SN7. You can see for the 6SN7 the load line is very low in the graph going in to the non linear regions in contrast to the graph for 6SL7's, so the resulting sound might be more tubey sounding which some people might like. I don't think the difference is huge though as I couldn't detect much difference myself.

NB: As a final note on this I would recommend only using bias points along line 2 and stock if you are going to try to ideally bias 6SL7's AND 6SN7's, that is if you want to use both tube types ideally biased at the same time. Only use bias points on line 1, or the line I didn't draw between line 1 and line 2, if you are only going to use 6SN7's and not mix with 6SL7's. The reason is that the output current might be too high for one tube type which could be damaging, as you can see line 1 is fixed at 18mA and this is way too high for a 6SL7 tube whose typical operating current is around 2mA. If in doubt only ideally bias for one tube type and don't mix them.

That is why a switch would be necessary if you want to use both tube types at the same time, and make sure that the output current doesn't go above 2.3mA for 6SL7's if you do mix tubes without a switch. Therefore you should double check the figures before implementing them to make sure of the output current limitations in case of error, but you should be ok anyway if you stick with line 2 and my figures.

 

[baronbeehive]

@Maxx134 This modded amp is truly end game, those high res speaker demos show what it can do. I know that the demos are varying distance from the speakers resulting in varying sound, when they're close the sound really is great, obviously you don't normally listen that close, but further field listening is still pin sharp on my speaker amp, APPJ.

The fact that this amp, and the LD can go to these levels in sound reproduction has shown me that the LD is well and truly there! Before, the only way I thought that the sound could be bettered is the sharpness of soundstage and the way the instruments jump out, but those demos showed me that I can reproduce that sound on the amp. Not only that but the sound signature is perfect for me, so it's good to just concentrate on the music and not on how the amp can be improved now.. that also goes for the baby amp lol!

So the only dependant factor now on how good the amp sounds is how good is the source material. Good high res music will show the amp off to its best, right up there with the top end gear IMO.

I won't go on any further about the SQ but people who have done the mods specified here will know what I'm talking about.

All that good work you did on trials and testing all that time ago certainly paid off, you got it spot on .

 

[talan7]

Finally received confirmation of my MK V1 shipping from Shenzhen audio, coming next week.

 

[talan7]

Amp arrived early, about to go in now!

 

[talan7]

Listening now with my Heddphone, very spacious sound. How do I turn up the gain. Manual says some hole at bottom of amp but I don’t see it

 

[AngryTank]

Listening now with my Heddphone, very spacious sound. How do I turn up the gain. Manual says some hole at bottom of amp but I don’t see it

If it’s like the mk8, you have to open it on the bottom unless you have something that fits In the vents to turn up the switch.

 

[baronbeehive]

Listening now with my Heddphone, very spacious sound. How do I turn up the gain. Manual says some hole at bottom of amp but I don’t see it

Excellent!

Open the bottom plate and find the 2 red boxes, 1 is circled:

Slide both white switches on both red boxes. You now have high gain.

We recommend high gain for even greater spaciousness and transparency with less negative feedback.

Edit: For anyone new to this we always warn that if you have had the amp on always give the amp 15 minutes or so for the caps to discharge first to make sure you don't kill yourself poking around inside!

 

[talan7]

How powerful are the caps? Can’t be to much

 

[baronbeehive]

How powerful are the caps? Can’t be to much

Enough to kill you, seriously, there is high voltage inside the amp, but so long as you observe the precautions as I said you will be fine. If you have had the amp on that is the time to be careful. If you haven't had it on before you open it up then that will be fine. If you have had it on always unplug the power and wait 15 minutes or so and it will be safe.

 

[talan7]

Opened up and raised the gain. My DT990 600 ohm sound wonderful. They sound even more open. This is a good amp. In time, I look forward to rolling tubes. Any recommendations?

 

[baronbeehive]

Opened up and raised the gain. My DT990 600 ohm sound wonderful. They sound even more open. This is a good amp. In time, I look forward to rolling tubes. Any recommendations?

Excellent, congrats !

What type of sound do you like, tubey or clear, what sort of budget do you have, expensive or cheapo like me lol?

 

[CopperFox]

Haha.. it's getting mighty crowded in there! The amp looks great, glad it's all up and running again. You took the PCB out of the new silver amp and put it in the black amp? Good work .

Yes. Well at first i put everything in the silver case, but there was an unlikely short circuit caused by two different pcb mounting screws partially piercing two different cables coming from one transformer - and the screws remaining in contact with those cables - which resulted in a smoked transformer. Never had any issue with cables getting stuck on or even damaged with screws before so didn't know to look out for that.

So it was either put the old transformers in the silver case or put the pcb in the black case, the latter looking more simple to do (and giving me a black amp). It was quite easy in the end as I could just desolder wires from the old pcb and solder them to the same spot on the new board one by one.

Check in again when you have an idea of what the cathode bypasses sound like.

They're probably now settled in after two weeks in there.

Here's how the 2*330uf cathode bypasses sound:

-Compared to the single 470uf, there is a lot more detail and nuance and the sound is smooth without the metallic bite/edge. With the 470uf the primary problem was excess attack which could make some tracks such as for example the 3:30-4:00 part on Sultans of Swing sound uncomfortable.
-Dynamics are good, not flat like it was with 2200uf and also better than with 1000uf. Sounds like it is still less than with 470uf though.
-2*330uf works well in both high gain and low gain. I like low gain better, primarily because bass gets loose and less extended in high gain. It sounds like something that could be caused by difference in output impedance.
-Out of the single 470uf, single 1000uf and 2*330uf, the last one sounds most refined.
-I'm now feeling the sound could actually use some more edge/bite.
-One obvious possible confounding factor is that the pcb and most of the components on it are fresher than when I had the 470uf/1000uf there.

This mostly fits in with the notion that higher capacitance here has more detail and less dynamics and vice versa. Nonetheless, I'm feeling that the 2*330uf 100v has more treble detail than 1000uf 50v.

I will still experiment with 550uf formed from one 330uf 100v and one 220uf 100v capacitor later. Possibly 2*220uf 100v as well.

However, it is fine tuning at this point. The differences could be small enough that the effect of impedance mismatch should be considered. So perhaps the impedance matching mod would be quite in place now.

There are several posts with mentions about the impedance mod back in the thread, but there doesn't seem to be a post where this mod would be described. What would be needed here to match the output impedance to my headphones, which are modded Monolith M1060C with 18 ohm impedance?

(I've also given some thought to getting an external impedance matcher such as the Raphaelite B10.)

 

[talan7]

Excellent, congrats !

What type of sound do you like, tubey or clear, what sort of budget do you have, expensive or cheapo like me lol?

I like deep, hard hitting bass, soundstage and lots of details.

 

[baronbeehive]

I like deep, hard hitting bass, soundstage and lots of details.

I can't really recommend hard hitting bass tubes, all I can say is that the best you could probably do would be to try Bendix 6080WB graphite tubes which have a hard hitting bass and airy detailed soundstage, but they are getting very hard to get hold of. Tungsol 5998 are probably best for soundstage and liquid detail, again expensive.
So perhaps you could look into Chinese tubes such as Psvane/Shugang and look up some of their reviews.

Also for driver tubes Tungsol 6SL7's are excellent for soundstage and liquid detail, and Mullard ECC35 and ECC32, or ECC33 which I think have stronger bass as well.

The amp doesn't really do hard hitting basshead type sound although the bass is quite powerful, so I would suggest you could try some headphones which do really hard hitting bass.