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Little Dot MK8SE / MK6 Super Mods (All verified mods are on first page)

Discussion in 'Headphone Amps (full-size)' started by redge78, Sep 26, 2015.
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  1. SonicTrance
    Baron is referring to top of anode resistor, so B+.
  2. baronbeehive
    Ah, right, I didn't realize the decoupling cap connection on the cathode resistor was ground, I thought it was the cathode side, so we are just providing the ground connection to the anode decoupling circuit, but wouldn't that circuit be broken without the cathode resistor in situ?

    Right, I didn't realise that the filter was B- for the CCS, I thought it was cleaning up the existing B- going by that previous circuit diagram, so the filter provides a clean B- as an alterative to the existing. I haven't looked at the filter construction yet so I'll post pics on that just to be sure.

    Thanks guys.
    Last edited: Sep 6, 2018
  3. SonicTrance
    Yes, ground connection for driver stage B+ decoupling.
    No, its connected to the pcb ground plane. Measure with ohm meter if you're unsure.
  4. baronbeehive
    These are the connections - CCS and revised driver stage decoupling:

    Cathode ground decoupling CCS cathode connection

    upload_2018-9-7_15-33-23.png upload_2018-9-7_15-34-28.png

    Anode decoupling, CCS B- connection, CCS cathode connection CCS cathode connection, CCS B+ connection

    upload_2018-9-7_15-35-36.png upload_2018-9-7_15-36-30.png

    CCS1 to CCS2 connection, CCS cathode connection, CCS B+ connection, CCS B- connection - other end.

    Bear in mind the connections are temporary, they will be soldered in permanently with the filter later.

    I will make sure no metal is touching metal before switching on!

    I think I'm good to go.... unless you can see any reason not to......
  5. MrCurwen
    Looks pretty good to me, I don't know about the connections to the board though, not my expertise.

    So how's it sound?

    I predict the extra B- filter has no effect on sound quality. The improved balance should take care of all common mode noise, as per explained earlier in great detail. I originally added it to the schematic as a "final blow" to the doubts about the efficacy of the balanced common mode noise rejection. (Common mode noise rejection has been known for over a 100 years so shouldn't be too controversial.)

    It's possible though it might, taking the circuit as a whole. Unknown interactions in a (semi)complex circuit are always a possibility. Interesting to hear results!
  6. baronbeehive
    I haven't switched on yet!!!!

    Just double... triple checking everything, cleaning the board etc. I always get stressed out at this time, so probably leave it for the moment, see what Sonic thinks.

    No I agree about the effects of the filter, not expecting any change, just good to know that there's no dirt in the system.

    I'll update you as soon as I think it's safe to do so...…!
  7. SonicTrance
    Switch it on! :)

    I can't see if all connection are correct though as I'm on thr phone. But I'm sure you're fine if you double and triple check!

    I too want to hear your impressions!
  8. SonicTrance
    Measure bias voltage at cathode node. Should read slightly higher at boot before the B- supply starts, then go to normal.

    Wheres your B- connection btw? Cant see it?
  9. baronbeehive
    It's here:

    5K1 resistor.... to …… opposite end of 470R from FET.

    upload_2018-9-7_19-27-31.png upload_2018-9-7_19-28-26.png
  10. SonicTrance
    Ok, all good then!
  11. baronbeehive
    .... actually I quadruple tested everything.... just to be on the safe side, I can't be doing with all this stress waiting for the meters to come on!

    Massive relief, it works.... and it sounds damn good, in keeping with this thread I don't want to exaggerate, I want to be as objective as possible, so these are my first impressions:

    I would say that the sound is of the same order as the best setting I found with the anode/cathode settings which is a relief because I was so impressed with this. I didn't want to exaggerate my impressions of this change of anodes/cathodes but looking back now I may have underestimated the improvement, I now think that the improvement of those changes was of the same order as a change of tubes from RCA to WE's, I don't mind having RCA's in now because they sound so good. This is what I said about these changes at that time: "To summarize my results there was one stand out position which hit me the moment I started listening, the sound was full, palpably real with good clarity and texture which you could almost feel. The sound had a presence, transparency, resolution and dynamism. This for me was the obvious setting to use."

    Anyway back to the CCS, again we're at a very high level now, and I'm having trouble picking differences, and also I'm having to rely on memory. The initial and main impression is one of total clarity, I may be imagining this but I felt that some harmonic distortion had disappeared. Overall the sound was of the same order as the best anode/cathode setting but totally free of distortion, it was like listening to the same notes but without any reflections or reverberations. Re: bass, mids, treble and soundstage I felt there was no difference, again all at this previous high level. One could not say that the bass had changed or was any sharper, or that the mids and treble stood out more or were more resolved, I didn't think this was the case. Also I couldn't hear any difference in soundstage, again at a high level as before.

    My recommendations on this change are: If you like maximum clarity go for it, if you are more romantically inclined and prefer a slight sheen to your music, then maybe stick with the existing design. Whatever you decide you will be pretty happy!

    So those are my intial impressions, I'm going to have to live with this for a while before I decide on what to do next, so the filter can wait until then. One thing is for sure, the level we are at now it's not going to be easy looking for yet more improvements..... or maybe.... !
    Last edited: Sep 8, 2018
    Maxx134 likes this.
  12. MrCurwen
    baronbeehive, good work!

    You are not imagining it, assuming you built the thing correctly it has lower distortion. To understand why I recommend you reread the big topology theory / experiment post from this thread. I tried my best to make it understandable but it takes some time and revisiting.

    When you take out distortion, there is EXTRA stuff underneath, music signal details. Add distortion and you mask stuff in the signal.

    Much more efficient to make the circuit do the balance, not to try and find a tube that is decently balanced. Have you tried different tubes with the CCS? Do they sound significantly different?

    Not totally free of distortion, there's a long way to go still. You'd be surprised.

    So I'm guessing no harsh IMD from B- ripple then? No 7H and up tearing your sweet music signal to shreds?

    Understand theory and topology. Makes this hobby less poking around in the dark and more fun.

    In the LD the limiting factor is physical space. Also the direct drive topology is problematic to improve.

    Since the output follower has such a high output impedance and no way to force fully balanced operation (you cannot use a CCS there since it's a pair of followers), PSU improvements would be the way to go.

    I'd go for actual (even very simple) regulation, not crazy C. Now there is just a voltage setter there. It sets the voltage and not much more. If the decoupling cap (right at the B+/- nodes) has a noticeable effect on sound quality, you are not dealing with any degree of PSU regulation.
  13. baronbeehive

    I think that was the post with a lot of ripples in water metaphors, if so I remember it well! I will check it out.

    What needs to be done to compliment the cleaner signal is to boost resolution somehow so that we can hear more of these microdetails, I didn't really feel that resolution had gone up.

    Not yet. I only have the TS 6SL7's for drivers apart from the GE's. I will try them next, possibly with the WE's, the resolution is better with the WE's for power tubes.

    I am trying to imagine a totally distortion free system.

    This might be something for Maxx to look at, I think he wants to do the CCS mod, and he has a stash of tubes to try, I will wait to see what he thinks. He has also heard top level systems which I haven't so he will have a better idea of how far we can go with this.

    No I don't think so, there was certainly nothing obviously objectionable like IMD would suggest. Also no higher order harmonics that I could discern. As I said it would be interesting to see how much microdetail we could reveal.

    We have a problem here though, the gain, and how high we can go with it. We could probably go a bit higher than the high setting but I don't know how high.

    Maybe the PSU improvements could be followed up. As I understand it we have a brutish PSU atm which performs quite well. I did wonder if the fact that we have the driver stage decoupling reduces the impact of the CCS, because the decoupling is helping stabilize fluctuations in power supply already.

    IMO the amp could possibly go a bit higher in resolution, soundstage, and bass performance to reach absolute top level, but it's already excellent in these areas now.
    Maxx134 likes this.
  14. SonicTrance
    Good work baron!

    I don't think there's anything you can do to the ps(s) without extending the chassis or have a external chassis for the ps(s), unfortunately.
  15. baronbeehive
    Thanks Sonic!

    Yes, that's what I thought about the PSU.

    Re: tube experimentation, we're looking for very linear tubes now, I assume, to extend the possibility of extra microdetail, but we already have the 6SL7/6SN7's. Anyway I'll leave that open to discussion, I'm very happy with the amp now, it's come alive!
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