I bought the Moon... and all I got was an Eclipse.

That'll be the Tube Dude's amp?

Forgive me if this has been covered before, but would you please tell us exactly how this null test was done?

For a null test to be menaingful, it has to be a test of a real amp driving a real speaker (with reactive and inductive elements in the load) with real music (i.e. with transients and all that stuff).

If you managed to come up with a test set-up which allows a null test under those conditions, I'd be very much interested to learn how it was done.

 

Well forgive me BD, but seeing as the last true developments in those fields were IMO analogue recording and the electostatic drive unit, both of which predate most forum members, I won't be holding my breath. I do see where you are coming from, but do not attach as much importance to it as you seem to.

 

Man fully battle stations, anything can happen in the next 1/2 hour......................

 

Merlin,

That's because you never heard what 30W of solid state integrated amp (no pre amp) with a virtually perfect null can do for your speakers.

So how can you possible know what your speakers are really capable of?

After hearing Tube Dude's amp connected to my 1K's, I had no choice but changing its crossovers. And now, even with my A1000, I can clearly see the benefits of it. Since I also heard Tube Dude's CD player in my system I can clearly say that the limiting factor of my system is the A1000, although I haven't had the chance of hearing the Eclipse with his amplifier yet. But judging for previous experiences I can imagine that it is really good... however, I really don't know for sure.

And in case you ask the A1000 DO really have a pretty damn bad "null"... So, here you have it, empirical knowledge confirms the measurements. It was this way we were able to put our feet on the Moon.

 

I advise you to read the whole thread...

 

I can't really be bothered. Apparently, your test set-up was this:

I can see several questionable elements in this.

First, the return current from the speaker does not go into the amp under test. That means the amp under test does not have to cope with the back-emf of the speaker - under normal conditions, the ability to sink the back-emf is an important feature.

Second, the output off the amp under test is supposed to be equal to that of the CD player source; normally, that means 2 V max. output. For a null test to be valid, I would want to do the test at varying voltage levels.

Third, and I may not have given this enough thought, does your test set-up not mean that what one really measures is the difference in output between the amp which is supposed to be under test and the supposed spare amp?

 

Markus,

In this circumstance sir, man I kindly suggest that a listening session will determine as to whether said 'Nullforce 10' will deliver the goods sonically.
Enough of scopes and full spectral anaylsis, figs are a good indication, those lugs holes are the final say. imho
As we all know, lab results and real world seldom tie up, many a prefect S to N & THD has been touted, yet fell at the first hurdle (listening), usual story, electronics designer given brief, construct a class leading cdp for MRP £2500, must have excellent s/n, ultra low THD distortion fig's (for the budget), amazing linearity & analogue sound. all the connectivity you can muster, seperate digital/analogue psu's etc.
You have a budget of £50k, now come back in 3 months, the guy does only to find his budget halved, so this class leading cdp now cost £500 all in the produce from start to finish, bet its sounds stunning, cynical moi?, nah just a realist

 

Now we are making serious progress...

1) You have to connect two speakers to the corresponding outputs of the amp under test. In that condition the return current from the speakers does go into the amp under test. As for the ability to sink the back-emf you really only have one choice: to make the amp's output impedance as low as possible (that's something that tubes won't do...)

2) Tube Dude can explain you better how well he has developed his technique (after Hafler). I only gave you a way of measuring it empirically. But if you can't get it that way you can't get it anyway.

3) No. The spare amplifier only amplifies the signal difference between the CD player direct output and the under test amplifier output. Therefore the spare amplifier quality doesn't matter. It is however advisable to have as much gain as possible.

 

BD, in your first description the channel under test of the amp under test isn't connected to a speaker at all, just to the ground point of the spare amp. In your new description, it (the amp) is connected to two speakers. It is also not clear if the two speakers are to be connected to the same output (= channel) since you say "outputs".

Could you please give us a diagram of the test set-up or a really comprehensive description of the set-up. From your current description(s), I can't really understand the set-up.

Doesn't the additional capacitance and inductance from a parrallel connection to speaker and spare amp change the result from normal driving conditions?

As far as I understand, your test set-up presupposes an integrated amp ("Turn down the volume of the amplifier being tested.") which you set to unity gain (hardly a real-world condition). There is a whole set of questions associated with this; it could well be that your test set-up intrinsically favours integrated amps with passive "pre-amp" stages. Does Tube Dude's amp have one of those?

Or it can be argued that what you're really measuring is the linearity of the volume pot at very high attenuation levels. Any comment?

 

Markus,

When I mentioned two speakers connected to the amp I obviously meant both channels driven but you are always evaluating only one channel at a time. But that way you make sure that all of the returning current from one speaker, at least, is going to the amplifier under test. The interesting thing about the arrangement I first mentioned is that you can do it without any speaker connected to the amplifier, only one speaker connected or both. In order to be able to hear the "null" (the speaker connected to the spare amplifier) you must however put the other speakers in other room.

In the link to DIY forum that Michael gave, I think you can see the diagram.

The question is the simpler the circuit the better you can acomplish a perfect null... no active premps will do it.

 

I think I remember that Wm doesn't use any active pre amps... why is that? Is it just another example of empirical knowledge confirming the measurements or does he knows something more?

(With the high output voltage from a CD player you don't need active pre amps anyway... a pot is all you need.)

 

Indeed, pot is all you need

(sorry guys, please continue)

 

Sorry BD
No pot required or used in Wm's systems, high output voltage?, my cdp output voltage is hardly typically high old boy @ .9v, thought it can be adjusted to 4.4v if said amp your using is a touch light with input sens dept.
Evidence?, Fraid I didn't need a network anayliser to suss why I use a Big W, my ears told me all I wanted to know

 

NEWSFLASH WM is from another planet , he even has talking ears

 

Oh great, thought I might have managed to keep that quiet a little longer

 

You did keep it quiet, twas your ears that blabbed

 

Well BD, in the case of my JBL's and Proacs, it is highly likely that the amp in question would lack the neccessary power to control the drive units properly, exacerbating the effects of LF acoustic feedback generated by the room/speaker interface. Of course this would mean unacceptable amounts of distortion making the system sound terrible. But at least the amplifier would be perfect

 

If this is what you mean, it still doesn't answer my questions.

 

Wm,

With digital volume control you always loose some resolution... definitely worst than a pot. Of course you can always make the experience yourself and then maybe your ears can tell you that you do need an analyzer...

All your ears are telling you now is that wadia digital volume control will always be better than any pre amp. It is, however, impossible to them to hear what you don't let them ear, even being from other planet.

Merlin,

I don't know if Tube Dude's amp lacks the necessary power to control the drive units of your speakers properly because I don't know how loud and distorted you want or need them. Every amplifier has its limits.

All I can tell you is that it drove my 1K's and the Craffts to very, very high levels... both being known as very difficult loads.

Markus,

Let me simplify things. With only one speaker connected to the amp being tested (you don't really need two speakers) you can make sure all the returning current from the speaker goes to that amp because of its very low output impedance when compared to other amplifier's very high input impedance.

The link you gave me doesn't work... But from this point on only Tube Dude can answer to further questions regarding all of his null test procedures.

 

This is all a big joke yea?