MC stepups.

nickg · Joined: 19 Mar 2005 Posts: 26

No, I use the same PD chain that T did, but with altered values to get the correct results.

I will play with the sim's later, I wonder if its worth adding Ckg to the model as well, I know its small in the case of a pentode conected E810F, but what value is it in the case of your (and Mark's) phono?

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

Andrew · Joined: 26 Apr 2006 Posts: 197

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

Andrew · Joined: 26 Apr 2006 Posts: 197

Andrew · Joined: 26 Apr 2006 Posts: 197

nickg · Joined: 19 Mar 2005 Posts: 26

It may be worth looking at the LTSpice help for inductors, there seems to be more than just idealised elements avalable. Most of what I read makes little sense to me at the moment, but I suspect it will to you Dave for modeling non-linear behavour. It also does suggest that the parasitic capacitance and resistance be added to the model instead of adding extra elements around the inductor model.

There is also a topic that discusses the leakage inductance in the coupling directive.

nickg · Joined: 19 Mar 2005 Posts: 26

I also wonder what the inductance and capacitance of the cartridge will be?

IslandPink · Posted: Sat Dec 23, 2006 7:18 pm Post subject:

Wrote a message but lost it when I tried to log in ...
Not sure yet on this mod despite a lot of listening .
More info but have no more time to post now .
Bye for a few days .

MJ

IslandPink · Posted: Mon Jan 08, 2007 4:36 pm Post subject: Load primary/secondary

Hmmm, it's a bit of pros/cons for me .
Went back to loading on the secondary a couple of days ago .

With load on the primary, the edge definition seems sharper and the 'shape' of notes is clearly rendered . A bit more 'HIFi' with well-defined soundstage placement in the left/right direction .

With loading on the secondary, less defined edges, but more body to the tones in midrange and bass and a bit more soundstage depth, at the expense of precision .

I marginally prefer loading on the secondary . I supsect there's some fraction of these differences that could be adjusted out by loading changes to be honest , but there are still some real changes there .

I notice S&B only refer to loading on the secondary btw .

Also I notice the 600 ohm LCR unit is not on their site currently ..hmmm..

Mark

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

it would be interesting to see the loaded vs. unloaded behavior of your step-ups when driven from a source impedance = to your cartridge.

dave

Andrew · Joined: 26 Apr 2006 Posts: 197

Dave,

Yes, but where to get one? A source with such low Zout?

Mark,

Better edges is what I'd expect.

My theory is that the secondary loading exascerbates the low pass filter (lowering the 3db point). The filter is a consequence of the real world (imperfect) transformer, the primary loading has less impact on the filter components than secondary. The sims I did show this. Now, if you can do without a load, and the cart is happy, then that will be ideal. Or work towards an ideal transformer with less loss.

Dave,

Did you get anywhere with the sims?

cheers,

-- Andrew

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

hey andrew,

a 2 ohm source can be had by placing a 2 ohm resistor in series with a 200 ohm resistor and driving the combo from a 50 ohm signal generator. Simply place 1V across the whole shebang and you will get a nice 2 ohm 1mv signal across the 2 ohm resistor.

you should also consider that going without a load on the secondary may give rise to other problems in the transformer so you need to be careful. I have seen cases where a load was required to damp some squirrelly behaviors.

dave

IslandPink · Posted: Wed Jan 17, 2007 9:53 am Post subject: Sims

Ok, guys, but what are you going to simulate ?
I don't believe the differences will be just about gross frequency response .
My suspicion is that with the load placed on the primary, and hence very low levels of current going into the transformer primary , you might see changes at low signal levels . Ideally I'd like to see graphs like John Atwood presented ( for the line-level transformer tests ) that showed 3rd/5th/7th harmonic over a wide range of signal levels . My hunch is that with low current you likely see a rise in distortion for low signal levels .

Mark

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

IslandPink · Posted: Fri Jan 19, 2007 10:21 am Post subject: More

Dave,
I will google Lenz's law and try to get up to speed on your ideas ...but my concern was not the core , but overcoming capacitive loading and wire surface effects . We're dealing with such tiny voltages, that the currents are inevitably small and I wonder about reducing the current in the coils even further .

MJ

Andrew · Joined: 26 Apr 2006 Posts: 197

We had a small soiree at the weekend. Great fun!

Nick was interested in exploing the primary loading idea with my S&B SUTs and so during a lull in proceedings we had a play.

Nick's excellent phono is LCR, with high gm pentodes on the inputs; the circuit is Nick's interpretation of the S&B designed the TL phono.

He had tried primary loading as it had described and didn't like it.

During a beer fuelled conversation the night before Nick expressed his concerns about the unloaded secondary, and effectively using the secondary as a grid choke, which is what I do. He felt those high gm pentode didn't like that arrangement.

It was suggested that we load the grid with a 1 Meg and put the 100R on the primary so that the effect load is pretty close to 100R but the pentode would see a resistive load.

My opinion was this worked a treat. I think Nick's point was that whilst triodes might like grid chokes, in this application, the high gm pentodes don't.

Mark, I'd be tempted to try again with 1Meg on the grid and 100R on the primary.

cheers,

-- Andrew

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

nickg · Joined: 19 Mar 2005 Posts: 26

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

IslandPink · Posted: Wed Jan 24, 2007 4:49 pm Post subject: Loading

"Mark, I'd be tempted to try again with 1Meg on the grid and 100R on the primary. "

That's almost exactly what I did -
I compared conventional ; 10k on secondary ..
with-
120R on primary and 1 meg on secondary

MJ

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

Andrew · Joined: 26 Apr 2006 Posts: 197

Hi Dave

Yes, that roll off with the secondary loading, it looks very familiar, doesn't it?

cheers,

-- Andrew

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

I jut realized that the source and load impedances were left of my plots so i fixed that.

the 1:7 40/u 4 is a designation.

1:7 is the turns ratio
40/u refers to the source and load impedances 40 ohm source/unloaded sec
4 is the variation number.

also note that with the 20 ohm source, additional loading on the secondary could make it match the 40R curve. The EMT cartridge was actually 20 ohms, but it only takes about 200pf of capacitance to make the peak go away from the lower source Z. When you consider the cabling and the miller C of the following stage, i suspect it is not an issue in reality. I actually tend ot go foe a slight low Q peak in the HF knowing there will be some capacitance across the secondary in practice. Of course if that number is known all the better then i can nail the desired response with the winding geometry.

maybe i should just call this "natural loading"

dave

Andrew · Joined: 26 Apr 2006 Posts: 197

Hi Dave,

Would you mind if I posted your image of your measurements of Frank's SUTs on our local forum; to show the roll off with the secondary loading?

thanks,

-- Andrew

dave slagle · Joined: 22 Jan 2005 Posts: 1357 Location: NYC

not at all.

dave

Steve Kaufman · Posted: Wed Jan 31, 2007 1:33 am Post subject:

Hi Dave

Peerless step-ups should arrive on Friday.

Steve