Acoustat Air Mod

[tyu]

--- About the Special Modification to your Acoustat Interfaces-----
Consider this a new tuning of the speaker. The resultant sound
is very exciting, especially on the best reference recordings.
Poorly recorded material will likely sound worse,
because of the increased detail.
I like to call this the “Air” or “Rock-n-Roll” Mod.
It’s use seems most suited to Rock, Pop or perhaps Jazz.
Classical Music will probably sound best in the normal (left)
position of the switch. All a matter of personal preference.
--------------------------- Enjoy ! -------------------------------------
Roy A. Esposito / soundslikenew / mod start date : February 2008"


Questions.............
If adding more res....like the 10ohm in the (Air mod) to the 16ohm res.... that's already being used as a sunt... from pos to neg...on the high frc tran primary .....
That's there too keep the bass tran secondary driving the two 50k res in the mixer... from being driven back up the mixers .01 caps ...on to the high frc tran secondarys.....an into Saturation.......
do I have this right?
So adding in even more res... like the 10ohm done by Roy...
help this even more ....to stop over Saturation.....there for you get more output ....an better topend........??
Dose anyone wont the high frc tran... to have any Saturation???...........ever?
Thanks for any an all onfo....on ESL setups

 

[tyu]

I have ask these Questions.............
Because I have pic up....looks like new pr...Acoustat 121-2a interfaces....with Roys parts from back before the Air mod I gess......Black gate 47mf cap....12 ga solid core ...looks like romax wire to me....thay have the C-mod with new .01mf 6k mixer caps....all new bias parts....an a 20meg omit bias feeder res....
I got these to add this....
Special Modification of Acoustat Interfaces.... because IF this is a new tuning of the speaker. .....I think most would wont to add the res. part....looks like justdd adding.....a 10ohm 20-30 watt to the c-mods 16ohm....that gives 26ohms
I see in the in the Sound lab ESL crossover setup thay have over 90ohm as there high frc tran input shunt......
Why here are we only using 26 ohms??....not higher?

Has anyone tested this Mod?....ran any simulation... graphs to see whats going on??...... We need No ...Voodoo magic...right?
What makes the resultant sound.... very exciting, especially on the best reference recordings.
Poorly recorded material will likely sound worse,
because of the increased detail.
It’s use seems most suited to Rock, Pop or perhaps Jazzs

Not sure what he means......if some one has lived with this mod....can give some insite.......only input I have seen ...is the people that get this mod like it.
I wont all the increased detail I can get on all music I play ....
but this was back in 08......

 

[bolserst]

…If adding more res....like the 10ohm in the (Air mod) to the 16ohm res.... that's already being used as a sunt... from pos to neg...on the high frc tran primary .....
That's there too keep the bass tran secondary driving the two 50k res in the mixer... from being driven back up the mixers .01 caps ...on to the high frc tran secondarys.....an into Saturation.......
do I have this right?

You have it backwards. The lower the resistance of the shunt, the lower the voltage on the HF transformer secondary from being “back-driven” by the LF transformer. So, higher shunt resistance = easier to saturate HF transformer.

Also, with the same 47uF series capacitance, the roll off point for the HF transformer crossover moves lower in frequency if the shunt resistance is increased. In other words more bass content will make it to the HF transformer which also increases the likely hood of core saturation.

So adding in even more res... like the 10ohm done by Roy...
help this even more ....to stop over Saturation.....there for you get more output ....an better topend........??

No. Adding the 10ohm will not help prevent saturation, it will make core saturation more likely. What it will do is make the load seen by the amplifier easier in the midrange. So, depending on what amplifier is used, you may get a bit more undistorted, cleaner output in the midrange.

I see in the in the Sound lab ESL crossover setup thay have over 90ohm as there high frc tran input shunt......Why here are we only using 26 ohms??....not higher?

All of the Sound Lab crossovers I have seen had a shunt resistance in the 6 ohm to 12 ohm range.
What model was that 90 ohm for? Can you post the schematic?

The higher the shunt resistance the higher the chance of saturation.
See comments above.

 

[tyu]

Right.....
So to add the 10ohm res..... the new added cap must be higher ....from the c-mods 57-8mf up.....to a unknown higher point....an that what well keeps the high frc tran from saturation....is this right?.. have you seen any simulation... graphs to see whats going on??
I well start at 80-100mf.......an tune the sound...

I have no reason to doubt what you are saying about the Sound lab setup....the res. must have been 4ea 24ohm paralleled..to get to the 6-12 ohms like your saying
thanks for you input

 

[tyu]

Not higher.....but lower cap size.....for more topend in this setup?
This Air type mod works best....... with some of the older 121 interface tran....that were not.... wired with Teflon leeds.....an do not have the topend that the Teflon output wire leeds give...I see this mod as one way to get better top end out of those older tran...there wire leeds look like the same pvc coating.... as the wire inside the panels.....
I just put in my new interfaces the older type tran with the Teflon leeds......then put in the medallion high frc tran......this made a big diff in sound....an I find this mod not needed in that case.....but for sure it changes the sound.....Have fun with Acoustats..

 

[bolserst]

…So to add the 10ohm res..... the new added cap must be higher ....from the c-mods 57-8mf up.....to a unknown higher point....an that what well keeps the high frc tran from saturation....is this right?

No. For a given load in a high pass crossover increasing series capacitance moves the crossover point down in frequency, not up.

have you seen any simulation... graphs to see whats going on??

There won’t be a whole lot to see in the response graph since you aren’t changing the mixer R and C values. You would see differences in the drive signal to the HF transformer and input impedance though. It will also depend a lot on the signal level as the primary inductance changes(increases) with signal level.

What is it that you are after? If you want to modify the transition frequency between HF & LF transformers to affect a mid-bass boost or cut, the best way to do that is adjust the mixer resistor values. See Attachment #2 here:
Acoustat MK121 LF transformer Taps and Mixer Resistors

Not higher.....but lower cap size.....for more topend in this setup?

Lower series capacitor will not increase the top end. If you lower it too much, you will actually start shelving down the top 3 or 4 octaves where the HF transformer is dominant because it forms a capacitive voltage divider(think L-pad) with the panel capacitance.

Lowering the series resistance will increase the top end, and that is what the “Air-Mod” does.
It removes all resistance in series with the HF transformer primary to maximize the resonant boost in the top octave.

 

[tyu]

Bolserst ......As others have said......thanks for all your help ...you have a vast understanding of how an why all these thing work....an you allways forgive me for not knowing.... an help with the info so I can do my work an reach my gold......

I have setup my new to me 121 interfaces....ever way for this mod to work an sound good...but it dose not add anything I fine to my likeing.....but that's me...
The c-mod....with 1ohm series res on the high frc tran input....sound the best to my ears...my hope as for myself an others is now we now know better what this Air mod is...
an how it works.....

 

[john65b]

Won't minimizing the R1 pot have same effect as the "no series resistance" Air Mod?

Confused - what is difference between "C-Mod" and "Air - Mod"? I did the "C-Mod", but don't know the "Air - Mod"

 

[tyu]

john ...."Happy holidays" to you an yours.....Look at the pic.....in Air mod...end up with 26ohm shunt....c-mod...16ohm shunt.........not for me..work well with older high frc tran....I have ..use the medallion tran forthe top end....no need.........may work for you....have fun...

 

[john65b]

Thanks tyu - you too...

That's the only difference? I will pass then. I am quite happy with what I now have.

 

[bolserst]

...my hope as for myself an others is now we now know better what this Air mod is...an how it works..

We understand the effect of removing the series resistance…it boosts the top end.
To really understand the effect of increasing the shunt resistance from 16 ohm to 26 ohm, and reducing series capacitance to 47uF, measurements would need to be made showing the changes that would affect the sound:
1) stator voltage response
2) load impedance on the amplifier
3) signal reaching the HF transformer primary

With the increased shunt resistance the transformer primary inductance will be a bigger player, so all 3 parameters I mentioned are likely to change with input voltage level. This also means a simplified SPICE model can't be used to show what the exact changes would be. My instinct is that the Air-Mod will have very little effect on 1), but 2) & 3) will be change noticeably.

Next time I have access to an Acoustat MK-121 interface, I will measure and post the results. If I can get enough information on the transformer core properties, I should then be able run more accurate SPICE sims to play the “what-if” games you suggested as far as varying shunt resistance and series capacitance.

Won't minimizing the R1 pot have same effect as the "no series resistance" Air Mod?

As Tyu mentioned, it would have pretty much the same effect although there would still be some end resistance since the contact can’t slide all the way to the end.

Confused - what is difference between "C-Mod" and "Air - Mod"? I did the "C-Mod", but don't know the "Air - Mod"

The C-Mod was an Acoustat interface manufacturer mod that added a shunt resistance across the HF transformer. This allowed the use of a much smaller coupling capacitance and removal of the damping resistance portion in parallel with the capacitor. These changes had the benefit of reducing the LF content reaching the HF transformer below the (HF-to-LF transformer) mixer crossover point.

As best I can tell, the Air-mod makes 3 changes to the C-mod circuit:
1) removes all series resistance
2) reduces the series capacitance by 10uF
3) increases the shunt resistance by 10 ohm