What are the best upgrades that I can do with the 121 interfaces? They are the 22" long versions on the Monitor 4's. As far as I know, they haven't been modded. They sound great, but curious on what will improve them more?
121 C-mod.....is the best thing for Acoustats i have done after 30 years of owning Acoustats......makes the 121 a LOT ezer to drive...an well give about 2-more db output......i have a 14ohm...an a 4ohm.....30watt ea own ea 121s........ the bottem poly cap is a 47-50mf.........sweet sound..........have fun
Long Live Acoustats....
Long Live Acoustats....
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![ACOUSTAT%2520SCHEMATICS-%2520CORRECTED[1][1].jpg](/community/data/attachments/359/359057-9390461c7130c29d6c5584ba29b48edf.jpg?hash=k5BGHHEwwp)
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Acoustat did offer an extensive upgrade for the MK-121 series, called the Medallion Transformer modification. This was a rather expensive upgrade involving replacement of both audio transformers and other associated parts.
Obviously, Acoustat is no longer around to perform this upgrade. It might still be offered by Sounds Like New. Even if SLN does not offer the full upgrade, they do offer refurbishing and other upgrades (on which I have no details). You can find contact info for SLN on the website www.audiocircuit.com in the Acoustat section.
The changes referred to above by Tyu are basically the 'C-Modification', which involves reconfiguring the high-pass circuit feeding the HF audio transformer. There are a number of options in how this mod can be performed, based on which MK-121 version you have. Replacing the electrolytic in that circuit with a polypropylene capacitor is highly recommended. This modification is beneficial regardless of whether you have the Medallion transformers or not. Complete information on this mod is also available at www.audiocircuit.com, using commonly available parts.
In re-examining the schematic provided by TYU, I see that this actually a variation on the C-mod, wherein the variable resistor is replaced by two fixed resistors, which is a fine idea as long as you don't mind giving up the variable HF balance control. Therefore, the schematic labelled as 'original' is actually the factory implementation of the C-Mod, and not the original schematic of your interface. The original circuit used a much larger capacitance and had no resistance to ground after the capacitor(s).
The 'C-Mod' information provided on the Audiocircuit shows the original schematic (i.e. what's in your interface now) and several implementations of the new circuit, including the option of using fixed instead of variable resistors.
The 'C-Mod' information provided on the Audiocircuit shows the original schematic (i.e. what's in your interface now) and several implementations of the new circuit, including the option of using fixed instead of variable resistors.
More info on the 121-c....................pic for all to see.....over an over an.....there worth it.................C-mod..............
this is the best part of these post
"This modification is beneficial regardless of whether you have the Medallion transformers or not........................
this c-mod is a must!
this is the best part of these post
"This modification is beneficial regardless of whether you have the Medallion transformers or not........................
this c-mod is a must!
Attachments
![MK-121C_upgrade[1].gif](/community/data/attachments/359/359607-74652b29d1431bf8c12baebaa99d5ca2.jpg?hash=dGUrKdFDG_)
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Step-by-step instructions on the Cmod starting from a MK-121A or MK-121B interface.
(no doubt also the handiwork of AcoustatAnswerMan)
(no doubt also the handiwork of AcoustatAnswerMan)
Here are some pics I took this am of one interface. Do these look "stock"?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
yes stock..............................the blu an the yello cap are the caps to setup the 121-C mod.....along with some new res....i have a 14ohm...or the 13ohm 30watt...............you have the other res...looks like...
Yours are the older setup...... this the way all the 121 should have been.....lot room for the 5k Bias.....to run around in a metel Box....
.look at what box thay went to...........10lb....in a 1lb box....
I pulled the bias out of this setup an made the bias i can set....4-7k.........
long live Acoustat............
Yours are the older setup...... this the way all the 121 should have been.....lot room for the 5k Bias.....to run around in a metel Box....
.look at what box thay went to...........10lb....in a 1lb box....
I pulled the bias out of this setup an made the bias i can set....4-7k.........
long live Acoustat............
Attachments
![audiomaison046-1[1].jpg](/community/data/attachments/363/363888-72333de6b9900c348eaf224a936ddfb0.jpg?hash=cjM95rmQDD)
Yes, these interfaces appear to be stock: Transformers are not Medallion, and there is no evidence of the C-mod. There is evidence of one mod: I refer to the small pc board on the larger pc board. This indicates the change from a 3-diode voltage multiplier to a 5-diode voltage multiplier, along with a new bias transformer. A much more reliable system. Acoustat upgraded many interfaces in this manner, or your units may have been originally built that way during the transition from one design to the other.
By the way, these interfaces are very clean and good-looking after all these years. Condition ++++. This chassis style is the earliest version of the MK-121 series.
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