Acoustat 2+2, MK-121-2a interface Bias Circuit update. Restore Treble and Dynamics for $50.

[@chany16888]

I watched your video with great interest; I have an Acoustat Spectra 22 with an MK2123 interface. One of the channels started to have lower sound output, and I did some research; most of the information pointed me to bias adjustment; I wonder if you have any suggestions? Acoustat is an excellent speaker; they no longer make them like this anymore.

[@Koolbob2]

I wish I could be more helpful, there isn't any bias adjustment on the MK-121-2a interface units, and I don't have any experience with any other electrostatic speakers. In researching the 2+2s I discovered a few Internet forums dedicated to Acoustat speakers, there's some good information there, but most of the activity on those forums died down a few years back. I found a Facebook page dedicated to the Acoustats and another for all electrostatic speakers, they are still very active and your best source for up to date information.

[@pmlaaudio468]

Hey mate, Do you have any information on replacement transformers? Or contact info for the acoustat engineer

[@Koolbob2]

Roy turned everything over to Mike Burgert who is also very knowledgeable and a super nice guy. Mike is very active in the 'Acoustat Speaker' Facebook group. I'd urge you to join that group, lots of great information there.

[@jae52500]

Do you need to adjust the high voltage bias after changing out components? I have 1100s, and I changed out capacitor and diodes and the speaker is slightly less "forward" than the other speaker. According to Andy Szabo on DYI forum, bias has to be measured and adjusted to restore the sound. I have his instructions, but was hoping to see a video.

[@Koolbob2]

@jae52500 Thanks for the information! I've been communicating with Roy who was an engineer with Acoustat and he did not mention anything about adjusting high voltage bias. I've tested both of the HF transformers and HF variable resistors with a multi meter and everything checks out fine. Roy thinks the 2+2s are working perfectly and that my expectations for high frequency output are unrealistic from a lifetime of listening to 'regular' speakers. Are the adjustment instructions available where you can send me a link?

[@jae52500]

In reviewing my notes, it looks like this adjustment may only apply to the Spectra series. I really like my 1100s, but after 32 years they're needing some internal tlc :)@@Koolbob2

[@paulk9230]

Nice video. How does it sound afterwards? Noticeable difference?

[@Koolbob2]

Thanks for watching, I've been working on the interfaces for a couple of weeks now. First I cleaned all the contacts and that got both speakers working at the same volume. I replaced all the parts 'bias' circuit parts in this video and a few sketchy wires and the improvement was very noticeable. An hour ago I replaced three capacitors in the high frequency transformer circuit and maybe it's my imagination, but I think it helped as well. Another friend loaned me a pair of Monitor Audio RS6 speakers to try out. I like the soundstage and smoothness of the Acoustats, but I prefer the upper midrange and treble of the Monitor Audio speakers, My old Omni Sound speakers have more dynamics than either of the other two. I'm having a hard time choosing a favorite, each does better with different music.

[@brandond92]

Good Video. You will probably get more views if you spell Acoustat correctly.

[@Koolbob2]

LOL, Thanks @brandond92! Autocorrect kept changing the spelling, thought I had it fixed, but autocorrect got the last word when I hit the 'publish' button. I'll see if I can change the spelling without taking down the video and starting over.

[@brandond92]

Oy vey!

[@miomanman]

Glad you made the video. I acquired a pair of these speakers from an auction, they work but don't sound great. Is there someone who does repairs on these in Michigan?

[@Koolbob2]

@@miomanman I discovered several forums and FaceBook groups for electrostatic speakers and Acoustat speakers specifically. These groups have been my primary source of information for restoring my 2+2s.

[@miomanman]

Ok,. I'll look. Thanks 😊

[@res00xua]

The voltages are dangerous.

[@Koolbob2]

Yes, I got careless once and got a heck of a jolt when removing one of the interfaces.