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Old 27th October 2017, 02:12 AM   #1851
bolserst is offline bolserst  United States
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Quote:
Originally Posted by csduetto View Post
Hi Andy - thanks for the offer. The articles I would be interested in are:
- Ultrasonic Bias Power Supply - When, Why & How, Wall transformers and Adjustment (by Andy Szabo)
- Popping Panels (by Andy Szabo)
- Grille cloth removal, cleaning and replacement (by Andy Szabo)
- Medallion transformer Modification (by Andy Szabo)
- MK-121 Interface Versions (by Andy Szabo)
Congrats on your 1+1s
Those particular articles appear to be available from the Internet Archive (aka Wayback Machine).
Acoustat article: Andy Szabo Techtalk: Ultrasonic Bias Supply
Acoustat article: Andy Szabo Techtalk: Popping Panels
Acoustat article: Andy Szabo Techtalk: Grille cloth
Acoustat article: Andy Szabo Techtalk: Medallion modification
Acoustat article: Andy Szabo Techtalk: Interfaces

Quote:
I am the new owner of the 1+1s with Original passive Subwoofer box and MK131B interfaces...I guess one fundamental question is whether to invest in upgrades just because of age or whether to just let your ears be the judge.
A couple years ago AAMan recommended trying the C-mod with the MK-131 interface. He posted a PDF file with instructions for the mod in Post#1353.
Attached below are some other C-mod instructions sets I had on file that you might find useful.
Attached Files
File Type: pdf Acoustat_MK121AtoCmod_kit.pdf (966.9 KB, 55 views)
File Type: pdf Acoustat_MK121BtoCmod_kit.pdf (312.3 KB, 21 views)
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Old 27th October 2017, 02:23 AM   #1852
bolserst is offline bolserst  United States
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Quote:
Originally Posted by csduetto View Post
Attached is a PDF of my hand drawn schematic as well as a picture of the inside. The main difference from a MK121 are the one missing Transformer as well as the RC network that is applied between R1 and T1.
Thanks for posting the circuit for your MK-131...I had never seen one before. Looks extremely similar to the MK-141, just a few component value differences I think.

Actually, now that I look at your schematic more closely, are you sure that the primary of your transformer is part of the same winding as the purple and orange wires? Most likely they are two separate windings, physically arranged one on top of the other, but not actually electrically connected. See attached MK-141 circuit.
Attached Images
File Type: png MK-141.png (68.1 KB, 266 views)

Last edited by bolserst; 27th October 2017 at 02:32 AM.
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Old 27th October 2017, 03:27 PM   #1853
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Bolserst-
Thanks for posting all the documents. Once again,you beat me to it.

Csduetto-

The bias voltage you measured is good and does not indicate any need for repair to the power supply. However, considering the age of your speakers, and the fact the capacitors (and sometimes the diodes) are known to degrade with age, you may want to consider replacing them now while you’re doing other work. I posted information about suitable replacement parts recently in some posts above.

Replacing the binding posts is a fine idea. Just make sure that the new posts are both properly insulated from the metal chassis.

I don’t have a schematic for the MK-131, but as pointed out by bolserst, it is very similar to the later MK-141. I don’t know the difference between the two transformers, as the change from ‘131 to ‘141 was before my time. However, the primary and secondary connections were basically the same, so your schematic is not quite right (but how would you know from looking at the outside of thetransformer?). The single transformer, limited frequency range MK-131 was first developed for the Modular Hybrid (MH) Series, and was also used on early Model 1+1S hybrid systems. The MK-141 was first used on the hybrid Model One, and at the same time, the Model 1+1S started using the MK-141.

When you said the old woofer had only “one set of connects” are you saying it was a single voice coil woofer? If so, I don’t think it was the original woofer. The original woofer was a dual voice coil model, so that inputs from both left and right channels would be summed into a single woofer. Likewise, there should be two sets of crossover components inside the woofer box, one for each channel and voice coil. The Dayton Audio RS270-8 appears to be a single-coil woofer, so you are listening to bass from only one channel. I recommend you should change this to a similar dual-coil woofer, or construct another box and crossover for a second, single-coil woofer. Or chuck the whole passive woofer idea and use an active system. Dayton also sells some decent powered subwoofers for not a lot of money.

Performing the “C-Mod” is recommended. It’s easy to do with commonly available parts, and will decrease high frequency distortion. I also recommend upgrading the C-Mod’s 47-uF electrolytic with a polypropylene capacitor.

The high voltage capacitor on the printed circuit board can probably be left alone,as it’s already a film type and not commonly known to degrade. It’s also tough to find the correct type with sufficient high voltage rating.

Last edited by AcoustatAnswerMan; 27th October 2017 at 03:30 PM. Reason: fix formatting
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Old 29th October 2017, 10:36 AM   #1854
JAHM is offline JAHM  New Zealand
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Hi Andy,

Thank you for your reply.

I hadn't considered a reduction in the bias voltage as the overall efficiency appears to be much the same as always. Both channels seem identical as the stereo imaging remains superb.

What I have also noticed is that the power indicator LED associated with the right-hand channel unit is no longer lighting up (the left-hand channel LED seems fine) so I intend to get inside the boxes in turn and replace maybe both LEDs. That will also give me the opportunity to check components on the boards and possibly replace any electrolytics I find. Thanks also for the advice about checking the values of the six resistors I find on the boards.

As I've done nothing to the speakers since my late brother and I assembled them when they arrived from the States, I have consulted the Owner's Manual and had forgotten that there are two screws that pass through the Oak base to hold the box down and then there are two bolts on each side of the box as well.

I have a friend who comes down from further north and stays with me for a few days every so often and next time (sometime in November) we plan to carefully tip each speaker over and support it, which should enable us to get under the base and remove the box. I'll definitely check the wiring to the panels to make sure all is well there too. I will definitely make notes about wiring colours and positions etc so that I put everything back as I find it, although I realise it's all stated in the Manual.

I had briefly considered the amplifiers as being a possible cause of the problem. However, as they are monoblocks and they are reasonably modern I quickly decided they are probably OK. I must confess that when I tested each amplifier after assembly, I brought up the mains voltage slowly until it reached 230 volts here in New Zealand before I adjusted the rail voltages (plus and minus), output transistor quiescent currents and output offset voltages. I then left each amplifier on for an hour before making the final adjustments to the aforementioned parameters to allow for temperature stabilisation, so I guess that's when each one reaches optimum performance when I power it up.

Best regards,
JAHM
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Old 31st October 2017, 07:01 PM   #1855
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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JAHM-


I recommend a slightly different procedure for disassembling your speakers. You should never pick up the speaker with the interface attached, because the internal structure of the panel is not intended to support the weight of the interface and base. This is true of all Acoustat models.


With help from a friend to steady the upright panel, remove the four bolts (two on each side) that secure the panel to the interface box. Gently slide the panel forward. This will expose the wires that connect panel to interface. You might want to put some thin cardboard on top of the base to prevent the staples on the bottom of the panel from scratching the base. Disconnect the wires and set the panel aside. If setting the panel down flat, do so very gently to prevent damage to the diaphragm.


Now you can remove the interface from the base.
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Old 1st November 2017, 08:26 AM   #1856
JAHM is offline JAHM  New Zealand
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Thanks again, Andy.

Your suggestion makes perfect sense and I shall certainly work on the speakers in that way. As mentioned earlier, I shall also make my own drawings of the wiring before disconnecting to make sure everything goes back as it was. I shall also look out some cardboard to prevent scratching of the oak base.

When I looked at the back of the interface box associated with the right-hand unit when the room was fairly dark I though I noticed the LED being lit up but I'm not absolutely certain about that. Interestingly, if I look at the LED at the rear of the left-hand speaker then look away slightly I no longer see the light. I may end up getting slightly brighter LEDs than the ones fitted. I know there are the ultra-bright variety of reds and greens but that might be going too far.

Best regards,
John Marchington
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Old 4th November 2017, 09:30 PM   #1857
DynamicPrecision is offline DynamicPrecision  Norway
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Hi. I've just bought a pair of Acoustat Z22, china made. I have some questions about the powersupply. The powersupplies that came with the speakers says AC/DC Adaptor Input: 230V ac 50Hz 60 mA Output: 9V 500mA 4,5VA.
A sticker above the power intake on the speaker says 9V AC.
What is correct, and what is recomended?
Thanks.
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Old 5th November 2017, 09:53 PM   #1858
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by DynamicPrecision View Post
Hi. I've just bought a pair of Acoustat Z22, china made. I have some questions about the powersupply. The powersupplies that came with the speakers says AC/DC Adaptor Input: 230V ac 50Hz 60 mA Output: 9V 500mA 4,5VA.
A sticker above the power intake on the speaker says 9V AC.
What is correct, and what is recomended?
Thanks.

I know nearly nothing about the Chinese-made Acoustat models. But from your description of the information, it appears that the speaker needs a 9-volt AC input at 500 mA (1/2 amp). So you need a wall transformer that can output 9 volts AC at a minimum of 500 mA, with an input voltage to match your local mains voltage. The 12-volt and 15-volt Acoustat wall transformers commonly seen for sale on eBay would NOT be compatible with these speakers.
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Old 6th November 2017, 06:22 PM   #1859
DynamicPrecision is offline DynamicPrecision  Norway
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Quote:
Originally Posted by AcoustatAnswerMan View Post
I know nearly nothing about the Chinese-made Acoustat models. But from your description of the information, it appears that the speaker needs a 9-volt AC input at 500 mA (1/2 amp). So you need a wall transformer that can output 9 volts AC at a minimum of 500 mA, with an input voltage to match your local mains voltage. The 12-volt and 15-volt Acoustat wall transformers commonly seen for sale on eBay would NOT be compatible with these speakers.
Thank you for your reply. My information and questions may have been a little unprecise.. The wall transformers I got has an Output at 9V DC, and the sticker on the speaker says Input 9V AC. I don't know if the wall transformers has been replaced. I measured the output of my powersupply, they gave 14,1V not connected to the speaker, 12,48V connected and 12,43 playing.
I wanted to try a better powersupply, and got to try out one that gave 9V DC. (since the one I had was a DC and the dealer was convinced my speakers should have DC in) The panels did'nt sound better.. So I guess the dealer is wrong and I need 9V AC in, as you wrote?

Do the panels on the Z22 have anything in common with older Acoustat's, or are they developed by Chineese Acoustat?

Thanks, Morten.
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Old 6th November 2017, 09:41 PM   #1860
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by DynamicPrecision View Post
Thank you for your reply. My information and questions may have been a little unprecise.. The wall transformers I got has an Output at 9V DC, and the sticker on the speaker says Input 9V AC. I don't know if the wall transformers has been replaced. I measured the output of my powersupply, they gave 14,1V not connected to the speaker, 12,48V connected and 12,43 playing.
I wanted to try a better powersupply, and got to try out one that gave 9V DC. (since the one I had was a DC and the dealer was convinced my speakers should have DC in) The panels did'nt sound better.. So I guess the dealer is wrong and I need 9V AC in, as you wrote?

Do the panels on the Z22 have anything in common with older Acoustat's, or are they developed by Chineese Acoustat?

Thanks, Morten.

It does seem there is some confusion on whether the speaker wants an AC or DC input. One might assume that label on the speaker is correct, but who knows. The good news is that applying a DC voltage to an input intended for an AC input will do no harm. This is not true the other way around. If you can examine the circuitry and you see diodes or a bridge rectifier close to the input jack, you can safely assume its intended for an AC input.


I've only seen photos of the Chinese panels. They do appear to be based on Acoustat's sheathed-wire design, and I'm assuming they continued with Spectra's segmented stators. They look to be solidly and neatly constructed. I have no idea what they used for a conductive coating.
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