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Modulus-86  build thread
Modulus-86  build thread
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Old 13th February 2018, 05:55 AM   #3871
tomchr is offline tomchr  Canada
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If your mains filter ever shorts to the chassis, you will have a shorted turn around the transformer. Have a look at pages 24 and 25 of the Power-86 Design Documentation. Here's an excerpt:

Quote:
Note that the metal bolt through the transformer must connect to the metal chassis at one point only. Do not allow anything to come into contact with the tip of the mounting bolt.
A safer way to ground the mains filter would be to run a short wire to a lug at one of the mounting screws for the filter. You can do that quite simply by just cutting the wires that currently go to the top of the transformers and connecting them at the chassis instead.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
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Old 13th February 2018, 06:20 AM   #3872
sercan85 is offline sercan85
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Quote:
Originally Posted by tomchr View Post
If your mains filter ever shorts to the chassis, you will have a shorted turn around the transformer. Have a look at pages 24 and 25 of the Power-86 Design Documentation. Here's an excerpt:



A safer way to ground the mains filter would be to run a short wire to a lug at one of the mounting screws for the filter. You can do that quite simply by just cutting the wires that currently go to the top of the transformers and connecting them at the chassis instead.

Tom
Thanks for your warning Tom i will change and share with you.. i will isolate my transformer from ground

Last edited by sercan85; 13th February 2018 at 06:32 AM.
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Old 14th February 2018, 06:40 AM   #3873
sercan85 is offline sercan85
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Click the image to open in full size.
Thanks your warning.. I change my gnd cables... transformers are isolate every contact and chassis..
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Old 20th February 2018, 10:27 AM   #3874
adrianbaugh is offline adrianbaugh  United Kingdom
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I'm planning a stereo build using 2 x Modulus-86. I've got the boards but have a question about transformer sizing. My speakers are 8 ohm so ensuring it works with 4 ohm speakers isn't my top priority, but it would be nice to do so just in case I change my speakers later on. I've read the build guide regarding power supply selection but I'm still not entirely clear in my mind.


The recommended transformers have 22V secondaries. That should give (22*1.4) = +-31V DC rails, which is listed in the build guide as "not recommended" for 4 ohm speakers.


However, my source has max. peak-to-peak voltage of +-2.5V and the DC gain of the Modulus-86 is 10V/V. So the maximum output I can obtain is still only +-25V, regardless of the supply rail voltage. Is that setup still safe to use with a 4 ohm load?
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Old 20th February 2018, 10:36 AM   #3875
sercan85 is offline sercan85
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I have sonus faber venere 2.5 6ohm and my friend has magnepan maggie .7 and it has 4 ohm 86db.. my mod86 so easy drive to this speaker... we listened
Maggie .7
Description 2-Way/Quasi Ribbon
Freq. Resp. 45-22kHz 3dB
Sensitivity 86dB/500Hz /2.83v
Impedance 4 Ω
Dimensions 15 w x 54 H x 1 D inches
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Old 20th February 2018, 03:44 PM   #3876
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by adrianbaugh View Post
I'm planning a stereo build using 2 x Modulus-86. I've got the boards but have a question about transformer sizing. My speakers are 8 ohm so ensuring it works with 4 ohm speakers isn't my top priority, but it would be nice to do so just in case I change my speakers later on.

The recommended transformers have 22V secondaries. That should give (22*1.4) = +-31V DC rails, which is listed in the build guide as "not recommended" for 4 ohm speakers.
Well... 22*1.414 assumes no voltage drop across the diodes and a zero conduction angle of the diode. In reality, you'll end up around 29 to 30 V at idle. This will droop to around 28 V when the amp is operated at output levels just below clipping. That's perfect for the MOD86.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
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Old 1st March 2018, 10:14 AM   #3877
adrianbaugh is offline adrianbaugh  United Kingdom
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My build is going rather slowly at the moment, thanks to work etc. However I've got the power supply built and tested, which is progress I suppose, and am pretty much ready to start constructing the Modulus-86 boards.


I had a change of mind about the choice of THAT chip: I'm now intending to use a THAT1206 in order to improve the overall gain structure taking my source into consideration. However it seems tricky to obtain the 1n5242 in small quantities in the UK - RS has a minimum order quantity of 200. Is the specific Zener diode critical, or would the BZX85C or BZX79C be a suitable alternative?
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Old 1st March 2018, 10:56 AM   #3878
adrianbaugh is offline adrianbaugh  United Kingdom
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Never mind, I found the relevant bit of the THAT datasheet which just calls for a 0.5W Zener, so either of those parts should be fine (BZX85C is 1.3W, BZX79C is 0.5W)
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Old 2nd March 2018, 05:11 AM   #3879
tomchr is offline tomchr  Canada
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There's nothing special about the 1N5242 I specify. For some reason North America use the 1Nxxxx parts, whereas Europe went the clever route and encoded the zener voltage in the part numbers. The BZX79-C12 will work just as well, as you've worked out already.

Tom
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Modulus-686: 240W/8Ω @ <0.00025% THD. Modulus-86: 40W/8Ω @ 0.000054% THD. DG300B & Other Tube Circuits.
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Old 7th March 2018, 11:22 PM   #3880
BigE is offline BigE  Canada
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are there any rev1 boards left?
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