hifisonix

Hifisonix Speaker Protection Board

Written by

bonsai

in

This simple, low cost speaker protection board measuring just 82mm x 50mm uses the ubiquitous UPC1237 from Unisonic, a Taiwan based semiconductor manufacturer. The circuit will work from 25V through to 75V and uses mosfets to switch the speaker load rather than relays which are problematic and unreliable. A current overload input is also provided, allowing builders to arrange to sense an amplifier output short circuit and rapidly disconnect the amplifier output. The presentation below describes the operation and how to select resistor values for different supply voltages (updated April 2023).   

ATTENTION: If you are using the speaker protection board with the new nx2 amplifier, R7 must be changed to 33k. The reason for this is these amplifiers use a random phase opto-triac that switches the current protect output on the amplifiers to the +ve rail. The UPC1237 maximum current into the current trip input cannot exceed 3mA, otherwise the chip will be damaged.

Speaker Protection Board
Speaker-Protection-Board-BOM

Here is a short presentation on the use of mosfets for speaker switching in amplifiers

Notes-About-Mosfets-for-Loudspeaker-SSR

Comments

42 responses to “Hifisonix Speaker Protection Board”

  1. mohammad balagar avatar
    mohammad balagar

    Is Speaker Protection available i need 2 pieces how can i order that with 1 postage cost?
    Thanks

  2. Bonsai avatar
    Bonsai

    Hello, yes Jan you can. Just send me an email and payment for single shipping plus 4 off boards to bonsai(at)Hifisonix.com on PayPal.

  3. Jan van Doorn avatar
    Jan van Doorn

    Hello Andrew,
    How can I order multiple (4) Speaker Protection Boards without paying 4 times the postage?

    Regards, Jan

  4. Paulus van Zon avatar
    Paulus van Zon

    Hello Andrew,

    According to the service manual + and – 73Vdc
    Regards,

    Paulus

  5. Bonsai avatar
    Bonsai

    Hello Paulus,
    can you tell me what your maximum supply voltage is?
    Regards

    Andrew

  6. Paulus van Zon avatar
    Paulus van Zon

    Hi there Andrew,

    I would like to order 2 pcb’s but I have a question.

    I would like to use them for my 2 Rotel RB-991.
    As you probable know, the voltage is right at the limit your design can handle.

    As i’m not educated in electronics a very good friend of mine is helping me out.
    He’s a bit concerned with the temp of the D3 and R11?

    What would you recommend?

    With regards,
    Paulus

  7. Bonsai avatar
    Bonsai

    Martin, you can either parallel the output devices (so link Left in to the Right in and Left out to the Right out) or you can leave one set of mosfets out and the associated VOM1271, but then you must link the unused VOM1271 position emitter LED cathode to anode.

    Regards

    Andrew

  8. Martin avatar
    Martin

    Hi, I Plan on using the speaker protect in my DIY Mono Block Design. Concerning the Output switching devices, do I Need to Populate Both Channels or just the pair for one channel?
    Thanks for the Design and Support.
    Regards,
    Martin

  9. Bonsai avatar
    Bonsai

    Hello Klemen, thank you for your enquiry. Unfortunately, we are not offering pre-assembled PCBs at this time but will only offer a few fully assembled products.

    Kind Regards
    Andrew

  10. Klemen Erzen avatar
    Klemen Erzen

    Hello, I would like to purchase two Speaker Protection Boards fully finished and they should be shipped to same address but there is no option to select how many products to buy in the web shop. Can you help me with this?
    Best Regards
    Klemen

  11. Bonsai avatar
    Bonsai

    No problem Giorgio, just send payment for the extra board(s) and I will combine the shipment. Unfortunately I have to send all shipments tracked for PayPal and also because some shipments get stuck in customs.

    Regards

    Andrew

  12. Giorgio Marchiori avatar
    Giorgio Marchiori

    Hi, I want 2 speaker board protection but the shop took me to the payment for one board straight away. I don’t want to pay twice the shipping, more expensive than the board, can you send me a paypal invoice?

  13. Bonsai avatar
    Bonsai

    It’s a blank PCB

  14. Tylor avatar
    Tylor

    Is this just the blank PCB and no parts?

  15. Bonsai avatar
    Bonsai

    Hello Hrold,

    the Speaker Protection Board does 2 channels. The boards are shipped from the UK.

    Unfortunately, I have to send the boards tracked otherwise I get problems with Paypal withholding payment to me. You can bundle orders and the $15 price will cover another 3 or 4 boards from the shop.

    Seasons Greetings to you as well!

    Regards

    Andrew

  16. Mo (HaroldHill on DIYaudio) avatar
    Mo (HaroldHill on DIYaudio)

    Hi, Andrew, A few questions for your: Does one board protect both right and left channels? Are the costs on the site in US dollars? And what country do your boards ship from?

    Thanks! (And season’s best to you?)

  17. Bonsai avatar
    Bonsai

    Hello Prasi, the boards are still available (see the Shop) and the measurement is 82mm x 50mm.

    Regards

    Andrew

  18. prasi avatar
    prasi

    hello Andrew, whats the size of boards and are they still available?

  19. Mike avatar
    Mike

    Thanks for your reply. I don’t believe the GFA-5800 has any short circuit protection other than multiple fuses. It also has a simple circuit for cutout at thermal overload. I will sign up for diyAudio and post the service manual with schematics. I most likely will not have time to do this until next week. Looking forward to a discussion.

    Thanks,
    Mike

  20. Bonsai avatar
    Bonsai

    Hello Mike,

    1. The board will work with 70V rails – you just have to fit the 57V Zener – details in the presentation.
    2. For the short-circuit protection, I’d haver to see the protection circuit of the GFA5800. It might be that this already has some sort of built in short-circuit protection, in which case the hifisonix speaker protection board will just piggy back off that.

    Are you on diyAudio.com? maybe you can post the diagram up there and we can discuss it on the forum?

    Cheers

    Andrew

  21. Mike avatar
    Mike

    Hello. I am considering modifying an Adcom GFA-5800 to use this board. The supply rail to the output MOSFETS is +70V. Will this board work as is purchased from your shop? Also I read your write ups and still do not understand how the current overload circuit works, i.e. how I would wire this input up to my amp.

    Thanks!

  22. Andrej avatar
    Andrej

    I am using Toshiba TK5R3E088QM, S1X mosfets.

    br

    Andrej

  23. Andrej avatar
    Andrej

    Hi.

    I built DC protection few days ago and I powered it (both AC sense and V+ input) with Hypex SMPS AUX supply (+20V). Test results shows that turn on delay and off state works as it should, providing thump free start up/off. Only thing that bothers me, is that if I put 12 DC offset voltage, protection will turn off speaker outputs in 1-2 sec, not in 100 ms as shown in manual. Is this normal, or should I need to modify values?

    BTW: Main power supply is +-45V.

    br

    Andrej

  24. admin avatar
    admin

    Hello Bill, let me take a look tomorrow and come back to you. The timings are governed by the UPC1237 internal circuits but in principle I don’t see why not.

  25. Bill avatar
    Bill

    Andrew,
    Is it possible to set the delay as high as 30 seconds. My Sissy sit 3 takes about that long for the bias to stabilize and I would like to delay any offset that may happen until then.
    Thanks
    Bill

  26. Bonsai avatar
    Bonsai

    Andrej, are all these voltages from the Hypex PSU, or are any derived from standard transformers supplies? If you have a standard transformer supply somewhere, you can just tap the AC off that.

  27. Bonsai avatar
    Bonsai

    Andrej,

    The problem here is the AC input uses the loss of 50/60 Hz to quickly shut the mosfet relay off to prevent any output thumps from the speaker. If you have any sort of c. 12-20V DC signal that shuts down VERY quickly after the AC power is removed, then this might work. Another option is to wire an opto-coupler from the mains side, but that will entail a dropper resistor (or better a capacitive divider to reduce power dissipation). It’s a pity the Hypex PSU’s don’t have this kind of output.

  28. Andrej avatar
    Andrej

    Hi.

    Would this protection board work also with AB class amplifier, powered by Hypex SMPS. Main voltages are +-65 Vdc. I have an option to use also separate AUX +12 Vdc voltages. Idea is to power protection board with +-65Vdc, but not sure what put on AC input terminal. Maybe omit D2 and connect +65Vdc directly? +12Vdc is probably to low voltages…

    Best regards,

    Andrej

  29. Andrej avatar
    Andrej

    Hi.

    It is possible to use this protection with Hypex SMPS3kA400 power supply? Voltages available are:

    2x65Vdc main PSU

    2x20Vdc boostrap PSU

    2x12Vdc regulated AUX PSU

    Problem is that all three voltages start at sime time. I could use both main or bootstrap voltages, but not sure how to connect AC input in this case, to have proper start up/off delay.

    Best regards,

    Andrej

  30. Bonsai avatar
    Bonsai

    Hi – the link is working for me – let me know if you still can’t download it and I’ll email it to you

    Andrew

  31. Tl avatar
    Tl

    Hi, I can’t seem to access the BoM for these boards, but I am interested in purchasing some. Are you able to check if the link still works?
    Thanks

  32. David avatar
    David

    Thanks for responding

  33. Bonsai avatar
    Bonsai

    Hello David,

    This is not something I’ve looked at but may be one for the future (I’m tied up finishing off the new preamp at the moment).

    🙂

  34. David avatar
    David

    Would you consider designing a variant incorporating configurable V- I limiters, with a table of component values for the most popular BJT output devices? I assume you would use the emitter resistors of the output devices to measure the current?

  35. Bonsai avatar
    Bonsai

    Hello Ranko, what are you building? I assume it is for the nx-Amplifier if so you must use a random phase triac on the amplifier module boards so the MOC3010 should work ok but I have not checked the pinout.

  36. Ranko avatar
    Ranko

    Is it possible to use different optocoupler, MOC3010, for example, because both of those you suggest are not available in my country and if I order them from abroad, I will have to wait at least one month?

  37. Bonsai avatar
    Bonsai

    Gregor, this is a very high current mosfet with high input capacitance (c. 10nF). As such, it will switch slowly. I see its only rated at 40V Vds.

    My recommendation is you go for something with lower input capacitance – a good figure to aim for is 2-3nF . The Vds rating must be c. 10% higher than the amplifier supply voltage – so for example for a +-50V powered amplifier, use a 63V part.

  38. Gregor avatar
    Gregor

    Hi.
    Can I use Vishay SUP40012EL-GE3 mosfet.

  39. Bonsai avatar
    Bonsai

    Andrej, you can also use the TLP191 from Toshiba

    https://www.mouser.co.uk/ProductDetail/Toshiba/TLP191BUCF?qs=f0GatGUIxV39z%252BM7IeGfYg%3D%3D

    it has the same pinout as the VOM127

  40. Andrej avatar
    Andrej

    Hi.

    Any alternative to currently not available opto VOM1271T?

    br

    Andrej

  41. Bonsai avatar
    Bonsai

    Hello Andrej, they will be available later this week.

    Regards

    Andrew

  42. Andrej avatar
    Andrej

    Hi.

    When this DC protection will be available to purchase?

    best regards,

    Andrej

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