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Thread: Harbeth Monitor 40 Active (pro version) specific

  1. #1
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    Default Harbeth Monitor 40 Active (pro version) specific

    This thread specifically relates to the Monitor 40 professional version.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  2. #2
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    Default Monitor 40 Active at the BBC

    Following a recent installation, here is a link to a little home-made video of the M40s in use. Nearly 100% of all programme trailers (of which there are very many these days) on BBC1, 2, 3 and 4 are mixed/mastered on these speakers in this room by a handful of experts. You can see the voice-over booth when I turn around with the camera. There is no sound on this clip.

    Note that the Harbeth 19" rack filters and amplifiers that drive each M40A are mounted into the tubular steel stands under the speakers. Note that when designing these stands I measured the typical sound engineers ears-from-floor distance. Small adjustments in height are possible as the M40s sit on 'ski slopes' which can be increased/decreased in elevation.

    The proximity to the rear wall is not ideal but the walls are lagged with sound proofing under the farbric covering.

    The link is at the bottom of this page: http://www.harbeth.co.uk/prospeakers...tive/index.php

    Best viewed in 50% or 100% size.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  3. #3
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    Default Re: Harbeth Monitor 40 Active (pro version) specific

    Alan:

    I would like to know the following:

    1) Why the original back plate crossover-amplifier pack of the M40 active was changed to a rack mounted unit?

    2) The new rack mounted crossover-amp uses MOSFET power amp modules. The power amp modules are designed at Harbeth or are commercially available units?
    It is possible to know its origin?

    3) Was the original back-plate crossover amp based on the TDA7294 power chips? Why you changed to discrete power modules?

    Cordially,
    Marcelo.

  4. #4
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    Default Re: Harbeth Monitor 40 Active (pro version) specific

    To answer your questions ....

    1) Why the original back plate crossover-amplifier pack of the M40 active was changed to a rack mounted unit?


    There are several reasons. The weight of the active 40 was at the limit of what one person could lift. In a 19" rack case there is so much more space available to lay-out the circuits. Also, if the customer should have a technical problem with the amp, he only has to return the external 19" case for servicing. Also, yI could increase the size of the PCBs and use larger inter-PCB connectors in the extra space available in the extrenal cases. Much easier all round. I'm very glad we did. (But the cost is greatly increased).

    2) The new rack mounted crossover-amp uses MOSFET power amp modules. The power amp modules are designed at Harbeth or are commercially available units?

    The MOSFET amps in the external 19" case are the same circuit design as in the internal-amp modules but the PCB layout is different - there was no need to miniaturise the layout when mounting in the bigger external cases. All circuit boards (there are 9 PCB's in the 19" rack-amps) are designed and made here. For my sins I have personally assembled every active M40 PCB for every pair made.

    It is possible to know its origin?

    The origin of the MOSFET circuit can be traced back to the Hitachi application notes from the 1980's. This MOSFET design is very rugged, has a minimalist circuit and has proved to be completely reliable in use. I'm sure that there will be many more sophisticated amp designs around but they will be more complex and hence, less reliable.

    3) Was the original back-plate crossover amp based on the TDA7294 power chips? Why you changed to discrete power modules?

    No. The TDA chips were used in another active speaker we made. The Monitor 40 Active has always used discrete MOSFTETs; T03 cans in the latest external rack cases, plastic TO247 in the earlier internal-amp M40s.

    I feel that the MOSFETs are a more rugged solution. This is only a feeling not a scientific opinion since, in the thousands of Active speakers we have made, I can not recall a field failure of the TDA chip. However, the TDA chip is highly integrated (complex internally) and simplicity enhances long term reliability. In a broadcast environment, 100% reliability is mandatory. Although the MOSFET design was more expensive than the TDA solution, I felt that the customer (mainly the BBC) would pay a little more for this design strategy. They have done.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  5. #5
    kwingylee Guest

    Default Harbeth Monitor 40 Active (pro version) vs domestic

    Alan:

    Is the backlog for the M40.1 active also 12 months?

    I do have a question about the M40.1 active vs M40 passive. Within my limited experience at least, I found that active speakers subjectively sound more dynamic. Is that also the case with the Monitor 40.1? Or am I just way off?

  6. #6
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    Default Re: Harbeth Monitor 40 Active (pro version) vs domestic

    I can not give you a precise date for M40.1 deliveries because so much depends upon whether your local Retailer or Distributor had the confidence to pre-order or not. If they did, then they will of course get deliveries asap. But the point of the order book is not that we are booked-out for 12 months ahead for all customers and for all models but that the astute customers have dovetailed their needs with our capacity and have planned ahead to serve you better. These are the basic rules of running an ISO9001 supply chain: integration from the top to the bottom because it reduces stress, maintains QC at a constantly high level and gives on-time deliveries. Not all markets can, will or like to commit ahead. This creates an issue when frustrated end users call us directly for delivery information for products that have been ordered for impossibly quick delivery.

    At this moment production tell me that they are completely flat-out until the end of January. Of course, that block moves forward daily and soon we will have reached capacity for February. Please talk with your local retailer and if necessary importer. They can tell you what they have ordered from us and what we have confirmed in writing as a delivery date per ISO9001 rules.

    We at Harbeth UK are acutely aware that we need to make a superhuman effort to commence M40. production but we can not let down customers for all the other models.

    M40.1 active - I have not even thought about such a speaker yet.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  7. #7
    Join Date
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    Default Link?

    Hello,
    The link from the second post is not working. Were can i find information and photos about the active 40.1 version? with their amps, etc...
    thanks

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