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The Allen USAP audio processor cards – theme and variations

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  • The Allen USAP audio processor cards – theme and variations

    Every Allen ADC organ has at least one USAP audio processor card. It takes the outputs from the tone generators and prepares them for output to the amplifiers via the RCA jacks on top of the cage. At the encouragement of JBird (verbal) and Michaelhoddy (“Love this esoteric stuff.”) I’ll start the discussion with what I know. I cannot comment on MDC or MDS models since I have no information or experience with them. Yes, it’s a long post but that is because it is a comprehensive as I can make it.

    Functionally, the AP card takes the analog audio signals from the tone generator boards (which have individual digital to analog converters - DACs - for each section) - via wire-wrap wires on the back of the cage backplane and mixes them down to a smaller number of output channels.

    What I find interesting from studying the backplane wiring in my 5300 is that more than one tone generator output is wired to a single input pin on an AP card. But there are more input pins on the card than output channels so some tone generator output mixing also occurs in the card. The AP card also has DACs that process the swell pedal positions (sent from the console multiplexer) to modulate the output volume going to the amplifiers. This card may perform additional tasks that I am not aware of so additional information is welcome if I've left something out.

    Variations on a theme.

    AP-1x cards have seven channels. The original AP-1 card has relays that were used to mute the audio output of the cage when the organ was turned on. When the ADC model amplifier was introduced, replacing the D-40 and S-100 amplifiers supplied on earlier production organs, it had muting relays built into it. So there was no need for them on the AP card and the AP-1A card has no relays. You can substitute an AP-1 card for an AP-1A card - but the other way around will cause turn-on thumps if you have amps without the built-in mute option.

    Where things get curious is the AP-1B card that I bought on *bay a while back. No relays but it does have what appear to be ECO (engineering change order) wires soldered on the bottom side of the board over the PC board traces. The copyright date on this board is 1983 but the build date stamped on it is 1990. I do not know how this card differs functionally from the -1A version. I have not yet tried in in my organ. A cursory inspection suggests it is the same PC board layout and components but with some wiring/function changes.

    A scan of the standard cage charts for the ADC models that I could find shows that there is a specific slot for the AP card in every model with a full size cage - from the ADC-4000 up with the exception of the 4900, which has a half-size cage. In fact that slot is labeled “AP” rather than having the slot number (11), just like the MA (master) and KA (key assigner) slots. The reason for this is that the cage backplane typically has printed circuit traces connecting the AP card edge connector to the RCA jacks on top of the cage.

    The AP-1 card and its two variants have seven output channels which connect to RCA jacks 1-7. The 8th jack on a cage is connected via a wire-wrap wire to another card slot, if that output is needed for that model. The second AP card in a cage is usually in slot 12 but not always.

    The AP-2 card is a 2-channel audio processor card used in 2-channel organs (ADC-1000, 2000, 3000) and as a second audio processor card when the Brass Choir and other TT-4 based options were added to certain model instruments. I’ve never seen a photo of an AP-2 card; I presume it has relays.

    Model variations:

    ADC-4000, 4100 and 5000: 2-manual, four channel organs with one AP-1 card.

    ADC-5400: 3-manual, six channel organ with one AP-1 card. With the BC option, the audio for that stop comes out on channel 7, so only one AP card is needed.


    ADC-6000: 3-manual, 7-channel organ with one AP-1 card. My information does not show a BC option for this model since the single cage has a full complement of tone generation cards filling every slot, thus there is no room for the BC cards.

    ADC-6800: a newer 3-manual, 7-channel organ using fewer but higher capacity TG cards than the 6000 so there is room for the BC option. When the BC option was installed, a second AP-1 is shown on the cage chart for the 8th audio channel. I have no idea why they didn’t use an AP-2 card for this additional channel.

    ADC-7000: 3-manual, two cage organ. The first cage has an AP-1 with six channels of output. The second cage also has an AP-1 card, using three output channels without the BC option and four with it.

    ADC-8000: 3-manual, two cage organ. The first cage has an AP-1 with seven channels used and the second cage also has an AP-1 card, using six channels without the BC option and seven channels with it.

    ADC-9000: 4-manual, 4 cage organ. I have seen photos of this model online but have no tech information. I see an AP slot in each cage but the cage photos are grainy. I don't know how many channels are on this organ.

    The various ADC theater models (3500, 3600, 4500, 4600, 6500) are all one cage instruments with a single AP-1 card; the ADC-6500 model has seven audio channels.

    Now we get into the changes in the x300 series instruments.

    ADC-4300: 2-manual 6-channel organ mixed down to four channels with one AP-1 card. There is no BC option shown on the cage chart.

    The ADC-4900: 3-manual organ is a curious beast - the copyright date on the spec sheet is 1989. It has a half size cage but has the TG-8 and TG-10 boards of the x300 generation. There is one AP card and six audio channels that get mixed down to four in an ADC audio mixer board. There is only one Alterable Voice card and no BC option.

    ADC-5300: 2-manual, 6 channel organ. It has a BC option but that output is on channel 8 driven by an AP-2 card in slot 12. I have no idea why they didn’t connect that TT-4 tone generator card output to audio channel 7 on the AP-1 card since that connection could have been done with wire-wrap on the backplane. Channel 7 is not used on this model. As we have seen with the recent purchase of a 5300, a second AP-1 card may be used in slot 12 instead of an AP-2.


    ADC-6300: 3-manual, 6-channel organ in one cage. This one is odd in that it shows the BC option on channel 7 and an AP-1 card in slot 12 with the numbers 3, 4 - which are great organ channels.

    ADC-7300: 3-manual single cage organ but it has 7 channels with a second AP-1 card shown in slot 12 for the BC option on channel 8.

    ADC-8300/8350: 3-manual two cage organ with an AP-1 card in each cage and space for a second AP card in each cage. The cage chart shows 8 channels for Cage A and 8 channels for Cage B when both optional stops are installed (Chimes and State Trumpet).***

    *** Interestingly, this is the first place I have seen a TT-5 card on a standard ADC model – for the Chimes on the swell. And the cage chart shows EIGHT EPROMs on that board!!! So my speculation in another thread that the TT-5 may have had 5 EPROMs was wrong. (I'd love to hear how much better those chimes sound compared to the standard ones that come out of a TG-8 board like on my 5300.)

    The information that I have for the ADC-9300 shows three cages. Cage A has one AP slot and 7 channels, cage B has two AP slots and 8 channels, and cage C has two AP slots and 8 channels – for a total of 23 audio channels. (As an aside, the cage charts for this instrument are difficult to read because of the non-standard layout and tone generating features, including a DG-3 card in each cage and a total of five TG-10 articulation generators.)
    Last edited by AllenAnalog; 03-28-2020, 09:35 AM.
    Larry is my name; Allen is an organ brand. Allen RMWTHEA.3 with RMI Electra-Piano; Allen 423-C+Gyro; Britson Opus OEM38; Saville Series IV Opus 209; Steinway AR Duo-Art, Mills Violano Virtuoso with MIDI; Hammond 9812H with roll player; Gulbransen Rialto; Roland E-200; Mason&Hamlin AR Ampico piano, Allen ADC-5300-D with MIDI.

  • #2
    Larry,

    Excellent treatise on the topic! Thank you for doing all the legwork.

    Is it possible to tell us which card is which in the photos? The first is rather blurry and I can't read the label. May I assume it is the USAP-1 card?

    Again, thanks for all your work on the topic.

    Michael
    Way too many organs to list, but I do have 5 Allens:
    • MOS-2 Model 505-B / ADC-4300-DK / ADC-5400 / ADC-6000 (Symphony) / ADC-8000DKC
    • Lowrey Heritage (DSO-1)
    • 9 Pump Organs, 1 Pipe Organ & 6 Pianos

    Comment


    • AllenAnalog
      AllenAnalog commented
      Editing a comment
      The photos do have captions but the font size that the system uses for that is rather small. It is in white, just above the four thumbnails, when you scroll through the full size photos.
      Last edited by AllenAnalog; 03-28-2020, 09:31 AM.

  • #3
    The cage-based MDS organs I've seen use an AP card; the smaller models (up to MDS-38, at least, and maybe MDS-40S) used a system similar to the MADC organs, so no card cage was used, and thus, no AP card. The expression was done using the ADC mixer board.

    The MDC organs certainly would not have used an AP card, as they did not have a card cage--they were built as an "organ on a single board" according to one dealer. They were basically stripped down and simplified MOS organs.

    Comment


    • AllenAnalog
      AllenAnalog commented
      Editing a comment
      The ADC mixer board (not to be confused with the USRM reverb mixer board or the USEM external mixer board) that I mentioned in the ADC-4900 description, can be configured in many ways. It has two inputs for expression pedals, two inputs for a rhythm generator and one input for "Tape in." It supports the ADR-4 reverb unit and a mono tape/headphone output. Quite the universal board, with 20 RCA jacks on it.

  • #4
    Originally posted by AllenAnalog View Post
    ADC-4300: 2-manual 6-channel organ with one AP-1 card in a short cage. There is no BC option.
    Larry,

    I may have to contradict you about the ADC-4300. I believe my ADC-4300 has a full cage with 22/24 slots, however, it is not completely full.

    Michael
    Way too many organs to list, but I do have 5 Allens:
    • MOS-2 Model 505-B / ADC-4300-DK / ADC-5400 / ADC-6000 (Symphony) / ADC-8000DKC
    • Lowrey Heritage (DSO-1)
    • 9 Pump Organs, 1 Pipe Organ & 6 Pianos

    Comment


    • AllenAnalog
      AllenAnalog commented
      Editing a comment
      Thanks for catching that error; I have corrected it. My information shows that it has 6 channels out of the cage but they are mixed down to four. I'm guessing that it also uses the ADC mixer board. Do you by any chance have a photo of the mixer board in your organ?

    • myorgan
      myorgan commented
      Editing a comment
      I do. I'll post it when I get to my other computer. I've also changed it from 4 to 6 channels. Not sure why Allen mixed it down to 4, but must've been for cost savings for those who needed it.

      Michael

  • #5
    I know that my MDS-38 used the ADC mixer, and the ADC-3160 I had also used it, as, I believe, did most of the MADC-3 organs. My MDS Theatre III uses it as well, I think the the MDS Theatre model uses it because of the 6 Trem 4 boards and ADR4 unit, in addition to the ARTE unit--it has such a large number of input and mixing possibilities.

    Comment


    • #6
      Thanks for all this info, Larry. Very helpful to all ADC owners. I had forgotten that the USAP-2 is the "step-child" version with only two channels worth of components on the board.

      As you mentioned up above, there are sometimes multiple DAC outputs from multiple TG boards tied to the same USAP input using the wire-wrap connections behind the backplane. Apparently, each TG board's DAC output is buffered right on the TG board itself with a resistor, possibly 1K, as that would accord with Allen practice in older DAC designs. This allows the outputs of two or more DACs to be combined simply by wiring them to the same input.

      With that knowledge in mind, it would seem possible to "customize" an ADC model to some extent by moving those wires around to different USAP inputs. For example, models that do not utilize all seven available channels on the USAP could be upgraded by moving certain stops to the unused channel or channels. Of course you'd be on your own adding an RCA jack and the other components in the output panel for the added channel(s), and soldering in jumpers to take the audio from the USAP to the jack(s).

      The question remains as to how expression is done on the USAP board. I assume that there is just one expression circuit per output channel, and that the data for that is routed from the appropriate swell show to the appropriate expression stage on the board. Or perhaps the expression is customized for a given model by the wire-wrapped connections.

      I have to wonder exactly how many different expression groupings are allowed on a single USAP board. Could there theoretically be seven? Or is it limited to three or four? The source of the expression data is probably the USMA or the USKA (decoding data sent to the cage by the USCM), and there may be a built-in limit on one of those boards as to how much expression data can be decoded within a single cage.
      John
      ----------
      *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

      https://www.facebook.com/pages/Birds...97551893588434

      Comment


      • AllenAnalog
        AllenAnalog commented
        Editing a comment
        You touched on something that may be a key as to why Allen adds a second AP-1 or an AP-2 card in a cage rather taking advantage of an unused audio channel on the AP card in the AP card slot. (The 5300 is a perfect example of that when you add the Brass Choir and need a 7th audio channel.) And why there seems to be an inconsistency between using a second AP-1 card rather than an AP-2 card when the second audio processor card in a cage is only needed for one more audio channel.

        It may have to do with how expression is applied to those 7 channels - perhaps it is fixed path in the ADC data structure. We know that the analog information from the swell pedals goes into the console multiplexer, where it becomes part of the digital data stream going to the cage(s). What if there were always a fixed relationship between the physical swell pedal location (left, middle, right) and the audio channel it gets applied to? I've seen photos of 3-manual ADC organs (like the 8000 and up) with 3 swell pedals (plus a crescendo pedal).

        Since I can't edit my original post, I'll add here that the AP cards use AD7523 8-bit multiplying DAC chips - one for each channel. Presumably that is the device that applies the divisional volume control.

        It is quite possible that if I studied the cage charts and the assignment of channels to divisions that I could create a spreadsheet that makes sense of this. But I don't have the time to ponder that big orange binder for another three hours right now.
        Last edited by AllenAnalog; 03-28-2020, 07:20 PM.

      • jbird604
        jbird604 commented
        Editing a comment
        Exactly what I was thinking. Allen never seems to waste resources or use expensive parts when cheap ones will do. Could be that channel #7 is hard-wired to express with #5 and #6, for example, so would be useless for adding on something they didn't want to express that way.

      • AllenAnalog
        AllenAnalog commented
        Editing a comment
        Yes, and since that 8th RCA jack on the cage can be wire-wrapped to any output on a 7-channel AP-1 card, you could then pick whichever expression data you wanted to control that stop. I think we are on to something here.
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