A-50 enclosure dimensions and XO schematic - newbie to classicspeakerpages
Posted 28 August 2007 - 11:45 PM
I went back and the other parted speaker drivers are now listed.
A much better view of it's crossover.
It appears that there is a large cap, coil, large resistor, and a small cap, maybe, as well, on the other circuit board.
This is a much more complex crossover than the A-25 and A-35.
I believe that the A-10 will have a similar, if not identical crossover, composing of the right board contents only, that is.
Posted 28 August 2007 - 03:16 AM
There is a parted Dynaco A-50 speaker system on ebay as I write.
The woofers and crossover is all that is being offered.
The crossover is very interesting.
I do not remember ever actually physically seeing one before.
It has the usual switch board on the left but I see another one on the right.
It appears to have a power resistor, cap and maybe 3 coils.
More to come up in the future about this.
Posted 28 July 2007 - 04:28 PM
>called a power oscillator. This is an oscillator with range
>0-25kHz (in decade steps) in the same box as a DC-coupled
>amplifier. I can try the (Dynaco/SEAS (factory?) tuning
>technique that I read about where you apply a 5Hz sinewave and
>adjust the aperiodic damping for minimum cone displacement. I
>guess this is the critical damping point. The other method
>would involve measurement of speaker impedance around
>resonance which is a bit more involved. It is quite
>interesting to see a woofer operating at 5 Hz. I haven't seen
>something like that since I stopped playing warped vinyl ;-)
My recollection is that it was a 5 Hz square wave input used during testing. You can do a Google search to confirm this (the indy.net site and a diy site).
Posted 20 July 2007 - 12:47 AM
I have rolls of gutter-guard and some fibreglass left over from another recycled box, but I think I might try the reticulated foam (~80 pores/inch) for vents that World Designs specifies. I also have some of that and it is much nicer to work with than fibreglass, both mechanically and aesthetically.
I am fortunate that I have an old bit of scientific gear called a power oscillator. This is an oscillator with range 0-25kHz (in decade steps) in the same box as a DC-coupled amplifier. I can try the (Dynaco/SEAS (factory?) tuning technique that I read about where you apply a 5Hz sinewave and adjust the aperiodic damping for minimum cone displacement. I guess this is the critical damping point. The other method would involve measurement of speaker impedance around resonance which is a bit more involved. It is quite interesting to see a woofer operating at 5 Hz. I haven't seen something like that since I stopped playing warped vinyl ;-)
Thanks for the pointer about B&O. I will google.
You might be interested to know that Encel Stereo in Melbourne, Australia, once sold a brand-x speaker ( with"SEAS" rubber-stamped on back of box) This had a genuine SEAS first-order XO to the tweeter consisting of a Jensen NPE cap (5uF I think) and a couple of cement resistors. Boxes contained a single 21-TV-EW and H-087 tweeter in a sealed box of about 12"x15"x9". Nice teak-veneered chipboard boxes with removable open-weave dark brown grills held on by friction fit. Sorry I can't recall exact values of components. My wife bought them in the early 70's and we still have them in the garage. They may well benefit from the same aperiodic vent mod. These are the sorts of speakers that go for $5 at the local recycling centre or thrift shop around here.
Thanks again for your help and suggestions.
Posted 20 July 2007 - 12:13 AM
The difference in ports could be the natural perspective difference of the 3D image projecting onto a flat surface, I don't know for sure.
Posted 19 July 2007 - 11:38 PM
I even remember saving the photo before to my computer, somewhere.
I see Scan drivers also.
It appears that there are not just two vents but the one across appears smaller that the vertical one.
Or do I need to clean my glasses again?
Posted 19 July 2007 - 08:52 PM
Posted 19 July 2007 - 07:04 PM
You may try to find older B&O speakers, they may have had that combination of 8" drivers.
Posted 19 July 2007 - 03:43 PM
Yes you could do a mini A-50, that would be fine, or something
like a mini double A-35 with a single tweeter, similarly an
A-25 double would be fine for a smaller enclosure but
with less low bass. A TL should work fine also, even normal
vented which will provide the most bass.
You might want to consider an MTM tower layout if you prefer
something more modern.
The A-50 crossover is the way to go IMO to keep it simple, we
don't know the inductor value probably between 1 and 3 mH. You
can just purchase a 3mH and unwind/tap to get an adjustable L.
The crossover could be improved, but you would need the tools
to do it.
Remember that these have paper voice coil formers and so you
should take it easy on power. There are much better modern
tweeters also. But, give it a try if you want, you have the
Dyna designs as an example.
I do think there was a less well known Dyna with two 8", I don't think it was imported to the US.
Posted 19 July 2007 - 02:53 PM
I realised that my drivers were 8" rather than 10', but thought they might still work well in A-50 type enclosure--with a bit of tweaking. Do you have any suggestions on a good design using two 15ohm 21-TV-EWs and H-087 tweeter?
>My schematic would be correct for the tweeter section of the
>A-50 if you short R1. Your schematic and Dave's are wrong.
Sorry for my confusion, but which schematic are you talking about? Can you please post the "correct" A-50 XO schematic for me.
Maybe I will just put them in an open baffle and forget about boxes Another alternative is one of the dual woofer+ tweeter vintage SEAS kit designs on their website or even a transmission line.
Thanks for your comments.
Posted 19 July 2007 - 02:17 PM
>Here it is again
21-TV-EW is an 8" woofer, A-50 and A-25 require the 10" 25-TV-EW.
My schematic would be correct for the tweeter section of the A-50 if you short R1. Your schematic and Dave's are wrong.
You can estimate driver positions from Advertising pictures, and there was one cut away design picture that showed the partition.
I've never worked on A-50s so I don't have any more to offer.
Posted 19 July 2007 - 02:58 AM
Posted 19 July 2007 - 02:45 AM
>Do the woofers have a 16 ohm or 4 - 8 ohm stamping on the
15 ohm label
>Does the tweeter have a 4 - 8 ohm or 3 ohm stamping on their
No label, but measures approx 4R with multimeter
>Can you download a clear photo of each?
See attached pics
>I have not seen the cabinet dimensions for the A-50 for about
Most likely 24"x21.5"x10"(deep)
>The internal cabinet dimensions are quite critical, you should
>not change them.
Agree wholeheartedly with that
>The internal vent opening size and covering material is very,
>very important as well.
I was hoping an A-50 owner might have looked inside their speaker out of curiosity,
although SEAS/DYNACO seem to have been fond of very gooey sealant around drivers.
>The fiberglass content is important.
See above comment.
>In my honest opinion, I believe that the schematic has the 10 ohm resistor in the wrong location, in that particular drawing.
>I have taken the liberty of modifying Dave's drawing to what I think is a more conventional scheme. But that doesn't mean I am right. Cap value given for 1st order XO-4 ohm tweeter 8ohm woofer-gives much higher XO point than around 2 kHz. My calculator suggests 20uF and 0.6 mH. I guess design depends on gentle rolloff of 6dB/oct XO and both drivers. Data sheet says--35Hz to 2000Hz for 21-TV-EW and 1500-20,000Hz for H-87. I guess SEAS is very conservative in their specs.
>It is very kind of David to have those drawings and schemetic
>posted on his web site, he is a very nice man.
>Agreed, I have corresponded with Dave and he has been very helpful. I didn't want to bother him with these questions as he seems very busy and his priorities may have shifted from Dynacos to things like Frugalhorn etc.
>I may well be wrong about that issue.
>The actual driver layout, with the front cabinet dimensions,
>can quite likely be moved about an inch or so without a great
>I have seen at least two different mountings.
>I have only seen round flange mount.
>One with the woofers on an angle and also woofers both at the
>There was the Seas version and there may have also been a Scan
>version at the beginning of production.
>Box I had (now destryed) was NOT original A-50 as it was smaller and sealed one compartment. XO and box were very badly constructed. I suspect that someone "shoehorned" two woofers and tweeter into an available box of about 40 litres (1.4cuft). 40litres is about right for these drivers as a ballpark conventional sealed design, but overdamps them to my ears. Maybe with lots of watts they would be better ;-)...
>Adding braces to the inside is a very good idea but the same
>internal volume must be kept.
>That's what I planned to do something similar to World Designs WD-25 design which is supposed to be modern copy of A-25.
>Do not increase or decrease the designed internal measurements
>appreciably as this will alter the bass at least.
>The 10 ohm resistor does not go across, or parallel the tweeter.
Is it more like the A-50 XO drawing that I modified from Dave's drawing? (attached) my mod seems more like a conventional cap and L-pad to provide constant impedance load to first-order XO. Dynaco may have placed C in negative line, but electrically that makes no difference. Please compare with A-25-XO-M attached which is different again.
>Using MDF is probably the best cabinet material today.
>With a nice veneer, although I favour solid wood front baffle over the top of MDF. Internal measurements would be kept correct.
>As far as punch goes, with the correct internal volume,
>drivers, amount of fiberglass, correct vent opening and
>covering, solid cabinetry, there will be bass, not necessarily
>boomy but there.
I now realise that fibreglass stuffing is also important. But I hate using fibreglass, do you think polyfil or something else would work? I prefer listening mainly to small jazz groups, folk, blues, bluegrass etc so Home Theatre bass is not a problem as long as they cover acoustic double bass range down to 40Hz.
>You should never use loudness or bass boost for increased bass
> I prefer to stay away from speaker designs that rely on large amounts of EQ to achieve accurate bass. Two SEAS 8" in large box should be enough bass for me!!! I have read that room placement against a wall is a good idea with A-series Dynacos.
>Fuse them when you are finished.
Good idea, What do you think of a lamp filament as "fuse"? It is self-resetting & at normal levels it provides negligible R, is equivalent in behaviour to a slo-blo fuse, responds to average current/time and gives an indication of when to turn down the volume. This technique was very popular with some studio monitors that I have used. BTW I have already burnt out another H-087 with too low XO point and high level--not hard to do.
Thanks for your interest and help.
Posted 18 July 2007 - 03:31 PM
Do the woofers have a 16 ohm or 4 - 8 ohm stamping on the paper label?
Does the tweeter have a 4 - 8 ohm or 3 ohm stamping on their label?
Can you download a clear photo of each?
I have not seen the cabinet dimensions for the A-50 for about 30+ years.
The internal cabinet dimensions are quite critical, you should not change them.
The internal vent opening size and covering material is very, very important as well.
The fiberglass content is important.
In my honest opinion, I believe that the schematic has the 10 ohm resistor in the wrong location, in that particular drawing.
It is very kind of David to have those drawings and schemetic posted on his web site, he is a very nice man.
I may well be wrong about that issue.
The actual driver layout, with the front cabinet dimensions, can quite likely be moved about an inch or so without a great difference.
I have seen at least two different mountings.
One with the woofers on an angle and also woofers both at the horiziontal.
There was the Seas version and there may have also been a Scan version at the beginning of production.
Adding braces to the inside is a very good idea but the same internal volume must be kept.
Do not increase or decrease the designed internal measurements appreciably as this will alter the bass at least.
The 10 ohm resistor does not go across, or parallel the tweeter.
Using MDF is probably the best cabinet material today.
As far as punch goes, with the correct internal volume, drivers, amount of fiberglass, correct vent opening and covering, solid cabinetry, there will be bass, not necessarily boomy but there.
You should never use loudness or bass boost for increased bass output.
Fuse them when you are finished.
Posted 18 July 2007 - 07:19 AM
Their XO was a first-order on the tweeter with series C and series/parallel Rs actually labelled "SEAS". The arrangement sounded OK, but I suspect the original design of the A-50 might be better. The pair of boxes lacked the "punch" that some people have used to describe the bass and low mids of the original A-50.
I have found the **outside** dimensions of the original boxes (28"x21.5"x10"). Three things I can't seem to find exactly are the dimensions/design of front baffle layout, the internal aperiodic vent or a XO schematic. I did find the A-50 XO on Planet 10 site, but also found a reference elsewhere that this could be slightly wrong. Someone suggested that 10R resistor should be in parallel with tweeter to form an Lpad. see attached .gif (Thanks to Dave Dlugos of Planet 10-hope it's alright to post this pic)
I also need to know thickness of original cabinets (3/4 chipboard??) or enclosure volume as i plan to make thicker walls and perhaps some bracing front-to-rear and side-to-side.
Also thought of making them as towers to avoid separate stands. Can anyone supply box plans and definitive XO schematic? Is there any advantage to making boxes bigger than original design? Or has anyone used these SEAS drivers in any other configuration eg d'appolito with tweeter between two mid-basses? Any suggestions for improvements on the original design would be appreciated. Please don't shoot me for posting such heresies in the Classic Dyanaco forum ;-)
Posted 22 September 2007 - 07:31 PM
I had misplaced my A-50 schematic, so now my question is answered.
The extra board has a coil, cap and w-w resistor to cutoff the upper woofers output, for some reason.
It was not done for the A-25 or A-35. MMMMMMM
It obviously must have been needed for this A-50 speaker combination.
Manufacturers usually don't throw in that many extras for nothing.
Here is the A-50 schematic from t-linespeakers.org.
Here is also a Dynaco artist's conception of the A-50, note the non-horizontal woofers and the horizontal baffle board inside.
I believe, and I don't think I am alone, there is a small error in the tweeter switching arrangement, in my opinion.
I believe that one of those 2.2 ohm resistors in the highest, or brighest switching position, is still in series with the tweeter.
If I am right, the removal of this resistor would give the tweeter about 2 db more output, but this may have been added for driver protection.
A photo of a parted A-50 from ebay has the 4 smaller resistors and 1 larger one for the switch, which conflicts with the A-25 switch I have in my hand.
It does agree with the t-linespeakers.org schematic, in numbers at least.
From attachment 8 above, the numbers of resistors on the switch is the same as the schematic.
My interest now is that the missing resistor, the 5th 2.2 ohm, is not in the A-50's schematic or board, but is in the A-25 tweeter circuit.
The schematic with the 10 ohm resistor in series with the tweeter would mean that the tweeter level would be about 5 db down, which will be at it's highest, brightest setting.
Switching to it's dullest setting adds another 8.8 ohms in series which means 18.8 ohms on series with the tweeter. MMMMMMM
Posted 22 September 2007 - 06:59 AM
I wonder why the extra coil, w-w resistor and board?
I can understand it with the smaller woofer of the A-10 but not the A-50.
Same crossover frequency as the A-25 and A-35.
Posted 15 September 2007 - 09:06 PM
Attachment #1 2719.jpg
Attachment #2 Ignore
Attachment #3 2722.jpg
Attachment #4 2723.jpg
Attachment #5 2724.jpg
Attachment #6 2725.jpg
Attachment #7 2726.jpg
Attachment #8 2727.jpg
Attachment #9 (2728.jpg) somehow got attached. It is an angle view looking at the slanted cross-piece with the coupling slot (covered with felt)
Here are more:
2229.jpg (attachment #1?) The old capacitors have been clipped out and the tweeter cap has been soldered in.
2730.jpg (attachment #2?) Both new caps are installed.
OK. The speaker was rewired, the cabinet was closed up, and I fired up the amplifiers. From here on, as Carl says, "It's all about the music."
>OK, here goes with photos and comments. >Continued in next message.
>>Thanks for your write-up.
>>If possible please take a before photo, or two, of the
>>crossover board and after mod.
Posted 15 September 2007 - 08:46 PM
2719.jpg The A-50 with custom cane grill.
2722.jpg Getting the patient ready for the operation.
2723.jpg Comparison of new and old caps (old caps were from the other system). Note how large the new ones are. The 24µF cap is really two 12µF capacitors soldered together
2724.jpg One woofer has been removed.
2725.jpg With one layer of sound absorbing material removed.
2726.jpg With two layers of sound absorbing material removed.
2727.jpg With vinyl shroud removed. Note old capacitors.
Continued in next message.
>Thanks for your write-up.
>If possible please take a before photo, or two, of the
>crossover board and after mod.
Posted 15 September 2007 - 07:29 PM
>I also need to know thickness of original cabinets (3/4
>chipboard??) or enclosure volume as i plan to make thicker
>walls and perhaps some bracing front-to-rear and
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