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Hello,
I wanted to reuse an old power-amp's chassis and +/-32V PSU.
Is there any way to make RevC work with this PSU?
Thanks!
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Is the output of the PSU 32VDC, or is the output of the transformer 32VAC?
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I just looked in the circuit diagram (Grundig MA 100):
- output of PSU is +32V/0/-32V
- rectifier is 4 * MR752 (or 4 * P600D)
- one T6.3A fuse each between transformer rails and rectifier.
- PSU caps are 2 * 22000uF/40VDC
The output of the transformer is not specified but I could measure it if it'd help.
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Sounds good. It's probably a 22-23V transformer, which is the low end of acceptable, but will work with the RevC (ideally 24-25V for 34V rails).
The RevC boards include an onboard power supply (rectifiers and caps), so the other parts of your PSU aren;t strictly needed. You could, if you wanted, use your PSU and jumper over the RevC PSU parts, but I don't really see an advantage to it other than saving money on parts (perfectly valid reason).
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I am with Brian, those rails would be fine, but since our RevC PCBs already have a PS on them I would probably take out the PS board on the old amp and just use the transformer. The voltage of the secondaries should be just fine. You really need to run at least one AC secondary to the RevC PCB anyway because it has a second power supply on board for the speaker protection circuit. You could bypass that, but I would never suggest it. Cheers! Russ Edited by user Saturday, February 17, 2007 8:40:26 AM(UTC)
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Thanks for your replies.
I'll gain a lot of space if I also remove the old PSU, but since the MA-100 is small, I'd better ask:
What's the overall size of one monoblock please? WxDxH?
(it is not shown on the product page.)
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Your welcome. :)
Size is
4.115" from back of LM3886 to front.
3.27" wide.
2" high plus standoffs so about 2.5" high.
Cheers!
Russ
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another question, indirectly related to board dimensions:
in the board kit's content description, there is no talk of heat sink; I couldn't find it in parts list; it is also missing on the photos.
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Ah. They aren't mentioned becuase we don't supply them. I may, however, offer some if there is interest. Sample
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from looking at the photo, I estimate one heat sink, size about 5" x 3" is needed for each board. right? is isolation required?
p.s.: sorry for all these question but I came across this amp only recently and its simplicity appeals to me. That said, I admit that by reading Mauro's My_Ref design discussion, I've yet to get above the basics.
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Yes that is approximately correct, and that size (with say 1" fins) would be just fine for a single channel. 5" x 4" is actually fine even for two channels. I will have to measure mine to give you exact size. I forget what it is, but it is approximately 5" x 4" x 1". I ordered several pieces from Ebay.
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That is correct, I usually use a 3" piece (could even go smaller, I suppose, as the 3" piece never gets more then slightly warm). The middle one in the picture is 3". These were purchased from the ebay seller barrredboss (three r's). I have some in stock. if you were interested in more than just two pieces, it might make more sense to order directly from him. I could predrill/tap the heatsinks to line up with the the RevC boards though, which might be helpful. Also, isolation is not required, at least for the kit, as we use the insulated package LM3886-TF (thermal paste now included with the kit). If you use a T-package, I highly recommend insulating the chip from the heatsink. [EDIT] Russ beat me to the reply. Edited by user Sunday, February 18, 2007 7:44:10 AM(UTC)
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Also, we ship the LM3886TF which is already isolated, so you don't need any further isolation, just some thermal grease. If you use your own LM3886T chips you will need an isolator for each. Cheers! Russ Edited by user Sunday, February 18, 2007 7:43:05 AM(UTC)
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I know this info must be burried somewhere in the respective diy audio forum thread, but the thread is long, so please allow my question here:
- The optional
RevC MUR Diode Set (8 - On Semi MUR820 Diodes)
replace which components in the parts list?
- and serve what purpose?
Thanks!
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They replace only the bridge rectifier. Some people prefer them, so just an option.
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a RevC kit consists of 2 PCBs each with onboard PSU. right?
If instead of one transformer with secondary 2 x 24 VAC, connecting the two boards in parallel on the secondaries,
I'd use a transformer with 2 x 48VAC secondary, connecting the two boards in series?
Hope you won't throw pears on me for daring to ask a seemlingly trivial question, - but what is not to sin? ;)
theoretically it should work, but would it affect the sound quality?
Thanks!
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ullus wrote:a RevC kit consists of 2 PCBs each with onboard PSU. right?
If instead of one transformer with secondary 2 x 24 VAC, connecting the two boards in parallel on the secondaries,
I'd use a transformer with 2 x 48VAC secondary, connecting the two boards in series?
Hope you won't throw pears on me for daring to ask a seemlingly trivial question, - but what is not to sin? ;)
theoretically it should work, but would it affect the sound quality?
Thanks!
Hello :) Please do not try this!!! It will only result in sparks and smoke. :) In short you must have a center tap, and there is not way to wire the AC side of two PSs in series. I promise I will not throw pears. But no this absolutely will not work. Cheers! Russ Edited by user Monday, March 12, 2007 8:56:08 AM(UTC)
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Thanks for not strangling me with a twisted pair ;) Too bad it doesn't work. I only thought about the middle man (center tap) after I'd posted my question. The good news: fortunately, I've not yet bought the 2 x 48VAC transformer which I happened to come across at eprey. ;) I agree if you'd put my question on top of the hall of shame ;) Edited by user Monday, March 12, 2007 9:49:25 AM(UTC)
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