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Old 26th June 2012, 09:55 PM   #481
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Quote:
Originally Posted by alkasar View Post
I am done with the reverse engineering to cross-reference L25 board.

For memory, the original IRAUDAMP7S is here, page 30

http://www.inductor.com/irf/iraudamp7s.pdf

L25D cross reference

http://img407.imageshack.us/img407/4...ationwithr.png

The design follows almost exactly IRF reference design.

some comments:

- The components values on the board follow the reference design, except for those to adjust according to power (in red in the schematic)
R7, R8, R17, R18, R12, R114, R115, R117, CP7, CP8

- pot P1 is not there. Instead, R11 is adjusted to 300R (resistor already sold on board)

- The protection led signal is not implemented (R14, CSD1, FET2, R3, D1)

- There is an additional 15V Zener, not on the schematic. Z? on board, already soldered. It is between pins 13 and 15 of IS2092
Sorry to bring this back from a long time ago, but I am looking to run an L25D at a lower voltage (35VDC +/-).

Would I be correct in interpreting the above post and others in this thread as meaning that it IS possible to run the L25D below the 60-70V +/- recommended range? If so, does it simply require changing a few resistors, as denoted by the reference document from IRF?

If I were at the beginning of this project, I wouldn't be asking this. I got all the way through construction and voltage testing before realizing my oversight. Someone help so I don't have to buy new amp boards?

Photo Album - Imgur
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Old 26th June 2012, 11:27 PM   #482
MrSlim is offline MrSlim  Canada
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In Theory, yes, you should be able to adjust the resistor values and get it to run at 35V, but to my knowledge, I don't know of anyone who has done it..

Someone has to be first..
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Old 27th June 2012, 01:30 AM   #483
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Quote:
Originally Posted by MrSlim View Post
In Theory, yes, you should be able to adjust the resistor values and get it to run at 35V, but to my knowledge, I don't know of anyone who has done it..

Someone has to be first..
Well the other option is to drop another $100 on new 50Vx2 toroids for the two amps. I think a couple dollars in resistors and some time is a better investment currently.

So, that entails:
R7 - Not listed in Table 5; 3.01K in Figure 33)
R8 - 100K
R17 - 33K
R18 - 4K7
R12 - 3K9
R114 - 220R, 1W
R115 - 10K
R117, R118 - 2K2, 1W
CP7, CP8 - Not listed in Table 5, presumably unchanged for lower voltage

The only other thing that is red in Figure 33 is FET1, which I assume will remain unchanged because its specs do appear to allow for 35VDC operation. Output power will be cut down considerably into an 8 ohm load.

Or I could swap the transformers out, get ~70VDC +/-, and enjoy not having to solder a bunch of components. Decisions, decisions.
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Old 27th June 2012, 10:54 AM   #484
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we made 2092 amp years ago, we found its frequency range larger when heavy load.how difficult to use it in pro audio equipment , EMI and radio influence are hot potato. guys have good suggestion?
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Old 30th June 2012, 11:33 PM   #485
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Quote:
Originally Posted by blairfrischx View Post
Well the other option is to drop another $100 on new 50Vx2 toroids for the two amps. I think a couple dollars in resistors and some time is a better investment currently.

So, that entails:
R7 - Not listed in Table 5; 3.01K in Figure 33)
R8 - 100K
R17 - 33K
R18 - 4K7
R12 - 3K9
R114 - 220R, 1W
R115 - 10K
R117, R118 - 2K2, 1W
CP7, CP8 - Not listed in Table 5, presumably unchanged for lower voltage

The only other thing that is red in Figure 33 is FET1, which I assume will remain unchanged because its specs do appear to allow for 35VDC operation. Output power will be cut down considerably into an 8 ohm load.

Or I could swap the transformers out, get ~70VDC +/-, and enjoy not having to solder a bunch of components. Decisions, decisions.
Some good news and some bad news here.

Good news first - it functions at 35V +/-

Click the image to open in full size.

See that little blue light? Beautiful.

All that was necessary was swapping out the resistors as noted in the quoted post.

Click the image to open in full size.

Now, on to the bad news. After removing, modifying, and rewiring the amp board in the one amplifier, I turned power on and POOF. Smoke. I accidentally wired DC+ to the wrong terminal on the board, and it fried something on both boards. The power supply rectifier/filter board was easy enough to fix - remove burnt traces and replace with thin wires. The amp board is another story entirely. I fear I may have burned up the opamp, rendering it useless. There are no obviously burned traces on the PCB or components, and yet it does not function, and the pretty blue light does not function.

Anyway, that's a problem that is simple enough to solve by buying a new amp board, replacing the resistors, and not wiring incorrectly. This post is more to announce to everyone that it is possible to swap resistors and operate at lower voltage.

Now here's an album of the project so far: Photo Album - Imgur
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Old 30th June 2012, 11:52 PM   #486
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good thing the boards are cheap
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Old 1st July 2012, 10:04 AM   #487
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Yes, It is definitely possible.

I also changed some resistor values according to spec sheet and now I'm running my l25d at +-53VDC
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Old 8th July 2012, 09:09 AM   #488
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How is overall sound quality?Is it comparable to hifi power amps?
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Old 13th July 2012, 05:10 PM   #489
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Quote:
Originally Posted by spirovious View Post
How is overall sound quality?Is it comparable to hifi power amps?
Sound quality is very subjective , but for me they sound very good ( L15D) .
I own several amps , vintage Dynaco Stereo 400 , Denon AV3808 and a Luxman 590 . for me the overall sound off the L15D's is a bit better than the Dynaco, much better than the Denon and equal at low volumes with the Luxman or a bit less with some music .the Lux gives some better image and more detail , at Higher volumes they are sounding better then the Lux .
Noise is quite a bit higher , but not noticable 20 cm from the speakers ( 93db/w Tannoys) In my home theater setup with Emotiva UMC-1 they are absolutely stunning ! Even some commercials on TV are fun to listen to!

Cheers ,
Rens
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Old 13th July 2012, 07:40 PM   #490
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Quote:
Originally Posted by blairfrischx View Post
...
Now here's an album of the project so far: Photo Album - Imgur
Sorry to hear about the "accident"...

I have a couple of questions if I may:

#1 - Did you use a Par-Metal chassis? If not, which one?

#2 - Where did you get the PSU boards?

Thanks!

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