LM1894N; Dynamic Noise Reduction System Dnr; DIP-14. 2.349€ Ex Tax: 1.910€. 2001) Includes: PIC PCB Part No. 5.92 1.85 DIP-14 DNR noise reduction. LM386N-1 LM386N-3 LM725CN LM1203N MC1350P LM1875T LM1877N-9 LM1881M LM1881N LM1894N TDA2002V TDA2040V OPA2134PA OPA2134UA.
= datasheet available Mfg Part Mfg Qty 2 3 ROHM 0 INDS 223 INDS 1174 ISI 4450 MOLDED INDUCTOR 4.7 LT 87 SMALL TO-5(BOX) 22 NATIONL 30 136-DIE N 3 NS 341 LT 1 LTC 100 LT 6 NSC 40 NSC 1000 NSC 25 N 5 LINEAR TECHNOLOGY 26 NSC 2600 NS 35 136-NS-87. NS 12 NS 14 EOL per Franchise Dist 3/2004 LINEAR TECNOLOGY 26 8 N.S 100 Overseas 20003.
HI fellows, I just received 4 LM1894N from China (hopefully no fakes) to build an Ibanez Noise Buster as an alternative to a Decimator (that I just can't fit into a 1590a). I found a schematic and a layout at the other forum that I am using as a template. Schematic: Some questions came up: Looking at C25 and C8 I realize that they are paralleled (both betweeen VCC and GRD). Can I just use a single 220uF to replace both of them or should I doubt the schematic or the original designers or am I wrong to do so? In the layout found on the other site, C3 was 1uF instead of 100p on the schematic.
Any sense in that? I found some other inconsistencies between layout and schematic so I really hope this one won't be a failure. Best regards, Lars. C8 is clearly polar, which really hints uFd not nFd. Two caps on the 'same' point is not wrong. These points may be several inches apart. There are no perfect wires (or PCB traces).
A cap over-there may not nail-down a point here. Look at old logic and long pro-audio boards, they were peppered with 'parallel' caps every inch or three. Whether this circuit needs two caps, or one mich be smaller, is dubious. However in DIY I would plan that it might, even just go ahead and install two caps. (If I was making a million I would prototype a few and abuse them on many power sources to see if I could avoid the few cents of cost.). Well, I am just emerging from my soldering hole where I threw this thing together on a not very elegant PCB layout.
Sorry for the two huge jumpers but it had to fit in a 1590a (it does, if you squeeze a bit). And it astonishingly worked first time. I have no idea how good it works, because I have to test this in my rehearsal room with the noisy Orange Squeezer and his White-Noise-Trash mates but on first encounter lined up with what I got at home, I might like it. It's not a gate (as expected) and that might be a good thing but it cuts noise from the higher frequencies quite efficiently. If somebody is interested, the LM1894 I bought The copied schematic without the switching part And the BOM (all 1uF are non-polar and SMD and all the SMD pads on the layout are 1uF 1206s): C1 47n C2 1u C3 100p C4 1u C5 8n2 C6 100n C7 1n C9 100u C10 8n2 C11 4u7 C12 47n C13 1u C14 100p C15 1u C18 1u C19 10u C25 100u C26 47u CX 22n U1 4558 U2 4558 U3 LM1894 U4 IN U5 9V U6 GRD U7 OUT VR1 1K D1 1N4002 R1 1K R2 510K R3 10K R4 10K R5 4K7 R6 10K R7 10K R8 4K7 R12 510K R13 470R R14 100K R26 10K R27 10K R28 180E R29 2K4 R30 100E. Seems like a lot of circuit for noise reduction. I can't see why Ibanez used three extra opamps.
(The input buffer is needed to hide the '1894's low input impedance.) Is treble cut what is happening here? Read the datasheet and app-notes: It is a sliding treble-cut. With large signal it opens to 20KHz. With 'no' signal it closes to 1KHz. In the intended use it gives a 6dB/Oct slope.
The Ibanez implementation cascades both sections of the stereo chip to give 12dB/Oct. Back-story: Dolby B tape encoding made Compact Cassette tolerable for music. While Dolby B was the 'cheap' form of Dolby, it wasn't really cheap, for the chip and especially for the license to use the chip and put the 'Dolby' badge on your box. Interestingly, mis-using Dolby decoding on a non-Dolby source took out much low-level hiss. Dolby never claimed that (only complete path with encoding/decoding).
National Semi jumped in with a 'single ended noise reduction' scheme. Such things were old; their patent claimed specific time-constants, and they copyrighted 'DNR'. For psycho-acoustic reasons, their time-constants were not very different from Dolby, but not exact copies; and Nat Semi never suggested a 'DNR encoder'. The gimmick was that DNR would play-back a Dolby tape close-enough to 'right' for most users. And the 'D' in both encouraged a little confusion. But the chip and license to use DNR was much lower price. IIRC, GM/Delco put DNR in a lot of car radios.
At the time, you could not get the DNR chip naked. You had to have the license. (Repair chips would nominally be available through the radio OEM; I doubt they ever were because chips don't fail.) I dunno if the license thing has withered over the years, or if these Chinese sources just don't care. I can't see anybody making these chips today. Not enuff market. There will always be vendors re-printing say CMOS chips as 'LM1894', outright fakes. But there was probably some un-sold supply when production ended.
If your chips work, they are probably Malaysia 1992 or similar NOS production.