Ibanez Noise Buster NB-10 questions

[lars-musik]

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 (here) that I am using as a template.
Schematic: http://www.dirk-hendrik.com/temp/ibanez_nb10.pdf

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

[garcho]

C8 should be 100nF (nano-Farad), C3 should be 100pF (pico-Farad), C25 is definitely 100µF (micro-Farad).

[Kipper4]

Seems like a lot of circuit for noise reduction. Is treble cut what is happening here?
I'm interested to see how you like it when it's built.
I can't see a good reason why even the Chinese would make a chip that didn't behave as the spec sheet says it would, although I've had some poorly performing lm13700s before depending on the application of course .

[GFR]

I remember an Elektor magazine project that was basically a discrete version of the LM1894 (I think it was a direct copy of a circuit found in some Philips tape recorders). Since it was intended to be used on tape recordings, I think the circuit as-is would not make a lot of difference when you already have the steep treble cut of a guitar cabinet...

http://www.abcelectronique.com/annuaire/montages/cache/787/reducteur-dynamique-de-bruit-le-dnl.html

[PRR]

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.)

[lars-musik]

Seems like a lot of circuit for noise reduction.

Well, Tonepad's MXR Noisegate counts around 40 parts about the same number as this one (unlike the Decimator with over 80 parts!) .

I remember an Elektor magazine project that was basically a discrete version of the LM1894

This is a nice idea! BUT now that I ordered and received the bugs from China....

...  the spec sheet says it would...

You got me there! I downloaded it but never looked at it. It says about my bothersome C8:
"0.1 μF–100 μF:   May be part of power supply, or may be added to suppress power supply oscillation."

As the C25 in question is part of the power supply I think I'll try to economise one of them, but not to

....see if I could avoid the few cents of cost.

but rather to save some space in the always too small 1590a.
If it misses in the end, I'll just stick it on the backside of the boards and do call it a prototype.


EDIT: Well, there was a little open space left on the pcb, exactly between pin 1 of the LM1894 and a ground trace. So I'll guess C8 will be on the pcb after all.
I am afraid I won't be able to build this before the new year but I'll definitely report back!

[garcho]

C8 is clearly polar, which really hints uFd not nFd.

It says about my bothersome C8:
"0.1 μF–100 μF:   May be part of power supply, or may be added to suppress power supply oscillation.

isn't it common practice to put a 100nF cap between the rails as close to the power pin of an IC as possible? not really common in DIYSB world necessarily but in mass-fabbed stuff?

[Govmnt_Lacky]

Just a tip...

If that is your reference for the design... be skeptical. There have been quite a few schematics from that site that have been proven incorrect when compared to the originals.

[armdnrdy]

There have been quite a few schematics from that site that have been proven incorrect when compared to the originals.

+1

[lars-musik]

 

Just a tip...

If that is your reference for the design... be skeptical. There have been quite a few schematics from that site that have been proven incorrect when compared to the originals.

Yes..
well..
quite...

I admit that as I can't come up with my own circuits I have got to take what I get.

In the end I rely heavily on your support to debug and improve and must say that until now, I have never been dissapointed by you DIYStompboxers!

I guess I'll have a go at this one even if the source is unverified and give you a BIG THANKS in advance!

[lars-musik]

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. 

This is the layout if somebody is interested, the LM1894 I bought here.

The copied schematic without the switching part here

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

         

[PRR]

> Seems like a lot of circuit for noise reduction.

Agree. 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:
http://www.ti.com/product/LM1894/technicaldocuments

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.

[GFR]

https://en.wikipedia.org/wiki/Noise_reduction

According to wikipedia the Philips DNL (that Elektor magazine later published as the project I mentioned) is 1971, unpatented, then National released the DNR in 1981. Dolby B was 1968.

I think at the time the NB-10 was introduced, the Rocktron Hush was very popular (for racks), maybe it was intended as stomp box work-alike.