PT2399 is bad - Page 1
Forum section: electronics / projects

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 11, 2019, 12:43:58 pm
content: Hi, i have these delay ICs : PT2399They mess up the audio at the input, like amplitude modulation.Even if it is not connected it disturbs the audio elsewhere.How van these ( fake chinese ) parts be so bad ?Any clues ?thanks

author: CJay
author_rank: Super Contributor
timestamp: June 11, 2019, 01:28:02 pm
content: The answer is that they aren't, I've used a few of them in repairs and they work fine.They're not HiFi but they're good enough for the purpose (CB radio echo boards)Maybe you have fakes or a problem elsewhere?

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 11, 2019, 01:36:49 pm
content: They are fake for sure, i ordered them in china.They all work good for the rest, its someting you wont notice directly.With feedback it is clearly visible, wihtout feedback there is only once a small offset,it occurs when changing frequency, use pitch modulation on high tones, then the scope shows clearly amplitude modulation on the delay time frequency.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 11, 2019, 03:09:04 pm
content: Quote from: Jan Audio on June 11, 2019, 12:43:58 pmyes i got a clue... the answer is in the question (bracket)..

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 11, 2019, 03:14:49 pm
content: Yes i understand, only how can a part be so bad internal that it ruins the signal elsewhere ?

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 11, 2019, 03:16:15 pm
content: because it is not what you expect it to be... do you have x-ray machine?

author: james_s
author_rank: Super Contributor
timestamp: June 11, 2019, 03:31:13 pm
content: An xray machine won't really help, silicon is virtually transparent to xrays, all you get is an image of the lead frame and bonding wires.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 11, 2019, 04:01:39 pm
content: Quote from: Mechatrommer on June 11, 2019, 03:16:15 pmIt is what i expected, thats why i,m so suspicious to find this.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 11, 2019, 05:14:03 pm
content: Quote from: james_s on June 11, 2019, 03:31:13 pmyou get the idea.... btw i have a bunch of opamps here, they are original as i expect them to be and they are really good. anybody know why they are good?

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 12, 2019, 11:45:52 am
content: I like to show why it is bad :https://youtu.be/mFtYeCCHpnw

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 12, 2019, 02:14:13 pm
content: sounds good to me even though you went nuts at the end. whats not good is your video focus. why your video cam is not good?its an echo processor, not delay processor...http://www.princeton.com.tw/Portals/0/Product/PT2399_1.pdf

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 12, 2019, 02:36:34 pm
content: Yeah the video is fuzzy and the problem is not clear. Is it correct to understand that you buffered the input signal through an external opamp and YET notice perturbation at the input of your opamp? Or is it at the input of the PT2399 and thus at the output of your opamp? The PT2399 would have to be pretty fucked up if this is the latter (loading an opamp's output enough to cause that!)Have you taken a look at the power supplies? They may be the culprit?

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 12, 2019, 02:55:03 pm
content: The scope is at the opamp input that is not in the PT2399, from there it goes to the PT2399 opamp together with the feedback.For the power supply i added a 47uF + 100nF at the PT2399.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 13, 2019, 01:35:32 pm
content: Here is a better video :https://youtu.be/PxMkfbVhBEg

author: Buriedcode
author_rank: Super Contributor
timestamp: June 13, 2019, 01:53:47 pm
content: Maybe I'm missing the point but it *sounds* fine to me. Your source has, what sounds like vibrato, or amplitude modulation anyway, and if you view the echo chips output you will see what looks like amplitude modulation as the repeats are added to the original sound.Perhaps a better test would be to send a sine wave of short specific length into it, with feedback (and low delay time, say 50ms), and capture the output, which sohuld show bursts of your original signal with decreasing amplitude and increasing distortion (after a few repeats this chip will distort the signal, like most echo guitar pedals do).I'm not suggesting the chip isn't "fake" but so far I haven't seen or heard the problem you say you have. That doesn't mean it isn't there, just that your tests dont' convince me.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 13, 2019, 02:45:35 pm
content: Yes, if i was scoping the output signal it looks a bit like that, only this is scoped at the input, should be clean.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 13, 2019, 03:05:19 pm
content: Quote from: Jan Audio on June 13, 2019, 02:45:35 pmright. input. so it has something with the IC input impedance. do you follow schematics as provided by the datasheet? like in the attached pictures? if yes i dont see how it can affect your input signal if your source impedance is lesser than 2Kohm or so. if you can provide schematics and at which point you are probing, then this should be much clearer. i'm trying to help to make you more clearer here.Quote from: Jan Audio on June 13, 2019, 01:35:32 pmstill bad

author: JPortici
author_rank: Super Contributor
timestamp: June 13, 2019, 03:09:48 pm
content: Quote from: Jan Audio on June 11, 2019, 12:43:58 pmQuote from: Jan Audio on June 11, 2019, 01:36:49 pmwhich is funny because last i checked PT is a chinese company

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 13, 2019, 03:21:11 pm
content: Oh, funny.Fake or not i dont care, availability i care.Should i remove the fake notice ?btw : they can still be fake.

author: Buriedcode
author_rank: Super Contributor
timestamp: June 13, 2019, 08:06:39 pm
content: Well, lets put the fake thing aside, and say you have built a circuit using this chip and it isn't doing what you expect it to be doing. This could be either because your expectations are different from what the circuit is supposed to do, or the circuit isn't doing what it is supposed to do.I'm going to add to the requests for a schematic of your setup. A blurry video of a scope means nothing if we don't know exactly what the circuit is, what the input is, and what you hope to achieve.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 13, 2019, 08:19:54 pm
content: Attempted to watch the video.In addition to the previous comment of an out-of-focus video, you should also make a serious attempt to have the oscilloscope properly triggered.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: June 14, 2019, 12:56:08 pm
content: Oh, there is some triggering switch on this scope.I dont know how it works, i bought it for €20,-The circuit is straightforward.I gave up on this PT2399, wont try again.Going to buy SRAM and hook up to this noisey DSPIC33FJ128GP802, will switch audio off to prevent noise when silent.Why is there no modern version of this PT2399 with longer delaytimes and higher samplerate ?If you have better luck with this PT2399, have you scoped the signal that goes in ?Thing is i build a whole synthesizer and added this delay chip, total takes 104 milliamp sofar without LCD.