THAT 1512 micpre noise issue

[timpanic]

Nice and thank you all for these good willing infos and that you all suggest several general things instead of having experience with that THAT1512 circuit. Like suddenly changing r7 even if it´s suggested by the manufacturer and noone ever seems to have a problem with this in a lot of designs. Fyi when I reduced the overall gain of the circuit to around 55db everything is fine and dead quiet.
Only when I want to reach 60 db the ciruit behave that way.
But these general pin1 problem sounds a little like fishing in the dark for me. Unless you had the same project on the bench or built a 1512 pre
it´s not really that helpful. You never know if the chip behaves exactly how it does here even with the things changed.
" running some heavier gauge wire from the ground points at each amp to the main ground." Was the first I did years ago. Didn´t change anything.
I finished hundreds of projects and I am into electronics since a long time so no newbie here,
I know about star grounding and stuff but I also know that a lot of these generell suggestion often does not hit the target at all.
When this all should be true nobody ever would have finished any GSSL ever
I know that you test a micpre with a termination resistor but I can do further more testing the way I want and I know that when I have nothing plugged in and an obvious noise appears at one setting at my metering something is not as supposed to be compared to other micpres I have here.

I use a lorlin switch for the gain with an anti log resistor curve that the last resistor now has 10 ohm instead of 5 ohms which helps a lot and did nothing to any grounding or rail layout yet.
When I gain up the circuit now I have pure silent gain til the last step with a mic plugged in. When I unplugged anything I just have a little hiss at the highest settings. When I did that before I have terrible hiss at the last settings. So maybe the that chip without any servo or addition only is stable til 55db.
The jdk R20 uses the same chip and also only goes til 55db.
So maybe the answer is THAT simple

 

[Cranehazard]

Yes it's probably spurious oscillations. This can also be caused by improper power supply decoupling.

 

[timpanic]

I agree with Matt you need to decouple the negative and positive POWER SUPPLIES of each preamp and maybe even each chip with the stated 20ohm 47uf filter, they may be . Some preamp manufacturers go as far as having seperate +15 -15 regulators for each preamp module they are all fed from a +24 -24 main set of regulators. This also gives you another 90db or so of power supply noise rejection. I have to disagree with everyone who thinks this is a grounding problem. I second that you can't listen to a mic preamp with no load it will always be the noisiest with no load and quietest with the input grounded. As said above, listening test it with 150ohm resistors on the inputs.

talking to each other through the power supply

Exactly what it seems to be. At higher gain settings the 1512 seems to do that.

 

[Cranehazard]

Might just be noisy at high gain settings.

 

[Newmarket]

Nice and thank you all for these good willing infos and that you all suggest several general things instead of having experience with that THAT1512 circuit. Like suddenly changing r7 even if it´s suggested by the manufacturer and noone ever seems to have a problem with this in a lot of designs. Fyi when I reduced the overall gain of the circuit to around 55db everything is fine and dead quiet.
Only when I want to reach 60 db the ciruit behave that way.
But these general pin1 problem sounds a little like fishing in the dark for me. Unless you had the same project on the bench or built a 1512 pre
it´s not really that helpful. You never know if the chip behaves exactly how it does here even with the things changed.
" running some heavier gauge wire from the ground points at each amp to the main ground." Was the first I did years ago. Didn´t change anything.
I finished hundreds of projects and I am into electronics since a long time so no newbie here,
I know about star grounding and stuff but I also know that a lot of these generell suggestion often does not hit the target at all.
When this all should be true nobody ever would have finished any GSSL ever
I know that you test a micpre with a termination resistor but I can do further more testing the way I want and I know that when I have nothing plugged in and an obvious noise appears at one setting at my metering something is not as supposed to be compared to other micpres I have here.

I use a lorlin switch for the gain with an anti log resistor curve that the last resistor now has 10 ohm instead of 5 ohms which helps a lot and did nothing to any grounding or rail layout yet.
When I gain up the circuit now I have pure silent gain til the last step with a mic plugged in. When I unplugged anything I just have a little hiss at the highest settings. When I did that before I have terrible hiss at the last settings. So maybe the that chip without any servo or addition only is stable til 55db.
The jdk R20 uses the same chip and also only goes til 55db.
So maybe the answer is THAT simple

So I'd say
a) ask THAT directly about gain limit wrt stability esp if there's no reference to it in the datasheet or any associated app notes.
b) look at what is actually happening at the output with a 'scope.

 

[timpanic]

Might just be noisy at high gain settings.

Yes. But then again when I only use 2 channels I can crank it up til 60db with the last resistor about 5 ohms and it is/was still very quiet. :/ Damn.
I can try a 20ohm 47uf filter at every 1512 then you suggest?
So 22ohm placed into every rail ( + - 15v) and 47uf to ground near the chip?

Would be nice to have anybody with the same chip who can check out his design because the old pcbgrinder pre threads seem to be dead.

 

[timpanic]

The biggest problem with your board is the lack of a ground plane. Performance will depend a lot on routing, trace width and copper thickness. If a ground plane were used and rails were capacitively coupled to it locally, that greatly reduces 0V resistance and 0V noise. So it's really the 0V trace that is winding it's way up and down all over the place across the entire PCB that is likely at fault.

If you look at consoles, many times you'll see that the 0V is a "bus bar" running the length of the console. This is a thick strip of metal that makes the inductance and resistance really small.

You might be able to hack it to work. Just to prove that what I'm saying is in fact the problem, cut the 0V trace between the last two circuits and tack a 22-ish AWG wire directly to a 0V point in that circuit and then run it back directly to the 0V point on the power supply connector. Meaning bypass the ground trace with a fat wire.

Another thing you could do is find places to tack on 10uF electrolytic caps between the rails and 0V local to each circuit. That might help stablize it.

You could also use 100uF caps at the power entry connector.

But without a ground plane, I'm sorry, but this board is not good.

I don't know what "pcbgrinder" is but there are many instances where people have created and sold boards that people think are good designs and they're just not. Circuits like this tend to be stable until they're not so it might seem ok but with one little difference it all goes to pot.

I only posted the old 4pre pcb layout from pcb grinder because it had the same problem for me years ago
as the same circuit shows now when I combine two of my newly made dual pre boards with the same circuit on it but with a better and much bigger grounding. As mentioned these working great standalone without needing anything changed so far.

It really seems to me the circuit is quite easy to handle with lower gain settings so that, as you wrote, under some circumstances and approach, the issue doesn´t appear and when changed or added things it goes to pot .

Just checked the jdk r20 ( sold by api ) only offers even only 54db of gain with the same chip. Exactly there where I can get a stable circuit with 4 pres going on. Maybe there is more to it.

http://www.jdkaudio.com/r20.html
Also I found exactly the same project here for example:
https://www.radioworld.com/tech-and-gear/products/solid-state-mic-preamp-pt-2
Again only two channels and only 50db of gain. Last resistor there is even a 33 ohm and some gain is added with the transformer.

But here same chip used in a single 500 modul with 66db gain.
https://www.diyrecordingequipment.com/products/cp5-mic-preamp-with-colour
The shortest troubleshot for me now would just be someone who once built this I thought well known circuit and managed to get 4 or more modules with a normal lm317 based psu to work and what gain he achieved. That would be the easiest thing to compare instead of the other way around starting with grounding in general .

 

[ruffrecords]

I agree, it is good practice to have a local charge source to reduce power supply current peaks which, with the inductance of the power supply leads, can cause instability. It is also good practice to bulk decouple the power supplies where they enter the PCB.

Edit: The other possible culprit we have not explored is your power supply. sS it a commercial unit or a home brew one?

Cheers

Ian

 

[timpanic]

Ian. Please build a 1512 micpre and report. I don´t need a basic elecronic schooling now, but thank you. My
Bench PSU is not the problem. I have decouple caps there at the entry of the board as well as I wrote and it didn´t do anything to the problem with higher gain settings.

If you´re so in the know about this micpre I wonder why nobody knows pcbgrinder and the hundreds of threads here about the 1512 mic pre projects. Til now I only have people commenting here without any knowledge about that particular circuit and its behavior with high gain settings.

Like here:
https://groupdiy.com/threads/that-1512-1646-pcb-layout-newbie-alert.55409/
or here:
https://halfshavedyaks.xyz/pcb/thatmic.php
or here:
http://www.fivefish.net/diy/sc1/
Not much difference here also. No intensive filtering going on on this board and Harpo doesn´t had a problem with this in the first place. Maybe I better post in these threads as here it goes along to generell about psu and grouding I am afraid.

 

[Bo Deadly]

It really seems to me the circuit is quite easy to handle with lower gain settings so that, as you wrote, under some circumstances and approach, the issue doesn´t appear and when changed or added things it goes to pot .

That's not quite what I said. Stability issues like you're experiencing are not specific to this particular THAT 1512 circuit. Stability issues are primarily caused by high gain coupled with a non-low impedance references. A ground plane and proper local supply decoupling on each circuit would help with that in your particular case.

But I think your immediate issue is that I don't think you're learning from this experience. You seem to believe that you just have to route traces to match what you see on a schematic. That is simply not the case. Even if you hacked this board by adding a strip of bus wire for 0V and local supply caps to help fix the stability issue, I think you would still have problems with unnecessarily high noise. Making a good layout requires a decent understanding of how currents create electromagnetic fields and how electromagnetic fields create currents (among other things). Most people making PCBs and posting about them or selling them on the Internet do not have a good understanding of this either. So, like most things on the Internet, just because you see a lot of posts about something, doesn't mean that what they're posting about is good or true or a good idea.

 

[MicUlli]

Always the same mess USE GND PLANE!

 

[timpanic]

That's not quite what I said. Stability issues like you're experiencing are not specific to this particular THAT 1512 circuit. Stability issues are primarily caused by high gain coupled with a non-low impedance references. A ground plane and proper local supply decoupling on each circuit would help with that in your particular case.

But I think your immediate issue is that I don't think you're learning from this experience. You seem to believe that you just have to route traces to match what you see on a schematic. That is simply not the case. Even if you hacked this board by adding a strip of bus wire for 0V and local supply caps to help fix the stability issue, I think you would still have problems with unnecessarily high noise. Making a good layout requires a decent understanding of how currents create electromagnetic fields and how electromagnetic fields create currents (among other things). Most people making PCBs and posting about them or selling them on the Internet do not have a good understanding of this either. So, like most things on the Internet, just because you see a lot of posts about something, doesn't mean that what they're posting about is good or true or a good idea.

Nothing new to me. So the layout was indeed faulty as I thought in the first place without a gnd plane or better routing.
I just was confused because the designer of that board once told me he hasn´t any problems with hiss or anything and I saw a lot of 1512 designs with this kind of layout and they don´t report this issue, mostly because they are only two channel versions of that design, which work totally fine for me here already and show no hiss at the same settings.

What did I learn: It seems people believe that other people believe that a lot of people have no good understanding of electromagnetic field and try to route traces to match the schematic except people like Bo so I would be happy to see his units and test them out. Do you have a homepage with your units or do you develop them for a company?

I have another pcb in the making with a gnd plane and four channels on one pcb with extra decoupling caps and direct +/- lines for each amp so I will see how that turns out.

 

[Newmarket]

Nothing new to me. So the layout was indeed faulty as I thought in the first place without a gnd plane or better routing.
I just was confused because the designer of that board once told me he hasn´t any problems with hiss or anything and I saw a lot of 1512 designs with this kind of layout and they don´t report this issue, mostly because they are only two channel versions of that design, which work totally fine for me here already and show no hiss at the same settings.

What did I learn: It seems people believe that other people believe that a lot of people have no good understanding of electromagnetic field and try to route traces to match the schematic except people like Bo so I would be happy to see his units and test them out. Do you have a homepage with your units or do you develop them for a company?

I have another pcb in the making with a gnd plane and four channels on one pcb with extra decoupling caps and direct +/- lines for each amp so I will see how that turns out.

So it was the 0V scheme that was the problem ?
While you were insistent that you had that under control and needed someone to replicate something using exact same device ?

 

[ruffrecords]

Ian. Please build a 1512 micpre and report. I don´t need a basic elecronic schooling now, but thank you. My
Bench PSU is not the problem. I have decouple caps there at the entry of the board as well as I wrote and it didn´t do anything to the problem with higher gain settings.

If you´re so in the know about this micpre I wonder why nobody knows pcbgrinder and the hundreds of threads here about the 1512 mic pre projects. Til now I only have people commenting here without any knowledge about that particular

I would not normally reply to a post like this but you are new here so I will respond. Diagnosing a problem remotely is always very difficult. You have been given lots of suggested reasons why your implementation might be acting the way is and experience shows it is often the bits we have not been told about that turn out to be the culprit - hence my question about the power supply. It does not metter if someone who replies has never built a 1512 based mic pre - basic engineering principles in high gain mic pres are the same not matter what active devices are used and you have been given plenty of good advice in that direction .However, one thing that does come through quite clearly in this thread is your attitude to the people who are trying to help you. To me you come across as somewhat confrontational and that does you no favours in this forum.

Cheers

Ian

 

[MidnightArrakis]

Nothing new to me. So the layout was indeed faulty as I thought in the first place without a gnd plane or better routing.
I just was confused because the designer of that board once told me he hasn´t any problems with hiss or anything and I saw a lot of 1512 designs with this kind of layout and they don´t report this issue, mostly because they are only two channel versions of that design, which work totally fine for me here already and show no hiss at the same settings.

What did I learn: It seems people believe that other people believe that a lot of people have no good understanding of electromagnetic field and try to route traces to match the schematic except people like Bo so I would be happy to see his units and test them out. Do you have a homepage with your units or do you develop them for a company?

I have another pcb in the making with a gnd plane and four channels on one pcb with extra decoupling caps and direct +/- lines for each amp so I will see how that turns out.

Your comments within this thread come across to me as being: -- rather arrogant, confrontational, condescending and personally righteous -- which, as has been already mentioned.....is NOT going to do you any good whatsoever, either now or in the future, of being on this forum!!! Actually, because of the "tone" of your recent comments, I was deciding not to respond back to you anyway, but I caved-in to my better judgement, so here I am.

I do not believe that you quite fully understand what the capabilities are and what the lifelong warehouses of knowledge that are contained within the various members of this forum, Buddy!!! So many of the members within this forum have been designing either "electronic equipment" in general or, "Professional Audio" equipment specifically for much, much longer than you have even been alive!!! So.....it just might behoove you to listen carefully to their comments, ideas and suggestions before you decide to snap back at someone with some condescending and snarky response!!! It is very easy for the members of this forum to "ignore" your requests for help in the future, should you not listen to what they are attempting to relate to you now.

As for the various PCB layouts that you have linked to.....well.....after I have reviewed them myself, I would have to say that they all basically >> SUCK BIG TIME!!! <<, despite who may have designed them. So, what do I know? -- I am merely a "Beginner" involved in the design of PCB's, as I only have over 40-years of direct hands-on industry experience designing PCB's for a variety of electronic companies and organizations that you have probably never heard of like Lockheed-Martin, Northrop-Grumman, NASA and others!!! In addition, to someone such as yourself, you more than likely believe that all of the members on this forum who design PCB's for their projects and make their files available for others on here who use any one of the various -- FREE -- PCB CAD-programs that are available for downloading, is the exact same thing as using a PCB-design program that costs $25,000 per seat. Right??? The PCB-design software that I use here-at-home has cost me several thousands of dollars and is not FREE!!!

Bo Deadly is correct in stating "Making a good layout requires a decent understanding of how currents create electromagnetic fields and how electromagnetic fields create currents", as this statement alone could basically be its own "field of study"!!! When I was designing PCB's within an R&D group at The NASA/Goddard Space Flight Center that was tasked to design and develop a whole new series of signal-processing equipment for use by both all of the Space Shuttle missions and to process the data from The HUBBLE Telescope, all of the PCB Designers within our group were sent to a weeklong course specifically on "Electromagnetic Grounding & Electronic Systems Grounding" that was taught by a well-known college professor.

The point being.....just because "some guy" has designed a mic-preamp PCB with a couple of IC chips on it and they haven't had any known issues while using it.....they could actually be having issues with their PCB that > THEY ARE TOTALLY UNAWARE OF < because they lack either the knowledge and/or the equipment to even know how to find out if there ARE any issues!!! Be warned.

So.....similar to what Ian had mentioned about "would not normally respond to a post like this".....how and what you wrote back to the other members within this thread just -- PISSED ME OFF -- enough, I felt that I had to throw in my 2-cents worth!!!

So....."Calm Down".....take a deep breath and >> LISTEN << to what the other members here are trying to help you with, OK??? You will attract a lot more "friends" here with some -- HONEY -- than you ever will with your -- VINEGAR -- !!! Get it???

/

 

[Matt Syson]

{I just was confused because the designer of that board once told me he hasn´t any problems with hiss or anything and I saw a lot of 1512 designs with this kind of layout}
This sentence reveals quite a lot in what it doesn't say, as what it does. Designing something is only one aspect. Testing it in real world for full performance under all likely scenarios is something else.
Having been testing large mixing desks for 45 years for several manufacturers and with results cross checked by major broadcasters 'stability' tests were just one aspect. Having 36 channels wound up to full gain with max boost on EQ sections is a pretty harsh test and way beyond a one or two channel toy. Yes the 'white noise' (hiss) tends to be around 0dBu (0VU) sort of level but it has to be free of hum and discernible tones (no oscillations). I had to make these checks because the commissioning engineers of the broadcasters would also give it a check afterwards. 24 channels of ADAT machines make more noise (and whistles) than almost any half decent analogue desk set for 24 channels summed by the way. That Corp have been making chips for many years and they would not be foolish enough to make the claims for their chips if the performance is not readily achievable by users. When super critical specificatioons are needed the chip makers offer tried and tested PCB layouts and give guidance on grounding, component types and positions etc. That PCB layout (shown earlier) is simply a mess.

 

[Newmarket]

Your comments within this thread come across to me as being: -- rather arrogant, confrontational, condescending and personally righteous -- which, as has been already mentioned.....is NOT going to do you any good whatsoever, either now or in the future, of being on this forum!!! Actually, because of the "tone" of your recent comments, I was deciding not to respond back to you anyway, but I caved-in to my better judgement, so here I am.

I do not believe that you quite fully understand what the capabilities are and what the lifelong warehouses of knowledge that are contained within the various members of this forum, Buddy!!! So many of the members within this forum have been designing either "electronic equipment" in general or, "Professional Audio" equipment specifically for much, much longer than you have even been alive!!! So.....it just might behoove you to listen carefully to their comments, ideas and suggestions before you decide to snap back at someone with some condescending and snarky response!!! It is very easy for the members of this forum to "ignore" your requests for help in the future, should you not listen to what they are attempting to relate to you now.

As for the various PCB layouts that you have linked to.....well.....after I have reviewed them myself, I would have to say that they all basically >> SUCK BIG TIME!!! <<, despite who may have designed them. So, what do I know? -- I am merely a "Beginner" involved in the design of PCB's, as I only have over 40-years of direct hands-on industry experience designing PCB's for a variety of electronic companies and organizations that you have probably never heard of like Lockheed-Martin, Northrop-Grumman, NASA and others!!! In addition, to someone such as yourself, you more than likely believe that all of the members on this forum who design PCB's for their projects and make their files available for others on here who use any one of the various -- FREE -- PCB CAD-programs that are available for downloading, is the exact same thing as using a PCB-design program that costs $25,000 per seat. Right??? The PCB-design software that I use here-at-home has cost me several thousands of dollars and is not FREE!!!

Bo Deadly is correct in stating "Making a good layout requires a decent understanding of how currents create electromagnetic fields and how electromagnetic fields create currents", as this statement alone could basically be its own "field of study"!!! When I was designing PCB's within an R&D group at The NASA/Goddard Space Flight Center that was tasked to design and develop a whole new series of signal-processing equipment for use by both all of the Space Shuttle missions and to process the data from The HUBBLE Telescope, all of the PCB Designers within our group were sent to a weeklong course specifically on "Electromagnetic Grounding & Electronic Systems Grounding" that was taught by a well-known college professor.

The point being.....just because "some guy" has designed a mic-preamp PCB with a couple of IC chips on it and they haven't had any known issues while using it.....they could actually be having issues with their PCB that > THEY ARE TOTALLY UNAWARE OF < because they lack either the knowledge and/or the equipment to even know how to find out if there ARE any issues!!! Be warned.

So.....similar to what Ian had mentioned about "would not normally respond to a post like this".....how and what you wrote back to the other members within this thread just -- PISSED ME OFF -- enough, I felt that I had to throw in my 2-cents worth!!!

So....."Calm Down".....take a deep breath and >> LISTEN << to what the other members here are trying to help you with, OK??? You will attract a lot more "friends" here with some -- HONEY -- than you ever will with your -- VINEGAR -- !!! Get it???

/

tbh whilst I share your criticism of the the OP's attitude here - I'll still say CALM DOWN in your use of shouting in CAPITALS (and yes I do know what I did there). Additionally, there's really no need to mention your previous employers / customers in every post. This isn't LinkedIn
And I don't believe that your comments wrt ECAD systems are particularly valid. It seems that many people here produce high quality via KiCad etc. Although it's def not my preference. It's all a case of cost Vs learning curve Vs complexity.
Cheers.

 

[timpanic]

So it was the 0V scheme that was the problem ?
While you were insistent that you had that under control and needed someone to replicate something using exact same device ?

No. I just reduced the gain range of my two two-channel boards and they are fine and quiet now and still perform
much better than the fmr rnp or a mackie board for example, which also produced nice music with unusable 60db gain setting.
I will try it out with my next design if I get more channels with this chip quiter with more gain.
I remember reading in one thread about someone who built a 1512 and also had noise problems with his
design so I was surprised that my two channel verison performed very well from the start.
It would have just been nice to have someone who built a multichannel version of that 1512 design, because there are a lot of similar designs out there and could have reported about this phenomena. Maybe I ask them directly.

But this all went into this boomer yelling at the clouds forum **** even if I am a boomer myself, with his own house, career, band, wife and two happy and healthy kids who now must hear that their father has no future :/ glad I already had a future and made it before my cringy downfall at groupdiy about lousy grounding from someone elses pcb design he made with god intentions and maybe still recording music with it even with a little hiss and without any pernission of the jazz and NASA electronic police who never tried it out but destroys it faster than electric current flows, For sure with good intention but also with a very arrogant high nose attitude where everybody else who has a question is a silly student with no clue. Not everybody needs to fly to the moon with his soldering iron.

Let´s leave it at that. I won´t bother anybody anymore.

 

[Matt Syson]

Yet again Timpanic has failed to understand. Using the expressions 'fine and quiet' are a million miles from 'I have tested my design using industry recognised procedures and can now confirm that my implementation, using the specified chips (whatever they may be) conforms to the standard that is expected by the chip's manufacturer. failure to read and understand all available documenbtation about the components (chips in this case) and then comply with the various constraints. The 50 Picofarad 'limit' on the output of many chips is a common mistake as is many attempts to make 'your' piece of gear super wideband. DC to MegaHz for a mic preamp is simply asking for trouble unless you have made very careful the whole design can manage to do this and would be happy with modulated RF being applied via the mic input connector. As mobile phones work in the Microwave frequency bands, any conductor of around 6 inches or so becomes an aerial so many aspects of 'your' design have to allow for this possible intrusion. Of course you can't hear (and would probably struggle to measure) the RF carrier of mobiles for example but depending on the modulation you CAN receive assorted chirps which will be amplified/demodulated. Many years ago I had to 'RF proof' a mixing desk against having a 2 watt 'walkie Talkie' laid on it's control surface (on top of the knobs). It required relaying all the circuit boards that others had designed. star point 'grounding' is a fantastic concept but difficult to achieve in the real world where everything has a physical size so your single 'point' has to become a network of interconnected points.

 

[MidnightArrakis]

tbh whilst I share your criticism of the the OP's attitude here - I'll still say CALM DOWN in your use of shouting in CAPITALS (and yes I do know what I did there). Additionally, there's really no need to mention your previous employers / customers in every post. This isn't LinkedIn
And I don't believe that your comments wrt ECAD systems are particularly valid. It seems that many people here produce high quality via KiCad etc. Although it's def not my preference. It's all a case of cost Vs learning curve Vs complexity.
Cheers.

The use of CAPITAL LETTERS and BOLD and Italicized words and phrases can also be used purely as an "EMPHASIS" in meaning and/or "tone" of conveyance. The use of CAPITAL LETTERS does -- NOT -- necessarily mean that one is shouting!!! Remember..... when we use our speech, we can convey so much more "information" through tonal inflection than we are able to by simply printing letters and words on paper or a computer monitor.

ENOUGH SAID!!!

/