THAT1512 Pre. DIY, reasonable replacement for Cheap Preamp Art?

[reinw33]

Hello everyone, (Tldr; in last line)

my external Preamp is broken, and I am wating for a replacement Zener Diode part to ship.

I've been considering to DIY a Preamp based on a THAT1512 with a transformer input and a line output stage of 600Ω.

I just don't know if it's worth it to build a THAT1512 based pre, based on performance purely, they say it costs 5$, actually even if it cost 150€ for pro audio production in terms of using it later on mainly as a mono preamp for voice, I would build it, or is it merely a learning experience in electronic projects that later on would get replaced by pro audio gear?, just like the phrase: "He who buys cheap, buys twice!"

I've been mostly repairing things in electronics so far, rather than designing or building - not so much, really simple DIY Kits and perhaps here and there other simple things, repairing Digitizers, Signalgenerators, Oscilloscope, not designing.

But I am confident, that I can build a Transformer input Preamp, based on That1512 and a suitable Line output, and even the transformer itself given enough time for winding and design testing, I have test gear for the hypothetical project too, like an oscilloscope, etc. etc..,


Just hypothetically, I would spend 100€ - 150€ maximum! for THAT1512 Preamp, and just buy an OEP/CineMag/Lundahl/Monacor/Etc etc. transformer, to make it a simple and fast project,


But Is this project a thing or reasonable in 2024 when it comes to pro audio?

I need an external Preamp, at least as a backup, I don't want to commit to this THAT1512 DIY project, without putting the Idea outthere first and perhaps listen to you and some shootouts if available.

I know my past external tube preamp the art mp studio is far from pro audio, and does have significant internal shortcomings, like carbon resistors and unmatched components, and Caps and too many of them etc...and there and should really be redesigned if anything and avoided to be modded too much.


Here is my dilemma, we hear that ICs have outperformed discrete circuits, but I would need a fancy 48V power supply, at least one, for the phantom power, then the ICs in the next stage would need sth. like ±20VAC dual bias,

One would have to basically use two power supplies, one for the phantom power (perhaps 5x 9V batteries that drop in V) and one for the ICs in the amplifying stage.
Or just one transformer with 48V center tapped, 24-0V and 0-24V, and use a voltage divider of some sort to supply dual ±20VAC,
but I can expect/see problems with that approach.

So I don't like the Idea of this project, I I've been thinking about building my own gear for quite some time,
the audio gear that we have available today afaik suffies itself with 1 PSU.

Regardless, assuming we would take care of the PSU issue.

On the other hand, I do build custom XLR cable connectors and a passive box is one of my ongoing prjects,
so I thought why not ask the community, possibly waste multiple small amounts of money on non-excellent projects or save up money for a powerfull and reliable pro audio Preamp, that costs much much more and perhaps has little bit more internal noise?

While I'm waiting, and even before having started to reapair budget gear like my art mp studio, I was searching for decent pro audio gear, and it it's unavoidable - pretty much - on the web not to stumble upon DIY projects.

TLDR:
So, what do you think about THAT1512/INA217/SSM2019 based preamps in general?, or do you have any specific experience with them in pro audio recordings? I need an external preamp for pro audio, would you or the groupdiy community here recommend this type of project (assuming it would be finished successfully) to someone able to build to build it, in order to use it for pro audio recordings compared to say (as a substitute) to todays modern professionally engineered mic preamps from reputable companies?
At last, think of the good preamp that you use or would use, and you give it a rating of 0 bad -10 best, and now you give the DIY preamp That1512 a rating, what would your number be for your personal pro audio needs or experience (talking about proper enclosure preamp with PSU)?

 

[drtechno]

Hello everyone, (Tldr; in last line)

my external Preamp is broken, and I am wating for a replacement Zener Diode part to ship.

I've been considering to DIY a Preamp based on a THAT1512 with a transformer input and a line output stage of 600Ω.

I just don't know if it's worth it to build a THAT1512 based pre, based on performance purely, they say it costs 5$, actually even if it cost 150€ for pro audio production in terms of using it later on mainly as a mono preamp for voice, I would build it, or is it merely a learning experience in electronic projects that later on would get replaced by pro audio gear?, just like the phrase: "He who buys cheap, buys twice!"

I've been mostly repairing things in electronics so far, rather than designing or building - not so much, really simple DIY Kits and perhaps here and there other simple things, repairing Digitizers, Signalgenerators, Oscilloscope, not designing.

But I am confident, that I can build a Transformer input Preamp, based on That1512 and a suitable Line output, and even the transformer itself given enough time for winding and design testing, I have test gear for the hypothetical project too, like an oscilloscope, etc. etc..,


Just hypothetically, I would spend 100€ - 150€ maximum! for THAT1512 Preamp, and just buy an OEP/CineMag/Lundahl/Monacor/Etc etc. transformer, to make it a simple and fast project,


But Is this project a thing or reasonable in 2024 when it comes to pro audio?

I need an external Preamp, at least as a backup, I don't want to commit to this THAT1512 DIY project, without putting the Idea outthere first and perhaps listen to you and some shootouts if available.

I know my past external tube preamp the art mp studio is far from pro audio, and does have significant internal shortcomings, like carbon resistors and unmatched components, and Caps and too many of them etc...and there and should really be redesigned if anything and avoided to be modded too much.


Here is my dilemma, we hear that ICs have outperformed discrete circuits, but I would need a fancy 48V power supply, at least one, for the phantom power, then the ICs in the next stage would need sth. like ±20VAC dual bias,

One would have to basically use two power supplies, one for the phantom power (perhaps 5x 9V batteries that drop in V) and one for the ICs in the amplifying stage.
Or just one transformer with 48V center tapped, 24-0V and 0-24V, and use a voltage divider of some sort to supply dual ±20VAC,
but I can expect/see problems with that approach.

So I don't like the Idea of this project, I I've been thinking about building my own gear for quite some time,
the audio gear that we have available today afaik suffies itself with 1 PSU.

Regardless, assuming we would take care of the PSU issue.

On the other hand, I do build custom XLR cable connectors and a passive box is one of my ongoing prjects,
so I thought why not ask the community, possibly waste multiple small amounts of money on non-excellent projects or save up money for a powerfull and reliable pro audio Preamp, that costs much much more and perhaps has little bit more internal noise?

While I'm waiting, and even before having started to reapair budget gear like my art mp studio, I was searching for decent pro audio gear, and it it's unavoidable - pretty much - on the web not to stumble upon DIY projects.

TLDR:
So, what do you think about THAT1512/INA217/SSM2019 based preamps in general?, or do you have any specific experience with them in pro audio recordings? I need an external preamp for pro audio, would you or the groupdiy community here recommend this type of project (assuming it would be finished successfully) to someone able to build to build it, in order to use it for pro audio recordings compared to say (as a substitute) to todays modern professionally engineered mic preamps from reputable companies?
At last, think of the good preamp that you use or would use, and you give it a rating of 0 bad -10 best, and now you give the DIY preamp That1512 a rating, what would your number be for your personal pro audio needs or experience (talking about proper enclosure preamp with PSU)?

So why a 600 ohm output ? Nothing really runs at that impedance anymore.
I use a mic transformer for the input: Jensen Jt-115K-E and for the output Carnhill vtb9071 Primary wired in parallel, output select-able paralleled or series secondary. Because the two common impedance are 2.5K and 10K into interfaces. 600 ohm is a dead animal unless you are connecting to 600 ohm transformer inputs.

 

[drtechno]

you could get away with a T-6110K-B connected backwards for 600 and 2.2K for condenser mic only preamp, and switch it completely out to dc coupling in dynamic mic mode.
The one I make I use dynamic mics and lowZ vintage condensers (U47, 251ELM etc) which I don't use phantom.
On interfaces I modify them to switch out the caps on the phantom. And have dynamic mics dc coupled and capacitor coupled with phantom. Which is a solution without going to transformers.

 

[Voyager10]

I'm not sure that a transformer is the right thing to go with a THAT1512.

Looking at the data sheet (https://www.thatcorp.com/datashts/1500data.pdf) the best noise performance is with a low impedance source. They give figures with 150 and 200 ohm souces. Above 500 ohms the input noise current will be dominant.

An input transformer is useful to match a low-impedance source to an amplifier input which performs best with a higher impedance. A typical 1:2 (turns ratio) transformer has a 1:4 impedance ratio, so a 300 ohm mic will look like 1.2k at the amp input.


As a suggestion, JLM Audio do reasonably priced mic pre kits which allow scope for customisation (e.g. fancy op amps, if that's your bag).

• Transformerless: JLM Audio Shop
• Transformer input: JLM Audio Shop
• Basic transformer input: JLM Audio Shop

All these will run off a single supply rail so you can just use a wall-wart for power, including phantom power. I've built a couple of the second ('BA') ones and they work well.

 

[ruffrecords]

So why a 600 ohm output ? Nothing really runs at that impedance anymore.

It is not clear to me what is actually meant by a 600 ohm output. Does it mean an output capable of driving a 600 ohm load, or does it mean its output impedance is 600 ohms or does it mean something else entirely?

Whatever it means, what you need is a low driving source impedance in order to minimize any HF loss/phase shift when driving cables. Most op amps have near zero output impedance but they do need series build out resistors so the cable capacitance does not cause instability due to the phenomenal open loop gain which often means their source impedance is typically 150 ohms.

Cheers

Ian

 

[drtechno]

It is not clear to me what is actually meant by a 600 ohm output. Does it mean an output capable of driving a 600 ohm load, or does it mean its output impedance is 600 ohms or does it mean something else entirely?

Whatever it means, what you need is a low driving source impedance in order to minimize any HF loss/phase shift when driving cables. Most op amps have near zero output impedance but they do need series build out resistors so the cable capacitance does not cause instability due to the phenomenal open loop gain which often means their source impedance is typically 150 ohms.

Cheers

Ian

600 ohm convention is transformer coupled line level and at both ends.
Interfaces are 2.5K and 10K balanced in.

 

[drtechno]

I'm not sure that a transformer is the right thing to go with a THAT1512.

Looking at the data sheet (https://www.thatcorp.com/datashts/1500data.pdf) the best noise performance is with a low impedance source. They give figures with 150 and 200 ohm souces. Above 500 ohms the input noise current will be dominant.

If you will look they will give you the reference input impedance rating which is 15K Which the Jensen transformer works. An input transformer from an API312 works fine also because I've tried it with good results.

Now when its set up as a DC coupled input, I set up the input to be 200 ohms input impedance otherwise its noisy.

 

[k brown]

Little to be gained from putting an instrumentation amp after an input transformer. All that's needed is a simple unbalanced gain circuit, then to a balanced driver or output trafo.

 

[ricardo]

You don't need an input transformer with THAT 1512. It is designed to act as an input transformer and gives really good results as is. Download the latest Datasheets and Application Notes and build them EXACTLY as specified.

Use an Impedance Balanced Output. 22R from the 1512 and 22R to earth.

You can use a single mains transformer to give the +/- 18V or so for the 1512 and a voltage doubler (tripler?) for P48

This is practically how ALL modern preamps are done.

 

[reinw33]

You don't need an input transformer with THAT 1512. It is designed to act as an input transformer and gives really good results as is. Download the latest Datasheets and Application Notes and build them EXACTLY as specified.

Use an Impedance Balanced Output. 22R from the 1512 and 22R to earth.

You can use a single mains transformer to give the +/- 18V or so for the 1512 and a voltage doubler (tripler?) for P48

This is practically how ALL modern preamps are done.

Hi ricardo, thanks for your reply.
For the supply of THAT1512 into THAT 1646 it's LM3XX IC's +-18V coming from the CT P48 transformer.
I wanted to open up my preamp usb interface and look into it, once I have when I have a backup, to see how they do the P48.
A voltage doubler is a very crude way of doing it in my opinion.
Frankly, I'm sick and tired of my usb interface and how it sounds.

Yes, the THAT1512 is designed for a SE input and output.
22R in parallel, I don't see much of a point in doing that except for perhaps better noise performance.
That 1646 has an input impedance of a few Kohms and output drive Z of 600 ohms with sth. an excess of +20dbu.
It doesn't hurt to have transformers tho, I have ordered two mic input and am still waiting for the FEDEX package.
The un/balanced line output Tx I probably have to build myself anyways, or I might use a cap for the first v1.0

 

[ricardo]

A voltage doubler is a very crude way of doing it in my opinion.

The question you should be asking is "does it do the job with low noise bla bla?" Simple & crude is good if it does the job.

Yes, the THAT1512 is designed for a SE input and output.

Actually Balanced i/p and SE output.

22R in parallel, I don't see much of a point in doing that except for perhaps better noise performance.

Do you really think 1646 has less THD, bla bla than 2 x 22R MO resistors? Do you need to drive 600R in excess of +20dBu?

It doesn't hurt to have transformers tho, I have ordered two mic input and am still waiting for the FEDEX package.

Actually it DOES. Your transformers will degrade noise, THD bla bla of the 1512. Correct transformer to improve performance of 1512/10 is available from Ye Olde Unobtainium Shoppe.

 

[reinw33]

"...Correct transformer to improve performance of 1512/10 is available from Ye Olde Unobtainium Shoppe."

Ha, that was funny at the end!
There shouldn't be an interstage Tx between those two opamps.
To be perfectly frank with you, at that time of your writing, I didn't look into the datasheet of 1512/10.
Nor opamps that need a 22R in general.
So I was ignorant about that.
They do specify 22u caps, but for balanced input for that 1512. They could be bigger though ofcourse.
Therefore I thought you confused 22u with 22R?
Do you know from experience a THAT1512 really really really needs 22R balanced output, specifically for driving a THAT1646 at close distance without problems across the frequency spectrum?
If so fine, yet I haven't had any experience doing that, because I'm still waiting for many parts to make at least a breadboards prototype.
But much has arrived already.
Appreciate your points ricardo.

 

[nielsk]

There are several consoles people "rave" about that use a simple transformer-less 1512 pre-amp
I love esoteric gear as much as the next studio rat, but the truth is a good engineer can make a record using this pre-amp
You can get a tiny loaded PCB that a gain pot goes onto and doubles as the mounting for a few $ of evilbay
This is what I use on my bench set-up as a test preamp, going into a balanced line driver chip
There is probably a 1606/46 little board out there as well
or just build it on perf board

 

[k brown]

Ha, that was funny at the end!
There shouldn't be an interstage Tx between those two opamps.
To be perfectly frank with you, at that time of your writing, I didn't look into the datasheet of 1512/10.
Nor opamps that need a 22R in general.
So I was ignorant about that.
They do specify 22u caps, but for balanced input for that 1512. They could be bigger though ofcourse.
Therefore I thought you confused 22u with 22R?
Do you know from experience a THAT1512 really really really needs 22R balanced output, specifically for driving a THAT1646 at close distance without problems across the frequency spectrum?
If so fine, yet I haven't had any experience doing that, because I'm still waiting for many parts to make at least a breadboards prototype.
But much has arrived already.
Appreciate your points ricardo.

Just to be "that guy" - 1510/1512, as well as INA103/163, SSM2017/2019, etc, etc, are/were not op amps. They are instrumentation amplifiers primarily designed for use as audio preamplifiers.

Op amps are general-purpose 'building blocks' that can used many different ways.

 

[ricardo]

They do specify 22u caps, but for balanced input for that 1512. They could be bigger though ofcourse.

Do NOT use bigger caps than the 22u specified at the input of 1512. Use the EXACT components & circuit in the datasheet & latest THAT application notes.

Therefore I thought you confused 22u with 22R?
Do you know from experience a THAT1512 really really really needs 22R balanced output, specifically for driving a THAT1646 at close distance without problems across the frequency spectrum?

The 22R from output of 1512 and the 22R to ground REPLACES the 1646 completely. It's called an Impedance Balanced Output. This will have BETTER performance in all respects unless you need to drive 600R to more than 20dBU.

If you design and have specially made a huge $$$ transformer for the INPUT of 1512, you may get 0.3dB better S/N ... if you are a true transformer guru (otherwise you will get worse S/N). LF performance & THD, though will always be slightly worse than 1512 without an INPUT transformer.

All from experience.

 

[k brown]

OP: What does something like the M-Audio Profire 610 not provide, that you're in need of? In standalone mode, it's two 1510-based preamps connected directly to balanced line outs. The pres are simultaneously sent to a very respectable A/D converter with SPDIF out. An added bonus is, it will run on battery. https://www.ebay.com/itm/145807226693?itmmeta=01J1E7DNP0F765WPXEPQZYDCYZ&hash=item21f2c9b745:g:yPMAAOSwgMJmWmIq&itmprp=enc:AQAJAAAAwAU5zL0zw6UMHdzmnVyE55UVsfzOdUQeQSiBfy6Y6H9dFDKboyDBLQj3xuc2GLkcLBeRMhEy7nOWL95rXLUCxFwpDqvp1YNwbilBhu1Kp0lKvV0wzuLw9SR3Y5/Jf1yN0xcfcaXjnrCPmnNIVtN5HfbVX/Um0MmeuPsp/etFhBc/P56Y9g5nbp4Wo7nok3itz+Mkpm0qUsku4cHv/3vX3/IARHDcVHqeVrYBposnCI8dbqSqOW4w/4A7/71gAlskhQ==|tkp:Bk9SR4zbtseLZA

Connected to a computer, it does a lot more, of course.

Or, do you just want to do DIY for the heck of it? (nothing wrong with that, of course)