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.