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

[reinw33]

Just curious why you are bent on transformers; it's been pointed out that they serve little purpose in front an instrumentation amp IC.

To me it's some of the transistors inside the IC that serve little purpose on the back of a balanced input transformer.
It's just what I have now and put together and see how it adds up.

 

[Brian Roth]

@reinw33 OK....fine. Use this and call it a day.

https://www.technicalaudio.com/pdf/...nsformers/Jensen_JE-115K-E_mic_input_xfmr.pdf

Bri

 

[reinw33]

@reinw33 OK....fine. Use this and call it a day.

https://www.technicalaudio.com/pdf/...nsformers/Jensen_JE-115K-E_mic_input_xfmr.pdf

Bri

Thanks.
I ordered input Txs, but because of supply shortage, I keep waiting and waiting and waiting for shipping.
So I end up winding my own Tx before the others ever get here.
But it's finicky stuff to do.

 

[slipperyflax]

Have you made any more progress?

 

[ricardo]

No Tx in, Tx out.

If you want that transformer vibe, I have just the thing for you as 70sPreamp.doc in my MicBuilders Files. You have to join

 

[MidnightArrakis]

Just curious why you are bent on transformers

Just because???.....

/

 

[Barry Farmer]

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)?

Unless you're in a situation where the need for galvanic isolation is absolutely essential, I'd build the 1512 preamp, omit any sort of ironmongery, in or output, and enjoy audio quality that no human ear will ever be able to distinguish from your $10,000 XYZ mic-amp.

 

[Ivan K.]

...For a simple 1512 based preamp (no 48V), check out Austinmics.com, Ribbon Mic Pre. $250. It is an easy build and with the 1512 datasheet in hand, easy to change the amount of gain, or gain steps. All components are thru-hole. If you don't like the servo he uses, there's room for the That capacitor solution. Also, easy to change component values if desired. The That datasheet shows a 48V phantom implementation as well. If you are fussy about the 7815 & 7915 PS, you can substitute lower noise LDOs .

 

[k brown]

...For a simple 1512 based preamp (no 48V), check out Austinmics.com, Ribbon Mic Pre. $250. It is an easy build and with the 1512 datasheet in hand, easy to change the amount of gain, or gain steps. All components are thru-hole. If you don't like the servo he uses, there's room for the That capacitor solution. Also, easy to change component values if desired. The That datasheet shows a 48V phantom implementation as well. If you are fussy about the 7815 & 7915 PS, you can substitute lower noise LDOs .

OP is looking for transformer in and out.

 

[pucho812]

Have you considered using a ina103 preamp chip? I have a design as used by a famous company as inputs for the 16x2 stereo mixers. Aside from the tubes in the stereo bus it’s all preamp chip and ic’s. Anyone interested?

 

[MidnightArrakis]

Have you considered using a ina103 preamp chip? I have a design as used by a famous company as inputs for the 16x2 stereo mixers. Aside from the tubes in the stereo bus it’s all preamp chip and ic’s. Anyone interested?

You might just want to "generically" post this information and see who jumps in as being interested!!!

> Do I understand you correctly that this circuit of yours is an IC-chip input and then tube-based stereo-bus and output? XLR-input connectors?

> Is this circuit also an IC-chip output? Or, is it tube-based with an output-transformer output? XLR-output connectors?

> Does this circuit also contain the filament and B+ power-supply for the tubes?

/

 

[MidnightArrakis]

@reinw33 OK....fine. Use this and call it a day.

https://www.technicalaudio.com/pdf/...nsformers/Jensen_JE-115K-E_mic_input_xfmr.pdf

Bri

Brian: Just FYI when I clicked on the link within your response here, this is what I got:

Account Suspended!​

Please contact our support team for further assistance.

/

 

[Brian Roth]

Brian: Just FYI when I clicked on the link within your response here, this is what I got:

Account Suspended!​

Please contact our support team for further assistance.

/

Hmmmmm....that is(was?) John Klett's website. He's been in the pro audio biz for decades. I hope he's OK.

Bri

 

[pucho812]

You might just want to "generically" post this information and see who jumps in as being interested!!!

> Do I understand you correctly that this circuit of yours is an IC-chip input and then tube-based stereo-bus and output? XLR-input connectors?

> Is this circuit also an IC-chip output? Or, is it tube-based with an output-transformer output? XLR-output connectors?

> Does this circuit also contain the filament and B+ power-supply for the tubes?

/

It’s not my design. But I have schematic. And yes it’s chip front end with tube summing. Tubes run off proper B+ of 250vdc and 12v heaters….
The main bulk of the input is an ina103

 

[cuelist]

It sounds like you're not at all sure about what you want. Is this primarily a DIY / learning project or something else? And for the configuation, you have to start by defining what you want this to be. A clean preamp, a coloured preamp?

As other have pointed out, fitting a transformer ahead of a 'transformerless mic amp chip' is just plain odd. If you want a transformer + THAT1512 (or similar) then look at a 1:1 transformer such as the Neutrik NTM1. Understand that the primary purpose of an input transformer is to bring the low source impedance of the mic up to the optimum source impedance (for lowest voltage noise) of the preamp's first stage. The THAT1512 and others are already designed to provide best noise performance with the native source impedance so no stepping up by the transformer is required. Most probably, even a modest step up, say 1:2, would worsen noise performance as well as worsen headroom.

 

[cuelist]

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.

No, input impedance and optimum source impedance are two entirely different things. Input impedance is the load on the source while optimum source impedance is the source (the mic) impedance that will give you the lowest noise.

 

[mhelin]

Jensen has an 1:1 transformer model JT-MB-CA which is designed for this application, fitting a transformer ahead of a transformerless mic amp (allthough it doesn't make sense for me either). Even the transformer coupled mic preamps aren't fully galvanically decoupled as they share the phantom supply ground and so cannot have the 'ground lift' implemented (except with dynamic mics). The transformer can though improve the CMRR (with THAT1512 at 0 dB gain from 60 to 122 dB, at higher gains less).

https://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-mb-ca.pdf

 

[KrIVIUM2323]

Anyone interested?

It's always interesting to see schematics! Could you post it into technical document section please?
The brand start by an M that's it? Iirc their tube eq use 2604 as input too.

 

[pucho812]

It's always interesting to see schematics! Could you post it into technical document section please?
The brand start by an M that's it? Iirc their tube eq use 2604 as input too.

they do. But I can't post those schematics out of fear.