TNT InDiscreet phono preamp, anyone?

[davidsrsb]

The designer reported that he found no advantage to using batteries and switched to mains powered

 

[vinylkid58]

I am considering a TNT InDiscreet rather than a kit, but a Pass Pearl seems pretty interesting as well. (OK there are lots of others including VSPS, and some others from TNT)

Anyone have experience w/the InDiscreet directly? What about the Pearl?

Hey Stew, did you build this or something else? After all these years I'm still running my Pearl.

jeff

 

[zintolo]

Hi all,

I would like to build it as a winter project, and I would like to know if nowadays there are better choices for the components (EG less noise), and if there are possible improvements on the circuit and the power supply as well.

Thank you in advance,
Kind Regards

 

[el156se]

@zintolo: the design is very well made already. Use a steel case (phono pre are very sensitive to EMF), and put the mains transformer as far as you can from the phono PCB, to avoid any magnetic induced hum. A good solution could be two separate chassis for phono and power supply, to avoid transformer induced noise. After you succeed, you could look for a lowest noise power supply. If you do not succeed, looking for 'better' components is in vain, as you could not discern what is better in a 'bubble of mains noise' 🙂

 

[zintolo]

Thank you for your reply el156se, indeed my request was related to the PS as well, as I guess there are easier solutions nowadays to have a silent PS without 8 minutes time constants. So from your point of view the priorities are: first layout second the PS.

I was thinking about a single stainless steel chassis with toroidal transformer and an internal separation plate between PS and signal pcb, but what can be done on the PS side to improve it with actual components?

 

[el156se]

@zintolo: I would kindly suggest, from my humble experience, to make a layout test on a wooden board, regarding the distance TRAFO to PCB and the 3D orientation of the transformer before to order/build the case! You could use headphones + amp to monitor the noise, and the input shorted when making a noise test, to find the proper position of the toroidal transformer related to phono PCB. This phono stage has a very small power consumed from the transformer, so the transformer will not radiate too much around, but you must be sure about that. You could try to screen later the toroidal with supermalloy sheet wrapped around the trafo in case of a given small case, but 'distance' is cheaper than permalloy/supermalloy sheets, as well as testing before to buy/build a case!! During this noise testing, a thin copper makeshift case, to avoid non-magnetic induced noise, could be useful around the Phono PCB (like a farady cage, to avoid electric induced noise - just for the testing pahse).

 

[zintolo]

Thanks again el156se,

I post here the link to the preamp, just to give a reference on what I'm talking about. Tere aren't any on this thread:
inDiscreet Phono Pre-amplifier [English]

this is the schematic:
https://www.tnt-audio.com/jpeg/indiscreet1.jpg

and this the power supply, the part that I think can be obtimized with modern components:
https://www.tnt-audio.com/jpeg/indiscreet3.jpg

 

[osscar]

Good luck with your project!
I had built one some time ago(original PCB, BC109 from CDIL) - no noise, works well. it wasn't my basic RIAA preamp, so I powered it from 9V batteries.
Sounds similar to NJFET RIAA, according to my observations.

 

[BDP]

Are there distortion measurements that someone has done on this phono preamp?
I acquired and assembled some boards and did a bench measurement. At 1khz 1 volt output I'm seeing 0.5%.

Also had some motor boating that was resolved by adding some resistance between the power supply and the amplifier stage. If you have some expertise in this area I would like to hear your thoughts? This is why I would like a distortion reference for comparison.

I'm also working on a mini pearl to compare.

BDP