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 Post subject: 2n5484 phono preamp
PostPosted: 29 Dec 2016, 03:19 
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Joined: 29 Dec 2016, 03:06
Posts: 18
Hi, I'm new on the forum and this is my first post.

I've been trying to design a simple phono preamp based on jfets, and I've come to this design

Imageimag

The gain and THD seem to be quite right for such a simple circuit

Imagesubefotos

Imagesubir fotos a internet

Fourier components of V(out)
DC component:-0.00435251

Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 5.272e-01 1.000e+00 -49.32° 0.00°
2 2.000e+03 1.399e-05 2.653e-05 -173.02° -123.69°
3 3.000e+03 6.353e-06 1.205e-05 -167.83° -118.51°
4 4.000e+03 3.297e-06 6.255e-06 -179.91° -130.58°
5 5.000e+03 2.640e-06 5.008e-06 -179.88° -130.55°
6 6.000e+03 2.200e-06 4.173e-06 -179.87° -130.55°
7 7.000e+03 1.886e-06 3.577e-06 -179.87° -130.54°
8 8.000e+03 1.650e-06 3.129e-06 -179.87° -130.55°
9 9.000e+03 1.466e-06 2.781e-06 -179.88° -130.56°
10 1.000e+04 1.319e-06 2.503e-06 -179.91° -130.58°
Total Harmonic Distortion: 0.003110%(0.003252%)

Here are the AC and noise analysis:

Imagesube imagenes

Imagesubir foto

Do you think is it worth trying?

Thank you


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 Post subject: Re: 2n5484 phono preamp
PostPosted: 29 Dec 2016, 18:03 
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Joined: 04 Jun 2008, 20:59
Posts: 3646
Location: Arizona, USA
Hi, Welcome to the forum. All projects IMO are worth doing...even if they don't work, you generally learn something. In the early days I did a lot of learning :D . I don't see anything obviously wrong with the schematic. I believe for a first project though I would try something that someone else has already perfected. SIMs don't always tell you how something will actually work and if is just off a few percent the sound could be rather marginal. For a first project that might be difficult to diagnose and fix. It couild end up as a huge source of frustration. But ...if you have an open mind and positive attitude it is worth trying. At worst you will learn how to build the next one.

Good listening
Bruce

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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 00:35 
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Joined: 26 Dec 2016, 03:46
Posts: 38
Location: Bayarea
Hate to burst your bubble, I just tested my first design of power amp just two days ago, I ran my FFT test using QuantAsylum QA400 and I got -98dB on the 3rd harmonic at 15V peak output driving 4ohm load and total THD of 0.0012%. Distortion is a lot lower if either I lower the output to 5V peak or driving 8ohm load. My 2nd harmonic is lower than yours. Power amp is always the bottle neck of the whole system in distortion. You should get a lot better result on a normal preamp with a good opamp.

If you get result with simulation like this, chances are it will be worst in real circuit. I am not telling you it's not worth a try, just to let you be aware. I would go with opamp design using OPA2604, OPA2134 or LM4562. They have distortion way lower than this, you are talking about 0.0003% or lower, which is 10 times better. Sorry.

http://www.ti.com/lit/ds/symlink/opa2604.pdf

http://www.ti.com/lit/ds/symlink/lm4562.pdf


Last edited by Yungman on 30 Dec 2016, 00:47, edited 1 time in total.

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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 00:47 
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Joined: 08 Aug 2009, 03:11
Posts: 2208
Location: Chilliwack, BC
Distortion isn't the end-all-and-be-all here.

The circuit in the OP is similar to the Boozehound one, which has been used in a few commercial designs. It's a really good one when the right components are chosen.

We have yet to have a phono stage shootout at an audio festival or in the store where an opamp phono stage, weather $200 or $2K, has won over a decent discrete ;)

We listen with our ears, not test equipment (thankfully) :D

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 00:58 
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Joined: 26 Dec 2016, 03:46
Posts: 38
Location: Bayarea
It's easy to try the opamp. OP's circuit is two stages with equalization in the middle, sub with one of the good opamp I linked and be the judge.


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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 02:44 
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Joined: 29 Dec 2016, 03:06
Posts: 18
First of all, thank you for your answers.

I forgot to mention that this is not my first project. I have already built two opamp based phono preamps: one with passive equalization, another one with split equalization (half passive, half active). Both sound very good, at least as good as my Onkyo built-in preamp.

But in an opamp design you lose half the fun: the circuit is already made by another person. The purpose in this project is to learn and to stretch my mind (and have a good time, of course), so I think I'm going to try it!

I can get some 2sk117 jfet from Germany. They are low noise audio transistors, similar to 2sk170 but with lower gain, maybe good for this circuit. I let you know.

Again, thanks.


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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 04:28 
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Joined: 29 Dec 2016, 03:06
Posts: 18
Curious: in simulations the 2n5484 has lower distortion than the 2sk117. Sadly less gain too...


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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 04:33 
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Joined: 26 Dec 2016, 03:46
Posts: 38
Location: Bayarea
JordiMB wrote:
First of all, thank you for your answers.

I forgot to mention that this is not my first project. I have already built two opamp based phono preamps: one with passive equalization, another one with split equalization (half passive, half active). Both sound very good, at least as good as my Onkyo built-in preamp.

But in an opamp design you lose half the fun: the circuit is already made by another person. The purpose in this project is to learn and to stretch my mind (and have a good time, of course), so I think I'm going to try it!

I can get some 2sk117 jfet from Germany. They are low noise audio transistors, similar to 2sk170 but with lower gain, maybe good for this circuit. I let you know.

Again, thanks.


I see, if you already did two already, you should consider move up to power amp. You definitely will be doing discrete and a whole lot more challenging.

If you build your preamp, you can comment on how it compare to the opamp ones.


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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 05:03 
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Joined: 08 Aug 2009, 03:11
Posts: 2208
Location: Chilliwack, BC
Don't forget the 2SK880 I mentioned in another thread. Crazy low noise and great sonics, but you need to do a SMD adapter.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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 Post subject: Re: 2n5484 phono preamp
PostPosted: 30 Dec 2016, 05:14 
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Joined: 29 Dec 2016, 03:06
Posts: 18
I'm aware of the 2sk880: its specifications are the same as the 2sk117, and the 117 doesn't need adapter!

The next step, of course, is power amp. I'm working on a design that John Broskie emailed me gently (a nice and generous man). I breadboarded it but for some reason it didn't work right, so I have to debug it and see what's happening.

By the way, do you think the 500mV output goal for a phono stage is right or a lower output can be enough?


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