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jFET phono preamp - boozhoundlabs
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=2933
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Author:  HT Performance [ 21 Jul 2015, 16:24 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

malinky how does it sound? :)


Cheers,
Miguel

Author:  andreidaniel [ 18 Aug 2015, 05:20 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

HT Performance wrote:
malinky wrote:
Have not looked yet.
Just asking about the modification suggested by `Ht performance` a few pages back.
Cannot find my printed circuit diagram at the moment, so I will have to look on the `Boozehound` site.


Hi!

I also felt the need for a little more gain, to feed the oddwatt tube amplifier, because I am running the 6SL7 tube instead of the higher gain 12AX7.

By that time, I made several calculations and also performance tests measurements and the RIAA response is perfect.

You can use electrolytic capacitors starting from 25v.

I am very sure, that if your project is currently well wired like the schematic, you will be extremely happy with this simple modification.

Let us know your listening impressions! :)

Image


Cheers,

Miguel


Hi! I found an online calculator for the Passive RIAA equalization: http://www.mh-audio.nl/calculateRIAA.asp
I think that the values are wrong in your case. As you'll insert the value of 27-28K resistor instead 75K as presented you'll notice another values for the components. As I have read on a document there should be respected the values for 318uS, 3180uS and 75uS.
Quote:
3/ Accurate RIAA! The three time constants in the original RIAAspec create four areas in the audio spectrum: under 50Hz, 50Hz to 500Hz, 500 to 2122Hz, and 2122Hz on up.

Source: http://www.pearl-hifi.com/06_Lit_Archive/14_Books_Tech_Papers/Wright_Allan/SP-15_Article.pdf

Have a look also in the http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=3046&start=40 topic.

Author:  zyu [ 19 Jan 2018, 13:37 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Attachment:
ql8Y9QnOYME18.jpg

Quick and fairly simple project, but not bad at all.
I took 1 day, I wanted to spend time with good. It was a great gift to my friend.
And yes, I will agree - is not enough gain.

Author:  Geek [ 19 Jan 2018, 14:15 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Math for values and in practise can be different due to impedances, stray capacitance, layout, etc. The important thing is how it actually sweeps against a reverse RIAA EQ.

We can also get OCD over error and it isn't needed as long as that all-important 500Hz-5KHz range sweeps flat to the reverse EQ.

Cheers!

Author:  zyu [ 19 Jan 2018, 15:41 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

RIAA VS iRIAA: 2 measurements for accuracy.
Attachment:
YCLrSGhLcCY.jpg


UMIK1 microphone

Author:  mwhouston [ 19 Jan 2018, 18:43 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

As you can see from the schematic boozhound has just tweaked the original Le Pacific. I think they are all good tweaks. The only one of these I have built is from the kit using all PIO caps. I liked it and added a Le Pacific MC stage so the unit could switch from MM to MC. Also added a second input for two TTs.

Ran the lot on two sets of batteries. I sold it some time back and it has re-sold a number of times so hard to say others really liked it.

Author:  Geek [ 20 Jan 2018, 01:42 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

zyu wrote:
RIAA VS iRIAA: 2 measurements for accuracy.


What's the "Y" scale? 1dB? 0.5dB?

Quote:
UMIK1 microphone


You... mic'd it? :eek:

Author:  mwhouston [ 20 Jan 2018, 07:29 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Geek wrote:
zyu wrote:
RIAA VS iRIAA: 2 measurements for accuracy.


What's the "Y" scale? 1dB? 0.5dB?

Quote:
UMIK1 microphone


You... mic'd it? :eek:


I don't get it either.

Author:  zyu [ 20 Jan 2018, 08:25 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Geek wrote:
zyu wrote:
RIAA VS iRIAA: 2 measurements for accuracy.


What's the "Y" scale? 1dB? 0.5dB?

Quote:
UMIK1 microphone


You... mic'd it? :eek:

1 dB on Y
I'll try to explain.
I often use the REW program to determine the frequency response of acoustics.
Perhaps many people know this software, but I'll paint it in more detail. We start the pink noise and hold the microphone. So we know the frequency response of our acoustics. This is our starting point. We leave the microphone at the same point, do not change anything.
Next, I add a chain of IRIAA and phono-corrector to the measurements.
I will lay out the scheme of irIAA. Haglabs
"The iRIAA Filter is a two-channel passive inverse RIAA response filter for use in testing phono preamplifiers. Unlike traditional networks, the iRIAA Filter includes a correctly placed upper 3.18us (50kHz) corner in its transfer function. Output level is switchable between -40dB and -60dB. Frequency response is accurate to within +/-0.5dB from 10Hz to 100kHz."
https://hagerman-audio-labs.myshopify.c ... iaa-filter
Attachment:
Снимок.PNG

So if I can get the original picture, then the RIAA iRIAA circuit mutually compensates each other.

Author:  mwhouston [ 20 Jan 2018, 17:47 ]
Post subject:  Re: jFET phono preamp - boozhoundlabs

Easy enough to build.

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