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Old 5th December 2004, 03:03 AM   #1
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Default Project Phono SE preamp

hi, I am just rebuilding my vinyl gears after stopping for almost 20 years.

TT: Project Perspective with 9" tonearm
Cart: Shure V15VxMR
Phono pre: Project Phono SE

My other gears as follows: -

Accruphase DV-55P CD player
Mark Levinson 38S pre
Mark Levinson 430 power
JM Lab Micro Utopia Be speaker

The sound from CD is OK for me but when I play vinyls, the bass is a bit thin although the dynamic is miles better than CD. I went through the circuit of the Phono SE and can see there could be a number of improvements: -

1. Do not use the original AC/AC adaptor and use an external AC/DC PSU with regulator. Bypass DC terminals are available on the Phono SE box.
2. Change the RIAA circuit components.
3. Place a good and suitable capacitor across the +ve and -ve main supply as decoupling.
4. Of course, the last alternative is to chage it completely to a new one (I prefer tubes).

Does anyone have experience in modifying the Project Phono SE before? Can he/she share me some clues?

Sunny
Hong Kong
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Old 5th December 2004, 07:27 PM   #2
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Schematic for Pro-ject phono box

is a diyAudio thread on this subject.

Do you use the search function on this board?
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Old 5th December 2004, 07:32 PM   #3
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The thread I referenced is for the Phono Box, not the SE version.

I don't have either, and I haven't seen a thread on the SE version. Perhaps you could be the first to research mods for the SE version here?
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Old 5th December 2004, 08:31 PM   #4
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Thank you for pointing the errors in Phono Box but mine is SE.

The RIAA is the first point that I try to figure out but I'm not a EE guru and is not able to calculate the component's value.

Is there anyone can provide his/her finding?

Sunny
Hong Kong
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Old 6th December 2004, 07:43 PM   #5
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Quote:
The RIAA is the first point that I try to figure out
I think you want to verify the frequency response of the RIAA equalization of your Phono Box SE.

The best way to do this is by testing, but you will need a signal generator or special vinyl test record to apply known audio frequencies to the inputs of your Phono Box SE, and an accurate AC voltmeter to measure the outputs. Access to these tools is not difficult but some technical ability is needed.

If you are trying to find the correct component values, you will first need the circuit schematic, since there are several different types of RIAA circuit designs, each with their own set of formulas for calculating values. I don't have this schematic.

Thin bass can be due to a tonearm with low effective mass used with a low-compliance cartridge, but you have a medium-mass tonearm with a medium to high compliance cartridge, so if anything this should boost bass a little. Is the dynamic stabilizer brush up or down? You may get better bass response with the brush down, remember to add 0.5g VTF to compensate for the brush being down.
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Old 7th December 2004, 12:19 AM   #6
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Thank you Nuvistor for your suggestion. I have signal gen and oscilloscope therefore I'll try to measure the frequency response first before I take further action.

I seldom play with the brush down because it affects the trackson on those records that are not flat. I'll try to add 0.5g to see how it works.

By the way, is there anyone here have the Phono Box SE circuit?

Sunny
Hong Kong
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Old 7th December 2004, 08:33 PM   #7
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If you are using signal generator with oscilloscope for voltage measurement then you should consider "inverse RIAA" circuit between signal generator and phono preamp input, do a Google search on "inverse RIAA" for more information. If you apply signal generator directly to phono preamp input you will see large changes in gain vs. frequency due to the RIAA equalization.
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Old 9th December 2004, 12:01 PM   #8
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Finally no need to modify the Phono Box SE, too lazy.
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Old 9th December 2004, 12:03 PM   #9
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Finally decided not to do any modification on the Project Phono Box SE. Too lazy.

I bought an ASR Mini-basis phono preamp and I must say it worths every dollar when compares to the Project SE. It is very musical and frequency response is balance. Silent background and the Double Bass is very very clear. I love it.

Sunny
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Old 16th December 2004, 07:53 PM   #10
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I heard the Emitter amps by ASR (formerly Schrader & Rompf) are great as well, anyone ever heard these?

Regards,

Jarno.
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