Bryan's Caruso Massimo Build

[Bahndahn]

LOL "flip up to destroy the world" -perfect

I have had success deconstructing and cleaning switches, a possibility for your preferred switches?

Looking great! I have long been inspired to make a little control panel for my build based on your work

[EpicenterBryan]

LOL "flip up to destroy the world" -perfect

Hey, how is your project going? Did you try out your easy driver? Do you have enough torque?

Bryan

[EpicenterBryan]

A quick update:
I checked all the cables, and it turned out I only used a handful of the wrong pins. So the rework was minimal. I also decided to tag the cables so it's easier to remove and replace the boards. Also discovered an error in the ground connection for a header I added to the Mod Out connector (photo is before update). While the boards were out I jumpered signal into all the VU driver board inputs and verified all the gain adjusters worked and all switch positions were routing correctly (and the switches worked).

IMG_3464.JPG

IMG_3467.JPG

I also had a chance to run some audio in from an iphone, and checked the RIAA switch. Shown here is the input signal on the left LCD, and the output with RIAA Encode active on the right. Notice the drop in the lows and boost in highs on the right screen. You can't see the meter needles, but they work as well.

IMG_3470.JPG

Now that the weekend is just about here, I'll run it through the paces.
A quick check of the FB input did point out a problem on one channel. No time to debug it further tonight.

Bryan

[dimi751]

Hi Bryan

Nice job sir, love the retro vu meters looking forward to see it finished.

[EpicenterBryan]

Made some progress, and have a few things I'm scratching my head about that I would like some inputs on.

First, progress:
I mounted that phono preamp that I modified so I can get back to my driver test bed for Groove Scribe. Remember? Trying to use a phono cartridge for feedback.. It's nice to have that mounted in a box with connectors.

IMG_3480.JPG

Also added a Pot to drop the current down on the VU meters. Decided not to PWM for possible noise reasons, so a simple pot still gives good results.

IMG_3481.JPG

Now for a little head scratching.
Let me explain the two photos. First - common to both:
The left pair of VU meters and left LCD displaying L and R input (noise input from Protools system).
The right pair VU's and LCD measuring L and R output drive.
No feedback L or R signal - FB pot to minimum.

OK, the first photo shows input (left set of meters) and output right (right set of meters) at the connectors Line In and Drive Out with the RIAA switch turned OFF. So if you look at the schematic, Q300 is turned off.
In this shot you see there is a LF roll off that I did not expect since the RIAA is off.

IMG_3486.JPG

In the next shot - same conditions. Except the RIAA switch is turned on. NOTE since there is a big gain (+20dB) in the HF, the meter calibration levels had to be adjusted -20db to keep the same scale. In this shot you clearly see the +20dB boost, but you also see a reasonably looking LF cut.

IMG_3493.JPG

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[EpicenterBryan]

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So I have a bit of confusion because the block diagram makes it look like the RIAA curve is switched on and off in front of the output drive section - switching in or out both LF cut and HF boost.

caruso block.jpg

But the way I think it actually works, is that the HF boost portion of the encoder actually happens between Mod Line In (Modlin) and Mod on the schematic. There is only one FET in that section and my on-line spice simulation tonight with a 100 ohm resister in place of the FET to ground (the on-line one has no model for a FET) shows the +20dB boost in the HF, not the complete LF cut in the RIAA curve.

Here is the result of the front end spice simulation: This is displayed in voltage not dB, so you will need to convert. But the input was 1V in the simulation, so at 20Khz, it was around +20db, and at 1Khz, around +1db, at 100Hz, -1dB, and -8dB at 20hz.

Simulation input stage.jpg

And here is the simulation with RIAA off... The scale is in volts, so you still need to convert, but you see around -1.3db at 20kHz, -1db at 100Hz, and -8.38 at 20Hz.

RIAA OFF.jpg

According to the simulation, the bass cut does not originate in the front end. It must be in the Drive section. Is there an error in the documentation / schematic relating to non-feedback heads?


Bryan

[EpicenterBryan]

I'm playing with the old drivers and feedback from the other project and Caruso Massimo so I decided to do a video update.

[Sillitoe]

Very cool Bryan, nice work!
Here are some great meters that I'm going to use for my feedback monitoring.
http://www.jlmaudio.com/shop/40-led-ppm/vu/gr-meter-kit.html
They do peak and vu at the same time.

[Ciuens]

Hello Bryan. Wonderful work. I loved these LCD displays.
The phase change is driving me crazy. I have no idea how to fix this.

[Ciuens]

Hello Bryan, you find out what makes the phase change? What software are you using to measure?
Cheers