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Bob Carver Sonic Hologram C-9 Mod

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Modification Details:

 - Replace all the resistors with Vishay Dale resistors of better precision (1% or less, down to 0.1%)

 - Replace all the old power electrolytic capacitors by Nichicon ones with better specs

 - Replace the Mylar capacitors by more precised polypropylene film caps

 - Replace the old RC4136 quad op-amps by the same type but new ones. The new ones have improved specs compared to the old ones.

 - Replace the 2 coupling output caps by polypropylene Audio MKP caps

-  Improve grounding

-  Replace the bypassing electrolytic caps at the power pins of output buffer op-amp by higher values (important change) electrolytic caps

-   Add 0.1 uF bypassing quality ceramic caps to all power pins of all op-amps 

-  Improve power supply ripple current

-  Reduce power rail voltages from  around 15 volts down to 8 volts

-  Change RCA connectors to better ones (mainly to have better look and easier to plug IC cables)

-  Add Gold-plated Neutrik XLR output connectors

-  Add AC sockets

- Change led to green one (just to look nice)

 

Tried to mod but not successful:

- Replace Input buffer and output buffer op-amps by better specs one (OPA1612) via BrownDog adapters. The OPA1612 has very good specs but the with wide bandwidth (40 MHz) compared to 3Mhz of RC4136 and it oscillates a lot. I have tried to tame it regarding oscillation for the output buffer and it is OK but then high DC offset is still there. I don't want to change the Carver C-9 design just to reduce DC offset so I gave up this improvement. Maybe OPA2134 (similar voltage noise level to RC4136 but others are better; 8Mhz) is OK for replacement without much taming work (people have done that) but not worth trying further for me.

 

Should have not modified: 

- Added the IC sockets. This does not improve anything; only adds negative impacts if any but convenient to try different type of op-amps. But overall, these IC sockets don't do any harm in this C-9 with RC4136.

 

Overall after modification:

- Noise ground reduces but still is the most significant one compared to other gears in my system but it is expected. Without music on, noise ground can be heard only when the volume is very high though. And I never listen to music at such high volume anyway. And with music on, my ears cannot tell much of the noise ground :).

 

- After lots of measurements and fine-tuning, the 3D is amazing. With good recordings, music is all over the room, extended sound-stage, music next to the ears, a couple of meters from each side, behind my back, etc. Overjoy! Online radio channel 1.FM Chill Lounge Radio and good recordings from Linn Records have excellent 3D imaging.

 

Here are some photos before and after:

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