2. amps-preamps
  3. 193642-3931

Help me mod my tube amp

Hi all,

I'm interested in modifying my Prima Luna Dialogue 4 amp. The amp is about 15 years old and still sounds pretty good. But in the past I've had fun modding preamps and speakers and seeing what can be improved, so I'd like to try improving the SQ of this amp. I haven't modded an amp before, so I open to suggestions about capacitor upgrades or anything else. You can see a picture of the internals of the amp here. This amp resides in a secondary system, which is:

Mac mini --> Benchmark Dac3 --> Prima Luna Dialogue 4 amp --> Dali Phantom S-180 speakers + Rhythmik F12G-SE-PEQ subwoofer (via high level speaker input)

Power: dedicated line --> Maestro outlet --> Shunyata Hydra 8 power conditioner. Cables are Shunyata and DH Labs.

Current tube configuration in Prima Luna amp: GE Military stock 12AU7, Gold Lion 12X7, Tung Sol KT120

These days, I tend to like things on the slightly warm side of neutral. I appreciate increased resolution, but not at the expense of organic tonality and musicality. Any help would be greatly appreciated!

Bryon

 

bryoncunningham
bryoncunningham OP
895 posts
 

Hi all-- Update on this project...

My tech replaced the stock capacitors on the input stage of my Prima Luna Dialouge 4 amp with Dueland CAST PIO Hybrid copper/silver foil caps (matched pair). He also replaced the stock capacitors on the PCB board for the autobias circuit with V-CAP ODAM caps (matched quads).

Here is a pic of the internals before the upgrade. Here is a pic of the internals after the upgrade. The Dueland caps are the large red caps in the upper left and right of the image. The V-Cap caps are in the middle of the image covered in blue shrink wrap. 

Listening results: increased resolution, better soundstaging, and more natural tonality. 

I know several of you have made suggestions about upgrading the tubes. The GE12AU7 tested weak on the bench, so I have temporarily replaced them with Electro-Harmonix 12AU7. To be honest, I am somewhat overwhelmed by the options for tubes. I've probably spent 20 hours reading about various tubes, but I still feel poorly informed. I know that is my fault, not yours.

I am open to upgrading the amp further. If you have more thoughts, I am happy to hear them.

Thanks,

Bryon

P.S. The guy who did the work is Blackie Pagano. I have no affiliation other than this one service. What a nice experience. He was so knowledgeable, honest, and kind. He's in the LA area if you're looking for someone.

johnss
610 posts
 

yes, all those upgrades def. help. If you are looking to go a bit more, all the plate and cathode resistors on the input tubes are flameproof metal oxide. Use the same values and replace with 5 watt MILLS wire wound. The front end will get 3-4 db quieter and low level resolution will improve. 

bryoncunningham OP
895 posts
 

Hi John-- Several people suggested replacing the resistors, which I am open to, but have no experience with. Forgive the naive question, but do you know what parameters are important to match when replacing resistors? Obviously the resistance in ohms, but do I also need to match the power rating, max voltage, max temp, or other parameters?

sns
3,820 posts
 

@bryoncunningham I recommended the Takman carbon film resistors, this what newer Prima Luna uses. These are very nice resistors and proven upgrade for PL.

tablejockey
4,039 posts
 

’Takman carbon film resistors, this what newer Prima Luna uses."

The OP’s amp has the same Takman resistors as the current  spec lineup. Takman was speced in the original Dialogue series.

 

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