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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
johnss
605 posts
 

Two main areas you can improve. 

A. the tubes. 

B. the cheap film caps used inside the amp. 

pretty simple if you know how to solder. 

1. Upgrade the input tubes to get rid of the Chinese tubes. Plenty of NOS or UOS US and Euro tubes available for these sockets including the industrial versions like the 5814A and 6189s.Same on the 12AX7s. 

2. Replace the 0.1uf metalized film caps on the voltage rails with copper foil caps or similar. 

3. replace the cheap metalized coupling caps with Jupiter copper foil caps or similar. 

4. replace the input tube cathode and plate flameproof resistors with same value MILLS wire wound resistors.  

russ69's avatar
russ69
3,573 posts
 

I think I would start by using Gold Lyon KT77s. Do you really need the power of KT120s?

sns
3,700 posts
 

I modded a Prima Luna Dialogue with Takman carbon film resistors, this what newer production PL uses. Duelund, Jupiter, many other choices for coupling caps, I went with Miflex T:PCU. I preferred EL34 vs KT, these 1990 era Svetlana and SED. NOS on signal, driver tubes, nice power cord. Do all this and you have very nice PL, I still listen to PL I modded with guy I sold it to, this with Spatial open baffle speakers, very nice setup.

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bryoncunningham OP
893 posts
 

Thanks everyone for the input so far. Several people suggested new tubes. As is probably obvious, I am pretty naive about tubes and open to your suggestions.

 

knotscottt: Yes, I run the amp in triode exclusively. I do not know whether the amp can use 12BH7a's rather than 12AU7's. I will try to find out.

russ69: I started using KT 120's all the way back when I bought the amp because I was coming from solid state and I was accustomed to bigger dynamics than the stock tubes provided. But I gather from your comment that KT 120's may be overkill?

johnss, sns, and viridian: Thank you for your specific recommendations. I will investigate options for upgrading each of the things you mentioned.

 

Bryon

 

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