• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EAR 834p clone weirdness - high frequencies dropped out

Posted this in another forum but figured I’d try here considering how helpful this community has been over the years.

Hi folks. I have a Zhili 834p clone with a separate PSU, the black and gold one. It’s been sounding pretty great. I upgraded the coupling caps a few months ago to VCAP ODAMs and it sounded even better. Just yesterday it sounded weird, sort of veiled and muffled. I confirmed by swapping in another phono pre as well as a couple of integrated amps. Did a bunch of tube and cable swapping, as well; I tried everything to the extent of my limited knowledge. All scenarios had same results with the 834p clone lacking highs regardless of whatever I swapped and all sounding great when the 834 was removed. I don’t know where else to look, would appreciate any insight or guidance you may have. My friend who gave me these caps and noted they may take some time to burn in and sound odd along the way, but this is a bit more pronounced or obvious than what I’d imagine cap burn in would be (myth or not..). I’m stumped!
 
Jeff, this is where I need the guidance. I haven’t checked anything yet due to lack of knowing where to begin. Everything checked out fine when I swapped the coupling caps, but that was done with a friend far more experienced and competent than I with this stuff (which isn’t saying much!).
 
dubadub, I wish that was it! We swapped the caps back in December. I settled in with my tube combo shortly after. It’s been playing and sounding great for a few months now prior to this annoying issue that began last week. Cymbals are barely present anymore.
 
That’s what’s confusing me, as well. I keep thinking it has to be a tube considering the issue is similar to what a tube on the outs can sound like. But I can’t land on any of the 12AX7s I’ve rolled through it having an issue. No matter what I put in there, at what position, it sounds the same. Likewise if I try a 12AU7 at V3.
 
That’s the plan, rayma. He’s not around for a few weeks unfortunately so I’ll probably just continue to wishfully think it will suddenly stop and get back to normal. I take the same approach with the water that keeps coming into my basement….
 
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I have various versions of this circuit in LT Spice. Dropping the HV down to 100volts doesn't typically reduce the high frequencies.

If the RIAA feedback loop is damaged, it typically reduces the low frequencies. Same for the cathode by-pass cap on V2.

What does make a difference in the HF is if there is a problem with the cathode follower circuit.
 
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