PPIMV Sounding "Fuzzy"

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prozak
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PPIMV Sounding "Fuzzy"

Post by prozak » Thu Nov 30, 2017 5:33 pm

Hi, I am new here. I just finished building a JTM 45 kit, (well mostly, the board was from another vendor)
so I Had it all setup and qualified, and biased and working great by a great amp tech here
in San Diego. He had me run through an Attenuator, and it sounded amazing pinged on like 8 or 10 on the
amp volume.

So back at my place, I decided its either that or put the post phase master volume mod in. So I opted for the
PPIMV.

After installing, I re-biased. all is good, however....

The gain sounds...."buzzy" or "Fuzzy", not Clear and chunky and crisp like a Marshal should sound. What am I doing
wrong? Is it a bad Pot?

I have done the mod by using the Lamar and also single wire method as well, with the same result. Also, all my tubes
are brand new, and tubes were tested by my tech.

I have also ensured that the grounding is correct, meaning, that only the shields of the shielded cable are going to the correct pin on the Dual Audio slope (see picture) per the diagram supplied. So.....if anyone has seen this, or I need to do another
change, or some trick let me know! Second set of eyes is always good...out there. Be kind, this is my first build
ya'all

Thanks

(I will attempt to upload pictures... :hairband:

Elad E
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Re: PPIMV Sounding "Fuzzy"

Post by Elad E » Sat Dec 02, 2017 5:54 am

Hi,

how low are you running the PPIMV?
somewhere below 50% the sound starts changing quite dramatically, below 25% it often gets fizzy if you run the volume high and get the preamp tubes cooking.

IME, low NFB and PPIMV below 50% is a one-way ticket to fizz-land. Is your JTM45 sporting the vintage correct 27K/16ohm configuration?

Also, what One-Wire Mod are you referring to? the mod I usually associate this name with is the Randy Rhodes style Superlead mod which ups preamp gain and introduces a buzzsaw style drive which is somewhat fizzy in nature, doesn't "get well" with a PPIMV and is quite the tonal opposite of the Marshall bass circuits (such as the JTM 45) to my ears.

alexradium
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Re: PPIMV Sounding "Fuzzy"

Post by alexradium » Sat Feb 24, 2018 4:13 am

actually the jtm45 has too much NFB for the MV to work good,and it also loads down the PI making it distort the output.

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