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Mods to my Ampeg SVP-PRO!

#43
jazzbass_5 said:
I wondered about that but more over I wondered about running the line voltage across the back like that and near that side of the preamp causing 60Hz hum. I know the SMPS switch at a high frequency (usually above hearing). I Don't hear any new noise and this particular preamp was void of the horrible noise that most SVP-PROs have. I know, I had a grey face that was noisey. It SEEMS to have a different sound and adjustability but again, I never could hear a huge difference when rolling tubes either, even V1.
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Just because you can't hear it doesn't mean it's not there. With those switching supplies parked in close proximity to the tubes, the grids can easily pick up nearby electrostatic noise and amplify it.
 
#47
byacey said:
Just because you can't hear it doesn't mean it's not there. With those switching supplies parked in close proximity to the tubes, the grids can easily pick up nearby electrostatic noise and amplify it.
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Agreed, I was thinking about the supplies beating with each other creating sum/difference products which could be a real mess. Certainly would be an FCC/CE issue in practice.
 
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#50
beans-on-toast said:
Indirectly that was my point earlier when I said to use an AC fan and eliminate one of the DC supplies.
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The idea was to use what I have on hand and not purchase anything because I was just having fun experimenting and getting my geek on.
I could shield the supplies but I dont plan on mass producing these and don't think I'll need to pass FCC/CE noise and interference standards. Hopefully I won't bother the neighbors TV or bring any aircraft down.
Playing through it more tonight and it does seem to have a different feel to it. Really wish I had one to A/B or someone else with SVP-PRO experience to listen. I've have determined my bass has a very high output.. but I've figured that for years.
 
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#51
jazzbass_5 said:
The idea was to use what I have on hand and not purchase anything because I was just having fun experimenting and getting my geek on.
I could shield the supplies but I dont plan on mass producing these and don't think I'll need to pass FCC/CE noise and interference standards. Hopefully I won't bother the neighbors TV or bring any aircraft down.
Playing through it more tonight and it does seem to have a different feel to it. Really wish I had one to A/B or someone else with SVP-PRO experience to listen. I've have determined my bass has a very high output.. but I've figured that for years.
Click to expand...

Use it as a testbed, see what works.

If you have an old AM radio with a manual tuner, tune it between stations, near the low end of the band if you can. It can act as an RF noise detector. Move it around the room, near fixtures, junction boxes, wire runs, breaker box, etc. You will hear a lot more static near any RF source. Then try it near the amp amd see how it compares to other noise sources.
 
#52
beans-on-toast said:
Use it as a testbed, see what works.

If you have an old AM radio with a manual tuner, tune it between stations. It will act as an RF noise detector. Move it around the room, near fixtures, junction boxes, wire runs, breaker box, etc. You will hear a lot more static near any RF source. Then try it near the amp amd see how it compares to other noise sources.
Click to expand...

I have an old Philco tube radio, with this work?
20171030_194559.jpg
 
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#59
JimmyM said:
Assuming you meant to type ECC82, ECC82 is a 12au7, and a 12dw7 is half 12ax7, half 12au7, so I'm not seeing what using a 12dw7 would accomplish.
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Total gain structure and biasing remains the same for 12DW7 tube for V4.
Tube 1/2 system V4-B acts as buffer stage (gain about 1) that "drives" both the graphic EQ section as well as the (active) midrange EQ control section. So its a good idea to have just a system of 12AU7 for V4B.
V4A stage acts with gain>1 like it is for the SVT and SVT II schematic, so its not so bad to have 1/2 system 12AX7 for V4A
IIRC the 12DW7 tubes had been out of production for a while when the SVP pro (and svt II pro) preamps had been designed. IME 12DW7 for V4 helps to "improve" the total sound a little bit. So finally I could get pretty happy with the total sound after swapping the V4 12AU7 (ECC82) tube for a (JJ) 12DW7 tube.

edit, of course I must have to appoligize for "rough" words in my post above. Sorry.
 
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