ADA MP-1 Tube Guitar Pre-Amp Noise-Mod

[musika]

Hello,

I'm most of the way through this modification to quiet down my ADA MP-1 pre-amp and I have a couple questions.

Is the TL072 chip that they specify need to be the  TL072IN High-Temperature/Low-Noise Op-amp?

Or can I substitute another?  They are not readily available.

Also, there are 2 12AX7's and they have plastic bases. 

Should  I take the time to upgrade to ceramic bases from plastic for these tubes?

Thanks!

http://www.scribd.com/doc/99237537/ADA-MP-1-Noise-Mod-Doc#scribd

 

[12afael]

what kind of noise do you want to eliminate?

I would change all the resistors at the tube stage to metal film, specially the anode resistor. but I hate that pcb is a pain to change parts, the pads are really small.

ceramic sockets are better than plastic but I doubt there is an inprovement in noise. metal contacts are metal contacts. sure if you find a gold plated socket could be better but for me main source of noise in tube are anode resistors.

 

[musika]

The pads are super small and it's a two sided pcb, so it's a real challenge to solder for sure. 

The noise is somewhat of an operating hiss that I am told can be improved.

Are those resistors you mention all contained on the small pcb containing the 12AX7 tubes?

 

[musika]

ADA MP-1 tube stage schematic photo.  So the anode resistors would be the 100k resistors?  Am I reading that correctly?

 

[PRR]

The anode resistors 12afael mentions are the 100K resistors which have (when on) 250 volts at one end and about 160V at the other end. I agree these may be most critical.

That schematic does not show the TL072 chips. I totally do not understand that modder's suggestion to use "high temperature" chips. There is not a lot of variation in hiss across different sorts, brands, or vintages of the TL072. It is what it is.

In any case, this amp is *HIGH* gain. It is going to hiss. Play loud. Do not stop playing. That's how it was made to be used.

 

[Rocinante]

In any case, this amp is *HIGH* gain. It is going to hiss. Play loud. Do not stop playing. That's how it was made to be used.

Someone  needs to write a book of prr quotes

 

[musika]

The recommendation states that the TL072IN replace a 2068 and a LF412 in the input and effects sections of the amp. 

 

[12afael]

sometimes people belive that puting a high slew rate op amp or a "better" op amp will improve the sound, some times this "better" is not the best fit for the circuit.

the friss law say that the the most important stage in noise is the one closest to the source(guitar), the tube stage are the nearest to the guitar so I would start with that.
http://en.wikipedia.org/wiki/Friis_formulas_for_noise