Modified my Formula Preamp

[luigi]

I just finished modding my Formula preamp and HOLY SMOKES what a difference. It is amazing how changing just 3 components changed the whole sound of this amp.

More marshally now but 100% MESA....and it doesn't have that annoying midrange honk anymore. I was seriously considering getting rid of it as the distortion was awful until I modded it and now it's in the rack.

Any of you Formula owners out there.....really should try this!

 

[zx81]

Did you do the "Andrew " mod?

 

[luigi]

Gosh....I forgot to say what I did!!

Yes, I did the Andrew mod and let me tell ya.....if you haven't tried it you are really missing out. The change in sound is really amazing and it is so easy to do.

I'm really happy with the formula now.

 

[zx81]

I'm really interested in modding my formula pre. Do you have soundclips?

 

[luigi]

sorry.....my rack is at our jam space so I don't have any clips. I do have the instructions for the mod though if you don't have them.

It's really simple and easy to reverse if you don't like it (which I can't imagine happening).

 

[zx81]

Thanks. Andy sent me his instructions, but any additional info is welcome.
Somebody told me he had experimented with several parts on different locations, and that the 1M resistor was the most important thing to change. He also told that a .69 uF capacitor seemed to work better with his (single-coil) guitars. Since my main guitar is a Les Paul, I think I'm going with the .47 uF.
About the mod being easy: I tried to mod my crybaby last week. When I desoldered a resistor, I took a part of the component board copper strip with it... Since that moment I have visions of smoking preamps and such. A friend of mine is going to do the mod. He has the soldering skills.

 

[luigi]

Only thing that you should be careful of is.......the components are soldered on both the top and bottom of the circuit board. What I did (just to be safe) was this:

1) took a very thin piece of wire and looped it around one end of the part I was removing.

2) While pulling gently on the wire, I applied the soldering iron to the top of the board where the part was connected.

3) Once the solder heated up....the part end just popped right out. Then I grabbed the loose part with my pliers and did the same thing...again gently pulling with the pliers as I heated the remaining joint.

I did put the cap that I changed on the back of the board because there was more room. The one that is there is only 35v (I think) but I replaced mine with a 250v mylar cap.

I did find that the 1M resistor changed the amp quite a bit...but I still went ahead with the cap change and I'm not sorry.

**IMPORTANT**
If you are not overly familiar with soldering get somebody who is better at it to do it for you....or practice a bit till you get it down and are a little more comfortable with it. Applying too much heat will lift the traces off a board and possibly damage the component you are working with. Also, get a good quality soldering iron.....30w - 40W should be fine.

 

[hooty]

Hi,

good to find some formula owners. I have serious hum problems in both lead channels. Is it a general problem with the formula pre or is something wrong with my one?

hooty

 

[luigi]

I don't have any hum issues with my Formula. I run it into a M/B 20/20 and it's pretty much hum free. I run a bunch of effects before the amp and a couple of modulation effects in the loop and it's all good.

1) Are you plugging straight into the preamp?
2) Have you tried lifting the ground (switching the Ground Lift Switch)?
3) Do you get the hum if you use the recording outs (say....into a PC for example)?
4) are you using single coil pickups or humbuckers? Active or Passive?
5) what are you plugging the Formula Pre into?
6) Have you tried moving the amp to a different area in your house? Bad electrical or flourescent lights can sometimes interfere with amps and stuff.

Cheers,
Luigi

 

[hooty]

Thanks for the reply. To answer your questions:

1) I plug my guitar in a Boss NS-2 and then straight in the formula.
2) I have already tried the ground lift but it doesn't solve the problem.
3) I haven't used the recording outs until yet.
4) I'm using a Rickenbacker 360 with passive single coils.
5) I plug my formula pre in the effects return of a Laney VC30.
6) I know that there are influences from bad electrical or fluorescent lights but I can't imagine that this would be the only problem.

An other thought is that the tubes are bad. I've bought the pre on ebay and haven't changed the tubes until yet. Maybe this is my next step.

hooty

 

[luigi]

Try plugging your guitar directly into the preamp and running the NS-2 in the loop. I would remove the pedal from the chain first though and test without it.

It is very possible that a tube is causing your grief. Replace the tubes...that would be my next step. I would also look around for another amp to try it on (just to be sure).

Does your amp hum without the guitar plugged in?
You could remove one tube at a time and see if the hum goes away. Remove the input tube....does the preamp hum? If yes, remove the next tube....does it hum? No....well the problem lies somewhere in that stage.

Do the controls affect the type/amount of hum (i.e. does turning the volume up/down on that channel affect it or does it change with the tone controls)?

It's possible that you've got a cap gone or some other component is causing it. If replacing the tubes don't fix it and it hums through another amp......either take the cover off and trace the source of the hum with a scope or take it to a tech if your not into that.

Cheers,
Luigi

 

[hooty]

Hi Luigi,

the problem is solved. The reason was a ground hum caused by my Boss NS-2! Thanks for your assistance!

hooty

 

[luigi]

Cool.....no problem with the Preamp...that's good.

Kinda funny though....the noise suppressor causing noise...hehehehe.

Cheers,
Luigi

 

[hooty]

And now I'm interested in modding my Formula... 8) But where can I get the instructions for this "Andrew-Mod"?

hooty

 

[luigi]

I sent you a pm

 

[hooty]

Hi Luigi,

I have sent you my email address... Thank's for the help!

hooty

 

[dongh1217]

could you please sent me one too? Thank you

 

[jjm35]

Hello, i just buy a used formula preamp in Ebay, i will receive it next week. I'd like to have the Andrew's mod instructions to mod it.
Thank you

My e-mail:
[email protected]

 

[archtop]

I would also be interested in the mod instructions, can someone pm them to me. Thanks :wink:

 

[ESN]

Hi, I'm very interested in modifying my Formula Pre, as it seems easy and reversible!
Could someone send me the Andrew mod instructions by mail or pm please?

Thanks!