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I am in need of modding my own Peavey 5150 II ( the mod I want costs 425$ from fjamods.com)

Fja won't do it the way I want to because he says it will cause noise issues.

Let me describe what I want and you tell me what you think:

I want to be able to have a post and pre control for the "crunch" mode of the rhythm channel. As it is right now, the post and pre controls are shared and can't achieve a true clean or true rhythm gain setting. its always a compromise.

So, this is what I want to do: First off, I want to keep the amp in stock appearance b/c fja installs miniature pots in between the regular pots and it causes the interface with the faceplate to get congested and cramped and I personally think it looks bad.

Since there are two seperate controls for each channel's resonance and presence, I wanted to make one set a dedicated resonance and presence control for the entire amp ( ala original 5150 ) and utilize the free'd up resonance and presence controls to do the mod I want to do, and turn them into the post and pre controls respectively.

Jerry at FJA says in order to do the "3 channel" mod the pots need to be as close to the original placement where those controls are so as not to introduce more noise into the signal ( which I understand)

I am trying to find a verified schematic so I can start figuring out how to do this mod myself, but is anyone willing to give me a hand?

I don't want to modifiy caps or tone, I like the way the amp sounds in stock form but the FUNCTION of the amp limits me from utilizing it to its full potential as a greatly versitile amp.

From what I can guess ( haven't looked inside yet) but what I can assume is that the spot where the resonance & prescence controsl are for each channel are in the same location, so would you just put "flying leads" or jumper the pads so its controlled by the one set of pots?

for the rhythm post and pre controls, since they are shared between the two, tapping into the switching path to make a parallel connection to the new set of pots would be necessary? idk... just trying to make an educated guess.

hope someone can help save me 400 bucks.


THanks guys, looking forward to the feedback.


puppiesonacid

Schematic: http://schematicheaven.com/newamps/peavey_5150-II.pdf

I think you've got the right idea. You're going to need shielded wire otherwise you will most definitely have noise problems. I'll have to stare at the schematic to be of much more help, and this week is packed, so see what you can come up with on your own and I'll pipe up when I can.

ok thanks! I'll take a look and hopefully have a revelation hahah.

I'm gonna have a look aswel and see if i can help out!

I've already worked out the bit about havin one set of res/pres knobs for both! i know how to do that from looking at the schematic so just gonna have a look and see how you could mod it! the good news is res and pres knobs are the same value for each channel. i was wondering if they'd be different to suit each channel, which would mean that if the lead used one set of values it might not suit the clean, but they're the same! so no worries!

OK so i examined it a lil further!

THe switching is all done by relays so i wanted to make sure i could think of a way that would not effect switching channels aswel. there are four relays in the preamp section.

K1 - Clean/Lead Resonance and presence
K2 - Clean/Lead Channel
K3 - FX Loop
K4 - Crunch

The way each relay works is that KA and KB are the switching contacts and switch when the coil KC is energized.

I saw that K1A and K1B switches to lead or clean res/pres. I had a big long post typed explaining all the details but il leave em out unless anyone wants more info. but basically the switching circuitry activates K1 and K2 and the same time. so that when you switch from lead to clean, you also switch to the corresponding res/pres controls. so if you look at the switching circuitry, coils K1C and K2C are switched at the same time. so you gotta disable K1 to stop the controls switching but in a way that doesnt disable K2. Here is how you should do this.

1) pull K1. and you might aswel take out CR54 as this step shorts it out. its a diode across the coil.
Short pins 2 & 3.
Short pins 6 & 7
Short the coil Pins 1 & 8 WITH A 820Ohm resistor.

I was gonna say short CR54 cos that would short the K1C coil and so it wouldnt switch BUT they are 12V relays and have 24V supply. K1 and K2 coils are in series. so its split 12V each. K3 and K4 are not in series with other relays and so have an 820R resistor in series with them to drop the voltage. so you cant just short Coil K1C you gotta remove it and replace with 820R

DeanM wrote:I had a big long post typed explaining all the details but il leave em out unless anyone wants more info.

please do, I am trying to get as much understanding of how to do this correctly as possible.

Thanks!

I've only looked at the schematic a couple times in between work.

I'll dig deeper into what you are recommending so I can follow it a little better.

Thanks,

puppiesonacid

DeanM wrote:I'm gonna have a look aswel and see if i can help out!

I've already worked out the bit about havin one set of res/pres knobs for both! i know how to do that from looking at the schematic so just gonna have a look and see how you could mod it! the good news is res and pres knobs are the same value for each channel. i was wondering if they'd be different to suit each channel, which would mean that if the lead used one set of values it might not suit the clean, but they're the same! so no worries!

yeah I figured this wouldnt be a big deal. I always set the res and pres the same for each channel ( my ears like the settings) so i figured why waste the space?

Thanks

ok so if im understanding you correctly, K1 is in series with k2. but k1's primary function is to simulaneously switch in tandum with K2 so the lead resonance/prescence controls are engaged when the lead channels is engaged.
Pulling K1 and that capacitor will free up the lead/resonance controls on the lead channel
so I would want to designate the lead prescence and resonance controls as the new post and pre controls for the rhythm channel when the crunch is engaged?

but you have to put an 820R in its place to keep the split rail voltage for the other relays to work properly ?

Am I understanding you correctly?

just to clarify I want to have the post and pre controls for the rhythm channel, the ones near the input stay in control of the clean channel, but when I hit the footswitch or the crunch button on the amp, have it switch to the crunch mode of the rhythm channel but have the signal go to the "new" post and pre controls ( the resonance and prescence controls of the lead channel) so I can dial in the gain and volume for the crunch mode, essentially making it a 3 channel amp.

Jerry at FJA told me yesterday that the way he does it is build a seperate relay switching system for this function. Unless there is something I am missing it just doesn't seem like the most effiecient way of doing this mod.

I really think we're onto something here guys... looking forward to getting this down.

Thanks,

Tony

puppiesonacid wrote:ok so if im understanding you correctly, K1 is in series with k2. but k1's primary function is to simulaneously switch in tandum with K2 so the lead resonance/prescence controls are engaged when the lead channels is engaged.

Yes thats what is happening when you switch channels.

puppiesonacid wrote: Pulling K1 and that capacitor will free up the lead/resonance controls on the lead channel
so I would want to designate the lead prescence and resonance controls as the new post and pre controls for the rhythm channel when the crunch is engaged?

but you have to put an 820R in its place to keep the split rail voltage for the other relays to work properly ?
Am I understanding you correctly?

No its not a capacitor, its a diode. its normal practice to place a diode across a coil so that when a the coil is de-energized, the collapsing field of the inductive coil is allowed to dissipate.

But yeah you are understanding correctly. it will free up the lead res/pres controls. K1 just shorts either one when it switches. for example when in clean mode the lead presense is is shorted and clean pres pot is grounded. when in lead mode clean pres is shorted and lead pres is now connected. Think of it like a voltage divider with a switch wired to the junction of the two resistors. and one pole wired to ground and the other wired to V+. so switching either way will either short the top resistor or bottom resistor. thats how the pots and relay are arranged.

and yeah you need the 820R in place of the K1C coil Its not so the other coils will work properly tho. K3C and K4C wont be effected. but K2 will now have 24V across i rather than 12V! so the resistor is to bring it back down to 12V so as not to damage the relay. you also need to shrt the pins that correspond to the NC contacts. if not then neither set of pots are switched properly. hence shorting pins 2&3 and also 6&7.

puppiesonacid wrote: Thanks,
Tony

Your welcome! I'm still kinda new to the forum so just glad i can contribute back!

I havent had a chance to look at adding seperate pre/post controls for the clean/crunch section yet tho. but i will when i have time! when you switch from clean to crunch it isnt changing to different tubes or anything so you can simply wire the pots onto that switching path. what it does is change the voicing of the clean channel and allows more signal to pass through and drive the tubes harder. so adding another set of controls to the other side of the relay wont help. you will prob have to do it with a switching arrangement like FJA does but when i have time il help you with that too. basically what i have in mind is copy the switching arrangement for the res/pres controls and adapt that to the pre/post controls! as i said il work on it later!!

DeanM wrote:when you switch from clean to crunch it isnt changing to different tubes or anything so you can simply wire the pots onto that switching path.

it wouldnt let me edit so to avoid confusion this should be can't

DeanM wrote:

DeanM wrote:when you switch from clean to crunch it isnt changing to different tubes or anything so you can simply wire the pots onto that switching path.

it wouldnt let me edit so to avoid confusion this should be can't

damn, thats what i was hoping to do. i thought it would be like craig andertons mod for adding new pots to have switchable "presets" for say a speed setting on a trem or something.

Well...if there really is no way around it then I guess doing the seperate switching circuit is the only other way to do it, right? I was just hoping to be able to do it with manipulating existing circuitry so I can keep the amp looking stock on the outside.

In addition, I really would love to get a lot of the popular 5150 mods out there. Im sick of not having this information out there, b/c there are only a few guys out there that seem to be really into the peavey 5150 modifications and they aren't sharing any of thier methods.

Thanks for your help so far, glad I'm understanding this stuff right.


Hope to hear from you soon,

puppiesonacid.

Looking through the schematic some more I gues I still don't understand why I can't do the modification using the existing circuitry by rerouting the signal path.

DeanM wrote:

puppiesonacid wrote:ok so if im understanding you correctly, K1 is in series with k2. but k1's primary function is to simulaneously switch in tandum with K2 so the lead resonance/prescence controls are engaged when the lead channels is engaged.

Yes thats what is happening when you switch channels.

puppiesonacid wrote: Pulling K1 and that capacitor will free up the lead/resonance controls on the lead channel
so I would want to designate the lead prescence and resonance controls as the new post and pre controls for the rhythm channel when the crunch is engaged?

but you have to put an 820R in its place to keep the split rail voltage for the other relays to work properly ?
Am I understanding you correctly?

No its not a capacitor, its a diode. its normal practice to place a diode across a coil so that when a the coil is de-energized, the collapsing field of the inductive coil is allowed to dissipate.

But yeah you are understanding correctly. it will free up the lead res/pres controls. K1 just shorts either one when it switches. for example when in clean mode the lead presense is is shorted and clean pres pot is grounded. when in lead mode clean pres is shorted and lead pres is now connected. Think of it like a voltage divider with a switch wired to the junction of the two resistors. and one pole wired to ground and the other wired to V+. so switching either way will either short the top resistor or bottom resistor. thats how the pots and relay are arranged.

and yeah you need the 820R in place of the K1C coil Its not so the other coils will work properly tho. K3C and K4C wont be effected. but K2 will now have 24V across i rather than 12V! so the resistor is to bring it back down to 12V so as not to damage the relay. you also need to shrt the pins that correspond to the NC contacts. if not then neither set of pots are switched properly. hence shorting pins 2&3 and also 6&7.

puppiesonacid wrote: Thanks,
Tony

Your welcome! I'm still kinda new to the forum so just glad i can contribute back!

I havent had a chance to look at adding seperate pre/post controls for the clean/crunch section yet tho. but i will when i have time! when you switch from clean to crunch it isnt changing to different tubes or anything so you can simply wire the pots onto that switching path. what it does is change the voicing of the clean channel and allows more signal to pass through and drive the tubes harder. so adding another set of controls to the other side of the relay wont help. you will prob have to do it with a switching arrangement like FJA does but when i have time il help you with that too. basically what i have in mind is copy the switching arrangement for the res/pres controls and adapt that to the pre/post controls! as i said il work on it later!!

so what would the end result of all that you mentioned be? if it's not what I'm looking for then it only changes the voicing of the clean channel?

hey man sorry i havent gotten back to you about this! I've been so busy this last week! i worked from 8:30 - 20:00 today!! but i havent forgotten dude!

DeanM wrote:hey man sorry i havent gotten back to you about this! I've been so busy this last week! i worked from 8:30 - 20:00 today!! but i havent forgotten dude!

im patient bro haha, Im working full time, married, own a house, and now im taking an online accounting course... so I know busy. Thanks for making a reply though, I really hope we can come up with something.

respectfully,

puppiesonacid

its been a while but just wondering if anyone could help develop this mod?

I haven't read your post in detail but here's my 2c:


To keep the stock look of the amp use double independent pots(push-pull),if you cant find the correct value you can always change the resistor inside(on some at least).
then do just switching.If you already thought of this .....disregard.

Fot the price of the mod and maybe a few more bucks , buy a dedicated amp for cleans,a combo or just a head and build an amp head switch.