Friday, March 27, 2009

Fixing up my 1987 Peavey Renown 400 Guitar Amp

Back in 1987 I purchased this Peavey Renown 400 Solo Series guitar amplifier new from Rondo Music in New Jersey. Shortly thereafter I replaced the standard black netting with groovy paisley fabric purchased from a local Ralph Lauren store.

The amp is somewhat unique in that the two Scorpion Plus 12 inch 8 ohm speakers are 200 watts each and the head can put out 210 watts. And that's continuous, not peak. The magnets on these things are 9 lbs. You know those amps that "go to 11"? Well I've never actually turned this up beyond about 4. You just can't do it because it gives you a strong sense that something bad is going to happen.

The functionality of the amp is fairly straight forward. It has two channels - Lead Gain and Normal Gain. There are lots of equalizer settings so it makes a good multi-purpose foundation for guitar or a PA. I used to run music through this at parties. The distortion is nothing special but there are jacks in the back to insert your effects between the pre-amp output and power-amp input.

After 20+ years of sitting unused in my mother's attic I tried to sell this filth covered 70 pounder at her garage sale for $40. But clearly it had problems so it didn't sell. One of the speakers was blown and the sound would cut out as you played.

But being the problem-solver type I decided to try to resurrect this beast. I'm not an EE but dad is and I managed to get some help from someone on a Peavey forum who actually knew something about this model. Fortunately it turned out there wasn't much wrong with the amp at all aside from a loose connection somewhere. If I jammed on the guitar while I whacked the casing with the rubber handle of a pair of heavy pliers I would get a little static and then the sound would cut out. I never identified the specific connection responsible but after I briefly remelted the solder joints on all of the filter capacitors and power transistors and re-hot glued some of the larger components, the amp has been solid ever since. I've never heard so much as a hiccup.

With the amp working well I set out to just clean it up. I scrubbed the cabinet inside and out with a dilute solution of Simple Green and wiped it down with a wash cloth. An old horse hair brush worked very well at getting into the Tolex. I used a lint roller to clean the fabric cover which was totally impregnated with dust. Note that the "3M/Scotch" lint rollers are much better than everything else. I used a tooth brush on the grooves of each knob. I did not submerge them or use a cleaning agent as I feared it might loosen the colored plastic tabs.

There is supposed to be a foot switch to toggle each channel and the reverb. But I lost it so I rigged up a hand switch instead. I went to Radio Shack and bought a Center-Off DPDT micro-switch for switching channels and a SPDT for enabling the reverb (an SPDT and SPST would work equally well of course but they were out of those particular switches). Now I can just reach behind and flip it to the left for the Lead Gain channel, to the right for the Normal Gain channel and center it to leave both channels on.

I used some alligator jumpers to test the switches and figure out the wiring. Then I made a switch plate to fit in place of the foot switch DIN using a small piece of aluminum roof flashing folded in two. I wired everything in parallel to the foot switch DIN connector so that if a foot switch should turn up I could just bolt it back in place without rewiring anything. Finally I put the DIN connector in a small plastic bag so that it cannot rattle around or short-out on anything.

I think it's definitely worth $40 now.


midiman said...

Hi mike,nice job you have done.I just got one these for £20(uk).I am trying to figure out the wire connections so I can build my own footswitch.Is this the correct "pinout" colour code-?

Mavis said...

Cool article -

I really like the funky grill cloth!

I have the other remaining working Renown 400.

I have kept it in working order since I bought it new in 1987 and just took it out again - I'm in a band after 20 years away and my little Fender with the single 10" speaker was about to blow up at practice so I had to bring in Big Bertha.

Still works perfectly and I got a big charge out of what you said "Never turned it up over 4 because you get the feeling that something terrible will happen."

shoorayner said...

This is great. My son has just been given one of these. The wires weren't connected to the speakers. I've reconnected them and it works pretty well. I'll open it up and check connections. The inputs are a bit rusty.

I'd love to know if I've got the speakers right before they blow!

there are 2 jacks at the back for parallell speakers. I've got a plug in this connected to the two speakers inside the case, which are in parallell. Is that right?

It starts to hum a bit when the reverb is up high. does yours do that?

you are right that you feel you shouldn't turn it up too high-- feels like a beast lurking inside!

Waveform said...

This is an incredible blog Michael! What a beautiful job restoring this Gem. Seeing this amp in your blog is very nostalgic to me, It was a part of my life when I was 11ys old. Back in 1985 I bought a Renown400 off my friend, and later sold it because I was a fool. When you said you’ve never raised the volume past 4, believe me I know exactly what you’re talking about. That sucker will put a man through a wall, and with a BOSS DS1, and a PH3 Phaser Shifter, that is an animal to be kept on a leash.
I just found two used R-400 solos at two different stores and they should be here by next week. I usually don't buy things without seeing them, but I couldn't chance it, I had to lock down on them. I’m really hopping the shells on these amps can be cleaned and doesn’t have any serous dents, or rips. According to the stores I got them from, they said they are in good shape, just really dusty.
Just curious, I think everything works according to what the store said, but I was wondering, I know you mentioned that your father worked on this. Can any of these components be replaced with the same matched electronics from say radio shake, or would that alter the sound in anyway? I’m just curious in the event that I would have to work on them in the future, I don’t want to hinder the tone in anyway. I know the transformer is another story, I mean I know transformers are usually custom wound, so that would be something I would definitely have to get that from Peavey if those went bad. But you know, can all the other electronics inside there be replaced? I found out that Peavey still sells the black outer coating for the amp shell the support rep was telling me that to rap the outer shell is a real art, and not something just anyone can do. If I have to, I’ll probably just bring it into a certified Peavey shop near my home, but I’m hoping I won’t have to. Once again, Great job on fixing this amp up, and the new cover really looks great!

Mike G

Mike said...

Yes Mike G. the parts in the Renown 400 can be easily replaced. The circuit construction very slightly predates modern PCB fabrication so the copper traces are big and robust and of course it does not have any tiny surface mount components. So if you find a bad filter capacitor or power transistor, you can easily mail order that part from mouser or digkey (but almost certainly not at Radio Shack) and replace things. The only thing you might have a hard time finding are some of the more exotic potentiometers with dual concentric shafts and such. So if you have any really scratchy pots you might try to take them apart and carefully clean the contacts.

Note that the Renown 400 is a compelling target for modification. For example, it is filled with 4558 op amps mounted in sockets (at least mine is). The 4558 is not exactly a high performance chip by today's standards. If I had the time I would love to see what would happen if I put all new OPA2132s in this amp. Or 5532s would be good too for about 1/6th the cost.

Waveform said...

Interesting about the op amps Mike, Thanks for the response!
Well, I got the two amps, they are both in mint condition, but one of them I have to replace a speaker and the other amp has a bad pot, but I’m amazed how new these amps look for being 25 years old. I’m giving one to my friend but I want it to be perfect. I have another friend who is a recording engineer, and like your father he is very experienced in electronic repairs, so I’m dropping the amp off with him to fix that post-pot, but everything else is working great. I was on the phone with Peavey, and although they sell most of these pots still, the ones that they don’t have, I guess you can substitute, say a 10K with a 25K according to the repair guy at Peavey as well as my friend who also confirmed this. I got the Funk-Out that Peavey sells, and it helped a little, but I think the pot is bad. But I didn’t know you could take apart a pot and fix it manually. Interesting.
By the way, I noticed you added a switch on the back of your amp for the pedal, I just ordered a switch from which has an identical switched for the Renown400 made exclusively for this amp. Channel/Combiner/Reverb. So, You might want to check there if your looking for one with your amp Mike.

The Other Mailman said...

Do you think that, given the power and speaker size, this amp could be used for bass? And if not, could it be converted?

Ross said...

Hi Michael,

Please tell me the color of the stock footswitch wires which control;

1. Clean
2. Lead
3. Reverb

I want to wire in a Tip-Ring-Sleeve jack to switch channels and the reverb (don't need the "Combine" function).



gerald giordano said...

I also have this monster.
My reverb will not stay off. It's in the pot.
If I keep wiggling the pot to make it briefly shut up
I'm going to completely destroy the pot.
Is there anything I can do short of replacing the pot to fix it?
I was thinking of putting an inline switch into the wire to the reverb box itself.
Will I mess it up if I open that circut or just twist the wires together. I gig every week so I need a qui k fix.

Richard Kent Berger said...

Can anyone suggest a powersoak mod to add a pot to limit the output of the lead channel post pot (the blue one). I want to get more control over this beautiful beast. It just comes on strong TOO fast. Thanks.

Mike said...

@Richard Kent Berger - If you google for "peavey renown 400 schematic" look for the 100 ohm resistor labelled R165. This is the power amp "feedback" resistor. If you solder a 10 ohm resistor right on top of the existing one (meaning in parallel), I think that would drastically reduce the power of this amp. Easy mod. I don't know how to add attachments here but in my scan someone actually wrote "if open will cause low gain". This is actually an inaccurate statement. If you were to create an open circuit (meaning remove it), the thing would probably explode in your face the moment you turned it on. What you want to do is add another smaller resistor in parallel with R165. Resistors in parallel reduce the resistance. If you reduce the resistance, more output is fed back (thus in engineering terminology it's called feedback) which throttles the input of the power amp. Meaning the output is fed back into the input to cancel some of the input signal and thus reduce overall gain. And a side effect of doing this is that it will improve linearity and bandwidth. Note that your amp may not really be just like the schematic on the net. But if your amp is anything like the schematic floating around, you can probably locate R165 on your board by looking for the large ceramic 0.1 ohm 10W resistor next to the speaker output wires. You can actually see this resistor in one of the pics here. That resistor is R164 which is connected to the same trace as R165. R165 is probably an average looking resistor. If you go to Radio Shack and get a soldering iron kit and a 100 ohm 0.5+ watt resistor and solder it in in parallel, I think it will dramatically reduce the output level. And all functionality will remain intact. It should sound exactly same, just quieter.

andybrattt said...

What an awesome job!! Well done.
Ima restoring one as well & have built a pedal for it.
My problem is that I got it with no input sockets & Im having trouble trying to work out the color codes & wiring!!
Do you have a picture of the Input socket part of the amp?

LVheretic said...

Hi Andy,
My parents bought me a new Renown when I was 18... have had it since and find I prefer its clean sound better than most so I use an AB switch between it and my Marshall JCM 1/2 stack. Anyways, I will see if I can get a pic of the socket when I get home.
Nick/Las Vegas

LVheretic said...

Ok, since I cannot post a pic, here is the link.

Basically, the footswitch is connected by a one row blade connector with 4 wires. As you face the back of the amp, footswitch is in the top right side. In order from the closest to the front of the amp the wires are BLACK, BLUE, GREEN and WHITE.

If you have not seen the footswitch itself, it has 3 buttons. Left to right are channel selection, combiner, and reverb.

Hope this is of some help to you. Nothing has been replaced or changed in my amp since it was bought so if there is anything that will help you along just ask.

If anyone has any ideas on why my channels bleed over each other please let me know. And no, the combiner is not switched on.


andybrattt said...

Hey thanks Nick!!
It was acually the wiring of the input sockets (high gain,low gain)
I replaced them with Dimarzio sockets & got some help from Peavey (Am impressed with their support indeed!!)
Think I got it right now..the Dimarzio sockets are similar to EMG sockets being ns switching sockets but the original Peavey look like this:

the Dimarzio ones I put in look like this.

The trick was to not only to earth both together but get the right (2nd earth, for want of a better phrase)
to the right connector on the high gain socket..
Some alligator clip testing got me there in the end but to have both sockets running at the same time I have to have one jack half way in..a function I will rarely use tho!!
Thanks for all your help & would still love to see a picture of the original internal wiring of the input sockets!!
New Zealand