KB60 IC questions

This forum is for talking about Peavey keyboard amplifiers.
dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

KB60 IC questions

Post by dadroadie » Mon Jul 23, 2018 1:52 pm

KB-60 complete schematic.pdf
(865.79 KiB) Downloaded 202 times
Hi to All,
I currently have an older Peavey KB60 that I’m working on for a friend. He picked it up used off of Craig’s List . It needs some work! He has borrowed my KB60 so often that he wanted to get his own.
I found something interesting when I pulled the chassis to check the solder joints. (It’s intermittent).All of the IC’s that are normally 4558 U1 thru U6 have been replaced with NE5532 chips (see attached schematic). I know this chip gives better response but if I remember correctly it also draws twice the current. Is this an accident waiting to happen? Should I replace them with the 4558 chips? As A note I looked at my KB60 and all of the chips mentioned are 4558s.
Also the reverb chip 87478IC (U7 on the schematic) has been replaced with a 70413080 IC. Does anyone know if this would be a substitute? The reverb does work with this chip but again I’m looking to make this amp as reliable as possible.
Any help or suggestions would be greatly appreciated. I know Peavey still carries the 4558 chip but I’m not sure about the 87478 IC
All the Best!
dad roadie

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: KB60 IC questions

Post by Enzo » Mon Jul 23, 2018 2:56 pm

Intermittent sound? Clean the cutout contact on the Power Amp In jack and also the one on the Pre-EQ Patch jack.

5532 will not give you better response, but it can reduce noise. 5532 has a lower noise figure. That is potentially lower noise, the old 4558s work darn well themselves, and noise may not have been an issue. But that is why someone would do that. U1, U2 are where it would likely make the most difference, if any.

Twice the current? Context is everything. In a mixer with 100 of the things, yes I'd be concerned. Your amp has a half dozen of them. Allow me a story. Imagine you are playing your guitar, and my guitar is twice as loud. Is mine to loud? If you are dimed on a 100 watt Marshall, then sure. But what if you were strumming the strings with no amp, and I was too. But my guitar strings made more sound than yours. In either case neither guitar is loud, so I am not "too loud". COntext matters.

SO back to your 5532, the data sheet says it draws about 10ma. That is then 60ma. The power supply will not be stressed by that.

The 87478 chip has nothing to do with your reverb. U7 is the compressor IC in the power amp. Your IC is a good sub for the original in some circuits. I will assume the amp is working? If so, leave it. I find if the amp is working, that is a good point to stop fixing it.

U4 is the reverb IC. It would probably be happier as a 4558. But if the 5532 is working there now, leave it.


These days 4580 is a more common general purpose op amp, and if I had to replace a 4558, I would most times go for the 4580 anyway.

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Mon Jul 23, 2018 4:39 pm

Thanks Enzo,
I'll leave the 5532s in the amp as suggested. I'm also going to check all the solder joints on the jacks and clean the contacts while the amp is out of the speaker cabinet.
This poor amp has seen a rough life. Someone actually sprayed the whole speaker cone with automotive undercoating ! The speaker did not have any rip's so I don't have a clue why. The stuff even got into the reverb tank! Luckily I have a spare speaker and I cleaned the goop off the tank so its now working. (I tested it with my KB60).
I did have a question on the 70413080 sub for the87478. You mentioned (see below)
The 87478 chip has nothing to do with your reverb. U7 is the compressor IC in the power amp. Your IC is a good sub for the original in some circuits. I will assume the amp is working? If so, leave it. I find if the amp is working, that is a good point to stop fixing it.

You had mentioned that this chip is used as a compressor IC in the power amp .Also that it is a good sub for the original in some circuits .
Is this one of those circuits? Also when I bench test the amp after doing the soldering and jack cleaning if this chip was defective what effect would it have on the amp the amp ?

Symptoms: the amp powers on. The volume pots are cutting in and out. The bass control is acting like a volume control. After plugging a cable in and out several times all the jacks I at least got some signal though. After pulling the board it does appear to have several solder joints that need touched up. That's as far as I have gotten so far.
I wanted to thank you again for your help and suggestions. I can see that you help a lot of folks on this site. I'm sure all appreciate It!
All the Best!
dad roadie

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Mon Jul 23, 2018 7:29 pm

Hi Enzo,
Thanks for the help,
I did repair the solder joints and cleaned all the pots and jacks. The amp seems to be working now with the exception of the reverb. When you turn up the reverb control at all the amp starts to feedback. I believe it might be a monophonic reverb pan. If I touch either of the springs when its howling it stops. Is that usually a good sign that the pans defective? I did but a 4558 in the reverb circuit but either chip (5532 or 4558) causes the same issue Looking at the pan it looks like it is not the original. I,m hesitate to open my KB60 up again and pull the pan but that may be the only why to tell.
Any other things to check or suggestions please let me know.
All the best!
dad roadie

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Thu Jul 26, 2018 4:31 pm

To All,
Just an update to the update. I may be barking up the wrong tree in regards to the microphonic reverb pan. I pulled the chassis and the tank and have both on my workbench. I'm using the headphone jack instead of the speaker to monitor the output. The reverb tank is sitting on some padding. so I do not believe it's seeing any vibration. As I mentioned I believe the springs have something to do with the feedback because I can get the feedback to stop if I put my finger on both of them. I would think if the pan was microphonic that it would need some sort of vibration to start howling. Could to strong of a signal from the amp clause this? I don't believe the pan is the original to the amp. If the input and output impedance is incorrect could that be the issue? Would anyone know what the correct impedance I should look for ? I may still need to order one. I have already swapped the Reverb IC chip as suggested with no change. Other than the reverb issue the amp really sounds clean and clear. Thanks in advance for any suggestions.
dad roadie

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: KB60 IC questions

Post by Enzo » Thu Jul 26, 2018 5:18 pm

The schematic says 87478, but you have a something else I forget. The something else doesn't ALWAYS work in place of a 87478, but does in many circuits. SO they sometimes used the something when they didn't have stock of the originals. SO I have no problem seeing it here. I might not like to see it in an old Phaser circuit or some such. If the amp works forget the IC and move on.


The only time the 87478 does anything is when the power amp is driven to clip. At that time it limits output to prevent clipping. You won't ever hear the IC other than when you find that you just cannot clip the power amp.

Reverbs can feed back. First, what number is on your pan? Should be 4EBxxx or 8EBxxx, the xxx's are what I need to know.

With the amp running and the cables unplugged from the reverb pan, touch the tip of each cable with a finger. One should result in hum. THAT one plugs into the OUTPUT jack on the pan.

Before you plug it back up, measure resistance across each pan jack. The resistance won't be wrong unless the pan is the wrong type, but we want to be sure the pan is not open at either end. Also, on the INPUT jack, measure resistance from the outer portion of the jack to the metal pan itself. There should NOT be continuity.

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Thu Jul 26, 2018 7:51 pm

Hi Enzo,
Thanks for your reply . This is the information that you ask about.
The way I'm testing : I pulled the chassis and the tank and have both on my workbench. I'm using the headphone jack instead of the speaker to monitor the output. The reverb tank is sitting on some padding away from the amp chassis so I do not believe it's seeing any vibration. As I mentioned if I put my finger on both the springs the feedback stops. Does this sound like a microphonic pan?

The number on the reverb pan is 31-145-94 this is the only information on the pan. I have no way to be sure this is the original pan but doubt it is.

I tested the cables unplugged from the pan with the amp on . I got hum when I touched the cable tip that was normally hooked on to the output on the pan.None on the input cable so I believe that's ok.

Measuring the output pan connection I got 369K ohms . On the input I got 96 ohms . If this is not correct do you know what it should be in case I have to order a new one?
The input contact outside connection (RCA) does not have continuity to the case. The output does. so this appears ok.

Everything else seems to be working correctly now thanks to your help!

Thanks in advance for any suggestions.
dad roadie

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: KB60 IC questions

Post by Enzo » Fri Jul 27, 2018 12:31 am

369k ohms sound open. Even 369 OHMS would be high. I expect around 200 ohms.

The OUTPUT end is just like a guitar pickup, it is a coil of wire.


That is not original, Peavey does not have part numbers in that format.

There are two sizes of reverb pan, the full size which are something like 16 inches long, and the short ones which are like 8 inches long. Long ones start with 4, short ones start with 8. SO whichever size you need, you need a EB2C1B reverb pan. SO 4EB2C1B or 8EB2C1B. Oh there is also the 9EB2C1B, which is also large size and has three springs inside instead of just two.

The pan can feed back electrically, though mostly we deal with acoustic feedback.

I could be wrong from afar, but I think your output transducer is open, and leaving the return circuit unterminated, so it acts like an antenna.

Do you have any other amps with reverb pans you could borrow for testing? Most solid state amps have what you need, as well as most Peavey amps of any sort. All tube amps like Fender than use a small reverb transformer use a different impedance that will not work here.

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Fri Jul 27, 2018 4:03 pm

Hi Enzo
Thanks for the reply,
Over the weekend I'll pull the reverb out of my KB60 (The one I'm working on belongs to a friend) and see if it works. The pan in mine is not the original so the number wont help. I contacted Peavey and they have the part .Their part number is 31011152- 2-SPRING SMALL REV . I have a feeling that it will be more the the MOD reverb units that Antique Radio Supply sell. Having the info that I got from Peavey do you know what the numbers you mentioned before would be the correct sub? If the Peavey price is close I will of course order it from them. Could I sub a 3 spring unit instead of a 2 ? I know that my friend likes to play some sulf music know and then with his guitar. Thanks again for all the help!!
dad roadie

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: KB60 IC questions

Post by Enzo » Fri Jul 27, 2018 6:44 pm

The 310 number is the PEAVEY part number. The 4EB2C1B number is the reverb manufacturer type. Each amp maker assigns his own part number to the same pan. If you buy one from other than Peavey, that 4EB number is the thing.

Accutronics was THE brand for years, but they were bought by Belton, and now we also have MOD pans. SO you won't find an original Accutronics pan new.

The 4EB2C1B is a two long spring unit. The 9EB2C1B is the three long spring unit. Electrically they are interchangeable. The circuit has no idea how many springs are in there. The three spring type doesn't make MORE reverb, it just makes a more complex reverb sound.

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Sat Jul 28, 2018 11:38 am

Hi Enzo,
The plot thickens!
I opened up my KB60 and pulled the pan . When I hooked my pan up to the KB60 I'm working on it still howls the same as the other pan. I then installed the pan I thought might be defective in my amp and the reverb worked fine. I must have been measuring incorrectly since both pans work in my amp. While I had it open I did swap the 874748 chip out of my amp to the other one one . It didn't change any thing so I put both back. Is there anything else you could think of that would drive the reverb signal to overload to the point of feedback? The reverb pan is ruled out, I checked the cables, and I have changed the 4558 chip already. I know there is not a lot left in the circuit. I may be grasping a straws but could it be the reverb pot? Any ideals would be most welcome.
Thanks again for the help!
dad roadie

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: KB60 IC questions

Post by Enzo » Sat Jul 28, 2018 1:36 pm

Don't guess, find out.

OK try this: The return cable from OUTPUT has a male RCA plug. Pull it off the pan, and (power off) measure resistance from the outer "petals" to ground. You SHOULD see close to zero ohms - ie. continuity, If you see around 100k, then the cable is wired backwards at the amp end. Step two is to measure from the tip of the RCA plug to ground. If THAt seems grounded, again, we are backwards. From the tip SHOULD be about 100k. If the number is not 100k, don't worry, all I care about in this test is if the ground is on the wrong side.



If that turns out to be the case, then the wires need to be swapped at the molex. Look on your layout. P103 on the end should be ground, and so should have the shield of the RCA cable.

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Sat Jul 28, 2018 2:45 pm

Hi Enzo,
I went and measured and got the following:
Output rca cable unplugged from pan but still connected to amp"
Outside of RCA connector (pedals ) to ground (about 19 ohms)
RCA tip to ground (100K)
Thanks again for the HELP!
dad roadie

User avatar
Enzo
Member
Posts: 9089
Joined: Fri Sep 12, 2008 10:24 pm
Location: Lansing, Michigan

Re: KB60 IC questions

Post by Enzo » Sat Jul 28, 2018 4:19 pm

OK, so it is not that.

dadroadie
Member
Posts: 22
Joined: Mon Jul 23, 2018 1:37 pm

Re: KB60 IC questions

Post by dadroadie » Sat Jul 28, 2018 4:59 pm

Hi Enzo,
Any other things that you would suggest that I check? I truly appreciate your time and sharing your knowledge. I'm just trying to help a friend out.
The symptom is best described as the reverb control when turned up at all driving the signal into a howling feedback, like sticking a microphone in front of a speaker. The reverb is present when turning the knob , But at 1 the reverb sounds like a normal reverb control at 10 and anything above 1 it feeds back. I think it has something to do with the reverb circuit. When the reverb control is at 0 the rest of the controls and the amp work fine.
Thanks again!
dad roadie

Post Reply