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Why 4 channels? [message #8192]

Wed, 07 February 2007 11:06

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

My K-200 A5 has 4 input channels. For the life of me, I can't figure out why they would waste so much space and money inside this thing to provide 4 completely separate input channels.

To reduce the noise, I'm thinking about cutting this down to just 2 functional input channels (which is still probably one more than I need as a bass player).

The A5 version has the "Ross PC102" input boards, which seem quite a bit different from the earlier schematic. The PC102 is about 5 1/2 inches tall, and about 3 3/4 inches wide. I'm just assuming the input transistors are at the top of these boards?, since the input trace runs up there. There's one NPN, and one PNP...does that sound right?

Anyway, I was thinking about just useing the two input channels on the left side...farthest away from the power transformer. I'm guessing I could just power the others down. Looks like there's a red wire running (looping) the power to all the input channel boards. My thought was to just unsolder the power wire that runs over to the two on the right side (channels 3 and 4). It would be pretty easy to re-connect it if I were ever to sell it...so it would be back to stock.

Anyone have any thoughts on this?

BTW, bench tested this baby last night, and it makes an even 100 watts RMS into 4 ohms at clipping. Going straight into the power amp section (blue wire from the summing board), the frequency response is amazingly flat, and distortion is very low. Much better than I expected from an amp which uses 2N3055 (basically voltage regulator transistors) for the outputs.

Dave O.

Dave 0 Wall-O-Bass
Webpage - <a href="http://webpages.charter.net/daveobieone/" target="_blank">http://webpages.charter.net/daveobieone/</a >

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Re: Why 4 channels? [message #8193 is a reply to message #8192]

Wed, 07 February 2007 12:57

stevem is currently offline

stevem
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Registered: June 2004
Location: NY

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Hi, well the A5 model is the PA head, and I remember back when (circa 1971)
my band got our k200 A5 that 4 channels was not enough, so on the channel for our drummers vocal mic I used a little 4 input 22 dollar mixer from radio shack so we could also get 2 mics on his drums.
Unpowering the preamp boards should work fine, how much less gain hiss you will loose I can`t say.
Kustom back then took the time to use matched 2n3055 T03`s, proibly the reason most of these heads to this day have not failed any of its original outputs.

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Re: Why 4 channels? [message #8194 is a reply to message #8193]

Wed, 07 February 2007 14:28

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

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Wow, I didn't know that was the PA head...that would certainly explain why 4 channels. The EQ curves do seem pretty well suited for guitar however...or bass for that matter.

I always learn something good from you Steve!!!

Our bands PA was the 6 channel 300...I added some horns to the tops of the colums.

Pretty sure mine still has the original output transistors. Come to think of it, I don't think I've ever seen a Kustom K200 or K400 with failed output transistors...although I'm sure it happened.

I was really impressed at the quality of parts in this amp. I've been checking all the caps for high ESR, and with the exception of the one in the reverb driver, they have all been like new. They even used very expensive metal-film resistors in the first stage pre-amps.

Kustoms were pretty high-dollar amps when they were new (I know, I bought some new), this would explain why. Folks actually got what they paid for!...besides the pretty covering. Mr. Ross should be proud!

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8197 is a reply to message #8192]

Wed, 07 February 2007 19:28

rodak
Messages: 511
Registered: October 2001
Location: Georgia

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High "ESR"? Don't think I've ever heard of that. What's ESR, and how to you test it?

www.combo-organ.com

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Re: Why 4 channels? [message #8200 is a reply to message #8197]

Wed, 07 February 2007 23:33

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

Equivalent Series Resistance

It is checked with a meter which runs a high frequency sine wave (usually 100khz) through the capacitor...and checks it's resistance.

As caps begin to age and fail, they will show high ESR long before the value starts to change. It’s not at all unusual to have a cap which measures right on in value (capacitance), but has high ESR, which will contribute to really lousy audio quality.

The nice thing is, you can usually check a cap reliably for ESR while it's in circuit with a good ESR meter.

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8204 is a reply to message #8192]

Thu, 08 February 2007 07:17

rodak
Messages: 511
Registered: October 2001
Location: Georgia

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Hey, you learn something new every day. Is an ESR meter expensive?

www.combo-organ.com

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Re: Why 4 channels? [message #8206 is a reply to message #8204]

Thu, 08 February 2007 09:18

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

Think I paid about $200 for my "Capacitor Wizard". Don't think that model is available any more. I love it because it has an analog meter. There are others however. Just type in "ESR Meter" in Google, and you will come up with some.

This one seems well thought-of...
http://www.anatekcorp.com/testequipment/atlasesr60.htm

I've finally tracked the hiss problem in my head down to the summing board, which also has the reverb driver/pre-amp. Sure wish I could find a schematic for that thing. I'm guessing it may have only been used on the A5 chassis.

Guess I'll change a few transistors, and see if that helps. There's a ton of carbon-comp resistors on that board however, with really low levels running through them.

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8207 is a reply to message #8192]

Thu, 08 February 2007 12:59

stevem is currently offline

stevem
Messages: 4733
Registered: June 2004
Location: NY

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Back in high school, shortly after we got our k200 PA, I wanted better highs out of the columes, so the guitar player the drummer and myself went over to the high school one eveining and took 2 of the atlas paging horns down off one side of the biulding, I made new speaker run cables to get everything hooked up and the next friday night we played a dance in that same high school nervous as hell that someone would know where those horns came from!
I guess those output transistors where pretty good to take that screwy impeadance load that I knew nothing about back than.

I have seen carbon comp resistors make noise with tube type 250 or more volts going thru them, not sure if changing some of them out would help, but their cheap enough to try Dave.

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Re: Why 4 channels? [message #8209 is a reply to message #8207]

Thu, 08 February 2007 16:39

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

How funny, we must lead parallel lives.
One of my first bands did the very same thing...only the horns were from a grade school!

I painted them bright red to cover our dastardly deed.

The horns didn’t last very long however, because I didn’t know how to high-pass them. Those old PA horns didn't like all that much bass. That PA screamed for a few months though!

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8212 is a reply to message #8192]

Fri, 09 February 2007 06:36

stevem is currently offline

stevem
Messages: 4733
Registered: June 2004
Location: NY

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Yea, our horns blew out also at some point, but by then that menber make up of the band had changed due to the guitar player getting his hands cut up badly in a basement window accident.
As I recall the next guitar player had peavey cabinets with a 15 and a nice big raidal horn that blew the kustoms away, we would only use the kustoms at that point for practice.

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Re: Why 4 channels? [message #8214 is a reply to message #8212]

Fri, 09 February 2007 08:53

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

BTW, finally found and fixed the primary hiss problem / source in my K200 A5.

As I suspected, it was in the summing / reverb board mounted to the floor of the chassis. There are some stages on that board with extremely low levels. That, coupled with marginal transistors was making for a lot of noise.

Replaced the transistors in the middle of that board last night, and the hiss level dropped by almost 15db!

Next I’ll give the reverb pre-amp a similar treatment…as it’s now the noisiest thing in the amp. With the reverb shut-down, you can hardly tell the amp is on now.

I may go ahead and post this under a new topic line…just in case there are some others with that version of head living with similar problems.

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8219 is a reply to message #8192]

Fri, 09 February 2007 18:39

JohnnyR is currently offline

JohnnyR
Messages: 12
Registered: December 2006
Location: Shelby, NC

Junior Member

Hi, normally, the unused inputs are grounded via the use of a switching jack for the input. The only open inputs should be the ones you are plugged into. I'd doubt the inputs are the cause of noise. If you'd like, let me know, I have several tips on noise reduction........JohnnyR

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Re: Why 4 channels? [message #8232 is a reply to message #8219]

Sun, 11 February 2007 16:54

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

True, the inputs are shorted, but I was thinking about reducing the amount of hiss added to the system by the amplifier stages following the inputs. Turns out, the pre-amps really don't add that much noise...so I now have all 4 running again.

Lately, I've been working on improving the internal grounding. Using that thin aluminum chassis to carry all the common grounding wasn't the greatest idea.

I've also stiffened up the regulated power supplies...which really helped to get rid of some of the nasty, buzzing distortion when the amp is driven hard into clipping.

Some folks may like that "crunchy" sounding distortion for guitar, but for bass, it sounds really bad to me...like a blown speaker.

I'm always interested in additional ideas for reducing noise. At this point however, the noise from my bass pick-ups is about as loud as the noise from this K200 head. It's getting VERY quiet!

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8246 is a reply to message #8232]

Mon, 12 February 2007 14:30

JohnnyR is currently offline

JohnnyR
Messages: 12
Registered: December 2006
Location: Shelby, NC

Junior Member

Hi, the noise can be minimized by using the single point grounding method. My amp is actually grounded at the speaker jack connection to the chassis. If you decide to go with a grounded cord, and eliminate the excess AC wiring, and the polarity switch, and ground the cord to the connection it originates from(not just anywhere on the chassis), you will eliminate the possibility of a ground loop. Also, I wish to express that an enclosed chassis made of aluminum is actually an excellent overall shield to EMI and RFI. Good quality Filter caps of a higher uF rating will also help get rid of AC ripple voltage and current flow at the DC supply rectified voltage. Good Luck!..........JohnnyR

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Re: Why 4 channels? [message #8247 is a reply to message #8246]

Mon, 12 February 2007 14:51

daveobergoenner@gmail.com is currently offline

daveobergoenner@gmail.com
Messages: 104
Registered: January 2007
Location: Missouri

Senior Member

Hi Johnny, and thanks for your thoughts!

My K200 A5 does not have a fully enclosed chassis...maybe mine is missing something.?. Mine only has a front, bottom, and back....no sides or top. I really wish it was fully enclosed. Would be great for RF shielding.

My K200 was also only grounded at the output jack, and via the chassis to all the other boards. I installed some heavy, stranded wires to create a star grounding system too. I also ran another heavy gauge wire down from the common point of the filter caps to the chassis...between the caps. That is now the chassis ground.

I haven’t yet replaced the power cord with a 3 pin. That would seem like the best thing to do, but most of the outlets in my house are not grounded...so the extra ground in the power cable wouldn’t do me much good around the house.

Before I went to the grounded power cable, I wanted to make everything else as quiet as possible. When I do add the grounded power cable, I think I’ll ground the green wire from that at the center point chassis ground I created between the filter caps.

I think Steve also suggested that the little cap from the power switch to ground should be removed when the 3 wire power cord is installed.

Dave O.

Dave 0 Wall-O-Bass
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Re: Why 4 channels? [message #8254 is a reply to message #8192]

Tue, 13 February 2007 07:11

JohnnyR is currently offline

JohnnyR
Messages: 12
Registered: December 2006
Location: Shelby, NC

Junior Member

Hi, depending on how your amp is assembled, you can add aluminum adhesive tape (aluminum duct tape), to the sides and top of the pieces which enclose the amp chassis. If there is enough clearance, you could staple some thin sheet metal to the pieces instead. By just making contact with the chassis, these pieces will effectively enclose the amp. Also, I used a shielded grounded cord, and tied my ground from the cord to the connection between the filter caps, where the speaker jack is tied. This ensured I would still have a single point ground. In your case, I would still add the grounded cord, and eliminate the polarity switch. You can always use an adapter to use with your outlets. I always have one when I go to gigs, because some of the old bars still have ungrounded outlets. If you get hum one way, just flip the plug around. Same thing as having a polarity switch. I, too, am a bass player, and the one thing I hate is noise through the amp. I also shield all my guitars and shorten the hot wires as much as possible, and use a high quality cord. My Kasino head is now very quiet, and I'm really happy with the performance. I hope you get the same result! Later, JohnnyR

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