Quote from: Jazz P Bass on November 08, 2023, 01:57:15 AMI installed a modern version of the ic & the customer wanted to know what was wrong with the amp.
The distortion was NOT the same.
So, I grabbed the ic from the reverb circuit & swapped them around & wallah.

Interesting. So it's not simply a matter of using newer *types*, like 4332 or TL072, but 4558 of more recent manufacture..

So did the manufacturer(s) update the datasheets to reflect the improved specifications, or did they leave them alone, figuring that as long as the new parts "meet or exceed" published values, they were ok?

Either way, kind of an annoying situation. Do you know, roughly, when the new-spec 4558 devices began appearing?

Quote from: joecool85 link=msg=414954558's are considered magic by many.  They aren't though, they just have an awful slew rate and are kind of noisy.  The DO happen to work well for electric guitar though.

Man, you sure do hear a range of opinions on old 4558s! But I wouldn't know, I come out of the vacuum tube world.

So how are they for synth stuff?

Quote from: phatt on November 06, 2023, 04:43:19 AMI'm assuming you are using this for el guitar? If so then the lack of bottom end is likely due to the presence of the horns producing so much treble it drowns out the Bass.

If you are chasing the sweeter tones that good guitar rigs produce then the last thing you want is hi Freq horns.

Analog synth, actually. It's primarily a keyboard amp.

QuoteAlso if the amp has a Scorpion speaker they are already very bright when compared to other famous guitar speakers.

This is the "type 1" KB 300 ca. mid-1983. It doesn't have a speaker badge on it, so I'm assuming it's a fairly decent average driver of that era. Definitely not a scorpion or widow.

The preamp has 3-band eq, so it's easy to dial the highs way down. I don't have the synth stuff setup right now, so I'm using some commercial reference recordings to evaluate the sound. The fact that I'm using a cheap CD player & BT link might be some of the issue.

Do you know if BT audio has a lossy compression step? Does it send raw PCM / WAV or something like mp3 on the fly?

Hi Tassieviking,

Maybe I just want to tinker.. a guy needs something to do!

No, the noise is not so bad, just more than I'm used to, coming at this from the hi-end / hifi world. Yes, the OAs are all socketed.. so very easy** to change.

The big psu filters are Cap-Tech parts, which were premium quality in that era. Yes, newer stuff is "better", but yet those parts are so much better than 60s-70s stuff already that I don't suspect them. They also have a weird mount pattern.. I don't think a 1-3/8" snap-cap will just pop in.

(** if we don't count r&r the chassis,which is a pain.)

While we're here.. I'd like to improve the low end - add another octave or two down low.. to at least one channel. But I'm not really sure which parts are determining the present cutoff.

Obviously I'll probably need to at least double the PSU storage, but that's fairly straightforward.

PDF schematic attached. Note that this is only correct to the early version without an XLR input and only a single row of jacks on the left

Hi folks,

Is there any point in changing out the 4558s in a (first model, mid-1983) Peavey KB 300?

Is there much of anything to be gained by this? The amp works fine, though it's maybe a bit noisier than I'd wish.

Thanks!

The basic diode symbol consists of a triangle with a bar across the point. Other diode types (zener, schottkey, tunnel, LED,etc.) are slight variations on this basic symbol.

But in all cases, the bar is the Cathode and the triangle is the Anode. This is universal.

Howdy,

I just picked up a KB 300 for a song. The unit is really nice, but the controls are dirty and the cord jacket is cracked just outside of the Heyco grommet. ETA: Cord is fixed.. Had to cut off 1" and re-set the cord in the grommet.

So the chassis needs to come out but I'm not having much luck. I found 4 screws on top (chrome strips) and 4 more in the back that secure the chassis to the case. Also unplugged the speakers & reverb tank.

The chassis can be shifted a bit, but won't slide out the rear.. what am I missing? More screws somewhere? ETA: Got it. Was hanging up on the edge of the chassis.

Also.. this is the early version (no XLR input), built in mid-1983. It doesn't have the pair of 5W resistors on the back of the tweeter horn. Should these be added, for safety? Do you know the correct value(s)?

Thanks!

Turns out that the 50R was intermittent open, and the reason the horns weren't running. Stupid thing measured fine on the bench but acted like 1-2M under load. Now it's gone, the horns work, and there's a 20R 5W in its place.

The driver turns out to be an Eminence 15" made in late 1997. I'm now assuming it's the original part. The codes from it are:

15504 15504 4OHM
  67-97320056 G2

The two tweeters are definitely original, all TE models have them. The 50R series resistor is just a "hi-limit" part to prevent burnout. It wasn't properly installed, really appears just scabbed-on by some hack.

I'm debating replacing it with a 20R, as that's closer to the datasheet spec.. haven't really decided yet, might try both values.

There is also a separate Volume control just for the tweets, it's a 25K pot in series with the tweets + 50R hi-limit. So no worry about too much tweeter level.

Hey, thanks for posting those. What I'd like to see now is a cabinet wiring schematic.. but I've so far been unable to find one.

Quick question: The amp uses a pair of Motorola KSN-1005A piezo tweeters, wired parallel. The mfg data sheet specifies a 30R series resistor to prevent burnout at high volumes. But since it has a parallel set, should this value drop to 15R? Or I suppose each tweeter could have its own 30R part?

FYI, as received the amp had a single 50R part in series with the parallel pair. This looks like a later (sloppy!) mod that was done when the 15" driver was changed.. or at least I think it was changed, as the soldering is really amateurish.

Re: Polytone MSRP

Glenn Murch at Murch Music up in Canadia recalls that back in the late 90s the mid-line Polytone Mini Brute II retailed around $900 (CAD, I assume?) The MB II is a single channel amp with a single 15" driver.

Based on that price of $900, the top-line Taurus Elite (3 discrete channels, pair of piezo horns, Hammond spring reverb, "modulator" Leslie effect circuit) would have been well above - perhaps around CAD$1200-1400? Fyi, the USD :: CAD exchange rate was about 1:1.4 in 1997.

Doesnt sound like a "budget" or "bargain" model to me.. but my knowledge of late 90s amp prices is weak at best.

I have almost no experience with instrument amps, and this particular amp is new-to-me. IOW, I don't know what's normal for it.

Can't reuse the old terminals as some idiot (...) threw them away!

I've concluded that the driver may be a replacement. The flying resistor is in series with the vol pot for the tweeter horns. It's a 50R 5W part that acts as a hard limit to prevent burn-out. Mfr's DS for the tweeters calls for 30R, but I guess 50R is close enough. Guess the new driver didn't have a place to mount this resistor?

The FS is definitely the latching type. I bought an original off ebay, it's on the way. Needs the actual switches replaced.. theyre on the way as well.

I don't believe that Polytone was a budget amp.. but I haven't found any MSRP info yet.

Thanks!

Got all that taken care of. Well.. almost. It seems that the terminal lugs on the no-name driver are some weird intermediate size: 0.205" aka 5.2mm. None of the 3 standard size connectors will fit - either too small, or they fall off. So now I get to deal with that idiocy.

Btw, the PA is rated at 125W.. and while it makes 135W at hard clipping, it maxes out at 80W clean.

Is this normal for SS gear? Am I talking to myself here?

Quote from: g1 on July 30, 2023, 12:05:07 PMI don't have the wiring, but it is supposed to work with other units as well.

Per CB, it does work with other devices that accept external tempo tap (save Boss, apparently). Though, the tap box has two different TRS jacks - one specific to the BE Dlx and the other for 3rd party devices.

According to CB, the LED only functions with the BE Dlx.

QuoteSo I expect tip to sleeve as the momentary tap switch, and ring to sleeve for the LED.  Possible there is a resistor on the LED.

Opposite what I'd guessed. I went with ring+sleeve for the tap switch as the ring is where it expects to see the variable CV from the exp. pedal.. but you may very well be right. Ditto on the resistor.. always good to have one where LEDs are used, and the BE Dlx has 22V rail.