Peavy "pop"?

Chris Brooks · From: Providence, Rhode Island

To Mike Brown or others,

New Bandit, running on 220 V. here in the Middle East, I get the old familiar fairly loud pop after I turn off the amp, with or without the instrument being plugged in, and even with the volume at minimum.

Is this normal? Harmful for the speaker? Seems like quite a 'spike' and very momentary too.

Thanks,

Chris

------------------
from the oasis ....

Jack Stoner · From: Kansas City, MO

I don't like the term "they all do that", but it applies to most of the Peavey's. According to Mike Brown it doesn't hurt them. I've never seen an amp that problems could be traced back to that. However, not all solid state amps have that pop. My MosValve 500 power amp does not have that loud pop when I power it down.

Blake Hawkins · From: Florida

The usual reason for an amp to "Pop" on power down is the large filter caps discharging through the output circuit.
Like Jack, I've seen this on many solid state amps.
I think, and I haven't tested this, that the problem could be minimized or eliminated by putting a bleeder resistor across the caps to discharge them faster.
Some engineering work would have to be done to get the proper value which would correct the problem and not change the characteristics of the amp. (read that "damage") So don't try this at home!
I have a 30 year old home stereo amp that has always done it and the company that built it told me the problem was caused by the output protection circuit shutting down when the power was turned off.
I still use that amp and it has never damaged anything.
My Peavy Nashville 400 pops on "power up"
but does not on "power down".

slick · From: Calhoun Georgia

I have a Nashville 400 and a bandit 112,both
pop when i power up.Never had a problem with
either amp.

Wayne

Mike Brown · From: Meridian, Mississippi USA

I checked with our Service Center technicians here at Peavey and this is what they had to say;

Turn on transients can be caused by bad DVL capacitors. They can also be caused by lack of good AC to circuit board or chassis ground. Also check the reverb molex pins for female open pins.

Chris Brooks · From: Providence, Rhode Island

Thanks for the replies, guys.

Jack, Jim, Slick, my other Peaveys did it too.

Blake, I seem to remember something about capacitors discharging, but I am not an electronics whiz.

Bottom line, I guess: Peavey turn-off transients are not harmful.

Chris

------------------
from the oasis ....

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I talked to Hartley Peavey about amps popping when being turned on and off. Peavey has a circuit to address this problem in their electronics. If I am not mistaken, it involves 1N4148 diodes "boot strapped" across the input and output, and hooked to the plus and minus power supplies. This prevents the input and output from exceeding the power supply voltage. Current is also limited with input and output resistors. The big problem is when a device is plugged into a amp. Capacitors from a external device can discharge into the amp, causing a loud pop. Even with this protection, there will be a loud pop--"IF THE VOLUME IS TURNED UP LOUD"! Turn the volume down and the pop will not be a problem.
Most manufacturers include in their circuit a way to discharge output capacitors. The devices I build have a path to ground on the output, where the output capacitor can not hold a charge for a extened time frame. This prevents the output capacitor from discharging into the device it is being plugged into.
I wouldn't worry about the design of the Peavey amp. If there is a loud pop, turn down the volume before you plug in or pull a plug. Just my opinion.

Mike Brown · From: Meridian, Mississippi USA

I suggest that you make all connections before powering up any device. If there is a ground potential difference between two chassis, extensive damage could occur. This is what we call "hot chassis syndrom".

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Mike hope you had a great Christmas and New Year! Remember that song, "Here In The Real World"? It would be wonderful if all musicians would turn everything off when they plug stuff in. With all devices having their own power supplies, there is always a difference in ground potential--ALWAYS!Nowdays, musicians have strings of stuff they plug in. Each has it's own power supply. To really be safe, all connections should be made with the power to everything off. Before power is turned on, all volume and gain controls should be turned off, or turned down as low as possible. Then bring gain controls up gradually. If you do this, there won't be any poping. This is the correct way to turn stuff on and plug suff in line. But Mike, remember the song, "Here In The Real World?"

Jack Stoner · From: Kansas City, MO

Keith, that's some good advice. But....we know it goes in one ear and out the other.
Just have to assume worst case when you design something. It can't be 100% bullet proof, but it should be designed, realistically, with as much idiot proof protection as one can without pricing it out of the market.

Blake Hawkins · From: Florida

Keith,
We are talking about two different pops.

The one that began this thread is not related to connecting or disconnecting anything.

My NV-400 pops with the volume controls at zero and nothing connected. Just turn it on and it pops.

I'm not worried about it, but I may just replace the DVL caps as Mike suggested.

Happy New Year!

Blake

Jack Stoner · From: Kansas City, MO

Blake, I don't the DVL caps are bad in yours. Mine has done it since it was new.

But, I don't get the pop with the MosValve 500 power amp.

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Just a thought here......

I think the "pop" is inheritent(sp) to most all amps. In my experiences as a Electronics tech, I believe the "pop" is the results of filter caps and other bypass caps comming up to full voltage when the amp is first turned on.

1) When the AC voltage is first applied to the circuits, several things happen upon the 1st and 2nd cycle of AC. Believe it or not, the full 120 voltage is applied to most ALL conponnets of the amp durin the first 1/2 cycle signwave of AC.

2) the filter caps are at 0 resistant to the incomeing voltage, hence the heavy current drain at turn-on time. It generally takes at least 2 (or more) AC cycles to charge the caps. There is a electronic formula that gets into play here but, we don't need to go there in this post.

3) Because most amps do not have a delay method to keep the resultant AC sinewave from reaching the speaker, you hear the "pop". While this is NOT a major problem with good quality speakers,(they can stand a instantaniously hit of maxiumn force,read as EMF) it can,over a period of time, result in the weak-ing of voice-coils in lowergrade units.

I have a Alesis RA-100 Reference Amp that I use and it has a built-in 4-second delay-on function. Hence, NO "pop" as the speaker isn't online untill everything has stabilized.

I'm not sure as to how they achieve this delay but as I see no relays or other mechnical devices, I believe it is a process of keeping the output Q's turned off till the power supplys and gain systems of it-self and outboard equipment stabilises. It would be nice if our amps (Peavey..... Are you listening, Mike Brown ??) had a function like this. I dont think it would add to cost of the Amp more than a few pennies.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Thanks for correcting me Blake. I did get a little off the original subject. I know amps can pop when powering up, with nothing plugged in, and volume control at zero. Bill has said, pretty much, what my thoughts are. This would be like having the speaker off until the electronics powered, or charged up. Then turn the speaker on. This is a very interesting design thought. What could be put at the end of the amplifier signal output to prevent a charge-up pop, even if other things were wrong? The signal is bound to be AC, since output capacitor would stop DC signals. I am sure there are other things that make the pop worse, like the volume being turned up.

[This message was edited by Keith Hilton on 04 January 2001 at 01:44 PM.]

Donny Hinson · From: Glen Burnie, Md. U.S.A.

How about just a different power switch (with an extra set of contacts...hooked in series with the speaker) that would disconnect the speaker at the instant the amp was turned off? Seems like that would be a simpler solution to the problem!

C Dixon · From: Duluth, GA USA

I have two Peavey NV 400's. One I bought used the other one I bought brand new. BOTH have a loud pop when powered in and then again when powered off. They have done this since the day I aquired them. The older one was taken to Meridian by me and worked on by a technician of Peavey. I asked him to get rid of the pop. His reply was,

"All of these amps pop and there is nothing that can be done about it"

Having been an RCA electronics Engineer for over 37 yrs I can tell you that NO quality Stereo HI Fi unit pops when turned on OR off. And they use Solid State devices!!

What many of these amps do is to use a "delay" relay in series with the speaker(s). This delay relay cuts the speaker OUT of the circuit a millisecond before the rest of the unit is switched off when the power switch is turned off. And does not connect the speaker into the circuit until AFTER the rest of the unit is turned on by a few milliseconds.

There is absolutely NO pop turning any quality modern Stereo Amplifier on or off. I doubt very seriously if the large buying public would tolerate it.

carl

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Carl, do you have any industry part numbers for the "relay delays" one can put in series with the speaker on a Nashville 400? I have two Nashville 400's that have always worked great and still work great. I checked and they both pop really bad. Mike there has to be more to this than what the guys in the repair department told you.

[This message was edited by Keith Hilton on 04 January 2001 at 09:31 PM.]

Blake Hawkins · From: Florida

Carl and Jack, Everything about this problem you both say makes sense.
We are dealing with a design trade off rather than a malfunction.
Carl: I think your trip to Peavy pretty well "puts the plug in the jug." If they can't stop the pop, then some sort of redesign is called for.
Since it is a great amp, and no longer in production I wouldn't expect Peavy to do it.
I'll take a look at the circuit and make a few 'scope observations.
My checks so far, have eliminated the stages prior to the Power Amp Input.
Since the compression light flashes, the pulse may occur between U6 and Q4.
I'm reluctant to do any major modification since I'm really more interested in using it rather than working on it.
Still....it'd be nice to know.
Blake

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

The 'Pop" cure is a relative simple one.

Put a time R/C network just before the final output Q's. This could be just a resistor/capactor network across the base/emitter of Q-X , causeing it not to be able to conduct (read as turn on) untill a certain number of t-cycles have happened. When the base voltage of Q-X reaches it's prober operating condition, the R/C network will be invisiable to the amp. This R/C network will also hold the system up when powered off by the fact that finals will be the last devices powered down (due to the slow drain-down time of the R/C/ network) allowing the front-end stages to cease ampifying the sine-wave first.

The bad part of this senario is that this could and should be a part of the OEM manufactoring process. I'm not sure if such could be retro-fitted into existing Amp PC boards or not. Like I said in an earlier post, Alesis RA-100 has this feature, I have looked inside of the RA-100 and find no relays or mecanical (sp) devices, so it must be R/C networks.

Another "fix" that works just as well is the placement of a "choke" in the front of the power supply. I wont go into the how and why of this cure but it dose work. I think the reason OEM Manufactors don't use this is because a choke is made up of an iron core and copper wire, which adds to the overall cost (and weight) of the amp.

I used a choke out of a discarded T.V. power supply and had a reasonable sucess in reduceing the turn-on "pop" in my Session 400 LDT. (1970-80's model)

Earnest Bovine · From: Los Angeles CA USA

Why do you care?

slick · From: Calhoun Georgia

Pop or not to pop that is the question???
As i said before i have two Peavey amps,and
one pops on power up,the other on power down.
I have had these amps for years,no problem
with either amp.With all due respect some of
us are nit pickers,or pop pickers.

Wayne

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Here is the BOTTOM line; I don't care if my Peavey amps pop or not. Hartley Peavey has helped me. If it were not for Hartley Peavey there would not be a wonderful HILTON PEDAL. Hartley Peavey, Mark Amundson, and Ben Jack are my advisers. When the going gets difficult, these are the people I contact. I will stand by these people and go down with the ship. Hartley Peavey is just like me. If there is a problem, let's solve it. I told Hartley about 10 months ago about the pop problem in the Nashville 400. I thought it might be in my pedal. We went through several electonic diagrams. I got the pop when my suff was totally disconnected from the amp. In other words,nothing connected to the amp. Big booming pop on turn on. Hartley Peavey will answer this problem. I have contacted him about it. Mike Brown is a good man! Mike is caught between people. Trust me, Mike Brown is on our side! Maybe I am one sided? Still yet, I know what Hartley Peavey has done for me out of the goodness of his heart. I will "never" forget his kindness--never. Try contacting Fender or Gibson, or any other manufactrer, and see how far you get. I don't care what happens, I'm on Hartley Peavey's side. Without Hartley' Peavey's help I would be nothing. Hartley is the kind of guy who would do anything to help you. He has helped me more than I can ever tell you. I would be nothing without him! I will stand behind Hartley no matter what. He has shown me so much love and help.

Rich Paton · From: Santa Maria, CA.,

Keith, it seems like there's a need for a simple add-on device to solve these popping problems. You could fill that need with your manufacturing capabilities and provide a useful solution.
I've had quite a few powerful PA and home amps, most factory equipped with delayed relays to allow the circuitry to stabilize before connecting the outputs to the load
(speaker(s).
Most solid state power amps of conventional design have a basic servo loop circuit in the biasing stage. This is one area which may need to fully stabilize before connecting the output to a load.
If you decide to experiment with such delayed relay connection circuits, I know that two basic types are commonly used in practice. One is a 555 type timer in monostable configuration, with its delayed after power-on output either directly powering the relay coil, or connected to the base of an open-collector transistor which switches the coil current. Of course, any electromagnetic relay installed in the vicinity of audio circuitry would need a suppressor diode across the coil to absorb counter EMF when the coil is de-energized.
A simpler, but effective approach is to produce a delayed control signal by using a unijunction transistor with an RC circuit on the control element. Using stable RC elements, this can produce a fairly accurate (time-wise, & repeatability-wise) voltage ramp function on the input lead, delaying its current saturation (on-state).
One power amp I use is an Alesis Matica 500,
good for 350 Watts RMS per channel at 2 ohms.
These are the relays used in it:
HATCO # HAT901CSDC 12
There is a note in the owner's manual, stating that the relays' closing have a 4 to 5 second delay, and also states that they will diconnect the load very quickly when the amp is powered down. Whether the relays are anything special or not is unknown. They are rated at 20 amps/2 HP. @ 120 VAC.
I hope this is of some help.

C Dixon · From: Duluth, GA USA

Slick,

With all due respect, I would suggest you speak for yourself.

I don't care how good the amp is. I don't care how well it sounds between the time it is powered on and off. The pop IS loud on BOTH my Peavey NV 400's, and is very objectionable to me, and IMHO, should never have left the design prototype stage, until the cause AND cure was found.

carl

Jack Stoner · From: Kansas City, MO

Blake has the right idea. It's there, but the Nashville 400 is out of production and although the pop is there it doesn't seem to have any harmful affects so there's no use losing sleep over it.

I like Peavey products, but many seem to be "built to a price". I know Mike Brown doesn't like to hear it, but things like the amp pop, molex connectors or the excessive heat in the Transtube Fex (because they did not allow for adequate ventilation) would not be there.

Forum Index > Electronics	Goto page 1, 2 Next	Next oldest topic :: Next newest topic