The Gallien-Krueger Amp Thump

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Bonus question for 1001RB users...

Ever seen your fan actually come on? I haven't yet. Let me know. GK says it will when the heat sink reaches a hot 65 degrees Celsius. My amp so far has never been that warm to the touch--good thermal management, I'd say!

Executive summary

Short on time and wanna see the upshod? As a result of my explorations here, GK issued this service advisory (Word document) on 12/12/2002 to their dealers. The "it has been brought to our attention" part refers to me. 8-) Despite having dealt with this defectivity issue, I'd have no hesitation buying a 1001RB again, and I continue to be pleased with mine. This web page was constructed to inform y'all about doing due diligence to make sure you walk out of the store with a good one. GK: good design, long tradition of reliable gear, but questionable QA and final test procedures on this power off thump issue.

The thump issue

My brand new GK 1001RB amplifier thumped my speakers mightily on power down...and that just didn't seem right.

We're talking about power-on and power-off transients that you hear from your speakers when switching your bass guitar amplifier on or off. In my opinion, it's really negligent to design an amplifier this way since such transients are damaging to speakers. Common design techniques for for high-power amps use either relays to disconnect the speakers physically during power-up-down, an electronic circuit to isolate them and control the tarnsient. Some manufacturers include speaker cut-off switches, and still others have no protection circuitry at all.

GK uses the electronic circuit technique in recent designs. My recent experience in shoppping for a GK 1001RB amp was interesting though. Though the manual claimed "power on and power off speaker protection," the unit I purchased made an awful noise when powering off, and I feared for the health of my Eden D210XLT and Peavey 115 BX BW drivers in the face of such a violent transient. I could avoid the issue by turning down the master volume control, but as an electrical engineer who has done electronic design for a living, I wasn't content to let this sleeping dog lie.

I noted the issue and posted to the good folks in the alt.guitar.bass and rec.music.makers.bass newsgroups (click here to see the posting/thread) to survey their experience. Some users noted that it happened to them too, others said they had no problem at all.

I contacted GK, going so far as to take a stab at Bob Gallien's ( president and founder) email addresses, and indicated that they either had a design problem, a defectivity issue, a manufacturing problem, or a combination of the three.

Impressively, both Bob and the director of engineering quickly responded to the email confirming a minor design change in the preamp GK1001RB and 700RB models that led to the issue. They stated: "We know for sure that the amps between mid-February and the third week of May have this thump." A design modification was made to correct the problem, and QA and final test procedures tightened in May of 2001. In early December 2001, local dealer inventory was still rich with models manufactured in the defect date range.

How to tell if a unit is affected?

1) make sure there's a speaker plugged in, 2) make sure power cord is plugged in, 3) set master volume is at 12'oclock or better for both woofer and tweeter, 4) turn unit ON, and finally simply 5) turn it off. Do you hear the loud thump of the power off transient hitting the speakers? The sound is independent of input and pregain settings.

The 4 digits of the serial number before the "E" indicate YYWW where YY is the digits of the year (01 for 2001) and WW is the work week (01-52) in which the unit was manufactured. If your date code is near 0107 through 0120, GK confirms that the unit has the affected design, though some individual units may not exhibit symptoms. Note though that many folks have found additional units after that date range that are also affected.

If you're not hearing a thump, I wouldn't worry about it.

I'm affected--what should I do?

If you have a model with a suspect serial number but have no thumping, count yourself lucky and go about your day. No other issues are known. It's also not known if your unit will degenerate at a later date. If it does, maybe you can try to use this web page as justification for out-of-warranty service (good luck).

If you're affected and want to get it fixed, GK indicated that a modification is available and is available free of charge within an existing GK warranty, which is encouraging. Visit an authorized service center to have the work performed.

What was initially disappointing wass that GK dealers were completely ignorant of this issue, and that GK wasn't taking more proactive steps to ensure customer satisfaction. I raised these concerns with Bob Gallien (on 12/12/01) suggesting simply that GK send a bulletin to dealers to screen existing stock for this issue.

On 12/13/01, alvin of GK Engineering responded in a very pleasing manner:

Todd,
...
Regarding the thumping 700RB combo that you came across at your local
dealer, I have instructed our Service Department to issue a Service
Memo to all of our dealers to check all of their stock of 700RB and
1001RB heads and combos for this problem.  I have attached a copy of
this memo for your reference.  Keep in mind that this process will
take a couple of weeks to reach all of our dealers since we have
dealers world-wide and unfortunately, not all of them have e-mail
accounts so we might have to send them hard-copies via fax or postal
mail.  We thank you for your investigation into this matter as it has
been very informative.

Best regards,

Alvin
GK Engineering

GK is doing the right thing here--bravo!

Help with the exploration (visit your local dealer)

When you visit your local music store, 1) make sure there's a speaker plugged in, 2) make sure power cord is plugged in, 3) set master volume is at 12'oclock or better for both woofer and tweeter, 4) turn unit ON, and finally simply 5) turn it off. Do you hear the loud thump of the power off transient hitting the speakers?

Note the model number and the serial number (at least the first 9 positions) and mail them to me. And...tell your dealer that they should probably send it back to GK as defective.

Affected models and serial numbers of tested units

1001RB
--------
1Y0136E03xxxxxx  No thump at all on power down.   will thump on power
                 up unless you wait a bit after the previous power
                 down. My current "good" unit with which I'm happy.
1Y0109E09xxxxxx  Thump, very loud.  My originally purchased unit.
1Y0109E09xxxxxx  Thump, very loud.  Guitar Center floor model
1Y0215E05xxxxxx  "Thump is very pronounced" 

700RB's
-------
1P0137E11xxxxx   Combo amp.  Loud thump. Guitar Center floor model.
1P0113E111014XX  Combo amp. Loud thump.  Reported by user via email. 


Others
------
400RB           older design, all will thump on PU and PD--no protection circuit.
400RB-II        status unknown
400RB-III       Has protection circuit, but design differs from 700RB
                and 1001RB.  Expect a slight thump click, but not nearly
                as loud as the one heard in defective 1001RB and 700RB's
800RB           older design, all will thump on PU and PD--no protection circuit.
1000RB          no known units affected
2000RB          no known units affected

Best Regards,
Todd H.

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