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Genz Benz Series 2 clipping too early?

D

dfuruta

Mar 7, 2008
26
0
iowa
#1
Hello,

Yesterday, I played a gig with several other bands. I am friends with many of the other musicians, and so I volunteered my Genz Benz Series 2/Avatar 212 for common use. When my band went on, I noticed that the levels were set rather high, and so I turned down. Early on in our set, I started noticing that both the preamp and the poweramp were limiting frequently, so I turned both the gain and the master down further. I thought I was fine, but then the amp started cutting out...I looked back, and it was going into thermal shutdown.

Our set was almost over, so I put both the gain and the master at 8:30 and finished playing.


Today, I tried playing through the head, and both the preamp and the poweramp clip if the gain is higher than about 9 o'clock. I was using a passive, fairly low-output bass with no effects, and this does not normally happen.

Any ideas as to what might have happened? I'm well aware that I made a number of possibly poor decisions, from letting people use the amp to finishing the set. Does it seem to you that it this is something that would be cost-effective to fix? If a repair will be expensive, it might be in my best interest to just purchase a more powerful amp.

Sorry for the length of the post, and thanks for any advice!
 
#3
What happened to that amp is not that uncommon, even though in theory it ought not to have occurred. Reasons don't matter but if you want to hear them I'll put in my two cents wrt that but there will be some slamming going on. Anyway, I think the entire output stage is going to have to be replaced and then the amp will have to be bench tested under load (dynoed). You're talking maybe half a day's work, maybe less, plus maybe $50-75 in parts. Ask the repair people if they can get matched transistors for you (unmatched transistors could've been an underlying cause, at least partially). Also consider putting a small box fan on the heat sinks if there isn't one there already and if there is room. I'm not familiar with that amp so I don't know. It can be wired into the chassis to the power switch, just drill a small hole & use a grommet. You might be able to get by with replacing only the 1 or 2 bad transistors, but what's the point -- the rest have been on the frying pan and it's only a matter of time for those, too. I say replace 'em all (long-term view).
 
#4
First of all, please disregard craig.p's dire assumptions, they are nothing but wild ass guesses based on a poor understanding of how your amplifier works.

First of all, if the input clip light now appears to illuminate early, this has nothing to do with the output section, but could indicate a drop in the low voltage power supply (that's where the clip light reference voltages are derived), it could also be something as simple as a partially shorted speaker wire (or the 1/4" plud came partially out), a partially shorted voice coil on your speaker (both of which will cause the amp's internal VI protection to limit the output to peotect the amp). Both of these faults will cause the amp to run hot and the protection thermal circuit will shut the amp section down before any damage is done to the output transistors.

Try removing the speaker load from the amp and see if the LEDs behave normally. Also, if by chance you are using excessive bass eq, that will also cause the (internal) signal levels to increase and the clip lights to turn on "earlier".

I doubt it had anything do do with letting somebody else use your amp, nor is it unrepairable, nor is it likely to be an expensive repair to a tech who (really) knows how to work on them. In fact, it's a really easy amp to work on for an "A team" tech.

Incidently, matched transistors are NOT required, the amp is designed to handle a very wide range of unmatched parts by design. You do NOT need to replace all the transistors either, there is no frying pan in this amp... the thermal protection keeps the output stage from getting so hot as to damage the transistors. The amp is also fan cooled internally, another possibility is that the fan failed (located on the left side at rear of the chassis), that's pretty easy to check by looking into the vents.

Feel free to PM me with additional questions or info., and we still support your amp and can arrange to get it repaired for you no problem.

Andy
 
#6
Thanks, everyone, and especially agedhorse, for your advice. It's great to see people stand behind their work like Genz Benz does. I'll try it without a load this afternoon and let y'all know what happens. I have the eq almost flat, so that's probably not the problem.
 
#7
As a follow-up to this, I received the amp and looked at yesterday. The problem was a broken effects jack, the tip on the return was bent completely under causing an intermittent contact with the normalling switch. Looks like either a plug with a bent tip or a cheapo plug that did not have the proper taper on the back of the tip got hung up on the tip contact when it was pulled out. Everything else met the original specs, and I could not duplicate any thermal issues. This amp is 11 years old. Cost of repair... $25.00, time required... 20 minutes.
 
#10
craig.p said:
What happened to that amp is not that uncommon, even though in theory it ought not to have occurred. Reasons don't matter but if you want to hear them I'll put in my two cents wrt that but there will be some slamming going on. Anyway, I think the entire output stage is going to have to be replaced and then the amp will have to be bench tested under load (dynoed). You're talking maybe half a day's work, maybe less, plus maybe $50-75 in parts. Ask the repair people if they can get matched transistors for you (unmatched transistors could've been an underlying cause, at least partially). Also consider putting a small box fan on the heat sinks if there isn't one there already and if there is room. I'm not familiar with that amp so I don't know. It can be wired into the chassis to the power switch, just drill a small hole & use a grommet. You might be able to get by with replacing only the 1 or 2 bad transistors, but what's the point -- the rest have been on the frying pan and it's only a matter of time for those, too. I say replace 'em all (long-term view).
Click to expand...
Thanks, Craig...haven't had this good a laugh in a while!
 

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