Distortion/Gain stage problem

[ke4tts]

I recently purchased a Wizzy-M which I am having a problem with. The Wizzy is being driven by the amplifier section of a GK MB150. The input to the amp is a double bass with a Fishman Full Circle and a Fishman Platinum Bass Pro preamp. At high volume levels, a cracking sound occurs on the intial attack of notes, especially the low bass notes. The EQ on the preamp is set to cut the lowest frequencies and the problem does not occur with my old Fender 15 inch cabinet (8 ohms, rated 150 watts continuous, 300 watts peak).

I sent an email to EA and got an answer from John. He says that the MB150 does not have enough power to handle the peaks and is causing the cracking sound.

Is there someone in the Raleigh, NC area who has an amp (300-500 watts) who would let me try the Wizzy with the amp? I could bring my bass and Wizzy to your location or you could bring the amp to my location - your choice. I would like to determine that a stronger amp will fix the problem before I spend more money.

If there is someone who can help me, please contact me offline at ke4tts@compuserve.com.

Thank you,

Jerry Davis

[tony moore]

Sounds like an issue with your GK's preamp to me. I have the same amp and have had issues. Try routing the output of your Fishman preamp to the FX return of your GK instead. You'll now only use the master volume control of your GK and won't use the input gain, EQ or FX send controls. Also, I'm assuming you have then gain set properly on your Fishman pre?

Also, I notice with my new Wizzy-M I'm hearing stuff I never heard before. I'm currently using a GK 400RB head and I now hear the noise floor from the GK that I wasn't hearing with the Avatar 1X12. I borrowed a friends AI Focus and the difference was amazing. Myself, I'm waiting for EA's iAMPmicro

Hope that helps,

Tony

[Ric Vice]

[quote=ke4tts]I recently purchased a Wizzy-M which I am having a problem with. The Wizzy is being driven by the amplifier section of a GK MB150. The input to the amp is a double bass with a Fishman Full Circle and a Fishman Platinum Bass Pro preamp. At high volume levels, a cracking sound occurs on the intial attack of notes, especially the low bass notes. The EQ on the preamp is set to cut the lowest frequencies and the problem does not occur with my old Fender 15 inch cabinet (8 ohms, rated 150 watts continuous, 300 watts peak).[quote]

I sent an email to EA and got an answer from John. He says that the MB150 does not have enough power to handle the peaks and is causing the cracking sound.

Jerry,
Unfortunately, I don't live in Raleigh (my brother does). I own four EA cabinets, but never used them with the MB series amps. Both of my Walter Woods are 400 watts plus.
John is the expert when it comes to EA stuff because he designed the cabinets. You should definitely try using some ones head with a little more umph to see what it sounds like. At least in my experience the Transmission Line cabinets take a good deal more power from the amplifier to "bring them to life."
There are other TBers that I thought used iAmps with the M line cabinets. There is also that new iAMP from Euphonic Arts that's pretty reasonable and will be on the market in January. It's definitely a "bare bones unit" but it's a lot more powerful. Sorry I can't be more helpful.



Ric

[Mike Dimin]

John is correct in that you are overdriving your GK. Tony's suggestion is a good one. I would also recommend starting out with the amp and pre's set flat. If you're running the fishman into the input of the GK, you have 2 preamp stages. It is easy to overdrive the power amp that way

[ke4tts]

Thanks for all the responses and suggestions. I have rehearsal tonight and I will try what you have suggested.

Jerry

[drurb]

Originally Posted by Mike Dimin

John is correct in that you are overdriving your GK. Tony's suggestion is a good one. I would also recommend starting out with the amp and pre's set flat. If you're running the fishman into the input of the GK, you have 2 preamp stages. It is easy to overdrive the power amp that way

From the information given, it is not clear at all that the power amp section of the GK is being "overdriven" in the sense that it has insufficient power to drive the Wizzy at the desired level. The advice regarding not having multiple front-end stages (pre-amps) is good in any case. The "cracking" sound may very well be the cone being overdriven by very intense, very low frequencies. In addition to the advice given above, the Fishman "low-cut" or high-pass filter should be used to attenuate frequencies below about 40 Hz. Trial and error with the suggestions given above should pinpoint the source of the problem.

[B String]

Originally Posted by ke4tts

Thanks for all the responses and suggestions. I have rehearsal tonight and I will try what you have suggested.

Jerry

Don't wait till you're in an uncontrolled environment and in
a hurry. (like a rehearsal) Take the time before to work it
out.
People here have been using 100 watt Walter Woods amps
for 25 years and making it work fine for big band gigs.
Absolutely learn how to use your amp. With all the tone
controls off, the GK is NOT flat! And, using the Fishman eq
pre into the GK preamp may not be helping either.
Going from the Fishman into the effects return of the GK is
a great idea and will probably sound better. You need to
put the master volume on the GK all the way up so you
have the most headroom you can get. You can also use
the boost if you need a little more oomph. Usually (not
always) the eq set in the middle is flat. Good luck.

[robgrow]

Awhile back, I did a comparison of a GK MB150E/III head, a Walter Woods MI-100-8, and a Series II Acoustic Image Clarus. All three amps are rated at about the same power level (~ 100 watts @ 8 ohms), and a quick check on the bench verified this. However with a subjective comparison, things were very different. With each amp driving a GK 112MBX, which is the extension speaker for the GK MB series, the MB150E/III sounded the least cleanest and clipped much sooner than the other two amps. The MB150 had the least headroom by far, while the SII Clarus had the most headroom of the three. Unfortunately, it's easy to overdrive the preamp and the power amp on the MB150.

[Mike Dimin]

Originally Posted by robgrow

Awhile back, I did a comparison of a GK MB150E/III head, a Walter Woods MI-100-8, and a Series II Acoustic Image Clarus. All three amps are rated at about the same power level (~ 100 watts @ 8 ohms), and a quick check on the bench verified this. However with a subjective comparison, things were very different. With each amp driving a GK 112MBX, which is the extension speaker for the GK MB series, the MB150E/III sounded the least cleanest and clipped much sooner than the other two amps. The MB150 had the least headroom by far, while the SII Clarus had the most headroom of the three. Unfortunately, it's easy to overdrive the preamp and the power amp on the MB150.

Thanks - great assesment

[Mike Dimin]

Originally Posted by drurb

The "cracking" sound may very well be the cone being overdriven by very intense, very low frequencies. In addition to the advice given above, the Fishman "low-cut" or high-pass filter should be used to attenuate frequencies below about 40 Hz. Trial and error with the suggestions given above should pinpoint the source of the problem.

Originally Posted by ke4tts

The EQ on the preamp is set to cut the lowest frequencies

Thanks for the post, I might have suggested the low end, as well, but I thought he already took care of that issue. I am still betting that with 2 pre's in the system, something is clipping

[Bob Gollihur]

Cool. Not to be a wiseass, but please change the thread title to Problem with GK MB150

[Mike Dimin]

Originally Posted by Bob Gollihur

Cool. Not to be a wiseass, but please change the thread title to Problem with GK MB150

testify

[fdeck]

Originally Posted by Mike Dimin

testify

Hey.

Actually, one thing I noticed is that the MB150 seems sensitive to input cable problems. I have had the crackling problem, and it was in a similar situation. I noticed it when I plugged in an extension cab. Unplugging the extension cab made the problem go away. I tried the cab with a different amp. No problem. Different preamp solved the problem too.

I was stumped until I figured out that I was hearing the crackling with the extension because the extension has better high end response. Then I tried my electric bass and the problem went away. Finally, I realized that when I tried the electric, I was using a different cable.

Long story long, I got rid of the offending input cable, and my speaker problem fixed itself.

[fdeck]

Just FYI, here are the curves for my MB150E combo. "Default" is with EQ knobs centered, and all effects (hi boost, contour, lo cut) turned all the way down.