Jump to content
Why become a member? ×

Loss of power


ceilidhswinger
 Share

Recommended Posts

Going through a bad time with gear at the moment, had my Trace Elliot GP 12 smx in in for repair recently as Output pot was noisy, tech guy replaced pot with another 50 k pot, not Trace, the same week my input gain pot was dodgy and cutting volume , my tech guy checked it out and said it was okay but that I now needed to replace input blend pot which he did but still feel I am having to drive amp more than normal to achieve my normal volume. Also my GK/ SB150S that I use for DB has lost power! couldn't get any volume unless I had it cranked right up! I use different leads for both set ups so not leads. both amps sound okay but not totally different volume and EQ to what I normally have them set at. am I going deaf or daft or both. In both cases I have a simple EQ tweak and away we go but now continually turning and and twiddling?? help!

Link to comment
Share on other sites

  • 4 weeks later...

Hi Delberthot, just got phone from my tech guy see below, at least its pleasing to know I'm not going deaf eh?

Hi folks, does anybody out there own a Gallien Krueger mb150s? mine is playing up at the moment with severe loss of volume, my tech guy looked and put a load thru it but as soon as he connected speaker reading went nuts, he read on a few forums that the limiter can sometimes play up on them and start cutting volume. So if anybody out there can send me wiring diagram or steer me in the right direction, I would appreciate it.

Link to comment
Share on other sites

I'm pretty sure my luthier has an MB150. When I was last over there he told me some interesting things about it. His is an old one, so this [b]may not apply to yours. [/b]
They have a switched-mode power supply that can be problematic. He is an electronic engineer by trade and took it to a fformer colleague who is a guru.
After searching out the schematics, he said it's a surprise it works. The design looks like it was done by an inexperienced grad and had some fundemental design flaws.
Short of it is, he substantially redesigned it for him and it is now working fine.

Link to comment
Share on other sites

Thanks for that MoonBassAlpha, mmm! that's interesting, these amp were reckoned to be the dogs bollocks when they came out too. I will let my man know, been on a few forums and seemingly problems with limiters and other stuff I know nothing about frankly.

But thanks again for taking the time to get back me.

Link to comment
Share on other sites

[quote name='MoonBassAlpha' timestamp='1317987811' post='1396977']
I'm pretty sure my luthier has an MB150. When I was last over there he told me some interesting things about it. His is an old one, so this [b]may not apply to yours. [/b]
They have a switched-mode power supply that can be problematic. He is an electronic engineer by trade and took it to a fformer colleague who is a guru.
After searching out the schematics, he said it's a surprise it works. The design looks like it was done by an inexperienced grad and had some fundemental design flaws.
Short of it is, he substantially redesigned it for him and it is now working fine.
[/quote]Are you sure that it was MB150? It does not have switch mode power supply. What is special about this amp is that it has +/-32V and +/-60V double power supply rails which are switched to the higher one when the signal if high enough. This is called Class-G (you can read about it here: [url="http://en.wikipedia.org/wiki/Electronic_amplifier"]http://en.wikipedia.org/wiki/Electronic_amplifier[/url] ) and it is quite popular way to get more power with less heat. So the rails are switched but the amp does not have switching power supply (which works completely different). This still can be difficult to fix if the amp fails.

Mark

Link to comment
Share on other sites

Hi again Mark,

Sorry to sound vague but I'm sure its the MB150S? bought amp from guy down in London a few months back, done a handful of gigs with it and its stil with tech guy, he has manual. I know theres a MB150 AND MB150S mines unless I'm mistaken is S.

I will pass on your info?advice to my guy and thanks for all your help.

will keep you posted

Calum

Link to comment
Share on other sites

I was asking MoonBassAlpha whether he is sure about the switching power supply in MB150 (and not you whether you know what amp you have :)). This amp is quite old and it was manufacured in several versions. I'm refering to the latest version: Series III. This one didn't have switching power supply (and most probably the older ones also didn't have it). Take a look at the power supply in this amp (see attachment). It's just typical power supply. The power amp uses class H topology (switched rails) - this is mentioned in the manual and also on Wikipedia (about Gallien-Krueger).
Regarding the problems that you have I'd advise to identify whether the problem is with the preamp or the power amp. In each amp you have SEND/RETURN effect loop. So you can for example connect SEND output from one amp to RETURN input in the other amp. In this way you will be able to identify if the problem is related to preamp or power amp. You can also connect both preamps to external mixer and see what signal levels you get.
In the TE I would check whether the pot that was replaced was linear or logarithmic. This is a typical mistake when replacing pots. I think that in GP12 both pots (input and output) were linear but different values: 500k and 50k. And the results could be exactly as you describe. Of course there may be several other reasons (e.g. old valve in the preamp).

Mark

Edited by MarkBassChat
Link to comment
Share on other sites

Thanks again Mark, I have copied this and I will let tech boy have a gander, re TE, I think you are right about pots, I seem to remember other tech guy I used waxing lyrical about linear or logarithmic and he said as long as value was the same, it would be okay. I will ask the guy that lookin at my GK about this too! This would certainly explain things.

Again thanks for taking the time.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...