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ADA Power Amps => Microfet => Topic started by: Harley Hexxe on July 09, 2016, 02:37:44 PM

Title: Microfet 100
Post by: Harley Hexxe on July 09, 2016, 02:37:44 PM
Hey Dante,

    I just noticed in your signature, that you have a Microfet listed in there. What is your appraisal of that power amp compared to the Microtube or the B200S?

     Harley 8)
Title: Re: Microfet 100
Post by: Dante on July 10, 2016, 11:48:04 AM
I seem to remember it sounding good, but mine only works in one side. Also if my memory serves me, it's a delicate unit...breaks easy. I didn't trust it, so it's a backup to my backup, in storage.

I haven't used it in years, it's in a 2u rack with my old Quadraverb. You want me to pull it out and give you an updated opinion? Maybe I'll get all motivated and try to fix the broken side.

Dante
Title: Re: Microfet 100
Post by: Harley Hexxe on July 10, 2016, 02:54:05 PM
 No Dante,

    I think you already told me what I needed to know about it now, and that would be these two things:

        1) If it's that delicate, then it won't make any difference in a shock mounted rack. It just won't hold up to being moved around to more than a gig or two before it ends up in a repair shop.

        2) It may have sounded good, but apparently not good enough to motivate you to get it fixed when you heard it. So from that I'm kind of getting a mental sound image of a MT100, without the presence control, which is just clean, un-altered amplification to the preamp sound.

       The B200S still leads the way in solid-state guitar amplification.

    Thanks Dante :thumb-up:
Title: Re: Microfet 100
Post by: Dante on July 10, 2016, 05:09:40 PM
I'd say your assessment is spot on  :thumb-up:

I did already have my B200s when I got the MicroFet, so I never really needed it. One of the channesl (I think chB) died shortly after I started gigging with it. I remember I used it with a Peavey TransTube, probably the best sounding preamp I've heard... after an ADA of course. It must not have been very remarkable a power amp, because I put it in storage.

That said, I took it out of storage just now. Man, the rack is brand new, I should really swap out this one for the 2u that I'm giggin with - that thing is TRASHED  ;D  As soon as I opened the case a memory came rushing back. There was a stripped out rack screw holding it in. I could not get that damn screw out. I ended up using a cold chisel and a BFH to pound it into submission. Needless to say, that chewed up the corner of the rack ear pretty good. As soon as I saw that chewed rack ear, I remembered the fun time I had trying to get that screw loose.

Since my MT200 is sounding puny in chB and since I have an extra rack space in my 4u rack anyway, I'm going to put the MicroFet in there and compare it with the MT200 using my MP-1 Classic and two 1x12 Thiele cabs. This should provide a pretty good A/B comparison, which is always fun for gear geeks like us

Party on Wayne, Party on Garth - Schwiiiingg
Title: Re: Microfet 100
Post by: Harley Hexxe on July 10, 2016, 05:29:12 PM
Dante,

    It sounds like from your description, that the case they built the Microfet into, is the same case they built the MT100. That's a flimsy design to begin with, and my only beef with the MT 100 apart from the fact that one channel always seems to go out on them. I do like the sound of the MT 100 better than the 200, but they're just not reliable. Maybe we'll figure out what that flaw might be one day, but for now, all my MT 100's will remain in storage boxes.

     Harley 8)
Title: Re: Microfet 100
Post by: Dante on July 10, 2016, 05:43:43 PM
I agree, I did like my MT100, but it kept crapping out on me. Usually, as you say, one channel.

I hooked up the MicroFet already, it was super easy. It will not work in bridged mono or chB, only chA. I just discovered that my MT200 will also not work in bridged mono. :/

At any rate, the MicroFet seems wimpy at first, but watch out, it gets loud. 12:00 on the MicroFet is is like 10:00 on the MT200, but it ramps up quickly after that. It's thinner sounding, almost transparent like a Fender amp, without the bottom warmth but very much putting out what is put into it. To my ears, the MT200 seems to color the tone a bit - warmer. fatter. better. spongy tube compression.

It's very similar to my new SS combo amp, thin. I think (like my combo amp) it would pair fine with an MP-2, because the MP-2 is so forgiving. It can compensate for a bad power amp (IMHO) and still sound good - good enough for who it's for. Not that the lil' Marsha is a bad power amp, it's just not as warm sounding as my Boogie toob amp was....but it cuts through the mix
Title: Re: Microfet 100
Post by: Harley Hexxe on July 10, 2016, 05:57:17 PM
Dante,

     None of the SS poweramps will bridge, not even the B200S. The Microtubes are the only ones that will do this. I seem to have gotten the opposite impression though, (MT 100 sounded warmer), in bridged mode with the stock tubes in it. The only way I was able to warm up the MT 200 was to use some high gain tubes in it that I would never use in the preamps, like the used Fender 12AX7's I put in one of mine, or some Sovteks that are similar, and dialing the Presence knob to about 10-11 O'clock.
    The B200S still warms up the preamp output better than either of them, and it's quieter.

    Your MT 200 should work in mono bridged mode. There might be a connection fault somewhere in the amp preventing this.

       
Title: Re: Microfet 100
Post by: MarshallJMP on July 10, 2016, 06:32:54 PM
I think a lot of problems are comming from the jacks.Some are special with one or 2 switches that act as senses for the bridge mode.(the mone bridge output jack and the mono in jack)
Title: Re: Microfet 100
Post by: Harley Hexxe on July 10, 2016, 06:55:19 PM
I didn't know about that, but that would explain it :thumb-up:
Title: Re: Microfet 100
Post by: MarshallJMP on July 10, 2016, 06:56:48 PM
I did found all the types except for one,the bridge out jack.Still looking.
Title: Re: Microfet 100
Post by: Harley Hexxe on July 10, 2016, 07:00:03 PM
No way to clean the contacts or repair the jacks?
Title: Re: Microfet 100
Post by: MarshallJMP on July 10, 2016, 07:05:31 PM
You could try but the best way is to replace it.These jacks are old and usually the contacts have tarnished.Also these are plastic jacks and the plastic can become brittle.
Title: Re: Microfet 100
Post by: Dante on July 10, 2016, 09:49:49 PM
Dante,

     None of the SS poweramps will bridge, not even the B200S. The Microtubes are the only ones that will do this. I seem to have gotten the opposite impression though, (MT 100 sounded warmer), in bridged mode with the stock tubes in it. The only way I was able to warm up the MT 200 was to use some high gain tubes in it that I would never use in the preamps, like the used Fender 12AX7's I put in one of mine, or some Sovteks that are similar, and dialing the Presence knob to about 10-11 O'clock.
    The B200S still warms up the preamp output better than either of them, and it's quieter.

    Your MT 200 should work in mono bridged mode. There might be a connection fault somewhere in the amp preventing this.

       

I swear, there's a bridged mono on the back of the MicroFet
Title: Re: Microfet 100
Post by: Harley Hexxe on July 11, 2016, 04:47:08 AM
I swear, there's a bridged mono on the back of the MicroFet

   Maybe that is why the B channel is blown. I was told SS amps don't like to see each other. :crazy:
Title: Re: Microfet 100
Post by: rnolan on July 11, 2016, 05:31:48 AM
Hey Harley, depends on the amp, they have to be designed to be bridged, e.g. I have my new DCM200L bridged to power the Mesa bass cab.  Also my TS100 can be bridged (I had it bridged into an EV 3 way TL for the MB1 before I bought the Mesa cab and DCM200L).

This channel problem seems very similar to one posted here in the past.  IIRC cleaning the jacks helps for a bit (particularly the jacks which do the switching) but best solution is to replace them.  Also the plastic jack sleeves are important as they are not meant to earth with the case (causes earth loops/hums as MikeB found out replacing his B200s jacks).

I had a MT100 (or was it a 200 Dante ??) US voltage for a little while.  It didn't float my boat so swapped with Dante for B200s (looks like I got the better deal Dante, although was working fine when I shipped it, I think I used it for 20 minutes all up...).
Title: Re: Microfet 100
Post by: Harley Hexxe on July 11, 2016, 05:43:24 AM
Hey Richard,
   I know it depends on the amp. Generally when it comes to guitar power amps though, they don't usually like to see each other.
Title: Re: Microfet 100
Post by: rnolan on July 11, 2016, 05:51:33 AM
Hey Harley, I suspect you are correct, and you don't see allot of models capable of bridging, seems Carvin have decided it's a good feature, I think they have been offering it on many of their amps over the years.  I was having a discussion the other day with an Audio File tube nut friend, he's bridging his stereo leak tube amps, needs some circuit tweaks but the result is the 2 output transformers purr as they don't have to work as hard.
Title: Re: Microfet 100
Post by: Harley Hexxe on July 11, 2016, 06:35:05 AM
Hey Richard,

     While that may look good on paper, and sound good in theory, it may be a disappointment in the end. After all, the character of an amplifier is the result of the output of the preamp and the poweramp working together. If the preamp output is strong enough, and feeds the input of the poweramp hard enough, then that will drive the output transformer harder. The sum of all these things is what gives the amp it's great overdrive tone.
    At least that is how vintage tube amps work. That over-driven tone is what every amp maker in the world is trying to reproduce, including ADA. That's the problem. They've taken the part of the equation I mentioned above, out of the picture, and replaced it with pristine amplification, and compensate for this by putting all the gain in the preamp.
    Your 50 watt Marshall is a perfect example. Disconnect the poweramp section of the amp, and in it's place, use your Carvin. Will it sound as good? Better? Not as good? Or maybe not good at all?

        Harley 8)
Title: Re: Microfet 100
Post by: rnolan on July 11, 2016, 06:57:30 AM
For what he wants to do it's a good idea as he's chasing supper clean HiFi.  I see it as 2 different approaches and to some extent objectives.  If you want the preamp/poweramp sound then what MJMP does is probably the closest using ADA MP1/2. And this works well when you can play loud (a constraint we all find ourselves with).  I use a power soak with the Marshall and run it really hard, the soak allows others to share the room  >:D , and me to maintain a sound I like.  The other approach is, as you say, put it all in the preamp, and use clean transparent poweramps.  Although some look for some more warmth in their poweramp, whatever gets the sound you're chasing.  And some use the MP2 cab sims and use PA style cabs.

I must say though, there is nothing quite like the Marshall fully cranked, no soak, nobody to tell you to turn it down, it's a wild journey full of energy (I'm sure you know..)  My current record is it could be heard 13kms away ::)
Title: Re: Microfet 100
Post by: MarshallJMP on July 11, 2016, 10:11:04 AM
That's the problem with tube heads,you have to cranck them,especially the older ones.And usually it's just too loud.And yes you can use a load to tame down the volume or like they are doing now lowering the supply voltages but it just doesn't sound the same.Also in a head the preamp and poweramp share the same power supply which also has an influence on the sound and the louder you get the more influence it will have.

Now as far as bridging amps goes, I never liked the idea.Maybe a brief explanation on how bridging works. So you have 2 poweramps and what they do is feed one amp the straight input signal and the other amp the same input signal but with a 180° phase shift. So one amp will do the positive signal while the other one does the negative signal. This will double the output voltage and current. That's why with a amp that can handle 4 ohm/channel you can use only an 8 ohm in bridge mode or else you would blow up the amps. Now on the output side one output is connected to the + connection of the speaker and the other amp on the - of the speaker.So you have to keep that signal isolated from any ground connections.So plugging a bridge ouput into let's say a microcab will blow the amp that drives the - of the speaker.And in case of the MT amps the B channel. Maybe this has got something to do why the B channel is mostly busted with these amps.You will see on the MT200 the bridge out jack is isolated from the chassis.
Title: Re: Microfet 100
Post by: Dante on July 11, 2016, 12:51:43 PM
Now on the output side one output is connected to the + connection of the speaker and the other amp on the - of the speaker.So you have to keep that signal isolated from any ground connections.So plugging a bridge ouput into let's say a microcab will blow the amp that drives the - of the speaker.And in case of the MT amps the B channel. Maybe this has got something to do why the B channel is mostly busted with these amps.You will see on the MT200 the bridge out jack is isolated from the chassis.

If I remember correctly, I blew the channel in my MT100 (from Richard) by connecting the cables while the amp was on. Don't do what I did  :nono:
Title: Re: Microfet 100
Post by: MarshallJMP on July 11, 2016, 02:30:43 PM
That might not be a good idea with these amps and actually any amp.

Hey Dante, did you check the fuse inside the MT100? There are 2 glass fuses on the PCB board,it could be that one of these is blown. These are 3A fast blow. Now if you are lucky the fuse blew before the mosfet's blew. So you could check them out (only one will be blown) and replace and see if it works. If it blows again then the power mosfet's are gone.Now if this happends you can always the 2 mosfets and 3 driver transistors.It will cost you less then 10$ in parts.
Title: Re: Microfet 100
Post by: Harley Hexxe on July 11, 2016, 03:05:55 PM
@MJMP:
   You finally answered the question I started asking 9 years ago when I first joined this Forum! That would help to explain why the B channel of the MT 100 is always blowing. There has to be a way to isolate the ground in them to stop them from blowing the B channel. With that information, maybe I can come up with a way to correct that.
 
@ Dante: That is what I was doing with my other Classic when it blew, I was hot-plugging in and out of the effects loop. So, the moral of the story is: Always turn off your ADA gear when changing connections!

 Harley 8)
Title: Re: Microfet 100
Post by: MarshallJMP on July 11, 2016, 04:01:29 PM
Oeps sorry it took so long  :facepalm:

Best thing to do if you use the bridge out is using plastic jacks ,this way the B channel stays isolated.If you use metal jacks the metal is connected to the out of B channel and if it touches a ground it will blow the B channel.

Now I find it strange that you blew up your classic, normally hot plugging an effectloop should not damage anything.With an amp it's a different thing but an effectloop... ?
Title: Re: Microfet 100
Post by: Harley Hexxe on July 11, 2016, 05:07:32 PM
MJMP,

    Well that is what I was doing when that Classic blew. I had the idea of trying to run a parallel channel in my effects loop, so I had the ADA effects in one channel, and was just going to plug a short patch cord into the other channel to even out the balance between the loops. That was when the preamp died.

     Harley 8)
Title: Re: Microfet 100
Post by: MarshallJMP on July 12, 2016, 03:21:25 AM
And it's completely dead or ... ?
Title: Re: Microfet 100
Post by: Harley Hexxe on July 12, 2016, 04:32:49 AM
MJMP,

    It's dead in the sense of any sound coming out. It turns on and goes through it's diagnostics.
Title: Re: Microfet 100
Post by: MarshallJMP on July 12, 2016, 07:29:26 AM
So nothing at all, soundwise?
Title: Re: Microfet 100
Post by: Harley Hexxe on July 12, 2016, 07:44:05 AM
It's been a long time since I tried it, but I believe no sound at all. IIRC, this is the one I tried to change a cap and maybe a resistor in the back corner of it, but my soldering iron wasn't hot enough.
Title: Re: Microfet 100
Post by: MarshallJMP on July 12, 2016, 12:08:29 PM
Ah you had problems with the tube channels?
Title: Re: Microfet 100
Post by: Harley Hexxe on July 12, 2016, 04:40:04 PM
It's been 2009 since I messed with it. I think the cap you told me to change was C47 (possibly), which is located near the back left corner of the preamp as you are looking at it from the front.

   That was the preamp I had hoped I sent to Matt Trull a couple of years ago, but as it turned out, it was the other one he repaired.

   As it is, I don't believe I got anything from that preamp at all except for some low frequency static after the hot-plugging incident. I may be taking this to a repair shop I've found, if they are still in business, and let them have a go at it.
Title: Re: Microfet 100
Post by: MarshallJMP on July 13, 2016, 03:34:24 AM
Yes a cap and a resistor,now the problem is mostly the resistor. BTW did you got my PM?
Title: Re: Microfet 100
Post by: Harley Hexxe on July 13, 2016, 04:58:30 AM
Yes I did, reply sent.

   If you recall, The soldering iron I used was only 25 watt. Not enough to get the solder joints to flow smoothly. I could use my 75 watt solder gun, but that may be a bit too much and I don't want to risk loosening the traces. I'll probably get a 40 watt iron and re-flow the solder joints and see what happens, but I think there may be more than just that.

    Harley 8)
Title: Re: Microfet 100
Post by: MarshallJMP on July 13, 2016, 02:12:07 PM
Don't use soldering guns, bad idea.

Does it make any sound at all, like noise or a click when you change anything?
Title: Re: Microfet 100
Post by: Harley Hexxe on July 13, 2016, 02:47:21 PM
I would have to get it out, put in a new set of tubes, and hook it up. I haven't messed with it since I tried replacing the cap and resistor, and it didn't fix the problem.
I have to get a 40 watt iron to get those soldered in correctly. Currently the only iron I have is a 25 watt.
Title: Re: Microfet 100
Post by: rnolan on July 13, 2016, 11:10:43 PM
Hey Harley, I bought one of these (http://www.radioparts.com.au/product/38571665/zd929c-48w-soldering-station-digital-display-doss#.V4cr2qJPw0g). Should cost you around $70 USD ish.  It's been a great iron, I use the small chisel tip and you can dial in the temp you want. One of the best tools I ever bought  :thumb-up: