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About MI-9584

  1. I seem to remember an old wives tale that when replacing outputs in multiple pair amps like DC -300's etc. The more desirable devices typically have lower gain as they current share better.Is this really the case?Or are state of the art higher gain devices better?
  2. Get your guitar tech off his *beep* n tell him to put his AC voltmeter on the output of the EQ right at the amp input as you play so he can get an average level.This is REALLY where EQ belongs.I don't like the EQ loop deal.Usually too much noise!!Whatever you get here will determine how hard you are hitting the amp.If there is over 2.0Vac of signal and the amp will do full with this or close to it then ur o.k. If there is considerably more than you are considerably more O.K.If there is considerably less than ur not O.K. !!A gain stage(notice,I did not say pre-amp) may be required for you.Remember,The Nova is just a Stomp box,no matter how sophisticated,it's still a stomp box.You may need to be a little more exacting in the system you gig with.No diss to you meant,I love to mix good musicians and you are probably of a caliber that needs to be more demanding of the equipment!!There are quite a few good guitar pre's made and that may be a route you have to take.
  3. Did Crown ever offer the D 150 for sale without a faceplate?Saw a D on ebay n asked to see a shot of the Faceplate(it was advertised as very clean,mint)which was declined by the seller as "this was the model meant for concealed installation and didn't come with a face.I don't ever recall this as an option.Any body know differently?
  4. I have to update this as I got it sorted out.Had a similar problem on an old Crown 30-30.One channel ok the other low vol.not exactly really nice etc. etc. Tracked that down after remembering one of the power amplifier rules.If it's blown up,catches fire,makes the speakers catch fire or just works great as an arc welder,Its one of the ACTIVE components!If it just behaves badly,A passive is the main culprit.Sure enough,the large electrolytics in the feedback on the 30-30 were so dried out they were simply not there!!!Checking the small electrolytics on the driver boards of the DC 300 by substitution was like turning on a lamp in the dark!It is stable,was able to set the bias & had ample adjustment on both input and output offset potentiometers to get it to.000vdc on the outputs.Just goes to show,Always check everything ......
  5. I had planned on that course of action but since the forum is loaded with very competent and experienced techs I thought by some slim chance someone had run up against this particular problem in the past and could offer a fix based on a repair history of an actual unit with the same prob.I should know better by now.When a tough dog finds its way to my bench its really a DOG!!! I was really just looking to get out of a troubleshooting hit n miss episode. I have a schematic but the secondary AC voltage isn't mentioned.I know it has to wind up as 60 Vdc + and - at the rails.I guess the theory books will have to be dusted off as I can't remember if this is an instance of divide by .707 or the 120 Vdc total of the two rails is 1.414 times what the secondary voltage is but i have seen the formula somewhere.Again,I was lookin for the easy way out.I'm not really worried about the trans and face as I am planning to make a face from a nice charcoal anodized rack panel i found at work and my second choice of the 1kva toroidal trans from Antek is probably the way i will go,its always a good point to ask.You never know what people have layin around!!I appreciate your time in responding and think you are right.Just make notes of the good channel and see the comparison to the evil twin channel.
  6. Did some checking as I figured it should show some output when it acts up so i connected aVTVM to the output and ran it up to see how much output it had.There was none!This had me baffled so i made a few voltage checks and what i found was the bias would go from .330 when stable to .550 when the channel acted up so the problem is raising the bias,not an oscillation.I think I will have to get the transistor tester out.This is probably going to wind up being a leaky active device or a leaky electrolytic on the board.Still looking for the correct power trans and a faceplate.I have another of these early amps so I may just get a rack panel and use my other face as a template and make a suitable replacement.Hey CROWN,Any dead units around i could buy a trans from?If not,What secondary voltage was the origional rated.I'll just get one from Signal trans or a nice1KW toroid from ANTEK. MI-9584
  7. Bought this as a cadaver off the "Bay" for $24 bucks without a Faceplate,level controls,power transformer.Yeah I know,what the *beep* was I thinking!Well anyway I found a medium sized trans from a Marantz 240 that gives me the +/- 60 V needed so i put it in.The monster fired right up on the variac at about 35 vac and started to work.I was in shock that apparently the drivers and outputs were fine.Ran it up to 60vac for an hour then 80 and finally all the way up.The only problem is with Ch 2 level up full . ch 2 must be oscillating as the current draw goes to 1.8-2.0 amp.If you back the level control(soldered in some 10k pots to help troubleshoot)back to about 75% the draw drops to about .45 A ac.With a non factory transformer I'm assuming this is fine.In fact everything is fine.Ch 1 is flawless!Till you crank the ch 2 level over 75%.As long as the control is at 75% or less.Ch 2 is fine.No distortion,no nastiness of any kind. Any clues where to look.Haven't checked passives on the board as I thought to check here first for a lead or two.It is the first generation.The REAL early one with the normal/hysteresis switches on the sides.Bootstrap supply is good too. I know there are alot of you guys that have hundreds of repairs under your belts,and i'm just lookin to find the best place to start.And if anyone has an origional faceplate or a transformer I'm lookin.Again,the early one with the five fuse caps along the front bottom edge.
  8. After buying it on that well known auction site as a $15.00 bargain i had planned to use it as a parts source only.But as usual my will to fix prevailed.After matching up two pairs of outputs from a nice stock of 2N3773's accumulated over the years,then sorting out the repair started and trying to figure out where the poor soul lost interest led me towards Q111,211 the bias transistors.A bias of .021 and .044 right and left would not do so replacing both got it up and running and with 180 ohms and 240 ohms as the selected resistors i knew i was close to a finish.outputs measured .026 and .003 volts across speaker terminals so a little setup of the input and output offset controls topped this amp off and have it working very well as i type.The problem is,as a cadaver,it is missing a face and one of the heat sink fin assemblies.I'm not going to be particular but i know someone has these parts just layin around.Crown still stocks the heatsink but at $54.00 or so for it and $75.00 for the wrong(black) face and no rack ears i am trying here first.I just want to protect the circuit board and internals from accidental contact so maybe i need the grill assembly that covers the board too(no bridge switch)I will pay for anything and shipping too.I will get the fin from Crown as a last resort but the amp warrants some help as it looks like *beep* as it is and is working perfectly. I can't buy one for parts cause some magic spell comes over me and they wind up on the workbench and you all know what happens there,I will need parts for THAT amp.Sorry to ramble but see what you guys can come up with.If necessary call my cell at 914-629-3878,I'm in the NY Metro area.PS. it's not the earliest one as it has the input output offset controls but it doesn't have an A in the model number.The serial number is D-9735 using circuit board number 9357.The fin is the later one that looks like a bunch of H's stacked together,not the one that has the fins at different angles.