Crate V100

[Mars Amp Repair]

Has anyone noticed that this new Crate tube amp has a switch mode power supply?!! I think it's a V100...cant' really determine that as the only marking is the logo on the front of the head. A 'V' over what could be a 'V'

I don't see lit on the Loud site for it.

I'm sure it will be fun to have to inform the cust that most likely every time a power tube shorts, so will the switch mode supply. What next glen

[Enzo]

Who says it will kill the switcher? A goodly portion if not most switchers have overcurrent sensing and will simply shut down if presented with a shorted load.

[Mars Amp Repair]

I hear ya Enzo,
I was thinking of the inductive kickback (back emf) from the output transformer that the supply line could encounter when a power tube intermittently shorts...I'm not sure even the switcher can suppress that kind of spike. I guess we'll see.

The switcher is paritially dead in this one. I'm not sure why yet. I am a bit surprized that Crate didn't make attempts to put the thing in a box for shielding purposes or even just for esthetic sake as it really looks foreign in there with the tubes & output transformer.

Are you a proponent of the switchmode power supplies in tube amps?

glen

[Enzo]

WHile they are more complex, and take some knowledge to service, I am a fan of switchers for many reasons. I don;t really care what type equipment they are in, so tube amps is no more special than a Yamaha DX90.

I have been servicing switching power supplies for close to 30 years now.

ANy spike from the system it powers would have to make it past the amp circuit flybacks if present, and then through all the intense filtering of the switcher secondaries. With the multistage LC filtration, I am not too worried. (Famous last words, I know)

[Mars Amp Repair]

yeah i hear ya.
I used to repair the low power ones in VCR's way back when. No too much of an issue there as if you missed a component & it blew up again, it would only take out a few inexpensive parts.

I've never had any 'luck' working on the higher powered ones, tho. They take special fast switching transistors & diodes that I just don't have a lot of experience with.

I have a Yamaha VA-76 $2800 keyboard with a switcher that was physically intermittent. It is a double clad pcb, so it didn't seem like it was connections, but I resoldered every thing & then the switcher just plain would not work.

Yamaha gives no info on the supply & just expects you to replace it. A new one costs me $330!! YIKES. I'd love to repair the thing but it has some weird components I can't identify. I also suspect that the switcher transformer might have been the intermittent culprit & I can't even procure that part if I need to...so what do ya do ;-[

Another issue I have with switchers in solid state power amps is the inability to bring the unit up on a variac after you've rebuilt the power stage to determine if the amp still has issues. You can only fire it up full power & wait to see if it blows again.

I just won't work on any high powered PA amps with switchers anymore for that reason.

...glen

[Enzo]

The channel parts of the switcher based PAs are still the same as ever. You can farm out the switcher repair and still repair the audio parts.

[Mars Amp Repair]

true, you could farm out the switcher if it were self contained. Many of them are integral to the amp & also need specific loads to make them run.

I doubt the switcher repair places have all the specs on all the unique switchers we find in the high powered power PA's. Fortunately, there aren't that many around.

Yorkville tried their hand at it a few years ago with their model 4.4 a 2000watt PA rack mount amp...as soon as they started to have problems folks dumped them like hot potatoes & Yorkville dropped the idea of a switcher in a high powered amp & went back to tried & true transformer power supply. NIce for the light weight, but worthless if they keep having issues. They claimed that it was a result of soldering that was not good enough for the frequecies involved, but I never found one with bad solder joints that were causing an issue.

Anyway, there are far more profitable $$/time repairs out there to do...and frankly a whole lot more interesting, too. I'll leave the switched high power amps PA amps for the guys who specialize in them.

We have a guy in town who hates guitar amps & seems to love the 1000watt plus power amps, so he's dah man as far as I'm concerned. More power to him...so to speak ;-]

If the service lit has info on the switcher & parts available for the lower powered switchers, I'll attempt to repair them. I doubt Crate is going to expect anyone to repair their supply or supply any info on them. It's just the way things seem to be going these days.

As always, to each his own...glen

[Enzo]

By farm out, I meant if your Crest amp with switcher has a blow switcher, send it to Crest. I am not aware of third party switcher repair shops.

dropped the idea of a switcher in a high powered amp & went back to tried & true transformer power supply.

Same exact thing happened back when these new fangled transistor amps came out - they didn;t work all that well, and were real picky about loads, and they liked to burn up. Fortunately we had tried and true tube technology to get us through.

[Mars Amp Repair]

I hear ya,
however the switcher power supplies have been around in wide use for about 25yrs and in most cases have become replaceable items as opposed to repairable items (as in computers).

I think Conner works with switchers all the time. I'm surprized he hasn't chimed in here. I like nothing more than to have some more insight to these things.

Well, I guess we'll have to see how many amp mfgs decide to save money this way & how economical they will make it to replace/repair the switchers once out of warranty. If they don't have any info on the switcher or supply of parts for them as well as don't make them economical to replace, it won't take long at that point for folks to learn to steer away from them.

A possible solution to the issue would be what Line 6 has done. They actually make all of their boards (large switchers included as in the Vetta & H147) very affordable. The idea of this comparably dinky keyboard switcher supply costing $330 as compared to $80.00 for the the one in the Vetta or H147 which supplies a 150Watt amp, just shows how much support Roland is interested in providing to for their equipment.

We shall see. I hope for either more reasonable replacements as Line 6 has done, or some decent service lit & parts availability. g

[bnwitt]

Man I'm still trying to learn basic solid state stuff and now they throw this at me.

Glen, could you describe how you use a variac to bring up and test a solid state amplifier? Is there a different benefit than using a light bulb limiter?
Barry

[Enzo]

The tube amps don't work until their heates are warmed, so it is very hard to bring them up on a variac. As opposed to "cap forming", in troubleshooting, the variac is used with a current meter. If current starts to ramp up as the variac is advanced, you turn it back down. if ti is trying to draw 3 amps with the mains at only 10v, you probably didn;t hurt things further, but you also never blew a fuse or applied full powr to anything.

A solid state amp will try to work from the get go. WAtch the mains draw as you advance the variac. You either get a little draw as the caps load up and the fan kicks in, or the thing starts to ramp up current quickly. Experience getts you used to seeing the momentary draw spike as the uneven supplies come up - some amps have a more pronounced bump than others. Mostly I just dial it up and watch.

And as I advance the variac, my initial charging bump might be over, but than somewhere at about 80VAC, current starts to rise. That can be because something doesn;t turn on at lower levels. The bulb, being all or none, won;t show any different the thing that draws over 80v and the thing that draws right from the start.

I recently had a current model Bogen in here that did exactly that. Had a shorted suppressor across the output, but also had some open resistor in a limiter circuit. AMp worked fine at half voltage, but not over a certain threshold. Would have been a ton harder to fix with a bulb.

Light bulbs are more an on/off thing.

Glen, not all make switchers obscure. I recall Emu had some large switcher in their EMulator or something. Emu had no schematic, they bought the supply whole from a vendor. I traced the thing out myself. Yamaha may buy a supply from a vendor as a commodity item and have no documants, but other times they do. PV CS800S has documents. The Crest amp I was thinking of did as well.

GK no longer supports the switchers they made for some of their little amps. They want you to sent tham $300 and they will retrofit a transformer. They may not support them, but I still fix them. One problem I almost always see in those is the legs snapped off the TO220 rectifiers. Poor mounting arrangement. But not the fault of it being a switcher.

COmputer powr supplies are fixable, just nobody does it. The arcade industry uses them too. Easier and cheaper to buy big silver computer powr supplies than to make their own. I used to carry parts and fixed them in the field.

And look at the parts source. Yamaha wants a ton of money for one because like everything else, they pack it as a separate part and import it. Last time I checked - 15 years ago - they wanted $9 for e three leg voltage regulator, yes a plain old 7805. A dead switcher compared to a dea powr transformer $$$? SOme othe company like say PV will be much more reasonable in cost.

[bnwitt]

Enzo,
I see. Now I realize that my variac is worthless for this as it has no current meter. I could build an outlet box with one though. What range of AC current meter would you recommend for this work?

[Mars Amp Repair]

Well,
my variac current meter goes from 0-15amps & really doesn't resolve well enough to use at the 0-3amp range, I use my bulb limiter in conjunction with the variac and connect 2 meters to the power stage to determine what is going on as I raise the ac up. Of course there in NO load connected at this point.

One meter is at the output of the stage at the common point for the emitter resistors (to circumvent any protection relay in the ckt) as well as another meter across the emitter resistors to determine how much current is being draw.

I raise up the variac & watch for any really excessive current being drawn from the the meter across the emitter resistor or any excessive DC at the common point of the emitter resistors...I can also watch the current meter on the variac for any excessive readings as in power supply issues, however the illumination of your 100watt bulb limiter is a good indication of this, too.

You do have to get a feel for at what point you expect the bias circuitry to kick in. At bit harrowing as you watch your emitter current going up. It usually kicks in beween 40% & 50%.

Hope that's helpful...glen

[Enzo]

My Variac has no current meter, my current meter is a separate item.

I'd have to agree with Glen that maybe just a 15 amp meter would be too much for watching small currents. A 3A meter sounds good. Certainly a switchable meter makes sense. A good adition for your bench would be a test outlet - plug the unit under test into it - with its own on/off switch, and a current meter.

ANd of course my DMM has current functions that cab be invoked with a couple clip wires.