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Ampeg BA600 - 115 bass amp combo, 6 months old, ROHS

Yet another owner forgoing replacement/repair within warranty. I imagine the importer has no replacements in stock as the whole batch has the same faults. Perhaps bass guitarists should use pneumatics and proper compressors to shift air. Mechanical rattle noise due to brass cylinder spacers used over the control pot bushes , loose bush nuts, so rattle. But more importantly At moderate levels an electronic crackle is the main problem. Remove the screws in the cab to release the amp and one caged nut falls into the amp space due to cracked cage. And a nut ( now known) falls out of its cage in the screened off ps+pa section. The PA although supposedly 600W uses only TO220 ,(4 x TOP66 in the smps). Amp and its casing 6Kg but 22x21x16 inch cab and 15 inch sp only 18Kg so maybe part of the problem. TO220 in the PA is 3 on pcb , 3 on one section of heatsink and 4 on another, no fans. As slab SMR nearby are 22R I assume for the moment the o/p devices are powerFET. Each bank of TO220 held down by cross bar and 2 screws. This is my scale of screwdriver torque

1 light finger pressure around handle 2 strong finger pressure 3 fist 4 2 hands 5 wrench 6 impact driver Testing the cross bar screws (they do have captive spring and plain washers) torque measures about 2 , 1 and then 1.5 and 0 The absent one either dropping out unseen as I knew a captive nut was loose inside or still trapped under ps or pa. So I assume silipads had compressed but these are 1.8mm thick porcelain, even less compressible than mica. They were still in place surprisingle but you could slide them with fingers and the TO220 nearest absent screw. As distortion was crackle rather than push-pull failure distortion hopefully solder failure , think I can see ring cracks with x30 microscope at awkward angle, pushing around the loose TO220 legs not obviously moving at solder points) rather than some thermal runaway devices. So how to do an airframe type castellated nut plus lock-wire fix? for these screws. 1mm wide pair of cross slots ground in the screw heads and st/st wire looped and twisted in a slot and around the cross-bar?
Reply to
N_Cook
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Cannot find that 20mm long screw lurking anywhere and extremely unlikely to jump through the grommeted lead ports into other section of amp and then fall out. Straight on , top and bottom x30 viewing of all TO220 soldering looks ok, surprisingly. Did find some nasty rework/fudge. 2 standard radial legged 10uF 50V, C19 and C54 soldered to standard SM pads, no thru board holes. Near it a SM cap, C61 measuring 15.2nF, had been soldered over conformal coating with one end not soldered to trace, as coating under. Owner has owned from new. 4x IRF450N power FET for 600W ?

Reply to
N_Cook

to

al

Its prob'ly that class D junk....

Reply to
boardjunkie1

to

radial

Its prob'ly that class D junk....

+++++++

Valid point, it does use 2x Int Rect IRS20955S, each one driving a pair of FETs and there is an IR application note out there for those being used in Class D. That would explain the socking great inductor/choke well out of scale with all the SM on that board. Will check that inductor is at the output and try and locate a clock line , presumably back to the SMPS.

Reply to
N_Cook

A generic problem with these will be mechanical noise from vibrating control pots.

7 of the 9 were loose , in 6 months of non-commercial use. Not brass cylinders over the bushes but are stop-ledged/ partial threaded leaving not enough space for chassis thickness, nut and normal star washer so they used thin plain washers. Luckily I have managed to fudge some thin star washers.
Reply to
N_Cook

Downloaded the datasheet and that IRS is for pwm/D class operation. Input ,pin3, goes back via Q9 to 74C04 buffer so digital. That large L , in a 53x53x24mm case is connected between the common points of both FET pairs and across the speaker (with an ohm or so somewhere not ascertained). That L1 measures 4K ohms , inductance not possible on LCR meter as a yellow block HV polyprop? cap , label obscured by L1, is also across it but measures 1.15uF apparently on LCR meter.

Speaker lead has a 4 pole connector for disassembly , 2 poles per wire, but same size connector on the pcb only 1 pole each. Worse than that the commons traces going to L1 are 3mm wide with solder run thickening for the current but the 2 output traces going to the speaker are 1.5 mm wide and plain tinned. So assuming 300 watt for a second into 4 ohm then about 9 amps. From the Enumber in ul.com, it is 1 oz board and using

formatting link
for 60 mil track and 9 amps for plain copper then 100 deg C rise , don't know how much the tinning coat would change things , say an unlikely doubling to 2 oz in effect, then 32 deg C rise , unacceptable ?

Reply to
N_Cook

Can you have the bridge of a bridge tied D-Class filter of form insted of

--L--Sp--L--

as single L and speaker and C in parallel

|-----Sp-----|

----|------L-----|------ |-------C----|

L is inductor ,Sp speaker,C capacitor

Reply to
N_Cook

I'd forgotten the double wound toroid inductor of 360uH in series either side of the speaker. What sort of value of inducance for L1 and its wire gauge/current carrying requirement for 300 to 600W use? C may be about 1uF

Reply to
N_Cook

I removed the filter cap to measure the inductance of L1 . Cap marked 1uF,

250V. This L1 weighs about 170 gm, estimating weight of remainder components and pcb from total of 290 gm. Through a hole I can see some wire about 1mm diameter. Using 1KHz RLC meter, L1 measures -2.2H on H scales and -140mH on mH scales, don't know what that means , will try and find a manual for an Avo B183. Maybe faulty, but measuring plain inductors through the scales is positive and consistent across neighbouring scales. 1KHz ac resistance is 230R, DC resistance is 4K so perhaps what is labelled as L1 is R and L in series. Perhaps R of 4K and L of .6H , to give 230R at 1KHz, but if wholly 1mm wire I cannot see how 600mH with 170gm of 1mm wire, strange core material?
Reply to
N_Cook

It almost seems perverse, 0.4 amps of mains current draw (at 240V) and 25 watts of 400Hz sine into 4R dummy load and a thermometer laid over the tabs of the 4x TO220 output device, rises only 8 deg C over ambient. And that with amp laying on bench so no convection over the external heatsink vanes, no wonder no fan needed.

Previous D class I've played with were Stagepas , not possible to monitor their operation without making up umbilicals to operate PA out of the little box. And as separate clock maybe "RF" problems doing that

Reply to
N_Cook

Do Ampeg make bass amps? There will be loads of returns of this model. Any large lump inside a bass amp is likely to vibrate if inadequately secured. That 2 x 2 x 1 inch lump is only secured by its screening can at 2 pointsplus inductor ends soldered. That was the main problem , proper solder would be hard pushed but PbF only lasts 6 months like this. By a daisy chaining cable ties between made anchor point at the ps , round the L1 can and out through the cable hole and tightened after the ps+pa screening case is back over. Also PbF failing on the speaker socket, would not have been so bad if they'd used the 4 pole connection like farther down the speaker line. Plus the absence of star washers on the pots. Ignoring the absent h/s bolt.

Reply to
N_Cook

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