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EmPro View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 07 June 2022 at 5:06pm
well...the BK was faulty on right ch,loads of cold solderings and faulty pott (didn't pass any signal from inputs) lucky me i had the potts from the Matrix ukp1300 (the blown one) and were identical, so cool,after all parts checked,full resoldering of the board,pot changed and new thermal paste betwin L aluminum and the rest of the case the right ch is fully working loud and clear, +-70vcc supply on this small thing lol,the left ch was working however it was full of cold solderings so i did full resolderings as well (module in the photo),now is fully functional for the next 20 years LOL


Edited by EmPro - 07 June 2022 at 5:10pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 07 June 2022 at 6:57pm
I've got the week off work so have been experimenting with an old Urei-JBL 6260 (I have three and a 6290) that I refurbished with new caps including uprated filter caps, uprated bridge rectifier and new TL054 opamps.

I believe Matti Otala had an input to the design of these amps.  There were made when there was a heightened concern of TIM distortion at the time.  Very robust 200w Sanken bipolar output devices only ran at around 35% of the power rating.  Huge transformer, well laid out board and very thick steel.

This old device still meets and exceeds specs. Measured just before the onset of clipping, Distortion at 0.05% at 1Khz and the more brutal harder distortion test at 20khz the distortion was 0.082 which is actually outstanding for a PA amp of this era. (For comparison my Crown K1 measured 1.86% just before IOC lights). To get these measurements I had to increase bias to 500mV. At around 560mV the amp starts thermal runaway measured by mains draw and heatsink temp. These amps have a very wide open loop and global and local negative feedback which is quite low. Amazing amps for compression drivers. I was hitting 220watts output in 8ohms at very near 1% distortion.  These amps are only rated at 150watts in 8 ohms or 300watts in 4 ohm.

Astonishing sound out of these units.  High frequencies are very detailed and smooth. 




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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 07 June 2022 at 11:51pm
JBL UREI series are well known for quality mate,unfortunately for me i never had the chance to put my hands on one,nice old amps ClapClap
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2022 at 7:27pm
I ran up my JBL-Urei 6290 today.  Big old heavy brute.  Saved it from being thrown away as it was faulty.  I fixed it with new opamps and all new caps.  It was hitting 350watts in 8ohms (rated at 300watts in 8 ohms) easily and clipping with 400watts. 

Managed to get the Crown K1 distortion figure down by careful calibration of the overlap/underlap adjustment.   One of Crowns Gerald Stanley's finest designs and a new version is still used in the I-Tech.

Class I (NOT class D design) Negative and positive switches are on at the same time at idle dumping the current into large inductors and then to swing positive or negative duty cycle increased on either switch..  So no dead time or overshoot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2022 at 8:12pm
Originally posted by EmPro EmPro wrote:

Jbsystems AX200 nice little 1U toy with toshiba 2SC5200/2SA1943 on outputs,i like the way they build these ones,just some loose connections in the psu side and up and running:


I used to own of these many years ago.  Thought it was quite decent for the price but had a really noisy fan!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2022 at 8:16pm
Great thread guys, loving the old school amps in particular. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2022 at 9:44pm
My ,,dark'' Cloud found his way to my room LOL no fans in my head,just pure and clear music Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 08 June 2022 at 9:55pm
Originally posted by shaun1264 shaun1264 wrote:

I ran up my JBL-Urei 6290 today.  Big old heavy brute.  Saved it from being thrown away as it was faulty.  I fixed it with new opamps and all new caps.  It was hitting 350watts in 8ohms (rated at 300watts in 8 ohms) easily and clipping with 400watts. 

Managed to get the Crown K1 distortion figure down by careful calibration of the overlap/underlap adjustment.   One of Crowns Gerald Stanley's finest designs and a new version is still used in the I-Tech.

Class I (NOT class D design) Negative and positive switches are on at the same time at idle dumping the current into large inductors and then to swing positive or negative duty cycle increased on either switch..  So no dead time or overshoot.

Not a fan of crown's K series,good performance,but just as the CTS series they often fail without any reason,and give's you headache to put them back in order again....one one my friends had a CTS3000 with a nice habit to fry speakers only on ch1 always...after hours of parts checked i found with the osciloscope that the amp looses the lf badly on that ch when pushed and distort badly frying the speakers,all that fault because it somehow loose the input ground as the volume goes up and bang speakers,on low volumes was working great,so i just did a wire jumper to the input ground and the amp was clear as hell on lf on sine wave,not blowing anymore speakers,before that amp to get in my hands had been seen and checked by three other engineers and all of them couldn't find anything wrong with it,and my friend loosed 4 speakers because of that,and eventualy comed to London to pass me the amplifier for the last chance.
Also i know loads of guys that had problems with CTS,XTI etc etc i don't trust anymore Crown,as i don't trust any bullshit door bells made after 2005 Ouch


Edited by EmPro - 08 June 2022 at 10:08pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 09 June 2022 at 8:37am
Ditto that. Is allways a few Crown CTS series on ebay, as "not working" or "powers up, but no sound" etc etc. No thanks. Pass. The case is probably worth a fiver as a project to put some modules in it, after throwing the insides in the dumpster, but that's about all.

While i'm on this subject, is some really stupid prices for scruffy broken amps thesedays on ebay,..."sold as not working, powers up but dead channels" etc etc, and then the muppet is wanting a £120 start price + postage. Absolutely mad. It's scrap mate.
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 09 June 2022 at 9:00am
,,While i'm on this subject, is some really stupid prices for scruffy broken amps thesedays on ebay,..."sold as not working, powers up but dead channels" etc etc, and then the muppet is wanting a £120 start price + postage. Absolutely mad. It's scrap mate. ''

Indeed they ask silly prices for proper blown up amps,only the case remains good,8-9 years ago i bought faulty amps with 10-20£ no problem,you pay 10-20£ on it plus 15-20£ postage so 40-50£ no problem,you pay another 100£ for parts for example maybe 150£ so 200£ total and the amp is like new proper working,but now??? you pay 200£ for a crap,not even usefull parts in it,so you pay 200£ for empty metal case Confused i even saw proper chinese craps as skytec,SPL etc etc sold as faulty power amps with 80-90£ wwttff and is 120£ new one Confused
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Post Options Post Options   Thanks (0) Thanks(0)   Quote EmPro Quote  Post ReplyReply Direct Link To This Post Posted: 09 June 2022 at 9:10am
My cheapest amp ever bought LOLLOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 10 June 2022 at 11:31am
Originally posted by EmPro EmPro wrote:

Originally posted by shaun1264 shaun1264 wrote:

I ran up my JBL-Urei 6290 today.  Big old heavy brute.  Saved it from being thrown away as it was faulty.  I fixed it with new opamps and all new caps.  It was hitting 350watts in 8ohms (rated at 300watts in 8 ohms) easily and clipping with 400watts. 

Managed to get the Crown K1 distortion figure down by careful calibration of the overlap/underlap adjustment.   One of Crowns Gerald Stanley's finest designs and a new version is still used in the I-Tech.

Class I (NOT class D design) Negative and positive switches are on at the same time at idle dumping the current into large inductors and then to swing positive or negative duty cycle increased on either switch..  So no dead time or overshoot.

Not a fan of crown's K series,good performance,but just as the CTS series they often fail without any reason,and give's you headache to put them back in order again....one one my friends had a CTS3000 with a nice habit to fry speakers only on ch1 always...after hours of parts checked i found with the osciloscope that the amp looses the lf badly on that ch when pushed and distort badly frying the speakers,all that fault because it somehow loose the input ground as the volume goes up and bang speakers,on low volumes was working great,so i just did a wire jumper to the input ground and the amp was clear as hell on lf on sine wave,not blowing anymore speakers,before that amp to get in my hands had been seen and checked by three other engineers and all of them couldn't find anything wrong with it,and my friend loosed 4 speakers because of that,and eventualy comed to London to pass me the amplifier for the last chance.
Also i know loads of guys that had problems with CTS,XTI etc etc i don't trust anymore Crown,as i don't trust any bullshit door bells made after 2005 Ouch


As you know the CTS has the switching power supply and the K series has liner transformer based supply. So, yes the CTS is more complicated and harder to repair but I actually find the K series not too bad to repair as long as you understand the topology of these amps.

Anyway, in the process of repairing a badly looked after Crown Micro-Tech 1200. Saved this one a few years ago.  It works, gives a clean output but the Fanformer has seized.  Even after trying to oil the shaft and bushes its very weak and runs hot.  So I'll replace it with a small 18V transformer and 240V fan instead. 

Also, pulled out a BK Electronics MXF 600 to test.  MOSFET based and has very good distortion figures far exceeding many other amps but labours a bit when testing under load.  Getting a drop of output voltage in low frequencies
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