Hi.
I have recently get a new job involving service and maintanance of a lot of PA equipment. A lot of really NICE ! equipment I may add. d&b, Crown, QSC, LABGruppen, Chevin, and a lot more
We have a lot of Crown amps, and these sometime get broken despite the good quality, and their reputation of beening able to handle "anything".
Right now there are five amp's (two Crown's) waiting for new output-transistors, and the original Crown-type is rather expensive. Thats why I've been curious in using MJ15024/25 transistors instead.
The question is: How many of each (NPN/PNP) transistors would I need too bee able too match them properly if I use the method described here : http://sound.westhost.com/transistor-matching.htm , and how many categories could I expect ?
Total match is probably out of the question so how big difference would You consider as a good match ?
My thought was to get the best matches, and use the transistors that I can't match in amplifiers that don't need matched outputs (like Studiomaster ++)
Would really appreciate some advice in this matter.
Lyra
I have recently get a new job involving service and maintanance of a lot of PA equipment. A lot of really NICE ! equipment I may add. d&b, Crown, QSC, LABGruppen, Chevin, and a lot more
We have a lot of Crown amps, and these sometime get broken despite the good quality, and their reputation of beening able to handle "anything".
Right now there are five amp's (two Crown's) waiting for new output-transistors, and the original Crown-type is rather expensive. Thats why I've been curious in using MJ15024/25 transistors instead.
The question is: How many of each (NPN/PNP) transistors would I need too bee able too match them properly if I use the method described here : http://sound.westhost.com/transistor-matching.htm , and how many categories could I expect ?
Total match is probably out of the question so how big difference would You consider as a good match ?
My thought was to get the best matches, and use the transistors that I can't match in amplifiers that don't need matched outputs (like Studiomaster ++)
Would really appreciate some advice in this matter.
Lyra
I usually just make sure all transistors are same batch number - I don't really think close matching is going to make much audible difference..
Cheers
Cheers
Hi Lyra
Whilst most Crown amps are very good, don't go near the Powerbase series. Several people I know just gave up on them and threw them away they were so unreliable. It was just not economical to fix them.
Whilst most Crown amps are very good, don't go near the Powerbase series. Several people I know just gave up on them and threw them away they were so unreliable. It was just not economical to fix them.
Centauri said:
The sound-quality wasn't my main consern....it is after all PA-equipment.... but more the stability issue.
.... it would bee nice to split up all the power equally between the transistors, and not in a way that one transistor is operating close to it's max while the others have a "comfortable time".........with the amount of power theese amps deliver this would be BAD !?
This might be one of the reasons that a Crown amp is a lot more long-term stable than for instance Studiomaster..... and niiizzzer sound too 😉
Lyra
I would bet the reason crown charges so much is because the devices are matched...
In another post somewhere i read that 50 is generally a good number to start matching with and that 10% is close enough....but again im quoting what i rememeberd from another post....
Some one else have any suggestions???
Zero
In another post somewhere i read that 50 is generally a good number to start matching with and that 10% is close enough....but again im quoting what i rememeberd from another post....
Some one else have any suggestions???
Zero
Lyra said:
Usually these amps have low value emitter resistors for the purpose of evening out the current sharing. If the transistors have the same batch number, then it is fairly safe to assume their parameters will be very close.
Cheers
PS: I service such pro amps for a living, and have never had any problems with the above approach (not including fake transistors though....)
i do a lot of matching up MOSFETs for people -- and some wonder why it costs so much more to get a "quad" or "quint" than a "couple" -- the reason is the "precision" (number of significant places) and the distribution -- in the case of MOSFETs if you want to match to +/- 0.01V you limit the number of candidates in your "bins" -- we will see how it goes with Renesas Lateral MOSFET's -- you could pretty well bet on the Hitachi's to be normal, or at worst bimodal. For the MOSFETs, at least to my experience, there is a strong correlation between Vgs and mu.
The ambient temperature will affect the measurements -- so if you get in a shipment it's a good idea to do all the matching at the same time.
for small signal BJT's there are a couple tests that should be done, i.e. HFE and VBE matching.
You find that in a group of smal signal BJT's the variation of DC beta will range from 97 to 140 in a group of a couple hundred, and the distribution is far from "normal". Doesn't matter if they are ON-Semi, Fairchild, PMC etc.
Here's the MOOG VBE matching routine:
the MCUTracer (it was originally designed for tubes, since tube curve tracers are so expensive) could be quite easily pressed into service to plot the characteristic curves of two semiconductor devices at the same time and calculate the differences. It would just be a matter of rewiring a couple resistors.
The ambient temperature will affect the measurements -- so if you get in a shipment it's a good idea to do all the matching at the same time.
for small signal BJT's there are a couple tests that should be done, i.e. HFE and VBE matching.
You find that in a group of smal signal BJT's the variation of DC beta will range from 97 to 140 in a group of a couple hundred, and the distribution is far from "normal". Doesn't matter if they are ON-Semi, Fairchild, PMC etc.
Here's the MOOG VBE matching routine:
An externally hosted image should be here but it was not working when we last tested it.
the MCUTracer (it was originally designed for tubes, since tube curve tracers are so expensive) could be quite easily pressed into service to plot the characteristic curves of two semiconductor devices at the same time and calculate the differences. It would just be a matter of rewiring a couple resistors.
OK thanks for the replies. Think I have figured this out !?
BUT....some other questions:
....could someone please describe the difference between MJ21193/94 and MJ15024/25.
When do I want to choose wich transistor ?
...and any idea witch one is the closest match to Crown original ??????
Lyra
BUT....some other questions:
....could someone please describe the difference between MJ21193/94 and MJ15024/25.
When do I want to choose wich transistor ?
...and any idea witch one is the closest match to Crown original ??????
Lyra
Hi Lyra,
Mj21193/4 v Mj15024/5; 93/4 is slightly faster (5MHz), SOA is higher at hi volts 93/4 2a @ 100v, 24/5 0.9a @ 100v.
The datasheets are on www.onsemi.com website
Prices are similar, if you require Vrail above 75v then choose 93/4 otherwise they are very similar, both are robust Tj 200degC Pt 250w.
regards Andrew T.
Mj21193/4 v Mj15024/5; 93/4 is slightly faster (5MHz), SOA is higher at hi volts 93/4 2a @ 100v, 24/5 0.9a @ 100v.
The datasheets are on www.onsemi.com website
Prices are similar, if you require Vrail above 75v then choose 93/4 otherwise they are very similar, both are robust Tj 200degC Pt 250w.
regards Andrew T.
Strange !!!! no temperature drift whith C4751-1
I have buildt this Tester/ matching device.
When I was replacing the outputtransistor in a Crown Macrotech amplifier yesterday I also tested som of the surviving original outputtransistors in my "new" tester....and guess what......!???
Theese transistors did NOT increase the current Ic when the got warm !? 😕 😕 😕
I could measure something like this:
MJ15024: Cold 1.75A, after 10 sec. (varmer) 2,02A, a somewhat huge increase in current, but it seems to stabilice more or less after 10-15 sec.
The original C4751-1: Cold 1.96A, after 10sec. 1,97A, and after 20 sec. without cooling (very hot) 1,97A
How is this possible ?????
BTW: I thought there might be something funny with the BJT, so I tested 2......both with almost no drift whatsoever.....
Lyra
I have buildt this Tester/ matching device.
When I was replacing the outputtransistor in a Crown Macrotech amplifier yesterday I also tested som of the surviving original outputtransistors in my "new" tester....and guess what......!???
Theese transistors did NOT increase the current Ic when the got warm !? 😕 😕 😕
I could measure something like this:
MJ15024: Cold 1.75A, after 10 sec. (varmer) 2,02A, a somewhat huge increase in current, but it seems to stabilice more or less after 10-15 sec.
The original C4751-1: Cold 1.96A, after 10sec. 1,97A, and after 20 sec. without cooling (very hot) 1,97A
How is this possible ?????
BTW: I thought there might be something funny with the BJT, so I tested 2......both with almost no drift whatsoever.....
Lyra
The Crown macrotech transistors are not graded by hfe but by Vbe. If you fit non-crown transistors, it WILL fail if pushed hard. I've seen them fail, repaired them properly, charged the customer. Non-graded transistor'd Crowns usually end up on ebay and become someone else's problem.
Vendor question
My question is a good place to buy the MJ15024/25.
Had luck with the vendor i've used in the past, usually buy 10 of each and cull from these.
My last order all the PNP's were all in the 90's, sent e'm all back. Ordered from Peavy yesterday, am thinking of giving Mouser a try.
Seems to me there should be a place to order these in matched pairs/quads/octos etc...
My question is a good place to buy the MJ15024/25.
Had luck with the vendor i've used in the past, usually buy 10 of each and cull from these.
My last order all the PNP's were all in the 90's, sent e'm all back. Ordered from Peavy yesterday, am thinking of giving Mouser a try.
Seems to me there should be a place to order these in matched pairs/quads/octos etc...
@ engelheimer, who was the vendor you used in the past?
You can buy directly from On-Semi or any of the major suppliers, Digikey, Mouser,
whatever14, and I'm sure others. If you get a not so good batch of them, just send them
back for a refund or replacement.
I would expect that Matched pairs, quads, sextets, octos, etc. would require
higher pricing that I'm nor sure DIYers would want to bare the costs.
I could be incorrect, depending on the price for matching.
None of the links are available any longer.
@Jackinnj, can you post a schematic and layout about your transistor matcher?
Maybe some typical numbers you use and formula for calculating?
This is not something they go over in the ELE courses that I am aware of,
or if they do it is senior level or grad level design stuff.
SUGGESTION:
1. Anyone thought of adding a library to DIYAudio site?
It would have to be different than the wiki, because the
wiki doesn't seem to work very well at all.
2. Anyone thought of adding live video streams, video messaging
area to DIYAudio? It would be handy to have areas where people
could watch other DIY members working on a project, board, amp,
pre etc in real time. It could be a member's only feature to keep
the riff-raff out.
NOTE: Nothing quite like being 12 years late to the party.
Cheers,
Sync
You can buy directly from On-Semi or any of the major suppliers, Digikey, Mouser,
whatever14, and I'm sure others. If you get a not so good batch of them, just send them
back for a refund or replacement.
I would expect that Matched pairs, quads, sextets, octos, etc. would require
higher pricing that I'm nor sure DIYers would want to bare the costs.
I could be incorrect, depending on the price for matching.
None of the links are available any longer.
@Jackinnj, can you post a schematic and layout about your transistor matcher?
Maybe some typical numbers you use and formula for calculating?
This is not something they go over in the ELE courses that I am aware of,
or if they do it is senior level or grad level design stuff.
SUGGESTION:
1. Anyone thought of adding a library to DIYAudio site?
It would have to be different than the wiki, because the
wiki doesn't seem to work very well at all.
2. Anyone thought of adding live video streams, video messaging
area to DIYAudio? It would be handy to have areas where people
could watch other DIY members working on a project, board, amp,
pre etc in real time. It could be a member's only feature to keep
the riff-raff out.
NOTE: Nothing quite like being 12 years late to the party.
Cheers,
Sync
Last edited:
As others have pointed out, the 15024/25 are a poor choice for high power audio. The SOA current is about 4A at 60V, about a tenth of that at 120V. This means that these amplifiers can drive resistors very well, but won't survive reactive loads.
The MJ21193/94 are the same at 60V, but hold up to >1A at 120V, so they will survive a wild speaker load
The MJ21193/94 are the same at 60V, but hold up to >1A at 120V, so they will survive a wild speaker load
It's not "high power" that is being considered.
The main difference between these devices is that high Vce is tolerated by the 93/4 much better than the 24/5
each pair of 93/4 and of 24/5 will both do a reliable 100W/pr when the supply rails are kept low.
But at higher supply rails the 24/5 will exceed SOA when Vce is higher.
High power comes from high supply rail voltages. The Crown amplifiers I have seen are using almost +/-60V. The 24/5 SOA is very poor with reactive speaker loads, when the current does not fall to zero until the voltage across the device is closer to the sum of the supply rails.
Worse, the relatively low current at maximum CE voltage makes the 0R47 emitter resistors rather ineffective at forcing current sharing, so one transistor with a hot spot will rapidly run away, hog the current and fail short.
Worse, the relatively low current at maximum CE voltage makes the 0R47 emitter resistors rather ineffective at forcing current sharing, so one transistor with a hot spot will rapidly run away, hog the current and fail short.
High power can come from lower supply rails.
4ohms load demands more current than 8ohms load.
2ohms load is even more demanding.
If the output devices can provide 100W of output power per pair, then 8ohms would run from much higher supply rail than 2ohms, roughly double the supply rail voltage.
eg. 200W into 2ohms from ±36Vdc
or 200W into 8ohms from ±65Vdc
For the same output power the 8ohms load places more voltage stress across the CE junction of the output transistors. High voltage SOA becomes much more onerous. Vce rules.
4ohms load demands more current than 8ohms load.
2ohms load is even more demanding.
If the output devices can provide 100W of output power per pair, then 8ohms would run from much higher supply rail than 2ohms, roughly double the supply rail voltage.
eg. 200W into 2ohms from ±36Vdc
or 200W into 8ohms from ±65Vdc
For the same output power the 8ohms load places more voltage stress across the CE junction of the output transistors. High voltage SOA becomes much more onerous. Vce rules.
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