i have a very nice altair amplifier ...its the MF16...that is a seriously big amplifier and also was a very good construction ...
unfortunatelly this amp is burned beyond repair ....or even though someone decides to repair device like that it will probably not be cost effective ....boards are burned from thunder ....halls here and there all mosfets are gone and so on and on ....
i am thinking on bulding a brother of qausi inside there but voltage is too high .... expect 85+85 volts with no load conditions
can i wind some more winds in the primary to low the voltage on the secondary ???? any other sugestion ???
unfortunatelly this amp is burned beyond repair ....or even though someone decides to repair device like that it will probably not be cost effective ....boards are burned from thunder ....halls here and there all mosfets are gone and so on and on ....
i am thinking on bulding a brother of qausi inside there but voltage is too high .... expect 85+85 volts with no load conditions
can i wind some more winds in the primary to low the voltage on the secondary ???? any other sugestion ???
If you are very confident on the quality of your workmanship, then you could add extra primary windings. You will need lots of turns to make a significant difference. The enameled wire must be at least the same diameter as the original primary.
The safest place for the primary is UNDER the secondary, but that is a lot of work. Take care!
This will reduce the VA of the transformer, but in return you will increase the off load and on load efficiencies and you will reduce the regulation. The transformer will as a result run cooler and should perform better upto it's original current rating.
The safest place for the primary is UNDER the secondary, but that is a lot of work. Take care!
This will reduce the VA of the transformer, but in return you will increase the off load and on load efficiencies and you will reduce the regulation. The transformer will as a result run cooler and should perform better upto it's original current rating.
Rather than rewinding the transformer you could try a smaller transformer connected as an auto transformer to reduce the input and thus the no load voltage.
As an example a 240 / 30 volt transformer will reduce the voltage by about 12.5%. The VA of the autotransformer only needs to be a proportion of the main transformer.
Regards
As an example a 240 / 30 volt transformer will reduce the voltage by about 12.5%. The VA of the autotransformer only needs to be a proportion of the main transformer.
Regards
Re: Re: transformer question
Probably. To lower the voltage by more than 10% or so, it's better to just take some turns off the secondary. For a small output voltage adjust, the adding a few primary turns may be easier and you shouldn't have to take the trafo apart. For toroids, you can wind a few turns of solid-core THHN and add it to the primary in phase. The more turns you add in this manner however, the worse the coupling becomes and the more leakage reactance and poorer regulation. I've even done this with EI's where there was a little room between the bobbin and core.
I would not recommend rewinding a primary from scratch unless you have experience doing it and the proper winding equipment. It's way too easy to scrape insulation off or to get too much voltage between turns. On lower-voltage secondaries mistakes are more easily forgiven.
analog_sa said:
Probably. To lower the voltage by more than 10% or so, it's better to just take some turns off the secondary. For a small output voltage adjust, the adding a few primary turns may be easier and you shouldn't have to take the trafo apart. For toroids, you can wind a few turns of solid-core THHN and add it to the primary in phase. The more turns you add in this manner however, the worse the coupling becomes and the more leakage reactance and poorer regulation. I've even done this with EI's where there was a little room between the bobbin and core.
I would not recommend rewinding a primary from scratch unless you have experience doing it and the proper winding equipment. It's way too easy to scrape insulation off or to get too much voltage between turns. On lower-voltage secondaries mistakes are more easily forgiven.
Two other possibilities:
- regulate the whole B+ down to what you need
- regulate the driver board's B+ down to the spec'd voltage, BUT put in an output stage that can handle the full B+ voltage!
Now, what happens? The driver board can never drive the output into clipping against the rail. So the clipping characteristic of the amp will be determined by the driver's clipping only. Heresy, but no reason it won't work fine.
_-_-bear
Third possibility <edit>: redesign the amp in question to handle the extra voltage... the same idea applies, you need the voltage gain to be able to swing the requisite drive to run the outputs to the rails (the usual method) so then you can use higher voltage supply... you might be able to get away with keeping the more difficult to adjust front end at a lower voltage (regulated, vdropped, or separate supply), as long as you have enough gain in subsequent stages available.
- regulate the whole B+ down to what you need
- regulate the driver board's B+ down to the spec'd voltage, BUT put in an output stage that can handle the full B+ voltage!
Now, what happens? The driver board can never drive the output into clipping against the rail. So the clipping characteristic of the amp will be determined by the driver's clipping only. Heresy, but no reason it won't work fine.
_-_-bear
Third possibility <edit>: redesign the amp in question to handle the extra voltage... the same idea applies, you need the voltage gain to be able to swing the requisite drive to run the outputs to the rails (the usual method) so then you can use higher voltage supply... you might be able to get away with keeping the more difficult to adjust front end at a lower voltage (regulated, vdropped, or separate supply), as long as you have enough gain in subsequent stages available.
ok
thanks everybody ....i will consider re winding the trafo to lower voltage ....
it seems to me that either adding from the primary side and/or removing from the secondary will also effect the power rating of the trafo .... so in this case will be easier to rewind the trafo and keep the charactirestics if not upgrade them ...
will see
still i will make this a quasi since semis i get are so cheap and the rest of the parts is available ...
regards sakis
thanks everybody ....i will consider re winding the trafo to lower voltage ....
it seems to me that either adding from the primary side and/or removing from the secondary will also effect the power rating of the trafo .... so in this case will be easier to rewind the trafo and keep the charactirestics if not upgrade them ...
will see
still i will make this a quasi since semis i get are so cheap and the rest of the parts is available ...
regards sakis
Why not port the BO quasi to handle 85V? I use same OPS / input
with +- 80v all day !
Make all rail caps 100V , Change T2/3 to 2sa992(120v) and T4 to another 2sc1845(120v). use mje15032 / 33's for drivers(250v) , make r8 240- 270R.
A lot easier than rewinding the trafo. With 27K Rfb you will never clip , but be aware , at the higher rails you will be approaching SOA limits.
OS
with +- 80v all day !
Make all rail caps 100V , Change T2/3 to 2sa992(120v) and T4 to another 2sc1845(120v). use mje15032 / 33's for drivers(250v) , make r8 240- 270R.
A lot easier than rewinding the trafo. With 27K Rfb you will never clip , but be aware , at the higher rails you will be approaching SOA limits.
OS
Agree. +-85V isn't that high. Actually, less than 10 pairs should be ok. How many will fit?
As a comparison, the Crest CA4 has +-90V rails and just 4 pairs of 2SC3281/2SA1302 in series-parallell (to get better SOA at high voltage). MJW21194 has better high-voltage SOA so series-parallell won't be necessary. Also, these are rated 200W instead of 150W like 2SC3281.
As a comparison, the Crest CA4 has +-90V rails and just 4 pairs of 2SC3281/2SA1302 in series-parallell (to get better SOA at high voltage). MJW21194 has better high-voltage SOA so series-parallell won't be necessary. Also, these are rated 200W instead of 150W like 2SC3281.
If your trafo regulation were darn near perfect you could get 400W/8R. It won't be, don't count on it unless it weighs at least 40 pounds. In the Real World (t.m.) it takes +/-93V unloaded to get 400W/8R under load, and that's at 1% distortion clipping. But you can probably count on 250, because that's what you used to get with a 1-1.5kVA EI core unit back in the good ol' days.
10 pairs of outputs overkill? Maybe. You could probably get away with 6. I used 7 metal can units on +/-85, and it will drive an ohm and a half cleanly. But the MJW's are a 150W unit, not 250.
10 pairs of outputs overkill? Maybe. You could probably get away with 6. I used 7 metal can units on +/-85, and it will drive an ohm and a half cleanly. But the MJW's are a 150W unit, not 250.
wg_ski said:
okay,
. I know you have longer experience with this so you are probably right. As you say, it depends on transformer size of course. The 230V mains over here helps a bit though. The mains itself usually has pretty good regulation, at least here in Sweden but is of course different from location to location. In some places the lights dim when a vaccum cleaner is started, but in other places circuit breakers need to have interrupt ratings of 10kA.edit:
I must have hit the wrong button on the calculator, 85V no-load isn't enough for 400W 8 ohm.
You would need perfect regulation for that if the rail loss in the amplifier is 5V...They aren't 250W like the metal transistors, but still 200W (see datasheet) - higher than the 2SC3281. Those 4 pairs in the CA4 won't drive 1.5 ohms of course - if you want that then your suggestion is sound.
The MJL's are 200 watt, the MJW's are not. They are in a smaller package so you can pack more of them on the heatsink and keep the beta droop under control a little more. For home use, even at 2 ohms, six trannies is probably enough for SOA. It's more than what you get in a store-bought pro amp. But if you want to be able to deliver 100 amp peaks without VAS loading then you might want more.
and keep the beta droop under control a little more. For home use, even at 2 ohms, six trannies is probably enough for SOA. It's more than what you get in a store-bought pro amp. But if you want to be able to deliver 100 amp peaks without VAS loading then you might want more.
Re: ok guys ....
The "brother of quasi" amplifier will work with +/- 85 volt rails without too much trouble provided attention is paid to a few areas.
The second stage will run hotter so a larger heatsink for these should be used.
You will need more output transistors (200v 200 watt) to improve the overall SOAR.
You will need stronger driver transistors. I recommend you use driver transistors that are at least 200 volt and 100 watt.
Everthing else should be fine.
Cheers
Quasi
sakis said:
The "brother of quasi" amplifier will work with +/- 85 volt rails without too much trouble provided attention is paid to a few areas.
The second stage will run hotter so a larger heatsink for these should be used.
You will need more output transistors (200v 200 watt) to improve the overall SOAR.
You will need stronger driver transistors. I recommend you use driver transistors that are at least 200 volt and 100 watt.
Everthing else should be fine.
Cheers
Quasi
wg_ski said:
The datasheets for MJL (TO-264), MJW (TO-247) and NJW (japanese style TO3-P) do all say 200W:
http://www.onsemi.com/pub_link/Collateral/NJW21193-D.PDF
http://www.onsemi.com/pub_link/Collateral/MJW21193-D.PDF
http://www.onsemi.com/pub_link/Collateral/MJL21193-D.PDF
It really only depends on chip size, you can even get a 700W device in TO247 (though, probably not suited for linear operation):
http://ixdev.ixys.com/DataSheet/DS99904A(IXTH110N25T-&-IXTV110N25TS).pdf
The case-to-sink thermal resistance will be better with the bigger device though! But, considering that peak power dissipation is at least 3 times the average (even for a continuous signal), the amount of silicon area matters much more than case area.
Good point about being able to fit more of them when they are smaller.
megajocke said:
Good point about being able to fit more of them when they are smaller.
With only 2 stages of current gain in that amp beta droop may be more of a concern than SOA. That's the real reason QSC used eight outputs per bank in the USA1310.
With a triple (with 200W drivers) you wouldn't have to worry about that so much, but triple QC's are their own headache. One that I doubt Sakis is ready to deal with since he's been looking for an easy to build amp for some time now.
i am reading this /.....
he he he ..... but i will not bother .....
what i am trying ta say is that yes ...i am looking for a relatively simple amp to make but that doesnt mean that a sophisticated amp is out of my range .... yes in this area my skills are much lower but that doesnt mean that i will not make it ....
if you reed my posts you will know that most of these amps i make work in small PA applications ....we are in to this for very long time now but lately we play to smaller events but many many more ....meaning that power requiered often is no more than 100+100 Watts ....strangelly it seems that jobs like that are plenty and money is less but too many times so still you make a lot of money from a lot of small jobs ...
so most of these amps i built have to be cost effective since they are built inside scrap boxes (amps that are burned beyond repair)
and yes the power of a brother of quasi will be by far more than it is realy needed .
on the other hand i never claimed that i can design (eventhough i repaired a gozillion amps so far and some of them very sophisticated )
i am simply a happy champ that likes to live arround many amps and diy audio forums
best regards and thank you .....
wg_ski said:
he he he ..... but i will not bother .....
what i am trying ta say is that yes ...i am looking for a relatively simple amp to make but that doesnt mean that a sophisticated amp is out of my range .... yes in this area my skills are much lower but that doesnt mean that i will not make it ....
if you reed my posts you will know that most of these amps i make work in small PA applications ....we are in to this for very long time now but lately we play to smaller events but many many more ....meaning that power requiered often is no more than 100+100 Watts ....strangelly it seems that jobs like that are plenty and money is less but too many times so still you make a lot of money from a lot of small jobs ...
so most of these amps i built have to be cost effective since they are built inside scrap boxes (amps that are burned beyond repair)
and yes the power of a brother of quasi will be by far more than it is realy needed .
on the other hand i never claimed that i can design (eventhough i repaired a gozillion amps so far and some of them very sophisticated )
i am simply a happy champ that likes to live arround many amps and diy audio forums
best regards and thank you .....
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