burnedfingers said:
Noted. I will have some house cleaning issues at the end and Chris has me worried about the feedback loop. The feedback loop is wide and goes all over the place! Just look at that dotted line through the schematic...
Not out of the woods yet.
Gotta press on,
Shawn.
DC 300a
Hi there all you guys.
What a really good thread. I have been using DC 300a's for about six years now and I have only partially rebuilt a couple of early mark ones. The first difficulty I faced was the lack of service information, which as time has gone by has improved quite a lot.
In the UK if it isnt valve it is crap! I dont agree with this so I set out to prove them wrong.
My 300a's are a mixture of amps the only thing they have in common is the name on the front panel!
I have never heard an amplifier that sounds this good! There is an eneormous amount of potential inside this case just waiting for someone to let it out.
Karl of KRM audio is one of my closest freinds and we sourced the ceramic op amps we hope they will work a lot better than the originals.
As to the huge smoothing caps, a slow start is vital with these, I know coz I have tried this mod already. And I am hanging my head in shame coz I have not built a slow start yet.
Anyway Shawn keep up the good work.
You are making an old man very very happy.
Stewart
Hi there all you guys.
What a really good thread. I have been using DC 300a's for about six years now and I have only partially rebuilt a couple of early mark ones. The first difficulty I faced was the lack of service information, which as time has gone by has improved quite a lot.
In the UK if it isnt valve it is crap! I dont agree with this so I set out to prove them wrong.
My 300a's are a mixture of amps the only thing they have in common is the name on the front panel!
I have never heard an amplifier that sounds this good! There is an eneormous amount of potential inside this case just waiting for someone to let it out.
Karl of KRM audio is one of my closest freinds and we sourced the ceramic op amps we hope they will work a lot better than the originals.
As to the huge smoothing caps, a slow start is vital with these, I know coz I have tried this mod already. And I am hanging my head in shame coz I have not built a slow start yet.
Anyway Shawn keep up the good work.
You are making an old man very very happy.
Stewart
Re: DC 300a
I can't wait to hear this one. I'm a little worried and the anticipation is starting to stir. I remember admiring it when I picked it up but it just never sounded right and in the end it was sketchy at best.
My Paypal thing is slow but Karl said he had sime inventory and not to worry. I 'll get my 739 in a few weeks and I guess and until then the plastic will do.
Crown has a schematic for Muting the inputs for a slight delay at turn on. It is on page 25 of their manual. Why not switch it over to a soft start and squeeze it in there? Perhaps there are better circuits than this?
Thanks a mint Chappy!
Good words for a medium aged man
?
Cheers,
Shawn.🙂
stewartwen said:
I can't wait to hear this one. I'm a little worried and the anticipation is starting to stir. I remember admiring it when I picked it up but it just never sounded right and in the end it was sketchy at best.
My Paypal thing is slow but Karl said he had sime inventory and not to worry. I 'll get my 739 in a few weeks and I guess and until then the plastic will do.
Crown has a schematic for Muting the inputs for a slight delay at turn on. It is on page 25 of their manual. Why not switch it over to a soft start and squeeze it in there? Perhaps there are better circuits than this?
Thanks a mint Chappy!
Good words for a medium aged man
?Cheers,
Shawn.🙂
Attachments
Hi,
smoothing caps are usually not an issue that requires soft start.
Toroidal transformers do benefit from the soft start but EI (as here) should not need soft start either.
Tom,
is that two 47mF per rail, or per channel, or per stereo amp?
I had +-20mF on each channel fed from a 625VA toroid (that's 80mF total). The older one started without blowing the T6.3A but the newer (twin primaries) one needed a soft start to avoid going bigger on the fuse rating. It then started on a T3A. So I went back and modified the first to run on T3A as well.
smoothing caps are usually not an issue that requires soft start.
Toroidal transformers do benefit from the soft start but EI (as here) should not need soft start either.
Tom,
is that two 47mF per rail, or per channel, or per stereo amp?
I had +-20mF on each channel fed from a 625VA toroid (that's 80mF total). The older one started without blowing the T6.3A but the newer (twin primaries) one needed a soft start to avoid going bigger on the fuse rating. It then started on a T3A. So I went back and modified the first to run on T3A as well.
"smoothing caps are usually not an issue that requires soft start."
Thanks, I needed a good laugh.
"Toroidal transformers do benefit from the soft start but EI (as here) should not need soft start either."
You going to buy him a new bridge rectifier when it blows?
A Hafler DH-200 has a small EI type transformer with a 5A fuse. Increasing the caps to 40mF per rail total resulted in the 25A bridge vaporizing.
Increasing the caps to 27mF per rail in a 200W Peavey guitar amp with a small EI type transformer caused the 300A (surge rating) bridge to vaporize.
I now use a 2R5 Keystone inrush current limiter in small amps when going larger than stock.
It also saves the power switch from welding.
It also saves the thermal switches from welding (much harder to find).
On amps that draw more than about 6A I use a relay to short out the inrush current limiter.
On the later Hafler DH-500 with the 0R5 inrush current limiter, I remove and replace with a 2R5 type, and change the relay to a three-pole type, shorting out the inrush limiter when the speaker relay pulls in (works much better than stock).
I add the Hafler relay board and a 2R5 inrush limiter to the Adcom GFA 555, it prevents thumps and the power switch eating itself.
Of course, if you like seeing the house lights dim when you switch on, and like replacing fuses, switches, rectifiers, etc.....
"I think you will find that the cap value is 47,000 mf per rail"
47mF = 47,000µF (alt 0181)
Thanks, I needed a good laugh.
"Toroidal transformers do benefit from the soft start but EI (as here) should not need soft start either."
You going to buy him a new bridge rectifier when it blows?
A Hafler DH-200 has a small EI type transformer with a 5A fuse. Increasing the caps to 40mF per rail total resulted in the 25A bridge vaporizing.
Increasing the caps to 27mF per rail in a 200W Peavey guitar amp with a small EI type transformer caused the 300A (surge rating) bridge to vaporize.
I now use a 2R5 Keystone inrush current limiter in small amps when going larger than stock.
It also saves the power switch from welding.
It also saves the thermal switches from welding (much harder to find).
On amps that draw more than about 6A I use a relay to short out the inrush current limiter.
On the later Hafler DH-500 with the 0R5 inrush current limiter, I remove and replace with a 2R5 type, and change the relay to a three-pole type, shorting out the inrush limiter when the speaker relay pulls in (works much better than stock).
I add the Hafler relay board and a 2R5 inrush limiter to the Adcom GFA 555, it prevents thumps and the power switch eating itself.
Of course, if you like seeing the house lights dim when you switch on, and like replacing fuses, switches, rectifiers, etc.....
"I think you will find that the cap value is 47,000 mf per rail"
47mF = 47,000µF (alt 0181)
I spent an enjoyable evening at the weekend visiting a friend who I had not seen for some time....turns out he is using a DC300A to drive a pair of IMF RSPM mKIV speakers. I must admit I was very surprised by the sound quality. It was excellent. No sense of strain or edge at all. I was expecting a very "Solid State", high feedback, "gray", "edgy" sound....couldn't have been more wrong!
It may have been a particularly symbiotic match as my friend admits he has heard the Crown sound bad with certain speakers, but, I must say that what I heard would blow many high end systems out of the water!
I also remember being at the Harrogate International Festival of Sound at around 1981 and hearing the Tannoy Westminster Royals for the first time....guess what they were demo-ing them with....yep, a pair of bridged DC300A's! This was in a theatre so a VERY large room to put it mildly. They still felt the need to rope off the first six rows of seats....I found out why when they put "The Sheffield Drum Record" (direct cut) on at an incredible volume. My ears were ringing for several days afterwards!!
It may have been a particularly symbiotic match as my friend admits he has heard the Crown sound bad with certain speakers, but, I must say that what I heard would blow many high end systems out of the water!
I also remember being at the Harrogate International Festival of Sound at around 1981 and hearing the Tannoy Westminster Royals for the first time....guess what they were demo-ing them with....yep, a pair of bridged DC300A's! This was in a theatre so a VERY large room to put it mildly. They still felt the need to rope off the first six rows of seats....I found out why when they put "The Sheffield Drum Record" (direct cut) on at an incredible volume. My ears were ringing for several days afterwards!!
Hi Djk,
I told you what I think and what works in the UK (I admit where I live).
You have rubbished my information without justification.
I have NEVER blown a 25A or 35A power rectifier with or without a soft start fitted.
All my amps are on toroidal supplies and only one needed a soft start to allow <=T6.3A mains fuse to be used. I habitually use a minimum of +-25mF/channel and this too has never blown a rectifier.
You are free to offer your experiences but try to do so without a put down.
I think the clarification on m=milli (10^-3 )and u=micro (10^-6) has gone astray.
Can Tom confirm the smoothing capacitance being fitted?
I told you what I think and what works in the UK (I admit where I live).
You have rubbished my information without justification.
I have NEVER blown a 25A or 35A power rectifier with or without a soft start fitted.
All my amps are on toroidal supplies and only one needed a soft start to allow <=T6.3A mains fuse to be used. I habitually use a minimum of +-25mF/channel and this too has never blown a rectifier.
You are free to offer your experiences but try to do so without a put down.
I think the clarification on m=milli (10^-3 )and u=micro (10^-6) has gone astray.
Can Tom confirm the smoothing capacitance being fitted?
I can back up the experience of Andrew T on this one. Same here, never blown a 35A rectifier with no soft start and 220,000uF or more per rail with transformers up to around 500VA. Never tried with bigger transformers but mains fuse blowing can be a problem anyway when using big toroids.
An amp that I'm using daily at the moment has twin 300VA toroids (one each for + & - rails) driven by a 15A Variac with a 25A rectifier per toroid. This is then smoothed by a total of 396000uF. = no problems. It's a 25WPC fan cooled JLH BTW. Sounds great 😉
An amp that I'm using daily at the moment has twin 300VA toroids (one each for + & - rails) driven by a 15A Variac with a 25A rectifier per toroid. This is then smoothed by a total of 396000uF. = no problems. It's a 25WPC fan cooled JLH BTW. Sounds great 😉
Hi Andrew,
Over here in North America, an inrush current limiter is not always required, but is always a benefit. Power switches tend to last much longer as has been pointed out. The big EI transformers need an inrush limiter for sure.
I do accept your point that toroids may have higher peak inrush currents. Inrush current limiting is a higher benefit here.
-Chris
Over here in North America, an inrush current limiter is not always required, but is always a benefit. Power switches tend to last much longer as has been pointed out. The big EI transformers need an inrush limiter for sure.
I do accept your point that toroids may have higher peak inrush currents. Inrush current limiting is a higher benefit here.
-Chris
Capacitance
T, the replacement caps are definately 47,000 micro farads each. 😀
The DC300A I have did make a good thump when it was turned on, even with the old caps. You could sometimes hear the giant power switch make a slight pop too. The Transformer is approximately 1200 VA!
I never thought much about the load presented to the rectifier by the caps at turn on. I find this an interesting topic.
I may build the softstart circuit after I get it going. It is a good idea regardless. 🙂
Cheers,
Shawn.
AndrewT said:
T, the replacement caps are definately 47,000 micro farads each. 😀
The DC300A I have did make a good thump when it was turned on, even with the old caps. You could sometimes hear the giant power switch make a slight pop too. The Transformer is approximately 1200 VA!
I never thought much about the load presented to the rectifier by the caps at turn on. I find this an interesting topic.
I may build the softstart circuit after I get it going. It is a good idea regardless. 🙂
Cheers,
Shawn.
Its 2x 47k uF per stereo amp that makes one for both positive rails and one for both negative if I am not mistaken. the original spec. was 13,500 uf, so if yours had 17k, then the new ones per rail are just over double.
That is nearly 4x what the design originally used, whilst it shouldn't cause any problems at idle, the benefits are disputable theoretically, and I have no idea what nasties may happen under transient conditions.
I can't understand why they are so despised, I have heard them, and whilst not to my taste, the specs. where superb for the time, they sounded fine, certainly not like broken glass.
The power supply is a strongpoint, the tx is huge.
So keep going, don't take too much notice of those who say change and improve the design, after all, Crown are extremely professional, and probably knew best. Its longevity is testiment to that. There aren't many amplifiers that have been around for so long.
Its a classic, preserve it, and do a great job.
That is nearly 4x what the design originally used, whilst it shouldn't cause any problems at idle, the benefits are disputable theoretically, and I have no idea what nasties may happen under transient conditions.
I can't understand why they are so despised, I have heard them, and whilst not to my taste, the specs. where superb for the time, they sounded fine, certainly not like broken glass.
The power supply is a strongpoint, the tx is huge.
So keep going, don't take too much notice of those who say change and improve the design, after all, Crown are extremely professional, and probably knew best. Its longevity is testiment to that. There aren't many amplifiers that have been around for so long.
Its a classic, preserve it, and do a great job.
lt cdr data said:
Cheers to that!
A note about my restoration:
When the resto is complete, only remaining items from the original amplifier are:
Enclosure
Transformer
Power Switch
Two output driver boards without components
I find it all very interesting as I never thought it would be possible. The night I cracked it open I didn't quite realise what would happen but I did know I would go as far as I could. Now I am suprised how far I've gone! 🙂
Shawn.
I have one of the original Carver M400 "magnetic field amplifiers". It used a triac based switching power supply. Most of them suffered exploded triacs in the first few years of operation. I thought that it was from the frequent lightning induced power surges (common in Florida) and the fact that there is no power switch, and it is on all of the time. I ran mine off of the auxilary power (relay switched) outlet in a Phase Linear 4000 preamp.
About every 10th turn on, the system would trip the 15 amp circuit breaker in the breaker panel. Every few months it would weld the relay contacts closed.
Andrew:
I believe in being safe rather than sorry. I have blown 25A bridges with as little as 27mF per rail. I will never do it again. Nelson Pass recommends a soft start with over 30mF per rail for the same reason. Obviously neither of us understand what is going on.
"Crown are extremely professional, and probably knew best."
Obviously you don't get it either. Crown went through four major design changes in the 300 in just a few years. The newer they are, the better they sound.
"There aren't many amplifiers that have been around for so long."
See above. Auto manufacturers use the same model names for decades too, do you think they are the same?
"Its a classic, preserve it, and do a great job."
As long as I don't have to listen to it (or fix it) , fine. It's your time, and your money.
"the specs. where superb for the time, they sounded fine, certainly not like broken glass."
90% of people can't hear in any meaningful fashion. Of the 10% that can hear, they pick the worst sounding gear. The 1% that can really hear seldom have the money for the good stuff.
"Most of them suffered exploded triacs in the first few years of operation."
Early Carver gear had a real problem with power line regulation. When the voltage went through a 'brown-out' the conduction angle on the triac would increase. The magnetic field in the transformer would saturate, and almost unlimited current would (briefly) flow. Some models would have the transformer start smoking (if the triac didn't blow first). Carver had a revision for some of the models to limit the maximum conduction angle. That, and replacing the rectifier diodes on the two lower voltage tiers, generally made them reliable.
I remember the first M400 I had. A 45W Yamaha would thump harder. I managed to blow up the M400 in the space of an hour. It ate the triac. I really liked the later version of the M1.0T, it had some real guts, and sounded good too.
Everyone is right, within the context of their experience.
My experience covers 30 years of being in sales, service, and then design of commercial audio equipment. My last power amp project at work was to make an existing 100W amp design work using International Rectifier hex-fets for the modulator of a 1.2Ghz military piece.
I believe in being safe rather than sorry. I have blown 25A bridges with as little as 27mF per rail. I will never do it again. Nelson Pass recommends a soft start with over 30mF per rail for the same reason. Obviously neither of us understand what is going on.
"Crown are extremely professional, and probably knew best."
Obviously you don't get it either. Crown went through four major design changes in the 300 in just a few years. The newer they are, the better they sound.
"There aren't many amplifiers that have been around for so long."
See above. Auto manufacturers use the same model names for decades too, do you think they are the same?
"Its a classic, preserve it, and do a great job."
As long as I don't have to listen to it (or fix it) , fine. It's your time, and your money.
"the specs. where superb for the time, they sounded fine, certainly not like broken glass."
90% of people can't hear in any meaningful fashion. Of the 10% that can hear, they pick the worst sounding gear. The 1% that can really hear seldom have the money for the good stuff.
"Most of them suffered exploded triacs in the first few years of operation."
Early Carver gear had a real problem with power line regulation. When the voltage went through a 'brown-out' the conduction angle on the triac would increase. The magnetic field in the transformer would saturate, and almost unlimited current would (briefly) flow. Some models would have the transformer start smoking (if the triac didn't blow first). Carver had a revision for some of the models to limit the maximum conduction angle. That, and replacing the rectifier diodes on the two lower voltage tiers, generally made them reliable.
I remember the first M400 I had. A 45W Yamaha would thump harder. I managed to blow up the M400 in the space of an hour. It ate the triac. I really liked the later version of the M1.0T, it had some real guts, and sounded good too.
Everyone is right, within the context of their experience.
My experience covers 30 years of being in sales, service, and then design of commercial audio equipment. My last power amp project at work was to make an existing 100W amp design work using International Rectifier hex-fets for the modulator of a 1.2Ghz military piece.
Hi,
Why go into Carver and Triacs when they have nothing to do with this topic nor it's specific enquiry (soft start for a Crown)?
it would help all here if you could tell how this happened, so we can avoid the same circumstances.
Why go into Carver and Triacs when they have nothing to do with this topic nor it's specific enquiry (soft start for a Crown)?
"Everyone is right, within the context of their experience."
Yes I suppose thats true.....I have had about 25 years experience both in servicing and also as a design engineer....and I've yet to see a 35A rectifier blow due to excess smoothing capacitance. That's my experience🙄
Yes I suppose thats true.....I have had about 25 years experience both in servicing and also as a design engineer....and I've yet to see a 35A rectifier blow due to excess smoothing capacitance. That's my experience🙄