JoeyDD said:
Paul! I did the exact same thing as you, but did not realize it until I had already assembled the amp. After a few months, it still works fine. My CL-30's measure 3.0 ohms when cold with a DMM; they are only in the circuit for 15-20 seconds then bypassed.
The reason I think they are working well is because I have never blown a fuse on startup. I've tried 6A and 5A (120V) and no problems. I guess it would be neat to try 4A and 3A and see if they blow, but I've not tried it.
Jacco,
Would the sec. voltage on the smaller transformer have to be exactly the same as for the bigger transformer? And would the front end capacitor bank have to be as big as for the outputs?
Lgreen,
Good to know it works fine; saves me another order from Digikey
. Do you know how much time it takes for them to cool down after they've been bypassed?
3 more exams before I can finish the Krells and finally listen to them!
Can't wait!
Paul
Would the sec. voltage on the smaller transformer have to be exactly the same as for the bigger transformer? And would the front end capacitor bank have to be as big as for the outputs?
Lgreen,
Good to know it works fine; saves me another order from Digikey
. Do you know how much time it takes for them to cool down after they've been bypassed? 3 more exams before I can finish the Krells and finally listen to them!
Can't wait!Paul
JoeyDD said:
Lgreen,
Good to know it works fine; saves me another order from Digikey
3 more exams before I can finish the Krells and finally listen to them!
Paul
I would estimate no longer than 10 seconds to cool down. When you build it, make them easy to replace so you can change them if it makes you feel better. Mine are difficult to replace.
Think about it, your always-on version would use more power than the sometimes-on standard version; AmpGuru is gonna be angry.
Tracking Number Status Delivery Information
1. 1Z 775 945 03 0894 113 7
Delivered
Delivered on: Dec 13, 2005
2:26 P.M.
Delivered to: US
Service Type: GROUND
Multiple Packages: 2
2. 1Z 567 432 03 2724 114 2
In Transit -
On Time
Sched. Delivery: Dec 15, 2005
Shipped to: MCKINNEY, TX, US
Service Type: GROUND
Your package is in the UPS system and is on time with a scheduled delivery date of Dec 15, 2005.
3. 1Z 775 945 03 0893 882 9
Delivered
Delivered on: Dec 13, 2005
2:26 P.M.
Delivered to: US
Service Type: GROUND
Multiple Packages: 2
Tracking results provided by UPS: Dec 13, 2005 5:26 P.M. Eastern Time (USA)
Did I mention I LOVE Mouser...
1. 1Z 775 945 03 0894 113 7
Delivered
Delivered on: Dec 13, 2005
2:26 P.M.
Delivered to: US
Service Type: GROUND
Multiple Packages: 2
2. 1Z 567 432 03 2724 114 2
In Transit -
On Time
Sched. Delivery: Dec 15, 2005
Shipped to: MCKINNEY, TX, US
Service Type: GROUND
Your package is in the UPS system and is on time with a scheduled delivery date of Dec 15, 2005.
3. 1Z 775 945 03 0893 882 9
Delivered
Delivered on: Dec 13, 2005
2:26 P.M.
Delivered to: US
Service Type: GROUND
Multiple Packages: 2
Tracking results provided by UPS: Dec 13, 2005 5:26 P.M. Eastern Time (USA)
Did I mention I LOVE Mouser...
to double the power transistors ?
HI
Soon I will start to put together the Krell KSA 50 . I have for these amp 46Lb heatsink . Three pice for each chanel so that 23lb per chanel .I would like to know if I double the power transistors , to use 6 pair instead 3 pair. Do I have to change the driver transistors or everiting is going to be fine.
I want to double the power transistors because my heatsinks are 15 inch tall. So to spread the heat better. I will use 28-0-28V or max 30V,and if the heatsink will run cool ,I will ad a bit more power .
I would like to know the opinion those who already experienced with these amp.
Thanks
HI
Soon I will start to put together the Krell KSA 50 . I have for these amp 46Lb heatsink . Three pice for each chanel so that 23lb per chanel .I would like to know if I double the power transistors , to use 6 pair instead 3 pair. Do I have to change the driver transistors or everiting is going to be fine.
I want to double the power transistors because my heatsinks are 15 inch tall. So to spread the heat better. I will use 28-0-28V or max 30V,and if the heatsink will run cool ,I will ad a bit more power .
I would like to know the opinion those who already experienced with these amp.
Thanks
kmj said:
Hi, KMJ. I just can't help but smile everytime I see your posts, reminds me of Post #2420. For some reason that one kind of personalizes this entire thread for me, and its sooooo funny. Good job.
Actually, the casing is not ground, its the collector, so you better not ground it! As Terry pointed out I had no way to isolate the TO-3 cases as mine had predrilled/pretapped holes for the TO-3s. However, I undertook a massive effort to isolate every mounting bolt, everything connected to the heatsinks multiple times removed from the heatsinks themselves, so they float at + and - 38V. I carefully used over 20 insulating nylon collar washers, and it all worked out as the holes fore everything were cooperative.
Tell you what, I've got good thermal coupling from transistor to heatsink, I torqued the &&%%$# of of those TO-3's and used Artic Silver compond. Its well known that its relatively impossible harm a TO-3 by overtighenting it. At least I read this on the internet so it must be true!
As an aside, live heatsinks are like big antennas that can pick up noise from outside sources, so keep this in mind, its better electrically to have them grounded.
Although your heatsinks can pick up the RF interfernce, you have two things working in your favour;-
1. the sinks are inside your grounded metal casing, perforated so far from ideal.
2. the Zobel will take a bit of the signal to ground although not as effectively as being on the output cable side of the Terminals.
Q. I wonder if you would benefit from a very small cap added from sinks to ground, maybe 100pF ceramic?
1. the sinks are inside your grounded metal casing, perforated so far from ideal.
2. the Zobel will take a bit of the signal to ground although not as effectively as being on the output cable side of the Terminals.
Q. I wonder if you would benefit from a very small cap added from sinks to ground, maybe 100pF ceramic?
naked transistors, live heatsinks
Surely mounting the trannies straight on the sinks will connect them to the supply rails, which are pretty comprehensively decoupled anyway?
Getting rid of the pads does seem like a good idea though. The best I could find have a resistance of 0.2K/W.
I'm hoping to use Heatsink: http://tinyurl.com/brwlz cut into two; PNP on one half, NPN on the other.
This claims to be 0.08K/W! According to my calculations, running 196W through six transistors (0.7K/W junction-to-case) without insulating pads, junction temperature will be only 42 degrees rise. This seems too good to be true, what am I missing?
Fan: http://tinyurl.com/9vwhk Greater airflow than recommended by heatsink manufacturer so it might be possible to run it at a little less than 24V and reduce noise below the specified 28dB.
Any thoughts?
AndrewT said:
Surely mounting the trannies straight on the sinks will connect them to the supply rails, which are pretty comprehensively decoupled anyway?
Getting rid of the pads does seem like a good idea though. The best I could find have a resistance of 0.2K/W.
I'm hoping to use Heatsink: http://tinyurl.com/brwlz cut into two; PNP on one half, NPN on the other.
This claims to be 0.08K/W! According to my calculations, running 196W through six transistors (0.7K/W junction-to-case) without insulating pads, junction temperature will be only 42 degrees rise. This seems too good to be true, what am I missing?
Fan: http://tinyurl.com/9vwhk Greater airflow than recommended by heatsink manufacturer so it might be possible to run it at a little less than 24V and reduce noise below the specified 28dB.
Any thoughts?
JoeyDD said:
There has been a posting conversation on that subject quite some time ago.
The view of a sizeable number is that the voltage for the front end should be the same or lower, in order to prevent saturation of the output stage, which would lead to clipping.
Big devices take much longer to recover, retaining the voltage losses mean the small devices saturate before the big ones and the amplifier will recover from clipping much faster.
Which holds much truth, question is whether to design for clipping conditions. If continuous power output is never high enough for the output devices to saturate, a higher voltage for the stages up till the drivers should enable a higher headroom number.
A company like NAD has proven the benefits of extended headroom circuitry. Admitted, with soft clipping circuitry added.
Separate power supplies with the same voltage equals the conditions of one with a single PS.
The front end should be capable of something like 100mA, often the drivers are hooked up on the same rail as the output devices.
Because of the low currents in the front end, ripple on the rails is low enough with capacitors in the 1000uF size.
The big cans are needed for the output stage because of the high current class A operation.
With one PS, the higher the bias the higher the ripple, which influences the front end as that feeds from the same rails.
The high ripple makes the front end operate less accurate and have less control over the output stage, resulting into sound degradation.
Gits as me put regulated voltages on the front end as an effort to improve conditions for that part of the amplifier even further.
Adding regulated voltages for the front end of an amplifier has relatively low costs, but a high rate of return, just my opinion.
I think you can find a great number of people on this forum who are convinced of the benefits of excellent amplifier voltage rail conditions.
K,
i am bit of a wild one, did American football in high school, i am covered with scars from head to toe and score 225lbs at the moment. Are you sure ?
{as off topic as can be}
Naah,
more like double specked nerd with A grades for gymnastics.
I was the school fool that drove his bike on the frozen school lake during morning brake in winter, to sink through the ice.
Sitting through the classes soaking wet wasn't that bad, having to stand in front of the class with the back of my pants torn was.
Having to meet the principal once a week for fighting was OK, explaining to my parents i needed new glasses again was not.
The parents of my friends thought i had a bad influence.
Ever been to Siena, Italy ?
Look ma, no brains :
http://profiles.yahoo.com/grandebouffe
Naah,
more like double specked nerd with A grades for gymnastics.
I was the school fool that drove his bike on the frozen school lake during morning brake in winter, to sink through the ice.
Sitting through the classes soaking wet wasn't that bad, having to stand in front of the class with the back of my pants torn was.
Having to meet the principal once a week for fighting was OK, explaining to my parents i needed new glasses again was not.
The parents of my friends thought i had a bad influence.
Ever been to Siena, Italy ?
Look ma, no brains :
http://profiles.yahoo.com/grandebouffe