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Old 17th June 2012, 07:24 PM   #101
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Default Bedini never used them

Avwerk,
Sorry to here that but all Bedini Amps have that network built on the boards, I have always used them. Some of the 150's also had other networks but people removed them.
The other thing is that just not hooking the Amp to the speakers does nothing to the stability. The Amplifiers are stable without load. You either had something else wrong with the Amplifier or some tweak adjustment.

The 25/25 all the way to the 250/250 all had that network in some form or another. The Zobel would have not helped if you caused the Amp to break into Oscillation while changing components. You can find many 150's running to this day with no stability problems even at 2 Ohms.

So please do not say I never used them. There seems to be allot of false assumptions about what I have done in my life in the audio field. Most just condemn because of false information on the Net or You-tube, they really know nothing of my work in any of these fields. In the market place you will find over 3000 Bedini Amps running to this day without what your talking about. I still do the repairs so I see what people try to do with the tweaks. To take this further any amp can do what your talking about and they do, so it's just not mine that does this. Anybody can break anything give enough time. So, just setting the record straight here.
John











Quote:
Originally Posted by AVWERK View Post
The AC vs DC fan debate is just that a debate. I used both styles because of the ..debate...
Having built 6 Krell monoblocks that use both types, I can not reliably tell a difference switched in or out that it does anything negative to the soundstage or on the scope for that matter.
The zobel is cheap insurance. Bedini never used them thinking I assume it does something negative to the sound. I smoked a 150 mk2 without anything connected to the outputs while changing components and then the phone rang....magic smoke from the distance? It oscillated itself out of exsistance

When you do power up you can use the light bulb method. I haven,t done that but it is excellent.
When I power up I ramp my Variac fairly quickly to about 1/3rd to get the trannies to switch while looking at the DVM set in the milivolt
range hung on the outputs. You can place a 2nd DVM across a emitter also.
Then I wait about 3 seconds while sweating like a dog with knees vibrating, nail bitting..the whole package.. A few beers might help here BTW!
If I haven,t had a heart attack yet and can observe the DVM coming down into the milivolt range then I can start slowly increasing the Variac while looking at both DVM,s and adjusting bias along the road ahead..

My variac gets stiff fairly easily if something is wacked and that why light bulb method is a better item to asist.
If you get this far you need to sit with it awhile and keep an eye, actually both eyes on everything.

Regards
David
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Old 17th June 2012, 08:57 PM   #102
spurlte is offline spurlte  United States
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Quote:
Originally Posted by AVWERK View Post
The AC vs DC fan debate is just that a debate. I used both styles because of the ..debate...
Having built 6 Krell monoblocks that use both types, I can not reliably tell a difference switched in or out that it does anything negative to the soundstage or on the scope for that matter.
The zobel is cheap insurance. Bedini never used them thinking I assume it does something negative to the sound. I smoked a 150 mk2 without anything connected to the outputs while changing components and then the phone rang....magic smoke from the distance? It oscillated itself out of exsistance

When you do power up you can use the light bulb method. I haven,t done that but it is excellent.
When I power up I ramp my Variac fairly quickly to about 1/3rd to get the trannies to switch while looking at the DVM set in the milivolt
range hung on the outputs. You can place a 2nd DVM across a emitter also.
Then I wait about 3 seconds while sweating like a dog with knees vibrating, nail bitting..the whole package.. A few beers might help here BTW!
If I haven,t had a heart attack yet and can observe the DVM coming down into the milivolt range then I can start slowly increasing the Variac while looking at both DVM,s and adjusting bias along the road ahead..

My variac gets stiff fairly easily if something is wacked and that why light bulb method is a better item to asist.
If you get this far you need to sit with it awhile and keep an eye, actually both eyes on everything.

Regards
David
I have to admit.... this is probably why I am doing this project. I don't drink much, don't gamble (If I put out any money, I want something in return quickly), and don't have much luck with the opposite sex. It hard to get me the excitement you describe and I am already sweating about "Are you sure you are ready to plug-in this monster?" Worth every penny!
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Old 17th June 2012, 11:38 PM   #103
AVWERK is offline AVWERK  United States
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Ok, John, i should have stated my Stock original 150 was modified with dual transformers when you were in Paramount, CA. Back in the 80, s and ran like a top back then without issue, but on this day nothing out of the ordinary except no load and nowhere on the board or output terminals was there a zobel network. That is certain. I ran it for years but this day oscillation took its toll. I still have it and fixed it.
You do remember your ADD,s about high frequency issues and grinding the tops off the TO3's and filling them with a special nonresonant material in this model right? in Stereophile?
I noticed you didn,t carry this over to any other models after that?

It should be noted back then Bedini,s were the amp to use on wicked electrostatic loads and were recommended all the time by dealers who didn,t even carry his line
Regards
David
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Old 18th June 2012, 12:51 AM   #104
AVWERK is offline AVWERK  United States
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Kap
My first pics I ever posted I think and not to good BTW.. were of my 100 with PMA boards back in Sept 2008 on page 221 #2208 thru 2210 in the Krell ksa100 mkII Clone thread by Mark B.
The other 4 are the 50's and the Synder 150's that haven,t been posted yet

These still run strong today without issue and my prefered amps on my Quad electrostatics. I also have Martin logan Sequel 2's that I switch in and out depending on the mood.
For not much money you could buy 2 more bridges and go dual/dual on the power supplys you hav there.
This eliminates any hum and any imbalanced currents that flow because of any mismatched caps even new caps might have. If you can match the caps then this isn,t really necessary but either way, what you have will work fine. You might place a .1uf mkp caps after the ac leads just before the bridge

Regards
David
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Old 18th June 2012, 04:45 PM   #105
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WOW LIKE your build David! I now recall your pictures, I saw them when I was scanning the thread just before I got the crazy idea to build one clone myself haha.

Hmm using two rectifiers is something I've considered. It does indeed not cost a lot of money so that would be no problem :-) But I've red that using two rectifiers not really offered measurable benefits, although there are theoretical benefits. Using two rectifiers had a disadvantage instead because using another rectifier would cost another 1 1.2V DC. Since the original has also one rectifier I thought to use one. Would be a nice experiment, if I have to order parts again I buy two extra rectifiers, I am curious what it does for the PSU :-)

By the way friends, I have some questions about grounding. What is best to do? I was thinking about using star grounding. So one bolt mounted through the chassis from which all ground cables are connected to. This way ground loops are avoided. I saw in the schematic of the original KSA-100 that the ground cables have a 10 ohm resistor in series with them. Why did they put a 10 ohm resistor in series with the ground cables.\? And from which point is it best to attach the ground cables? I think from the copper bars which the capacitors are attached to, but I don't know for sure.
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Old 18th June 2012, 06:55 PM   #106
lgreen is offline lgreen  United States
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Default nice

Your heatsinks may get pretty hot. Mine do. I used live voltages on each heatsink section as the heatsinks are designed to be live and have insulators between the sections. Yes not very safe. Had to be super duper extra careful to keep everything isolated. Every screw, nut, washer and so on. Not recommended but good for thermal performance. Still not recommended as I have come to appreciate safety more than I did back then.

Click the image to open in full size.


Could you post a schematic of your overall wiring setup? AC comes in, goes through thermister(s), bridges transformers etc....

Sort of like this:
Power Wiring Link

This would help everyone see where you put the caps to reduce sparking etc....

You made me go back and look at my website and amps, they look horrible on the inside, birds nest wiring everywhere, but never had any problems and they all work.

Keep plugging away and don't rush your build.

EDIT- To answer your question above, I think the 10 ohm power resistor you see connecting to the groud is to connect the circuit star ground to your chassis/ AC ground (wall ground). Nelson uses a CL-60 in the same spot in some of the Pass projects. I suppose the reason is that your case is grounded to your wall AC ground for safety, but noise from the AC ground is attenuated by the time it reaches your circuit star ground through the resistor/NTC.
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Last edited by lgreen; 18th June 2012 at 07:07 PM.
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Old 18th June 2012, 07:33 PM   #107
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Hi lgreen,

Actually, I use the same principle :-) The heatsinks I use are anodised so they are isolated but that is offcourse no guarantee. Mine have insulators between the different sections of the tunnel coolers too. There are little pertinax strips between them. The output devices are directly attached to the tunnel coolers, just like in your build. Originally there were BUX81's attached to the tunnel coolers (without isolation). The tunnel cooles came from industrial, very professional PSU's (very big one's btw). It actually worked great, so I think it is not a real problem for safety, but I have ofcourse to be careful.

You actually inspired me to build a Krell haha. Your website was the first I saw about a Krell clone. That was when I thought, I want to build one too! :-). I REALY like your tunnel cooler, nice colour. When I have some leisure time left I will draw a little schematic of the wiring.

Wiring is one of the most fun parts of building an amplifier to me. I try to make the wiring as nice as possible. I use a lot of decent connectors to make very reliable connections. I will certainly take my time to do this :-).

Ahaa so that is why. That sounds like a logical explanation, thanks!
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Old 18th June 2012, 07:54 PM   #108
lgreen is offline lgreen  United States
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Quote:
Originally Posted by Kaplaars View Post
Hi lgreen,

Actually, I use the same principle :-) The heatsinks I use are anodised so they are isolated but that is offcourse no guarantee.
Be careful. I only sparked a heatsink one time, still has the black mark on that spot! I didn't want to go with live heatsinks but I couldn't figure a way to insulate my TO-3's and still use the original mounting holes and metric screws. For some reason I couldn't get the right parts.

I am concerned that your build will get too hot. But you can always dial down the bias.

I use two CL-60's in series per primary bypassed by a relay after so many seconds. Even after 10 seconds, still biiiiings (you physically hear the transformer inrush) after the relay clicks. After 5 years I replaced the CL-60's as the lettering was getting black, still does it every time.

My Krell is 7 years old this year and sounds better and better.
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Old 18th June 2012, 08:33 PM   #109
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I think that heat will be a large problem indeed. It is like what someone in the 'big' Krell clone thread said: 'you think your heatsinks will do but then reality kicks in' haha. The heatsinks are quite large, about 20cm lengt 16 cm width and 13 cm height per section. Realy hope that will do. I've tested the capacity of the heatsink again with resistors (I have another section left which I use as dummyload, so big resistors are attached to this heatsink). When I dissipate 400W with active cooling (full speed) it gets hot, but not too hot, would say 60 degrees. When I dissipate 625W it gets very hot very fast. I think that when I use it for more than 5 minutes the resistors will smoke away. That is a bit logical because the resistors can fairly dissipate with each other a maximum of 400W, but I had to try :-). I hooked the dummyload to the almost completed PSU of the amplifier. This way I could also test the PSU itself.. The transformers have absolutely no problem with delivering 625W. No hum, nothing, dead silence :-) But when I hook the dummy only to the negative side or positive side of the PSU, and thus charge only one side of the transformer, there is hum from the transformer, which is not loud, but certainly audible. Think this is due to unbalanced charge.This is typicly a case when you actually have to have two bridge rectifiers :-).

I am curious how the heatsinks will do in the cabinet, because temperature in there will rise faster, and I've attached two sections together. Wost case scenario I have to decrease bias. That would not be a big disaster, but we want offcourse the real deal, so we have to aim for full bias :-)

I use a softstart kit. This kit has one relay which powers the amplifier up. There are 4 NTC's which are bypassed about 6 seconds later by a second relay. The advantage this kit offers is that I can use a momentairy switch. So I dont have to run AC wires to the switch, and to use a big switch.

By the way lgreen, little offtopic, but I saw that you've build an ExtremA also! This design is a bit popular in Holland, it is designed bij Sander Sassen if I am correct. How does this amplifier sound compared to your Krell? I read very good reviews, but.... there are very few finished ExtremA's, the only one I know of next to yours is this one: forum.zelfbouwaudio.nl • Toon onderwerp - Nog een ExtremA
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Old 18th June 2012, 09:04 PM   #110
lgreen is offline lgreen  United States
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Quote:
Originally Posted by Kaplaars View Post
By the way lgreen, little offtopic, but I saw that you've build an ExtremA also! This design is a bit popular in Holland, it is designed bij Sander Sassen if I am correct. How does this amplifier sound compared to your Krell? I read very good reviews, but.... there are very few finished ExtremA's, the only one I know of next to yours is this one: forum.zelfbouwaudio.nl • Toon onderwerp - Nog een ExtremA
I would not use the word "designed" but rather would say "co-author."

The ExtremA sounds like a lab amp, powerful, precise, wonderful. So long as you don't clip it. At clipping it rings for some unknown reason (subsequently confirmed to me by other builders). Aside from that, it is truely a reference quality amp with an uncolored sound.

The Krell has deeper bass and slightly softer highs, clips gracefully but you never really dare turn it up that loud because even at 50WPC the bass will knock you over. Its a great amp to build because its a known working design and there is a good strong community of support.

Edit- Please note that the DX HRII from Carlos, in my view, approximates the bass of the Krell with the crispness of the ExtremA in a class AB amp that won't take a year of effort to build block-by-block. It has effortless power and sounds fantastic at any volume level (even very low volumes). While I no longer am into audio, if I ever came back I'd build another Carlos amp because it is that good. Every time I turn it on I wonder how it can sound so good for its size and ease of build. I would encourage everyone to make a "known good" Carlos amp as an alternative to other more common designs.
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Last edited by lgreen; 18th June 2012 at 09:12 PM.
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