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Old 19th June 2012, 05:30 AM   #111
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Default zobel network

Avwerk,
Yes I do remember that the amplifier was sent to Stereophile just running on the drive transistors, that is what I remember. The network is on the boards for that problem or yours has been removed. The 25/25 diagram is posted here you can see it as I just did not use the inductor. The amplifier did not have parasitic oscillation problems. The later amplifiers all had the inductor in line for capacitance in the speaker cables. I think you will see it 22ohms and .1Uf, just no inductor. you can see the inductor on the One Megs posted here.
John







Quote:
Originally Posted by AVWERK View Post
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 19th June 2012, 11:07 AM   #112
spurlte is offline spurlte  United States
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Default "Sounds better and better"

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Originally Posted by lgreen View Post
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.
Sounds better and better. That sounds very encouraging, but the "live heatsinks" is new news to me. Please when you elaborate more on the power distribution, could you express more with regarding "live heatsinks". BTW, I love the wiring drawing. Thank you so much. I remember when my child was 7 years old too.
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Old 19th June 2012, 11:52 AM   #113
spurlte is offline spurlte  United States
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Angry Oh, the Europeans.

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Originally Posted by Kaplaars View Post
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
If this was only in English :-(
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Old 19th June 2012, 04:11 PM   #114
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That is great to hear. I am curious to the so called 'slam' which everyone who has listened to a Krell mentions.

I've red about Carlos's amp. That seems a nice amplifier indeed! Think that would be a nice project in the future. Thanks for the tip!

Hi Spurtle, via the Google Chrome web browser you can translate whole websites, very handy :-). The topic starter mentions that he is statisfied with the sound but has some problems with jamming of the amplifier when he turns the amplifier on. Especially when he applies a large input signal. He also mentions temperature gets very high.

If you are interested, here is more info: ExtremA, a reference class-A DIY amplifier. - Introduction
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Old 19th June 2012, 07:15 PM   #115
lgreen is offline lgreen  United States
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Quote:
Originally Posted by Kaplaars View Post
The topic starter mentions that he is statisfied with the sound but has some problems with jamming of the amplifier when he turns the amplifier on.
I had that problem as well- when using a variac. When just turning it on the problem does not arise.
ExtremA Latch Up
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Old 19th June 2012, 09:30 PM   #116
Rewind is offline Rewind  Sweden
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Originally Posted by lgreen View Post
Could you post a schematic of your overall wiring setup? AC comes in, goes through thermister(s), bridges transformers etc.... /NTC.
Hear, hear! I have the pcb and transformers, and I'm ordering the parts soon. I would love to see a complete drawing of the KSA-100 MKII on how to connect everything to the mainboard, adapted for noobs. Without it I would feel rather suicidal.
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Old 19th June 2012, 09:44 PM   #117
a.wayne is offline a.wayne  United States
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Well,
Is Jim's boards good, same as the originals done here in the past ...?
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Old 19th June 2012, 10:14 PM   #118
lgreen is offline lgreen  United States
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Originally Posted by a.wayne View Post
Well,
Is Jim's boards good, same as the originals done here in the past ...?
They don't look like the versions of the boards done here. Jim's boards appear to follow the physical layout of the original Krell boards where the boards here were laid out by people here. Jim's look like the original boards where the boards done here don't actually look like the originals (same electrically). Not counting the color differences.

At least that is what I think from looking at the pics.
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Old 19th June 2012, 11:37 PM   #119
Rewind is offline Rewind  Sweden
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Quote:
Originally Posted by lgreen View Post
They don't look like the versions of the boards done here. Jim's boards appear to follow the physical layout of the original Krell boards where the boards here were laid out by people here. Jim's look like the original boards where the boards done here don't actually look like the originals (same electrically). Not counting the color differences.

At least that is what I think from looking at the pics.
I was told that Jims Audio pcb was inferior to this one: Krell KSA 100 MK II mkii ksa100 ksa-100 PCB Kit Class A amplifier diy AMP | eBay
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Old 20th June 2012, 12:27 AM   #120
a.wayne is offline a.wayne  United States
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Pricey ........ worth it ...?
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