I used 2sc4793,a1837 for drivers on my OPS.
I will try this (jumper basestoppers) tomorrow morning.
Thanks.
I used 2sc4793,a1837 for drivers on my OPS.
I will try this (jumper basestoppers) tomorrow morning.
Thanks.
Ahhh , I now see. yes ... the HK680 (slewmaster base design) uses those
exact devices - NO basestoppers + those 33-47pf predriver shunts are
standard here.
What predrivers do you use ?
OS
The .1u at C10 attenuates HF above 100hz another 6+ db , have seen this
on some OEM non-inverting servo's. Simulation validates the concept ...
(steeper slope >100hz).
Both the HK990/accuphase use this 2 stage filter/integrator (non-inverting).
The H/K uses 2.2u/ 2.2u ,the accuphase uses .22u/2.2u.
With the servo out ,this matter's not.But, you will need the servo for the finished
amp.
OS
I used mje340,350 as predrivers.
Please explain these Csa also ,do you mean an R.C CIRCUIT?
I used 47pf at this position.
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OS,
Does the NAD-Slewmaster have a capacitor multiplier integral with the design or would I use the cap multiplier that I got from PMI for other amps I was working on? I understand I would probably have to change some component values if I am going to run at 70V but I think that has been done by others or do you think this idea of a cap multiplier is inferior to just a good power supply such as a CRC type of power supply?
Does the NAD-Slewmaster have a capacitor multiplier integral with the design or would I use the cap multiplier that I got from PMI for other amps I was working on? I understand I would probably have to change some component values if I am going to run at 70V but I think that has been done by others or do you think this idea of a cap multiplier is inferior to just a good power supply such as a CRC type of power supply?
Hi Kindhornman,please see here .http://www.diyaudio.com/forums/solid-state/244903-vssa-through-hole-pcb-build-thread-36.html
Post #351,360,361 same test configuration.
thimios,
Are you pointing at those post numbers because you think you again had a ground loop problem between the signal generator and oscilloscope or that your dummy load was causing a problem? I wasn't sure which of these two situations you were pointing to that could explain the hash that you had been seeing.
Are you pointing at those post numbers because you think you again had a ground loop problem between the signal generator and oscilloscope or that your dummy load was causing a problem? I wasn't sure which of these two situations you were pointing to that could explain the hash that you had been seeing.
In that posts #360,361 you can see a non oscillating amplifier ,tested with same configuration.
I have pointing this because you say about H.F present on my generator.
As for ground loop problem between the signal generator and oscilloscope this has been solved.
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Thanks Thimios. As long as you know that rf is not the case and it is not a ground loop now the detective work begins, what is causing the instability you are seeing. I am quite sure between you and OS you will narrow in on the problem and find the solution.
Steven
ps. I was trying to find a post that would have given a zobel network value to place before the input to band limit the input frequency to see if this is a high frequency oscillation problem you are seeing but didn't find what I was looking for. I am not knowledgeable enough myself to recommend the values needed to make this simple filter but that would show if it is indeed a high frequency oscillation causing your problem.
Steven
ps. I was trying to find a post that would have given a zobel network value to place before the input to band limit the input frequency to see if this is a high frequency oscillation problem you are seeing but didn't find what I was looking for. I am not knowledgeable enough myself to recommend the values needed to make this simple filter but that would show if it is indeed a high frequency oscillation causing your problem.
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I tried putting 2sa1943 c5200 as driver outputs.
With these, the amplifier oscillate badly.
Then i tried NAD V1.2 ,same bad oscillation.
Putting again 4793 ,1837 i tried again v1.2 &1.3
First photo 20KHz (V1.2)
Second 20KHz(V1.2) BUT now i have add 100pf//33pf(c107,109)
30KHZ,40KHz,50KHz,100KHz(all v1.2)
last photo v1.3/ 20khz....
With these, the amplifier oscillate badly.
Then i tried NAD V1.2 ,same bad oscillation.
Putting again 4793 ,1837 i tried again v1.2 &1.3
First photo 20KHz (V1.2)
Second 20KHz(V1.2) BUT now i have add 100pf//33pf(c107,109)
30KHZ,40KHz,50KHz,100KHz(all v1.2)
last photo v1.3/ 20khz....
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Please ATTENTION.
You must read these at shematic,734ma as 0,734mA & 846mA AS 0.846mA
Sorry fo this.
I deeply reviewed 1.2 vs. 1.3 layout - just one "bug" ... but it should
not have the effects I see. (below) change the location of the servo FB
resistor (R28) to where the jumper (was - in the pix) - negative feedback
will then be isolated from the diamond input , no board change.
beyond this, the 1.3 is identical to the 1.2 ... I can't understand why the
problems exist ... as you could lay the 1.2 over the 1.3 , 80 percent of the
traces line up exactly with each other.
PS - also try the inverting FB servo - see if this gets you a V1.2.
Try to "copy" the 1.2 on the new board , this will determine whether
it is a layout or actual design issue.(or a dodgy component ?)
OS
not have the effects I see. (below) change the location of the servo FB
resistor (R28) to where the jumper (was - in the pix) - negative feedback
will then be isolated from the diamond input , no board change.
beyond this, the 1.3 is identical to the 1.2 ... I can't understand why the
problems exist ... as you could lay the 1.2 over the 1.3 , 80 percent of the
traces line up exactly with each other.
PS - also try the inverting FB servo - see if this gets you a V1.2.
Try to "copy" the 1.2 on the new board , this will determine whether
it is a layout or actual design issue.(or a dodgy component ?)
OS
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Hi Lazy Cat, can you give more datails?Yes, try with a different input stage topology.
Yes, try with a different input stage topology.
Yeah , like the leach (spooky) ... all this CFA BS "flamewars"
.Most of The best 3-10K$ audiophile amps are VFA/ refined leach amps.
Of the 100's of reviews of both the VFA/CFA accuphase/marantz/HK I've read...
Both types receive rave reviews ... there is no CFA preference. Most of what
I've seen is the current feedback marketing "voodoo" highlighted on the product descriptions.
My opinion is that a VFA is easier to make precision .. (offset ,THD , fault tolerance).
It does seem to be a lot of work to make a CFA match a VFA in all
categories.
So , 
just a lot of self serving BS ...PS - all the "survivors" - (30 year amps) I see are VFA.
OS
Yeah , like the leach (spooky) ... all this CFA BS "flamewars"
Most of The best 3-10K$ audiophile amps are VFA/ refined leach amps.
Of the 100's of reviews of both the VFA/CFA accuphase/marantz/HK I've read...
Both types receive rave reviews ... there is no CFA preference. Most of what
I've seen is the current feedback marketing "voodoo" highlighted on the product descriptions.
My opinion is that a VFA is easier to make precision .. (offset ,THD , fault tolerance).
It does seem to be a lot of work to make a CFA match a VFA in all
categories.
PS - all the "survivors" - (30 year amps) I see are VFA.
OS
OS ,i must say that ,from a little listening test ,i prefer this NAD from SPOOKY.
bass is more compact and always under control ,high frequencies more clear also,this is my opinion.
PS you didn't answer my question about these Csa/b ,did you mean an R.C circuit?
What's your opinion about changing values of c107.109 up to 150pf?
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