And a couple more (4,5,6,7,8) all 5 VAS trannies are thermally coupled on the "roadsign" (flat HS in middle) , CCS has the little HS (25C/W - overkill) , the drivers are 12.5C/w.
Two things happen with the 2 resistors shunting the VAS.
1. OLG is reduced from 70DB to 63DB.
2. H2 is increased slightly (simulation), with audition (with and without) , adding these resistors makes the amp sound "mellower" . Also resistor at the tail , R6/220R has the same effect.
While everthing sounds better than my greatest expectation (OMG , the headroom) I am still chasing ground issue. A little Hum was there , I pulled my hair out
and found that taking the speaker return individually from the star of each amp reduced it a lot. Attached is general layout of grounding , If anyone could post pix's or diagrams (I did search , found some aussieamp pix of grounding and read self and rod elliots articles). I now have to put my head inside the speaker and strain to hear the hum , but I can still hear it...... 
is this a unreasonable expectation.??OS
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I will have to research this ... ahh, will just put it in and see !! Daniel gave me a LOT of audiophile bypass caps (big thanks) ,muse ,wima's, HQ poly's. I have already replaced any dubious ceramics or used devices in the amp.
My wife has suggested that I have become to much the perfectionist (fanatic),seeing me stick my head into the woofer.
As far as that goes , I can not hear hum at 1 meter , not at 1/6th meter..... I have to put my ear right to the dustcap of the woofer and eliminate any environmental noises to percieve it. Is this in the ballpark of what I can expect ,or am I getting some EM picked up from my monster toroid?? My hearing is still good at 44 (can hear the earthworms "suck" back into their holes as I walk outside at night) so maybe I am chasing ghosts.
I also tested my ripple rejection by slamming one channel (300w+) while putting my ear to the speaker dustcap in another room (25ft. cable) ,while muting the test channel. This seems to confirm that I have very good PSRR, as I heard no sound out of the test channel AT ALL.
Objectively , I measured for both DC and AC at the OP , DC was 1.5 - 2 mV , AC was not measurable on the lowest scale - <.1 mV.
Edit: searched for 100nf signal ground cap - Chipamp people say use a ceramic disk !
the one place one can/should use one in an audio amp. OS
Hum sucks once you know it's there. It would probably spec fine for most high end manufacturers, but not audiphiles with their head in their woofer.
I'm with you though. I sent an Odyssey amp back twice before I realized they probably weren't changing anything and that I was just being unreasonable. However, some amps like my bedroom system containing a cheap Audiosource Amp One/A has no detectable hum. Neither does my HT setup using a Panny XR-55. High end sucks!
I'm with you though. I sent an Odyssey amp back twice before I realized they probably weren't changing anything and that I was just being unreasonable. However, some amps like my bedroom system containing a cheap Audiosource Amp One/A has no detectable hum. Neither does my HT setup using a Panny XR-55. High end sucks!
ostripper said:
My wife has suggested that I have become to much the perfectionist (fanatic),seeing me stick my head into the woofer.
As far as that goes , I can not hear hum at 1 meter , not at 1/6th meter..... I have to put my ear right to the dustcap of the woofer and eliminate any environmental noises to percieve it
I wonder what that would Spec ? amp has gain of 28db , with
1.44v input I get over 120db out of the 4 fisher 12" 3-ways. A whisper is 15-30db , I can hear one of those across the room... so I can assume my hum is somewhere around 1-10db ,so would I be wrong to spec my hum at over -100db?
No changes to circuit , except the 100nF cap and the addition of quick connects to the 2 amp's star points(no more iddy biddy PCB terminals).
http://www.mouser.com/Search/ProductDetail.aspx?R=63067-1virtualkey57100000virtualkey571-63067-1
These are sooo tough , much current and VERY hard to break off.
10 and 12 gauge wire from speaker and the main star will be more desirable.
OS
HUM GONE !!
Stealing the grounding techniques of a few aussieamps I saw and Jkeny's 100nf cap combined for ABSOLUTE silence. I learned that the amps stars are the best place for returns when 2 amps are powered by the same supply , not at the common supply.
I am sure it helped to "supersize" everything (quick connects , 10/12 ga wiring). Without the physical grounding changes, the cap attenuated the harmonics of the hum (buzzzzz) , so I left it in to augment my physical changes.
With all I have learned perfecting this one , my rears are next..
perhaps a aska 55 clone for them w/ integrated PS.
I will also have the mighty $7000 genesis stealth to compare the supersym to.
OS
Stealing the grounding techniques of a few aussieamps I saw and Jkeny's 100nf cap combined for ABSOLUTE silence. I learned that the amps stars are the best place for returns when 2 amps are powered by the same supply , not at the common supply.
I am sure it helped to "supersize" everything (quick connects , 10/12 ga wiring). Without the physical grounding changes, the cap attenuated the harmonics of the hum (buzzzzz) , so I left it in to augment my physical changes.
With all I have learned perfecting this one , my rears are next..
perhaps a aska 55 clone for them w/ integrated PS.
I will also have the mighty $7000 genesis stealth to compare the supersym to.
OS
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ostripper said:
There's caveats either way. I sent you an email about some specifics, but it was too long to post here. Basically, ceramic caps are available in quite good quality, and ceramic doesn't time smear.
The ceramic cap gives you only one copy of the signal, and it arrives intact when the ceramic is well built and also physically large enough to handle the voltage.
Sometimes a really cheap polyester "bubble" cap is more useful because of its high inbuilt resistance; however, you can simulate that with a ceramic in series with a resistor or like R,C,R.
A polypro cap or miniaturized box polyester can work like a ceramic paralleled with a cheap polyester cap. See the time smear? That's like RC paralleled with a smaller C, sometimes repeatedly. This (multipath) does a lot for efficiency, but it also does some fun extras to the signal that may or may not be beneficial, such as causing a high speed op amp to go bonkers.
Example of the trouble with polypro: Physically modeling a very expensive audiophile tweeter cap with 2 cheap caps and one resistor makes something like 8uF series to 47R which is then paralleled by 1uF (looks like a triangle). Yes that "sense of space" is completely fake and its reproducible for less than $1.
This is great fun, but it doesn't match the audio recording. Perhaps its good for the rear channel application?Well, I hope I got the details right. In any case, there are quality ceramics available--usually ham radio supply will have them.
Make no mistake , I am not a ceramic hater by any means.
They do have their place in my designs (input RC , bypass , etc), but not Cdom ,main input cap, NFB HF compensation. Some of the new CDE multi-layer ceramics are very usable in the signal path.I was referring to as dubious the "old style" 2 disc caps from the days of old. Please don't blaspheme the "little bro" supersym by filling it up with ceramics.
For your 68pF's ,Absolutely get some CDE silvers , feel free to use whatever esoteric input cap you desire. For the zoble... "overkill"
(400v .1u motor bypass) polystyrene.. just to be safe. I could of made this amp much faster (39pf Cdom stable) , but opted for unconditional stability into any load (90+ phase margin without lead comp) ,plus I had 10 68p silvers.
After a week of running your boards and running the big ones , I am quite pleased to say they are ready for prime time. I have thrown every ignorant form of abuse at these amps (long hard hours of paralleled 8R loads , 90f days , extensive listening tests,
AND my VST synthesizers
) , they have not only survived.. but surprised 
. I would not trade these for the8K$ original stealth's , because they sound better "top to bottom",with no real weakness anywhere , but put out 1/10th the heat with only half the heatsinking.
I have my own way to do that , BEFORE the amp. (attached)
OS
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ostripper said:I was referring to as dubious the "old style" 2 disc caps from the days of old. Please don't blaspheme the "little bro" supersym by filling it up with ceramics.
. . .
AND my VST synthesizers
. . .
OS
As for the amp boards, I'll use exactly the parts you specified, and actually may be after even more specific info.
Your amps stood up to synthesizers? Wow, more like WOW!!!
Yes, that takes a lot of headroom.
Nothing like a few sawtooth and square waves at 300watts for confirming HF stability. I had the synth so loud with the 4 fishers that the echos were bouncing off the local mountain. The zoble- 10R resistor did get a little warm ,but my FFT showed 2nd and
4th harmonics reaching 50k+ at 300w , with "real " music , a cold zoble was the rule.
I guess this could also be a high end instrument amp as well.
Was doing the rush "tom sawyer" thing with a emulated mini-moog...
OS
As far as substitutes , this has to do with driver dissipation and output beta. With the separate drivers on larger HS's (8C/W) or
the drivers on the main HS, the MJE's would most likely be able to drive 5-6 pairs of the NJW's because they have a min. HFE of 75 @75V.
The MJL's are the same but with better SOA. The fairchild or toshiba's ,(2sa1943/sc5200) have a lower hfe unless they have the "o"classification. The only subs that would require a little more Ic from the drivers would be the MJ metal cans (mj21193 -15024 , etc). In this case you moght consider using another pair of NJW0281/0302's as the drivers instead of the mje15032/33. For anything short of driving 2 ohm loads the present drivers seem to be adequate (I have been driving 3R loads all week).
I fixed the link , had a HDD failure a week ago.
http://71.203.202.56/pdf1/Electronics/Projects/Audio_amp/Frugalamp/In%20development/FA2S/
File is FA2S_final.gif. Later I will do the BOM and boardwork and it will be a PDF in the frugalamp root folder.
OS
Looking forward to "Little Bro" arriving in the mail. I'll try to do right by it, and when I'm unsure, I'll ask questions.
In regards to "these really crank," well, I'll probably have to build up some more sturdy speakers. A 90w 8 ohm 3-way isn't looking too difficult with on-hand components and it makes a "fits into house" style speaker; but, is that enough power handling?
In regards to "these really crank," well, I'll probably have to build up some more sturdy speakers.
A 90w 8 ohm 3-way isn't looking too difficult with on-hand components and it makes a "fits into house" style speaker; but, is that enough power handling?
That would depend on your rail voltages (ps). 30-0-30vac would give 80/135w (8/4) and a 40-0-40 would give 120/200w.
I used 120w sony 8" 3-ways and the woofer would bottom out at 2/3 output with the "little bro". The safest thing to do would be to
run 22k resistors for feedback to limit the gain for the smaller amp. You could supersize the PS -600VA/60KuF @80v 40-0-40vac (56-0-56vdc) and just change to 27k later as you move up to a 200w/ch speaker setup.
Don't get scared of the discretes , as you can see , I am only 1 year old here and only 2 burnt outputs (did not screw one down)
If you are careful (double/triple check all work) or do tricks (run input stage /drivers first WO/the outputs), you will get it first try with only a bias adjustment to deal with.
OS
ostripper said:
That would depend on your rail voltages (ps). 30-0-30vac would give 80/135w (8/4) and a 40-0-40 would give 120/200w.
I used 120w sony 8" 3-ways and the woofer would bottom out at 2/3 output with the "little bro". The safest thing to do would be to
run 22k resistors for feedback to limit the gain for the smaller amp. You could supersize the PS -600VA/60KuF @80v 40-0-40vac (56-0-56vdc) and just change to 27k later as you move up to a 200w/ch speaker setup.
Don't get scared of the discretes , as you can see , I am only 1 year old here and only 2 burnt outputs (did not screw one down)
If you are careful (double/triple check all work) or do tricks (run input stage /drivers first WO/the outputs), you will get it first try with only a bias adjustment to deal with.
OS
"Little Bro" arrived in the mail! Thank you!!!
I really want to just rush and put this together, but really I should wait and do it after pedaling across Oklahoma so I can take my time and concentrate (and recover from a really crazy tan).
There's also a mahogany enclosure, a radio board, a sound card source, and a matching speaker.
Glad your package arrived, BTW , I started my ride in bremerton, washington (Puget sound)with a cart and "dumpster" bike ... 63 days later (3575 miles) ended up here in knoxville , TN. That taught me to NEVER give up. Deserts , snakes , thirst , chased by indians in montana , just keep on going.
When you get recovered ,I will MAKE sure you get it(amp) perfect. The "big bro" is now pushing MY 15" sharp speakers (had to give the ones I had back
) ... today I went to the thrift shop and there they were.. A perfect pair of sharp 15" 3-ways for 30$.Also , thanks for caps (and other fun stuff) The 2 cerafines are going in my 50w rear FA1B/dx/aska clones as are the 3300u/ 50v's (need 2 more).
OS
ostripper said:. . .
Also , thanks for caps (and other fun stuff) The 2 cerafines are going in my 50w rear FA1B/dx/aska clones as are the 3300u/ 50v's (need 2 more).
OS
Um, parallel the cerafines with the wimas to complete their bandwidth, if you need a clean hi-frequency on line level and up.
The 3300uF have several interesting signal uses (amp output cap, headroom boosters, impedance match circuit). Do you need more for any of those purposes?
These are the B's... the 47uF cerafines are good for the bootstrap, ASKA amps use similar blackgates as an expensive upgrade option (hundreds of dollars $$). I think the fuss with using a esoteric audiophile cap here is that the bootstrap does full output swing local feedback to complete the voltage stage , so a "audio only" cap might give a "return" in this application. Your 3300uF,s , I will use for
the PS (40-0-40VDC) of the rears. These amps will have very light duty , so they don't have to be anything special, But I do need 2 more caps.
I had to upgrade my speakers , I still can't believe the 30$ pricetag and how loud and scary the sound is with the supersym.
OS
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