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8100/XT
- Thread starter TVJunkie12
- Start date
Had an 8100 with a Cobalt Blue card on a classic rocker. Replaced it with an Omnia 3T.
Much happier with the sound.
I'm keeping the 8100 to feed a back-up transmitter, but if anyone wants to play with the Cobalt Blue card, make me an offer! (My Omnia's two composite outputs feed the main transmitter and an STL to a booster, the 8100's 3/4 cards are used in an ST--so I'm using the Omnia's L & R outputs to feed the 8100 as just a stereo geni.)
Much happier with the sound.
I'm keeping the 8100 to feed a back-up transmitter, but if anyone wants to play with the Cobalt Blue card, make me an offer! (My Omnia's two composite outputs feed the main transmitter and an STL to a booster, the 8100's 3/4 cards are used in an ST--so I'm using the Omnia's L & R outputs to feed the 8100 as just a stereo geni.)
C
CW
Guest
FredRichards said:
If you were asking Frank, I would think he would say "Buy a new Omnia from me!"
=Understood. But sometimes the boss just will not let loose of the bucks.
Does anyone have "mods" for the stock 8100 cards that might punch it up a bit?
Does anyone have "mods" for the stock 8100 cards that might punch it up a bit?
Cut the foils in the ground leg of the safety clipper pots on cards 8 & 9. Remove the chip that sits longways behind the hard - soft clipping pot on card 6. Those mods take 10 minutes tops, are easily reversed & will make your jaw hit the floor when you hear the difference. Works equally well with or without the XT2. Look at the Left Filter Output meter on a bright song before and after the mods. The db difference in that reading will pretty closely reflect the increase in loudness to expect. 3db is not all out out of the question. Please report back with your experinces...FredRichards said:Understood. But sometimes the boss just will not let loose of the bucks.
Does anyone have "mods" for the stock 8100 cards that might punch it up a bit?
Does anyone have "mods" for the stock 8100 cards that might punch it up a bit?
[/quote]Cut the foils in the ground leg of the safety clipper pots on cards 8 & 9. Remove the chip that sits longways behind the hard - soft clipping pot on card 6. Those mods take 10 minutes tops, are easily reversed & will make your jaw hit the floor when you hear the difference. Works equally well with or without the XT2. Look at the Left Filter Output meter on a bright song before and after the mods. The db difference in that reading will pretty closely reflect the increase in loudness to expect. 3db is not all out out of the question. Please report back with your experinces...
[/quote]
I take it that you are relying on a composite clipper downstream to act as a "safety clipper" to catch those occasional overshoots caused by the filtering & clipping process?
-C
[/quote]Cut the foils in the ground leg of the safety clipper pots on cards 8 & 9. Remove the chip that sits longways behind the hard - soft clipping pot on card 6. Those mods take 10 minutes tops, are easily reversed & will make your jaw hit the floor when you hear the difference. Works equally well with or without the XT2. Look at the Left Filter Output meter on a bright song before and after the mods. The db difference in that reading will pretty closely reflect the increase in loudness to expect. 3db is not all out out of the question. Please report back with your experinces...
[/quote]
I take it that you are relying on a composite clipper downstream to act as a "safety clipper" to catch those occasional overshoots caused by the filtering & clipping process?
-C
BobOnTheJob said:
I'll try that, Bob. What I can probably do is record an MP3 of "before" and "after".
Any ideal setting you care to recommend prior/post testing?
I like to start with all 4's on Release, Coupling & Threshold and work toward lower numbers if the loudness/distortion tradeoff allows. +0.5 on Clipping. The HF Limiting pot will have no effect once that chip is pulled. If you can play nack the before & after on a board with conventional VU meters, it would be interesting to know how they compare.FredRichards said:
Since my previous question:
"I take it that you are relying on a composite clipper downstream to act as a "safety clipper" to catch those occasional overshoots caused by the filtering & clipping process?" seems to have gone unanswered, let me point out why I asked.
The effect of this modification you were describing indicates you were / are relying on a composite clipper downstream to catch the overshoots that will result from removing the safety clipper system in cards 8/9.
If you eliminate the safety clippers, the 8100A WILL throw out brief overshoots ...especially during high frequency transients. If you are seeing increases in the demodulated Left / Right levels with NO increase in total modulation peaks, then you are seeing the results of a very active composite clipper (or -worse yet- something acting as one) whacking away at the composite baseband overshoots.
If one were to do this modification WITHOUT a composite clipper downstream, then one would have SIGNIFICANT modulation overshoots during HF transients on the composite output of the 8100A, and would be operating illegally unless total modulation were reduced...in which case, the station in question would be noticeably quieter than before the mod (after compensating modulation levels to accommodate for the overshoots).
One caveat to doing this modification WITH a composite clipper in place is that you are trading off one effect of audio distortion from clipper peak control for another one. Most notably, stereo image aliasing and other by-products from the significant increase in clipping on the composite baseband. This will be heard during moments of programming where there is audio in only the left or right channel. What you will hear is a noticeable increase in "munching" type distortion noise on the opposite channel in tandem with high frequency program energy.
While one can argue that this is acceptable as very few will experience the conditions that blatantly reveal the side-effects of composite clipping, I thought I'd point this out. Especially since you guys seem to be Optimod fans...and I know that the "munching" effect I described (amongst other things) drives Bob Orban nutty...hence the reason he has been so dead against Composite Clipping over the years.
-Cornelius
"I take it that you are relying on a composite clipper downstream to act as a "safety clipper" to catch those occasional overshoots caused by the filtering & clipping process?" seems to have gone unanswered, let me point out why I asked.
The effect of this modification you were describing indicates you were / are relying on a composite clipper downstream to catch the overshoots that will result from removing the safety clipper system in cards 8/9.
If you eliminate the safety clippers, the 8100A WILL throw out brief overshoots ...especially during high frequency transients. If you are seeing increases in the demodulated Left / Right levels with NO increase in total modulation peaks, then you are seeing the results of a very active composite clipper (or -worse yet- something acting as one) whacking away at the composite baseband overshoots.
If one were to do this modification WITHOUT a composite clipper downstream, then one would have SIGNIFICANT modulation overshoots during HF transients on the composite output of the 8100A, and would be operating illegally unless total modulation were reduced...in which case, the station in question would be noticeably quieter than before the mod (after compensating modulation levels to accommodate for the overshoots).
One caveat to doing this modification WITH a composite clipper in place is that you are trading off one effect of audio distortion from clipper peak control for another one. Most notably, stereo image aliasing and other by-products from the significant increase in clipping on the composite baseband. This will be heard during moments of programming where there is audio in only the left or right channel. What you will hear is a noticeable increase in "munching" type distortion noise on the opposite channel in tandem with high frequency program energy.
While one can argue that this is acceptable as very few will experience the conditions that blatantly reveal the side-effects of composite clipping, I thought I'd point this out. Especially since you guys seem to be Optimod fans...and I know that the "munching" effect I described (amongst other things) drives Bob Orban nutty...hence the reason he has been so dead against Composite Clipping over the years.
-Cornelius
Not true...If you'll look at the schematic, you'll note that the ground side of the safety clipper pot is a shunt and removing it causes the safety clipper to be driven harder. This mod completely eliminates the need for a composite clipper unless there is overshoot in the STL. This mod will hang the total mod meter on 100%...period.cgould said:
ahhh...
Now I hear from ya. I guess I finally caught your attention!
Pardon, as I do not have a schematic readily available to review. Yes, if you hit the safety clippers harder, you do build more loudness...and distortion, ...and more HF trash around the pilot tone region...which WILL cause stereo image aliasing...only a little worse than what a composite clipper will do.
There are folks that will find this perfectly acceptable...but everyone should be aware of what's going on when going this route.
This is why Bob designed "Card Zero". To do the same thing without trashing the pilot tone.
Now it makes sense what you were saying about not caring about garbage around the pilot tone area, as your goal apparently is loudness at any cost. This may work in some markets where this goal is the norm. With all of this being totally clear now, someone else *may* care about the side effects...especially in light that many car radios use pilot tone contamination as a cue to blend to mono. Normally, garbage around the pilot tone is a sign of poor FM stereo reception. Other radios are very touchy about program-related trash around the pilot tone, and this trash comes out (literally) as high frequency aliasing distortion in the demodulated L-R audio.
Another source of aliasing will come from mis-tuned safety clipper induced harmonic content that WILL extend into the 23 kHz region of the L-R subcarrier sideband.
Since Bob's "card zero" significantly filters the post-clipper audio energy above 15 kHz, the pilot tone, and subcarrier will be fully protected.
Just want to make people aware of the rest of the story when modifying this area of cards 8/9. There are reasons why it is designed to be so conservative with respect to the safety clippers.
-Cornelius
Now I hear from ya
. I guess I finally caught your attention!Pardon, as I do not have a schematic readily available to review. Yes, if you hit the safety clippers harder, you do build more loudness...and distortion, ...and more HF trash around the pilot tone region...which WILL cause stereo image aliasing...only a little worse than what a composite clipper will do.
There are folks that will find this perfectly acceptable...but everyone should be aware of what's going on when going this route.
This is why Bob designed "Card Zero". To do the same thing without trashing the pilot tone.
Now it makes sense what you were saying about not caring about garbage around the pilot tone area, as your goal apparently is loudness at any cost. This may work in some markets where this goal is the norm. With all of this being totally clear now, someone else *may* care about the side effects...especially in light that many car radios use pilot tone contamination as a cue to blend to mono. Normally, garbage around the pilot tone is a sign of poor FM stereo reception. Other radios are very touchy about program-related trash around the pilot tone, and this trash comes out (literally) as high frequency aliasing distortion in the demodulated L-R audio.
Another source of aliasing will come from mis-tuned safety clipper induced harmonic content that WILL extend into the 23 kHz region of the L-R subcarrier sideband.
Since Bob's "card zero" significantly filters the post-clipper audio energy above 15 kHz, the pilot tone, and subcarrier will be fully protected.
Just want to make people aware of the rest of the story when modifying this area of cards 8/9. There are reasons why it is designed to be so conservative with respect to the safety clippers.
-Cornelius
After thinking of my last post, I've realized that this approach is actually a little worse than removing the clippers, and using a composite clipper downstream (which I originally thought BobOnTheJob was talking about.)
Since all of this extra energy is being fed INTO the FM Stereo generator card, the aliasing situation will be much worse. This is because the extra harmonic content created by overdriving the safety clippers will significantly exceed the FM stereo system frequency response limit, which is 38 kHz divided by 2...which is 19 kHz.
This in many ways is no different than digital audio, where the maximum audio bandwidth is the sample rate divided by 2.
With FM stereo, there is the added complication of the pilot tone sitting right at the Nyquist point (if you will) so bandwidth is actually a little less than what could be achieved by using Nyquist formulas of digital audio.
Having said all that, there will be significant aliasing images not only from what's going on from the extra harmonic content extending into the FM Stereo subcarrier regions, but also from the L-R modulator generating aliasing components due to exceeding the audio bandwidth at the stereo generator inputs.
These extra L-R modulator components will extend DOWN through the 19 hKz pilot (further contaminating it even more) and into the upper regions of the discrete left and right audio. The L-R modulator aliasing images caused by this extra harmonic content will also extend up beyond the upper 53 kHz limit of the L-R subcarrier, significantly polluting any subcarriers you may have with the rhythmic crashes of HF content on the main channel.
Not a pretty picture. Again, Card Zero prevents this while gaining some extra loudness. It doesn't sound as clean on the high end as a stock 8100 card 8/9 clipper alone, but there is no free lunch either way with this really old technology when more loudness is needed.
Just thought I should point out the rest of the story here...
-Cornelius
Since all of this extra energy is being fed INTO the FM Stereo generator card, the aliasing situation will be much worse. This is because the extra harmonic content created by overdriving the safety clippers will significantly exceed the FM stereo system frequency response limit, which is 38 kHz divided by 2...which is 19 kHz.
This in many ways is no different than digital audio, where the maximum audio bandwidth is the sample rate divided by 2.
With FM stereo, there is the added complication of the pilot tone sitting right at the Nyquist point (if you will) so bandwidth is actually a little less than what could be achieved by using Nyquist formulas of digital audio.
Having said all that, there will be significant aliasing images not only from what's going on from the extra harmonic content extending into the FM Stereo subcarrier regions, but also from the L-R modulator generating aliasing components due to exceeding the audio bandwidth at the stereo generator inputs.
These extra L-R modulator components will extend DOWN through the 19 hKz pilot (further contaminating it even more) and into the upper regions of the discrete left and right audio. The L-R modulator aliasing images caused by this extra harmonic content will also extend up beyond the upper 53 kHz limit of the L-R subcarrier, significantly polluting any subcarriers you may have with the rhythmic crashes of HF content on the main channel.
Not a pretty picture. Again, Card Zero prevents this while gaining some extra loudness. It doesn't sound as clean on the high end as a stock 8100 card 8/9 clipper alone, but there is no free lunch either way with this really old technology when more loudness is needed.
Just thought I should point out the rest of the story here...
-Cornelius
M
menotti1
Guest
cgould, you are soooooo correct and if Mr Orban chimed in,he would agree.Folks this is old technology..now pardon me while i get in my 56 desoto and go to the store...ha...Man this Omnia 6 ex sounds so great.i tweaked in a real sweet spot.i'm done stick a fork in me..Geaux LSU my alma mater,beat alabama in just a NICK of time;;heeeeeeeee
Cornelius,
That is why i set the safety clippers to the same level as the overshoot corrector!
As standard the safety clipper are set approx -1db from the overshoot corrector,so my 8100a/xt2's safety clippers only clip the peaks that the overshoot corrector misses(or adds).
I think this is a favorable trade off,and of course has exactly the same loudness as using card 0.
I have the card 0,but prefer to not use it.
In my own experience,all my other upgrades have made a huge difference,like better detail and lower distortion.
That is why i set the safety clippers to the same level as the overshoot corrector!
As standard the safety clipper are set approx -1db from the overshoot corrector,so my 8100a/xt2's safety clippers only clip the peaks that the overshoot corrector misses(or adds).
I think this is a favorable trade off,and of course has exactly the same loudness as using card 0.
I have the card 0,but prefer to not use it.
In my own experience,all my other upgrades have made a huge difference,like better detail and lower distortion.
BROADCAST said:
Right...and this mod makes perfect sense as you are tweaking things so that the safety clippers are LESS active than they are stock. This also reduces the amount of "out of band" stuff being fed into the Stereo Generator card.
I've re-chipped Optimods with better op-amps in the good 'ol days, and it does make a difference. One has to be careful as there are very few power supply bypass caps on the op-amp supply rails, and no HF rolloff caps across any of the feedback resistors on the op-amp circuits. Works fine for TLO-72's, but can make life a bit tricky on really high slew rate op-amps...but I'm sure you know that too!
Been busy deep in DSP code lately, and I tell you...as a designer, I'd rather jump in front of a bus if it meant going back to the breadboard and soldering iron days!!!! In DSP, we're only limited by the laws of physics, and our imaginations!
Or in my case....CPU muscle power on my development PC....
Can do in one day what it took 3 months to do with soldering irons, protoboards, etc.
-Cornelius
All I ask is that you TRY THE MOD before criticizing it. In theory, there will be an increase in trash in the pilot region. However, the increase in drive to the safety clippers is pretty modest...on the order of an extra 1-2db. Like anything, if you drive it excessively hard, it will sound like garbage. The beauty of this is that you can have great loudness while NOT generating audible distortion by going easy on the XT2's compression (2-3db sounds nice) and adjusting the clipping to taste. If you can hear distortion with these mods, you have far better ears than I. This will not work with the Zero card....the distortion will be intolerable (I have info on removing the Zero card...something I've done 3 times & counting). But from one who has done this many times to several who have never tried it, please try it first. If you want to critique it after you've heard it, feel free...
BobOnTheJob said:
I have tried all kinds of mods on the 8100/A over my 20 years of doing processing. At one point, I had 8 8100/A's in my basement, all of which I modified various cards to see "what would happen if". I've also studied that design backwards and forwards, and know what's in the little black boxes, etc. so I'm not talking outta my booty here.
I may be rusty on the particulars of some of the component locations as it's been a few years since I've moved beyond the box -- but I do totally understand the design limitations and such!
I have also designed many of my own processors over the years, and I can tell ya, whacking away at a couple of uncompensated diodes *after* pre-emphasis, AFTER the 15 kHz lowpass filters, right before the inputs of a stereo generator is gonna give you aliasing distortion, and contamination of your FM composite baseband...period.
Yes, totally removing the attenuator pots from around the safety clippers will get you really loud, but at a pretty hard price. It may work for you right now, but anyone with any FM coverage challenges (or paid SCA subcarrier clients) will pay dearly from all the trash that will be on the composite baseband.
Like I said, it's not a free lunch. Every mod had its tradeoff, and Mr. Orban had his reasons for stopping just short of many of these mods.
Think about it for a second. Would he intentionally design a product that folks have tried to unseat from the throne it's been on to be crippled on purpose? Why would Orban *not* want to get another 3dB of loudness from his box, and install attenuators on the safety clippers?
Just pointing out things people should keep in mind before cutting traces out of the 8100! The rest is up to everyone else to decide!
-Cornelius
When using the standard psu,you are very limited in using different opamps.
I replace the transformer and fit a square heat spreader underneath both 2n3055's on the back,and also fit a heatsink in between!(i have a pic of this).
Then after a couple of resistor and fuse changes it is good for double the current!
I can now use opa2134's in all the 072 places(8100a and xt2),and both units have led meters!
As i had 2 lots of 8100a/xt2's i calibrated both before i modified one set(they both sounded the same before modification).
After modifying the led metered 8100a/xt2,the difference was supprising! ;D
Also i have unpotted all the modules in the 8100a/xt2 and know the circuitry well,but there are a few good mods to be had!
The 8100a/xt2 is superbly designed when you think back to when it was made!
I replace the transformer and fit a square heat spreader underneath both 2n3055's on the back,and also fit a heatsink in between!(i have a pic of this).
Then after a couple of resistor and fuse changes it is good for double the current!
I can now use opa2134's in all the 072 places(8100a and xt2),and both units have led meters!
As i had 2 lots of 8100a/xt2's i calibrated both before i modified one set(they both sounded the same before modification).
After modifying the led metered 8100a/xt2,the difference was supprising! ;D
Also i have unpotted all the modules in the 8100a/xt2 and know the circuitry well,but there are a few good mods to be had!
The 8100a/xt2 is superbly designed when you think back to when it was made!
BROADCAST said:
Yup, Broadcast! All true!
Analog design is a tradeoff of cost vs. return. The 8100/a could have had more designed into it than it had, but the cost of building it vs. what they would get back in sales would have been the limiting factor...so a lot of extra stuff is left out, and only the bare minimum needed for good performance on the design as it was schemed up in the late 70's was left.
It is truely is a classic design, and an amazing feat by Orban no doubt about that! I wish I could be a fly on the wall when all those "aha" ideas were popping into his head...
This is the reason why so many STILL talk about and study that design to this day! Orban raised the bar so high that it took a new generation of designers with DSP code to top it! That's something you can't take away from him!
-Cornelius
And as we know the early dsp boxes were not even as good as the 8100a/xt2!
Sitting next the my 8100a/xt2 is the 8200!
The trouble is,i can get my modified 8100a/xt2 louder than the 8200,for the same perceived distortion on midrange :
I would expect the 8200 to be cleaner on mpx spectrum though,but the midrange stays more forward on the 8100a/xt2,probably due the 6 band limiters,whilst the 8200's band 3 has a wide frequency range!
Also another simple but very effective design.............the 222a,say no more!
Sitting next the my 8100a/xt2 is the 8200!
The trouble is,i can get my modified 8100a/xt2 louder than the 8200,for the same perceived distortion on midrange :
I would expect the 8200 to be cleaner on mpx spectrum though,but the midrange stays more forward on the 8100a/xt2,probably due the 6 band limiters,whilst the 8200's band 3 has a wide frequency range!
Also another simple but very effective design.............the 222a,say no more!
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