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What's the difference between Trident 80 & 80B ?
Old 14th June 2006
  #31
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I told ya he knew more than me on this.
Aaron Householter
www.studio1117.us
Old 15th June 2006
  #32
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Thanks for the tips, Jim. Maybe someday I'll understand what you wrote. heh What would that complicated process accomplish sonically?



So I had a conversation with Brian Roth about changing the opamps to the LF351's instead of the stock TL071's I have. He says the schematics are the same for both, and that technically they shouldn't sound different. So, my question for all of you is, do they really sound so different? And is it worth replacing all 600+ opamps? Also, he recommended not replacing the NE5534 on the mix amp of each module because of something to do with power consumption.

He looked up the various manufacturers and noticed that several of the companies that used to make the LF351's have discontinued their lines. Does the manufacturer matter, or is it just having those instead of the TL071's.

I'm thinking I'm going to try replacing them on one module and A/B against the stock opamps on another module. I'll post some results here when I get a chance.
Old 15th June 2006
  #33
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Re. Philbin's post....

I have used LF-351's in place of TL071's (and vice versa) without any problems since they have the same pinouts and similar overall specs, but I never printed out both spec sheets and set them side by side to see what the different "nuances" between the two are. I do know the power consumption is essentially the same between the two.

I had suggested to Philbin to leave the 5534 summing amp alone since a "hotrod" chip in that circuit position might do goofy stuff, like oscillate.

National *has* discontinued the LF351 (but not the dual LF353). Mouser shows LF351 stock from Fairchild and STM as I recall.

I've always wondered about "second sourced" chips...are they the exact same die layout, or does each manufacturer do their own thing? I've heard rumors that 5534's from different foundries measure/sound differently.

Bri
Old 15th June 2006
  #34
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Phelbin, Lotsa info flown on Trident upgrades in this thread:
https://www.gearslutz.com/board/showt...rident+upgrade
HTH
Old 15th June 2006
  #35
Quote:
Originally Posted by phelbin
Thanks for the tips, Jim. Maybe someday I'll understand what you wrote. heh What would that complicated process accomplish sonically?



So I had a conversation with Brian Roth about changing the opamps to the LF351's instead of the stock TL071's I have. He says the schematics are the same for both, and that technically they shouldn't sound different. So, my question for all of you is, do they really sound so different? And is it worth replacing all 600+ opamps? Also, he recommended not replacing the NE5534 on the mix amp of each module because of something to do with power consumption.

He looked up the various manufacturers and noticed that several of the companies that used to make the LF351's have discontinued their lines. Does the manufacturer matter, or is it just having those instead of the TL071's.

I'm thinking I'm going to try replacing them on one module and A/B against the stock opamps on another module. I'll post some results here when I get a chance.
That mic pre mod is to lower noise and have consistant dynamic response at all gain positions, something the stock design doesn't do. When I first sent this schematic over to Bill Whitlock at Jensen transformers, he said it was the worst design of a transformer coupled mic pre he'd ever seen.

Forget the LF351's, too close to the 071's to make enough difference. Try the LT1357 in the stereo summing cards in place of the 5534, much more gain bandwidth, low noise, high open loop gain and very fast slew rate of 600 v/us.

Jim Williams
Audio Upgrades
Old 16th June 2006
  #36
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Quote:
Originally Posted by Jim Williams
Forget the LF351's, too close to the 071's to make enough difference. Try the LT1357 in the stereo summing cards in place of the 5534, much more gain bandwidth, low noise, high open loop gain and very fast slew rate of 600 v/us.

My 2-bus has AD829 opamps instead of 5534's. Any comments about those?
Old 17th June 2006
  #37
Quote:
Originally Posted by phelbin
My 2-bus has AD829 opamps instead of 5534's. Any comments about those?
Yes. Pull them. If there's not a 50pf cap from pin 5 to ground , it's in an unstable state. The AD829 adds a sandpaper scratch to the top end, not pleasant. It's also probably not stable due to it's very high bandwidth. Capacitive loading on the busses will make these wideband opamps unstable. Get a pair of LT1357's from digi key. Remove the input coupling caps on the buss board and drop in a pair of Panasonic ferrite beads. If you use a second 1357 in the inverter stage, you can eliminate the output coupling caps.

Jim Williams
Audio Upgrades
Old 17th June 2006
  #38
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With respect, I think Jim may have things the wrong way round..... on the old 80B micamp, the lower loading on the transformer as you turned the gain up, gave the effect of increased damping and some HF cut with some mics. Yes the design was a bit of a 'pigs ear' but as Malcolm once told me, it was designed for rock and roll and the mic amps worked fine with high levels hammering in to them!

The original EQ section (designed by John) is quite conventional, but the way it was laid out, it sounded good. True it used early versions of the TL071 but this did not seriously degrade the noise performance and I doubt that any improvement could be gained by changing them; short of a complete redesign.
Old 18th June 2006
  #39
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Jim, you seemed to imply that the summing amp needs to be unity gain stable. Perhaps I am all MIXED <g> up here....

Looking at the 80B manual, they used 12K buildout resistors onto the stereo bus. All buildouts are either driven from an opamp or are grounded if unused. The feedback R in the summer is a 4K7, which indeed would require the summing amp to be unity gain stable IF only a few inputs were connected to the bus.

However, at all times, there will be 12K divided by 32 sources in parallel, or 375 Ohms onto the bus. Hence, the summer will be operating with an "equivalent" gain of 4K7/375...gain of approx. 12.5 (approx 22 dB).

Of course, any given input to bus output will pass through the summer with a net LOSS of approx 8 dB. Yet, with all of the paralled R's onto the bus at all times, the closed loop gain of the summer will be 22 dB.

Or am I missing something....

Yes, I realize there are many other factors at play here as well, with an opamp like the AD829 (not that I'm suggesting it!). One good attribute of the 829 is that it's open loop gain is constant at 100 dB-ish out to 10 kHz. "Daylight" small-signal response is not a good thing....

Just food for discussions!

Bri
Old 19th June 2006
  #40
Noise gain and loop gain will go up with increased inputs. The opamp must be unity gain stable due to the feedback phase compensation caps. These return the opamp gain to unity at high frequencies. The caps must be there or the added capacitance on the inputs will cause severe ringing at the least and full on oscillations at the worst. Plus, having 10 mhz or more bandwidth amplified on the mix buss is also going to add to HF noise, possible EMI, etc. unless it's filtered out.

If you think about it, that inverting input of a opamp has a potential gain of 10,000 or more and this travels down the buss board being gain teminated by remote resistors. It's sort of like cranking the Marshall 100 watt to 11 and throwing the cord on the floor.

Best part about that old Trident stuff is the single opamp usage. It leaves lots of choices for improvements, some of which could have never been imagined when this stuff was designed.

Solder on...

Jim Williams
Audio Upgrades
Old 19th June 2006
  #41
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I must have had a brain phart <g>, getting noice gain mixed into this discussion! Of course, any capacitance across the feedback R will reduce the inverter's gain to zero at some high frequency which would be the same as a unity gain non-inverter (output pin tied directly to inverting input).

Bri
Old 19th June 2006
  #42
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Old 19th June 2006
  #43
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So what should I do about the opamps on my mix bus?
Old 19th June 2006
  #44
Call 1-800-digikey and order 4 LT1357CN8's. Plug them into the sockets on the mix pcb. Do the cap mods with the ferrite bead. You will like it. It will clean up large mixes which tend to fall apart due to too many inputs requiring too much opamp loop gain. The 5534 gets you 60 db at 10k hz, the LT will give you 85 to 90 db at 10k, much less distortion with a large mix.

Jim Williams
Audio Upgrades
Old 20th June 2006
  #45
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How's an LT1468 compare in the same location? A bit more difficult to stabilize?
Old 20th June 2006
  #46
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Series 80 vs 80B

Quote:
Originally Posted by Jim Williams
Call 1-800-digikey and order 4 LT1357CN8's. Plug them into the sockets on the mix pcb. Do the cap mods with the ferrite bead. You will like it. It will clean up large mixes which tend to fall apart due to too many inputs requiring too much opamp loop gain. The 5534 gets you 60 db at 10k hz, the LT will give you 85 to 90 db at 10k, much less distortion with a large mix.

Jim Williams
Audio Upgrades
Jim: Please confirm that you are recommending to replace not only the 5534s but also the TL071s on the mix daughter board with 1357s. Also, why are the output coupling caps unnecessary when the 2nd chip is replaced with the 1357s?

Thanks
Geoff
Old 20th June 2006
  #47
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Wow! This thread sure got hijacked!
Old 20th June 2006
  #48
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Quote:
Originally Posted by absrec
Wow! This thread sure got hijacked!
Yes...and it went this direction at a very convenient time for me. heh


Quote:
Originally Posted by Jim Williams
Plug them into the sockets on the mix pcb. Do the cap mods with the ferrite bead. You will like it.
So, I replace the capacitor with a ferrite bead? And which ones am I replacing?
Old 20th June 2006
  #49
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Interestingly, the LT1357 spec sheet I downloaded in the past few days shows open loop gain of around 65 dB (+/-) at 10 kHz, almost identical to a NE553x spec sheet I also have.

Bri
Old 20th June 2006
  #50
Replace C109 and C114 with the ferrite beads. Use a 47pf feedback cap, an NPO mono ceramic. If you use a second LT1357 in IC29, the output blocking cap, C113/118 can be bypassed with wire. Also try the 1468, I find the 1357 to have much greater speed and openess.

The Bode plot of the 1357 shows 85 db gain at 10k hz. Perhaps the plot was missed by an octave reading it. They mark it in power levels, not 10k, 100k etc.

Jim Williams
Audio Upgrades
Old 20th June 2006
  #51
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Series 80 vs 80B

Don't blast me but I'd like to further hijack the post. Can anyone provide me with or point me to the mods required to switch the monitor inputs in and out of the mix buss. My console was never modded in this manner and I'd love to have this flexibilty.

Thanks
Geoff
Old 20th June 2006
  #52
Quote:
Originally Posted by retrograde
Jim: Please confirm that you are recommending to replace not only the 5534s but also the TL071s on the mix daughter board with 1357s. Also, why are the output coupling caps unnecessary when the 2nd chip is replaced with the 1357s?

Thanks
Geoff
The LT1357's are a precision device with very low offset voltage. The output offset voltage will be a few millivolts so one could just short out the output caps, they are no longer necessary. Just about any single package opamp will work in that space, remember to put a 10 pf mono ceramic NPO cap on the second stage feedback loop to cancel ringing. If other opamps are auditioned, leave those output caps in. I've also used National LM6171's in that second position, but the output caps were needed.

Jim Williams
Audio Upgrades
Old 20th June 2006
  #53
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Tridents

Quote:
Originally Posted by Jim Williams
The LT1357's are a precision device with very low offset voltage. The output offset voltage will be a few millivolts so one could just short out the output caps, they are no longer necessary. Just about any single package opamp will work in that space, remember to put a 10 pf mono ceramic NPO cap on the second stage feedback loop to cancel ringing. If other opamps are auditioned, leave those output caps in. I've also used National LM6171's in that second position, but the output caps were needed.

Jim Williams
Audio Upgrades
Jim: Thanks for all olf your help.

Geoff
Old 21st June 2006
  #54
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Jim, I was referring to the center graph at the bottom of page six from this data sheet:

http://www.linear.com/pc/downloadDoc...22,P1114,D1899

Still looks like 65 dB open loop gain at 10 kHz for an inverter with 15V rails.

But, I imagine it's great opamp.

Bri
Old 21st June 2006
  #55
Quote:
Originally Posted by brianroth
Jim, I was referring to the center graph at the bottom of page six from this data sheet:

http://www.linear.com/pc/downloadDoc...22,P1114,D1899

Still looks like 65 dB open loop gain at 10 kHz for an inverter with 15V rails.

But, I imagine it's great opamp.

Bri
Looks like I missed that one. Somehow I remember when it came out in 93 it was higher and the graphs didn't show harmonic distortion, perhaps the data sheets were amended since then. Still, a great part.

Jim Williams
Audio Upgrades
Old 23rd June 2006
  #56
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I need to print out both spec sheets so I can set them side-by-side (easier than trying to flip between PDFs on the computer screen! <g>).

From this:

http://www.analog.com/UploadedFiles/...496AD829_g.pdf

I do see some interesting characteristics. For one thing, the input noise specs are quite decent.

At the bottom of page 10, left column, they claim "The AD829 is stable with no external compensation for noise gains greater than 20." But, from my calcs on an 80B (32 each 12K bus resistors and a 4k7 feedback R around the summer, I come up with a noise gain of only 12.5 which indicates some external compensation would be necessary.

**IF** that is a correct assumption, then figure 10 at the top of page 7, which indicates an open loop gain of 100 dB out to almost 10 kHz with no comp. cap, would have to be scaled back by some unknown amount due to that capacitor...I think!

But, it sure looks like a "live hand gernade" unless tons of care is taken to ensure it's perfectly stable in a particular circuit...

Bri
Old 23rd June 2006
  #57
Quote:
Originally Posted by brianroth
I need to print out both spec sheets so I can set them side-by-side (easier than trying to flip between PDFs on the computer screen! <g>).

From this:

http://www.analog.com/UploadedFiles/...496AD829_g.pdf

I do see some interesting characteristics. For one thing, the input noise specs are quite decent.

At the bottom of page 10, left column, they claim "The AD829 is stable with no external compensation for noise gains greater than 20." But, from my calcs on an 80B (32 each 12K bus resistors and a 4k7 feedback R around the summer, I come up with a noise gain of only 12.5 which indicates some external compensation would be necessary.

**IF** that is a correct assumption, then figure 10 at the top of page 7, which indicates an open loop gain of 100 dB out to almost 10 kHz with no comp. cap, would have to be scaled back by some unknown amount due to that capacitor...I think!

But, it sure looks like a "live hand gernade" unless tons of care is taken to ensure it's perfectly stable in a particular circuit...

Bri
It's a hand grenade. Noise gain could be added extrenally by the use of a small resistor between the 2 input pins. It still doesn't solve the unity gain config at high frequencies due to the feedback cap. This opamp is tempermental with capacitive loading, on either the inputs or output. Add the combined capacitance of the buss board with that 290 mhz bandwidth and trouble is coming.

I've not found a IC opamp with greater than 25 mhz gain bandwidth that is stable in this inverter/summer situation. This is why I stop at the LT1357. I have grounded base discrete summing amp pcb's I've installed in many consoles. They originally came with AD829's on them with the 50 pf unity gain comp cap. The compensation cap does severly lower slew rate to 60 v/us. These cards no longer use the 829 due to sonic problems with the part as many better choices are available. It currently uses an opamp with 175 mhz bandwidth, completely stable in this topology.

Jim Williams
Audio Upgrades
Old 23rd June 2006
  #58
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Hello Brian Roth! Long time no see.

20 years ago, who would have predicted we would be discussing Series 80 mods on the (then non-existent) internet in 2006? Freaky.
Old 23rd June 2006
  #59
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Quote:
Originally Posted by absrec
80B used Audiofad faders which are supposedly some of the best faders money can no longer buy. They started using Alps in the 65,70,75 and 24 series. P&Gs were used on the short monitor faders.
For the record, the Trident Series 80/80B,70 and Trimix used Audiofad faders.

The Trident Series 65, 75 and 24 came later, used Alps faders and were transformerless consoles.

Old 24th June 2006
  #60
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Quote:
Originally Posted by Jim Williams
It's a hand grenade. Noise gain could be added extrenally by the use of a small resistor between the 2 input pins. It still doesn't solve the unity gain config at high frequencies due to the feedback cap. This opamp is tempermental with capacitive loading, on either the inputs or output. Add the combined capacitance of the buss board with that 290 mhz bandwidth and trouble is coming.

Jim Williams
Audio Upgrades
Thanks for the hands-on info, Jim! I have never messed with the 829 myself, and was a bit spooked by it.

I wish I was closer to Philbin's studio so I could take some field measurements of his 80B with the 829 mod.

Bri
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