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Old 8th April 2010, 11:26 AM   #101
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Quote:
Originally Posted by Jan Dupont View Post
tief;
That was back in 2003
I don't recall the models, but you can do a search on their Legacy amp pages
I see. Perhaps you recall the Crown-specific term for their circlotron amp devices and the years of manufacturing. I have found only this:
Crown Amplifier Technical Information
Discontinued Amplifier Products

Or was it maybe a quasi compl. topology like this:
http://www.crownaudio.com/pdf/legacy..._schematic.pdf
Crest Audio : Schematics
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Old 8th April 2010, 11:44 AM   #102
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Sorry tief but I'm so away from that issue now, that I had cleared my RAM for other projects
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Old 8th April 2010, 12:36 PM   #103
ilimzn is offline ilimzn  Croatia
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It is possible to implement this topology using many types of output devices. For instance, Atmashpere uses it for their triode OTL amps.
James Bongiorno addition tot he knowledge pool regarding this topology is his patent that demonstrates how to automatically bias the output stage if BJTs are used in it. That being said, GENERALLY the bias for the output stages equals the voltage between the load midpoint and the driver ground. With this in mind it's possible to implement proper bias for any type of output device. For a MOSFET, a Vgs multiplier fed with a constant current would do the trick.
SITs and tubes are a bit more tricky. In theory, you need to compensate for power supply voltage variation, as both act as triodes - anode/drain voltage variations translate to anode/drain current variations at constant grid/gate voltage. If both output halves devices were perfectly equal, the variations would cancel out differentially. In reality, the differences translate into generation fo intermodulation components with the power supply ripple. This is somewhat less critical with tubes than with VFET/SITs just becasue tubes used generally have lower mu and gm. SITs also require the bias voltage to be present before the output stage power supply voltages appear. With tubes thi is mostly automatically true if the bias voltage is generated using semiconductor rectifiers (as indeed happens in 99.9% of cases) so it's present before the tubes warm up enough to conduct. With VFETs, worng power sequencing means dead VFETs, as simple as that.
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Old 23rd January 2011, 06:57 AM   #104
braxus is offline braxus  Canada
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SUMO Power Amp

Post 39 and 40 are what I'm interested in. I have a Sumo 9+ and was wondering if anyone replaced the stock op amp with what was suggested in posts 39 or 40? If so what were your results?

Also what other things would you do to update the stock amp? Someone else suggested this:

"There are a pair of low quality 0.1F coupling caps per channel, replacing with a higher quality cap will really help. I would also consider adding a 22F bypass cap on top of each of the four 10,000F main filter caps."

Are these mods sound advice for a stock 9+ amp?
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Old 25th January 2011, 12:59 AM   #105
braxus is offline braxus  Canada
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I posed an a set of questions to a tech who rebuilds these amps and asked him some questions. This is how it went:

Question- "The stock fan is pretty quiet, but may be worth while to replace (it's old). It's a 120VAC type with a 390R series resistor."

His Response- The fans can be noisy but a bigger problem is that with time and heat they fail and the amp will run too hot if this is the case. The Nine Plus actually runs quieter than the original Nine. If it is getting noisy it is wearing out.

Q- "The Sumo is a push-pull class A amplifier with sliding bias, it increases its bias as the output increases. James Bongiorno received a patent for this circuit, and of course others have now built similar sliding bias circuits."

R- This is just a description of the biasing circuit which is technically not really correct as it is a true Class-a design. The point is that it is Class-A, it draws more current than a normal amp from the wall, runs warmer and it sounds good.

Q- "The opamp is an LM353(selected), and pretty long-in-the-tooth by todays standards. An OPA2604 is a drop-in replacement, and much better sounding. Others could be used, but they would have to be selected for high-voltage operation. "

R- The opamp can be replaced, although I get excellent results with the stock opamp. I'm listening to a rebuilt Nine right now and it sound quite good with the LM353.

Q- "There are a pair of low quality 0.1F coupling caps per channel, replacing with a higher quality cap will really help. I would also consider adding a 22F bypass cap on top of each of the four 10,000F main filter caps. "

R- See the Sumo Nine board pictures on my site in the Gallery. There are around 10 ceramic disc capacitors per channel that inhibit the sound in there own way as there is a solid improvement in purity of the sound when they are replaced. A better approach if you are going through the trouble to add 22uf bypass capacitors to the power supply filter caps, since the power supply PCB has to be removed to get at the connections, is to reolace the main filters with the better sounding/high temperature rated caps available today. Sonically better than any bypass.

Q-"Does what he suggest sound like good advice for the 9 amp? Would you have any comments on mods to this amp yourself?"

R- You can see pictures of what I do on mysite GASaudio.net. Listed by level of improvement I'd replace the disc caps, next the speaker terminals are crap and always worn out and making poor connection, input connectors (some versions are worse than others), the main power supply filters, then replacing the resistors with 1/2 watt low noise metal film. Hopefully I have answered your questions. Please feel free to ask if any others come up. Mike

So does what he said sound easy enough to do and is it better then what was suggested before in my last post? Do his mods make good sense?
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Old 24th June 2011, 09:05 AM   #106
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hi, i just bought this amp today from a dealer and it sounds pretty good. it's satisfactory, in fact. it's tad veiled though which i hope the op-amp swap will improve.

what kind of pcb does it use, btw? looks like antiquate fiberglass. do anyone know the technical name for the material?

Last edited by PreSapian; 24th June 2011 at 09:28 AM.
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Old 24th June 2011, 10:08 AM   #107
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Quote:
Originally Posted by Jan Dupont View Post
Some CROWN amps has the same...
Quote:
Originally Posted by Jan Dupont View Post
..........Interesting. Please let me know some models - thank you.........
tief;
That was back in 2003. I don't recall the models, but you can do a search on their Legacy amp pages.
................I see. Perhaps you recall the Crown-specific term for their circlotron amp devices and the years of manufacturing..............
Quote:
Originally Posted by Jan Dupont View Post
Sorry tief but I'm so away from that issue now, that I had cleared my RAM for other projects
A technican by a Crown service center tell me, that Crown never used the circlotron topology

Last edited by tiefbassuebertr; 24th June 2011 at 10:17 AM.
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Old 26th June 2011, 08:23 AM   #108
jackies is offline jackies  United States
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So anyway, I want to upgrade the opamp in mine too, and was wondering, does it have to be a fet-input opamp? There's this awesome LME49860 that takes +/-22v...
Could I just put it in SUMO NINE PLUS?
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Old 26th June 2011, 09:38 AM   #109
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Quote:
Originally Posted by jackies View Post
So anyway, I want to upgrade the opamp in mine too, and was wondering, does it have to be a fet-input opamp? There's this awesome LME49860 that takes +/-22v...
Could I just put it in SUMO NINE PLUS?
Not without the risk of the occur of unwanted oscillation effects. I guess, several steps of re-design by compensation are necessary for optimizing the roll-off in the upper frequency aera respective the square-wave behaviour. The LME49860 (also 2xAD797) are much more better than the model "LF421CN".
For Dual-AD797 OP-AMP order ebay item No 220677386848
For additional redesign ask Mr. Scott Wurcer (diyaudiomember) - go to
http://www.diyaudio.com/forums/membe...tt-wurcer.html

Also a discrete OP-AMP solution could be very interesting.
This would be much more easy for me, because I can investigate the behaviour for stability on the simulation aera by CAD software (not really possible by integrated OP-Amps).
Here a thread about this:
AD797 discrete clone - comparison of seven variations
In the attachement the schema from the death links by post #2 and post #21
Attached Files
File Type: pdf Sumo Nine Plus Schema LF421CN.pdf (70.7 KB, 206 views)

Last edited by tiefbassuebertr; 26th June 2011 at 09:44 AM.
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Old 26th June 2011, 10:44 AM   #110
banat is offline banat  Serbia
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Interesting simple design of A class Hybrid Circlotron (PPP) by Audiodesign : Hybrid Circlotron Amplifier with only 3 components on the signal path
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