| EE_Mark |
I built 15 of Daniel Meyer's Tigersaurus' about 30 years ago and I still have them. Now I'm building up a couple of the Slone 400 watt opti-mos amps. Has anyone here built them? I'm curious to get some feedback on them but since I'm still in the fabrication process I hope the feedback will be good (but I want any feedback regardless of whether it's good or bad).
Thanks! |
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| joan2 |
i still have about 10 pcs pcb with parts stuffed in except for the 40409.40410 rca trannies....
this amp has good low frequency performance, but not as good as the leach amps in the mids ang highs... |
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| Christer |
Search the forum. I know at least Rarkov built a pair of Optimos
and there is a thread about them. He seemed to like it at lot. |
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| 5th element |
Rarkov built the 200 watt optimos amp not the 400, however I doubt there is much difference between the two designs apart from more power. I have built two of Slones amp designs, both from the high power audio amplifier construction manual (is that right???). These were the 80watt, very low distortion amp, and the 200 watt PA amp. (Designs 11.4 and 11.8) Both of them sound brilliant, I dont really have any comparison for them as regards to other DIY amps or many consumers amps for that matter. But I can say tha both amps sound significantly better then a Quad77 integrated (£700). So much so that my parents asked me to build them a pair of the 200 watts with a matching pre amp, to replace their Quad.
Both are very smooth, but not at the expense of detail, on the contrary they are very detailed and transparent, with loadsa umph where its required. They never become harsh and fatiging, if the sound you get hurts its not the amps, unless ofcourse you cause them to clip, but thats another story. I would even say they have tube like trebble, but having never heard a tube amp this would be a bit of meaning less comparison! But all the "magical" tube sound I have read about in hifi mags, the decription matches rather well to what I hear.
The 200 watts have increadibly tight and controlled, tuneful bass. This is directly driving a peerless 850146 in a sealed cabinet of about 66 litres. The 200 watt is better in the bass then the 80 watt and I cant really comment on the mids and highs as I havnt really done any critical listening comparing the two amps. Thats kinda hard when your main speakers are three way fully active so you cant swap and change amps as you please, as you need them all to get a good sound! I will be doing a comparison however probably this weekend if I dont have too much work to do.
Bottom line is, I dont think you will have any problems with Slone amps, most of the DIY amps available are high quality designs which will give expensive consumer amps a good run for their money. Its probably all personal taste and I like the sound of the Slone amps, build one and I dont think you will be dissapointed, I have not been yet. |
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| Christer |
| quote: | Originally posted by 5th element
Rarkov built the 200 watt optimos amp not the 400, however I doubt there is much difference between the two designs apart from more power. |
AFAIK there are no different versions of it. You just add more
output devices and increase the rail voltage. It is designed to
be modular in that sense. Might affect the sound, though. |
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| Rarkov |
Hi,
Both Christer and 5th Element are correct. I built the 160W OptiMOS but raised the rail voltages to achieve 180-200W. I will post some pics on my website before too long. I absolutley love these monoblocks. A couple of things that I've noticed is they are very resistant to power supplies...I have my PSU next to my amp PCB with no sheilding and there is not a hint of hum through the speakers. However, the chassis hums somethimes, but that is due to a lack of inrush protection...which cannot be blamed on the excellent OptiMOS.
200W produces amazing control in the bass and gives me exactly the signiture of sound that I'm after. It's perfectly balanced! :nod:
The 400W version is said to exhibit the 200W version's "same outstanding performance results". Randy Slone goes on to mention 6 bullet points of modifications. This require
Resistor changes
New rail voltages (+-85V)
New fuses (7A)
New MosFETs (SemeLab's Double-die BUZ901CDP & BUZ905DP)
New Heatsinks (0.2C/W)
The number of output devices stay the same (4 per channel) but the heat dissipation seems collosal for a Class B amp!
I would think you could build a 250-300W amp with little or no modifications to the circuit. It is very rugged. However, I would suggest modelling in PSpice and checking that no components exceed their rated specification.
Good luck and let us know how it goes! You'll be very pleased!
Thanks,
Gaz |
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| MichaelB |
Hi,
I've contacted Mr. Slone two weeks ago to get some answers on parts used in the OptiMOS design. His extreme friendly answer had revised schematics for the commercial versions (the ZUS-Amplifier) of the OptiMOS, both 200W/400W and a new 800W Version attached.
For obvious reasons I can't post them in this forum.
EE_Mark: maybe you should contact him directly? He seems to be a very nice and helpfull guy. |
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| EternaLightWith |
ZUS? Is that what he calls it? Or are you r referring to something else?
David |
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| EE_Mark |
| quote: | Originally posted by MichaelB
Hi,
I've contacted Mr. Slone two weeks ago to get some answers on parts used in the OptiMOS design. His extreme friendly answer had revised schematics for the commercial versions (the ZUS-Amplifier) of the OptiMOS, both 200W/400W and a new 800W Version attached.
For obvious reasons I can't post them in this forum.
EE_Mark: maybe you should contact him directly? He seems to be a very nice and helpfull guy. |
I've talked to him on several occasions. Yeah, he's a real nice guy. I don't have any questions for him - I was just wondering if anyone here had built one of his amps and how they liked it. After reading the responses I'm more excited than ever to get mine completed! |
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| MichaelB |
ZUS Audio Inc. is the company selling the Amplifiers.
See http://www.zusaudio.com but do not expect it to be a very exciting site... :apathic: |
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| sam9 |
I've built a couple of his amps. Both were of the moderate power variety (125W or less). Single long tailed pair topology which I take to be Slone's variation on Self's Blamless amp theme. As a learning experience, I laid out the pcb's myself. It took me three tries and lots of learning. (I know know a bit more than before about parasitic oscillations and how to avoid them.) If you were to use Slone's PCB layout, I would not expect you to have the same problems (ore lean as much about parasitics) as I did.
I built these as parts of secondary systems (bed room and office). This was a mistake as I now prefer those two rooms for listen rather than my living room where amplifier duty is served by a 20+ year old Carver M400. Next major project is obviously an amp for the living room.
I'm leary to asign adjectives to the sound from an amplifier partly because of the over-blown prose one can read in high-end publications. Nonetheless, there is something about Slone's amps . . . . I guess they just sound real good. |
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| Brad Kizer |
I recently finished a pair of Opti-Mos boards and gave them a listen. In a word, OUTSTANDING!!! At least for my ears anyway. Because sound is subjective to the listener I won't tell you to rush out and build one but quite simply it is the best amp "my" ears have ever heard. Audio has been a hobby of mine for over 30 years and I've owned a listened to quite few amps. Briefly what I heard was the smoothness of a tube through the midrange and top end with the punch of solid state on the bottom.
If you like big power he has a new design coming out called the Totem Pole. 800 wpc. :bigeyes: Also a new preamp is in the works.
Hope this helps.
Brad |
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| 5th element |
Yep it seem unanimous then Slones amps ROCK!
:D :D :D :D :D :D :D :D :D :D :D :D :D :D :D :D : |
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| OPTI-MOS PAT |
| I almost finished his latest and greatest version of his 200 watt Seal electronics/ZUS Modules. I am waiting for his low impedance power supply board. I will post pictures when I receive it. |
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| Nick Walker |
Yep - I built a dual mono version with dual power supplies and my own pcb - it doesn't look as nice as your's under the hood.
I had some problems with oscillation at first and blew an expensive tweeter. Got it to work with some help from Randy.
I also made a few circuit changes of my own. Fab sound now. |
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| OPTI-MOS PAT |
Nick Walker,
What version did you build? These are Sep 03 2003, I would think if there were any problems in earlier versions that it would have been worked out. What was the fix? Do you have any pictures?
Pat. |
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| Nick Walker |
I had some problems with oscillation and hum. The oscillation might have been due to non-Hitachi devices, or using a self etched pcb. I got the MosFets from Rapid Eletronics in the UK but they were described as Hitachi so I don't know.
To elimante the hum I actually went to an extreme of building a dual mono supply with two torriodial transformers and rethinking the grounding and internal wiring. I learnt a lot about this sort of noise in the process and could probably go back to a single 500va 50-0-50 transformer - however given that it sounds superb the motivation to do so is low.
Elimating the oscillation was a lot harder. I tried all sorts of things, some still remain, however the eventual fix was simply to increase the size of R23 & R24 gate ressistors to 1k on the 2sk1058 MOSFETs. This looks unbalanced to me, given the gate resistors on the 2sj162 mosfets are only 470ohm. I've seen another approach which is to add a capacitor to even up the gate capacitances. Examples using a capacitor seem to use a range of values anywhere from 30-300pF. I don't know which is the better approach but would appreciate any advice on this subject.
Here's the link to the circuit that I built, it's actually dated 0ct 2001 and revision 2, the pcb is from his audio projects book.
http://www.sealelectronics.com/kits/images/OPTI1001.pdf
Before arrived at this solution I made some other changes in my hunt for the cause. I stripped out all the protection, converted the softclip VAS cascode bias into a standard zener regulated bias arrangement and changed the NFB take off point.
A few of my component values are also slightly different, e.g. 1000uF for C10 the NFB DC block capacitor, 220pF for C12 & 14 the larger of the miller compensation capacitors. I lowered the mosfet source degen resistors to 0.22 ohm, I read somewhere that lower is better (true or false?) but given that the mosfets appear to be not well matched I should maybe change them back to 0.5 ohm?
I lowered R3 & R14 to 4.7K to increase the zener current flow on the input stage cascodes because I wasn't seeing a stable 24V there.
I recently also increased the input resistance to 22k and have lowered the gain to 23x because my pre-amplifier is putting out quite a high signal.
I have a couple of questions about the circuit that puzzle me, I don't get why the collector resistor on the input stage cascode is 1k on the -ve differential input and 2.7k on the +ve input.
The differential tail currents also seem low to me, i.e. 0.6V/470 = 1.3ma and I'm tempted to lower R6 and R13. Many of the examples in his power amp manual have a higher tail current source of around 4ma or 2ma per leg.
Nick |
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| subwo1 |
| Over 20 years ago, I put together a Tiger amp. It too had a tendency to get a little fuzzy around negative peaks as seen on the scope trace. I think the problem would appear while I was trying to modify it to put out more power. |
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| tcpip |
| quote: | Originally posted by Nick Walker
Elimating the oscillation was a lot harder. I tried all sorts of things, some still remain, however the eventual fix was simply to increase the size of R23 & R24 gate ressistors to 1k on the 2sk1058 MOSFETs. This looks unbalanced to me, given the gate resistors on the 2sj162 mosfets are only 470ohm. I've seen another approach which is to add a capacitor to even up the gate capacitances. Examples using a capacitor seem to use a range of values anywhere from 30-300pF. I don't know which is the better approach but would appreciate any advice on this subject. |
I'm a total novice to amp design, so take all my remarks in that context.
I believe he's already mentioned the asymmetry in his book, where he says that this is needed to counteract the different junction capacitances of the N-channel and P-channel devices.
I bought the infopack of the OptiMOS from him, i.e. construction notes, parts list, PCB layout, etc. There, the parts list says "680Ohm (or 1KOhm)" for these resistors. I found that mention pretty strange, because I'd have thought that anyone wanting to play with the resistors would go in smaller steps, from 680 to 750, to 820, to 1K. Now that you mention your experiences, maybe Randy believes 1K is a good alternate value?
Incidentally, the notes he sent me contains the PCB layout for a single-sided PCB. But many constructors report that they've got a double-sided PCB from him. I guess he had both versions.
What's the heat dissipation like? Do the heatsinks get hot? Isn't it unusual for any Class B amp in "home listening" conditions to get more than slightly warm? Finally, it doesn't matter how big the amp is... for Class B, the dissipation should be proportionate to how much you're outputting to the speakers, shouldn't it?
But I'm really glad so many of you seem to really like the OptiMOS. I too have decided to build the "Fig 11.4 design" (an ultra-low BJT CF OPS design) and the OptiMOS. I'll need all your help once I start.
Did any of you guys use "audiophile grade" components like Caddock or Dale or whatever brand of OPS power resistors and so on? |
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| lucpes |
The OPTI-MOS kit sound sounds very nice :) I bought two kits from him, however at the current moment my amp is totally naked and I'm too lazy to build a case...
First project ever and I had absolutely zero problems... Components include low-esr Xicon caps and god-knows what resistor brand... (wouldn't think it matters). 1xKVA trafo & 30.000uf per supply rail/kit. The 1KVA trafo has the advantage that the rails do not get ANY chance to sag under load. It's stiff as a brick!
Mods: removed input caps* (better imaging!) & reduced gain to accomodate my preamp signal, soldered PS wires (and fuses in their slots :devilr: ) directly to PCB which vastly improved things in the 'bass slam' department.
Heatsinking is enough - does not get at all hot unless you have low sensitivity 4ohm speakers like me and find upsetting the neighbours being fun (never seen it go above let's say... 40C - warm to the touch)
*higly recommended! |
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| lucpes |
http://www.sealelectronics.com/kits/images/OPTI1001.pdf
Checking my limited knowledge: to decrease gain you need to increase R17 to say 470R (and maybe increase R2 to 22k)?
There are 10pf caps on the mosfet gates in the latest OPTI-MOS rev. (oct 2003), c16 has a series 270R added, input diff pair changed to MPSA56, input protection D1&D2 are gone, and some more layout/resistor changes. I only have the schematic on paper, can't post it here...
Did stripping the protection circuit out had any benefic effects? I guess I can find out by myself by just removing q17 & q 18.
I'm also very curious about the mosfet source followers... if you keep the prot circuit in, decreasing source res values to .22 will get you more current capability before the prot kicks in? What if I increase R25 & R32 to 100R? Any other considerations here? The mosfets are not that well matched (Randy said it doesn't matter if the mosfets are matched or not) so I don't know if this would be a good idea... |
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| Nick Walker |
Gain is simply (R20 + R17) / R17
R2 and R20 determine the input resistance and need to be the same value.
I can't say if there's any sonic benefit to removing the protection circuit becuase I took it all out during my process of elimination and have not put it back.
Do you mind describing the other layout and changes you've hinted at, I would really like to know!
Nick |
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| lucpes |
| I'll ask Randy Slone for permission to post the updated schematics here... |
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| tcpip |
| quote: | Originally posted by MichaelB
I've contacted Mr. Slone two weeks ago to get some answers on parts used in the OptiMOS design. His extreme friendly answer had revised schematics for the commercial versions (the ZUS-Amplifier) of the OptiMOS, both 200W/400W and a new 800W Version attached.
For obvious reasons I can't post them in this forum. |
I am not sure that there will be any ethical or legal problem if you discuss the mods here. Randy has published the basic schematic with full explanations in a book and on his Website. And he's freely answered questions posted by any of his readers or builders. I am quite sure he wants to see his insights and experience benefitting us amateur builders. If we were aiming to compete with Zus Audio professionally, it would be a different matter. Even in that case, I feel he's basically a teacher, and he's not interested in being ultra-careful with tips and tweaks to his published circuits. Whatever he does for Zus Audio is not published, and I wouldn't discuss those circuits here even if I had access to them.
Randy is fully aware that professional designers can read his books, copy his circuits, and get into business. I get the feeling that he's not too possessive about that.
Of course, I don't have any authority to speak on his behalf... these are all my opinions.
| quote: | Originally posted by lucpes
I'll ask Randy Slone for permission to post the updated schematics here... |
Yes, please do. I think there's enough interest among us to do a revised OptiMOS, and we're all amateur builders... Randy would probably not mind us discussing it. |
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| lucpes |
Here's the image for quick view, see the bigger sized one in the post above.
Revision 4 OPTI-MOS units
Designer: G. Randy Slone, SEAL Electronics, http://www.sealelectronics.com |
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| millwood |
did anyone see the tantalum caps on the input?
:) |
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| lucpes |
| quote: | Originally posted by millwood
did anyone see the tantalum caps on the input?
:) |
I must confess that it sounds lots better without those. |
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| sam9 |
In another context, I ran some SPICE models where the oppossed zeners (see the ealier Opti-MOS schematics) at the input plus 10uF of input capacitance dominated the noise floor and swamped distortion until you reached fairly high frequencies. Objectively, it didn't mater much since the figure were so low anyway but it just felt irritating that after a certain amount of effort to layout very low noise and distortion design that these two unglamorous items would be the limiting factor. I figured out that increasing the capacitance (or taking the brave step of removing it) and removing the zeners made a big percentage inprovement in THD+N. But to reiterate 50% of very, very little is still very, very little. If you get my drift.
On the new schematic it looks like Slone moved the function of the zeners (over-voltage protection for the input transistors) to the switch diode pair between the bases of the same transistors. I'm not convinced yet that the low noise transistors selected gain you more than you loose by having to add protection components.
It also appears that protection transistors have been added to the VAS. I somehow thought that was only needed with an enhanced beta design. Maybe not . . .
Overall, as Slone tries to get this closer to commercial production it looks like he's trying to mitgate even minor and improbable problem areas. |
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| Christer |
| quote: | Originally posted by sam9
On the new schematic it looks like Slone moved the function of the zeners (over-voltage protection for the input transistors) to the switch diode pair between the bases of the same transistors. I'm not convinced yet that the low noise transistors selected gain you more than you loose by having to add protection components.
|
Obviously the diodes are suppose not to conduct until you overload
the input, so the question is, does a diode generate noise even
when not conducting? Hm, I suppose it does if you measured
such an effect for the earlier zeners? |
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| andy_c |
| quote: | Originally posted by sam9
(...)It also appears that protection transistors have been added to the VAS. I somehow thought that was only needed with an enhanced beta design. Maybe not . . . (...) |
It looks like when there's a short at the output, and if the current limiting transistor Q13 weren't there, the max current in Q19 (and Q14 and Q15 as well) wouldn't be reached until Q19 saturated. Since the base of Q15 is at half the supply voltage in this case, its collector can't go much above that. So the max current in Q19 would be about (32.5 - 0.7 - 0.3) / 150 = 210 mA. This assumes Vce(sat) of Q19 is 0.3 and the voltage across D6 is 0.7. This would probably burn up Q14, as it would be dissipating about 6.3 Watts (since it would have about 30V across it). So Q13 saves the day in this case by limiting the current to about 26 mA. |
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| Nick Walker |
| Can anyone explain why R6 is 2k7 whereas R18 is 1k, I don't understand why they are not the same. |
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| slowhands |
| quote: | Originally posted by Christer
Obviously the diodes are suppose not to conduct until you overload
the input, so the question is, does a diode generate noise even
when not conducting? Hm, I suppose it does if you measured
such an effect for the earlier zeners? |
Zener diodes always conduct some small amount of current, even at voltages below their rated breakdown. They are not ideal components, but are handy within their limitations. Even at their rated voltage, they have a dynamic resistance which means the zener voltage changes with appied voltage.
So as voltage clamps across the input, you must accept their limitations to get their benefits. In the musical instrument amp world, where line voltages can be put on inputs, they save the amp from total destruction at a cost of a negligible increase in distortion. For home use, they are not appropriate and may be dispensed with. Slone makes their purpose clear in his book, they typically are only for musical instrument input protection circuits, used together with extensive frequency filtering also.
I believe the back to back signal diodes across the bases of the input pair have been used to protect op amp inputs for years. Diodes are not perfect devices, and will themselves cause distortion while preventing damage to the input pair. This is the right tradeoff for a musamp, not so good for home hifi, in my opinion.
While testing amps, I have damaged the input pairs by overdriving the inputs above 6VAC. They get leaky and have higher offset voltage, a not uncomman defect in amps I repair, so I think this happens in use quite a bit. This validates that there is a practical benefit to adding some protection against that kind of abuse -- it does happen, so plan to survive if you expect overvoltage inputs to occur in normal use. |
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| tcpip |
| quote: | Originally posted by slowhands
I believe the back to back signal diodes across the bases of the input pair have been used to protect op amp inputs for years. Diodes are not perfect devices, and will themselves cause distortion while preventing damage to the input pair. This is the right tradeoff for a musamp, not so good for home hifi, in my opinion. |
I'm not sure I understood this correctly, so please can you help me? I was wondering what if I connect eight signal diodes in two series-chains of four each, between input and signal-ground. Each chain of 1N4148 will have four diodes, hence will conduct only when the potential difference will go beyond about 2.4V. Will such diodes also introduce distortion?
And what about the 1N4007 diodes that are used between the speaker output and the supply rails of the power amp? Will those also cause distortion?
I'm really new to all this, so some of my questions may sound stupid. Sorry. :D |
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| mcp |
| quote: | Originally posted by Nick Walker
Can anyone explain why R6 is 2k7 whereas R18 is 1k, I don't understand why they are not the same. |
It has to do with the VAS (Q14) loading the input stage. By having R18<R6, the designer is trying to maintain equal current in the two legs of the differential. |
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| Thoru |
Hi,
I'm planning on building a Slone (fig 11.4) amp too. I just see some problems, which are porbably allready solved by you guys.
The text states at page 338 that I can replace the Q12 and Q14 (MJ series) with 2S series, but the schematic allready lists 2S sersies, why?
Is there a reason for the fact that fig c.6-8 doesn't match with the photo on page 336?
R33 is connected to R34 etc with a wire. Judging from the PCB artwork fig c.7 this is a normal sized wire, isn't that suboptimal?
I hope someone can answer these questions. If this board is OK, then I'll probably order it from SEAL. I don't have the experience to design my own at the moment.....
Thanks in advance,
Remco Poelstra |
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| sam9 |
Thoru,
I called Slone in the early part of last year to buy 11.4 boards. He said that due to the time he was spending with ZUS-Audio, the only boards still avaialable were the Opti-MOS. I went ahead and laid out my own double sided boards. It took three trys to get it right but the results are a very nice amp. If you are able to start over a couple of times without getting discouraged it is a good learning experience.
Some of the learning involved just getting better with the layout software. The rest mosatly involved learning to keep the input and VAS sections far, far away from the output. The 11.4 is a CFB and is subject to mysterious oscillations (benign and otherwise). In addition to board layout two things were a real help to getting it going. 1-well shildieded input lines; I cut up some interconnect cable that has a sturdy woven copper shield and 2- move the output inductor (+5W resistor) and the zobel circuit off the PCB and closed to speaker terminals. If you do this watch the location of the output inductors as they can inject cross talk into the other channel as well as add feedback back into your input. Keeping them at a couple of inches away from anything is a good idea. |
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| Thoru |
Hi,
Thanks for your reply.
Apart from the fact that I like to concentrate my learning on other things (it's my first amp and high power circuit in general that I build), I like mostly to keep the costs low. I actually don't have money to build an amp, so I prefer not to have to start over and over again. But if it's the only solution to go than I'll do it that way. I've to learn it one day or another.
Thanks for the tips so far, I hope it saves me one or two tries :).
Remco Poelstra |
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| Nick Walker |
| quote: | Originally posted by mcp
It has to do with the VAS (Q14) loading the input stage. By having R18<R6, the designer is trying to maintain equal current in the two legs of the differential. |
Thanks mcp. I did some simulations on Spice and that works, but the change is small about 6uA difference change or 2.1%, going from 1k to 2.7k, however the greater difference seems to be the ability to supply more base current to the VAS stage which is up 60uA or 337% |
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| mcp |
Hello Nick
Yes, your Spice modelling is correct - an improvement in base current to the VAS.
What is happening in circuits of this nature is that the VAS is "zapping" the diff leg. By making the legs asymmetrical, more current is able to flow through the R1K leg, thus compensating for the "loading" on the 2K7 side.
This technique tries to emulate current mirrors. |
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| tcpip |
| quote: | Originally posted by sam9
I called Slone in the early part of last year to buy 11.4 boards. He said that due to the time he was spending with ZUS-Audio, the only boards still avaialable were the Opti-MOS. I went ahead and laid out my own double sided boards. It took three trys to get it right but the results are a very nice amp. |
Will you be willing to share your PCB layout files with us? I too am very interested in building this Fig11.4 amp, and having the PCB layout in a format where I can edit them would be a huge help.
Thanks. :) |
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| thanh |
HI All!How can i calculate the value of R6 and R18?
Thanks a lots! |
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| sam9 |
Tcpip,
I have some cranky old software that doesn't like to produce images except in it's own format or Gerber files. I have also finally figured out how to make PDF files with it.
So tell me which format, PDF or Gerber you prefer. It may take me a couple of days to locate the old files so be patient.
By the way, they are double sided requiring soldering on the top unless you use though hole gromets. Also used use mini-resistors likew the Panasonic ERD or ERO sieries (body length is 3.5mm) because I was trying to squeeze into a smallish enclosure. |
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| tcpip |
| quote: | Originally posted by sam9
I have some cranky old software that doesn't like to produce images except in it's own format or Gerber files. I have also finally figured out how to make PDF files with it.
So tell me which format, PDF or Gerber you prefer. It may take me a couple of days to locate the old files so be patient.
By the way, they are double sided requiring soldering on the top unless you use though hole gromets. Also used use mini-resistors likew the Panasonic ERD or ERO sieries (body length is 3.5mm) because I was trying to squeeze into a smallish enclosure. |
I now understand that it may not be of much use to me.... what I was hoping for was the raw data files in something like Eagle, so that I could edit them. :) Thanks for your patience anyway. And please can you send me the PDF files, so that I can at least take a look at a layout other than Randy's, and it may help me make a layout of my own? Do you think it's feasible to fit one channel into a PCB of 3.2"x4" size? (That's the size that the free version of Eagle allows.) I don't mind DSPTH, there are fabs here who do a very good job with them at affordable rates.
Thanks again. |
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| sam9 |
"Do you think it's feasible to fit one channel into a PCB of 3.2"x4" size?"
I think so if you look for items that can be placed somewhere off the PCB. For startes: fuses, output inductor and damping resistor, Zobel network.
Some things can be made smaller. A few examples: Use a 47uF bi-polar cap for the input instead of oppossed tantalums. Use single pins rather than terminal blocks or just solder a wire from a single hole - these don'y need to be at the board's edge which could ease the layout constraints. Stand the 5W resitors on end, but take care because they are subject to stress and the solder joints are easily damaged.
You may be able to make a more compact layout by connecting the Vbe (bias) transistor to the board bt wires rather than placeing the footprint right next to the heatsink/board-edge. |
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| tcpip |
| quote: | Originally posted by sam9
I think so if you look for items that can be placed somewhere off the PCB. For startes: fuses, output inductor and damping resistor, Zobel network. |
Thanks for these inputs. I'll try now. I didn't understand that last bit about the Vbe transistor's placement, though. And do you really recommend a bipolar cap for carrying the signal? What kind of bipolar is this? Won't it be better to just use two 10uF MKP/MKT caps in parallel?
BTW, I got a diyaudio-routed message from you. I tried replying to it, but it immediately bounced. It appears that your concentric dot net email address is not valid any more. Is that the address you've retained in your diyaudio profile? Can you write a message to me giving me any alternate email address?
Thanks and regards,
Tarun |
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| sam9 |
I'll fix my member profile so you can email me. I've changed my ISP.
"And do you really recommend a bipolar cap for carrying the signal? What kind of bipolar is this? Won't it be better to just use two 10uF MKP/MKT caps in parallel?"
Yes, a bipolar is sub-optimal, but it takes up a lot less space (8mm diameter) which seemed to be an issue. You can find them in the online digikey catalog - they are made by Panasonic they just eseentially two caps constructed in oppossed orientation in a single can. Two 10uF film caps in parrallel would be superior and just one would do the job. The deal with my bipolar suggestion is that an electrolytic of sufficiently high value has a such low resistance that the signal pases through with out charging or discharging it -thus is in almost not there. A 47uF bipolar electrolytic is actually like two 100uF caps. I would not do this so long as I had the board space available for a 10uF film cap.
The Vbe comment is based on experience laying the PBC. It is electrically connected pretty intemately with the VAS but you want to have it physically near either the heatsink and output devices or near one of the small driver transistors in order for it to be in contact with then for thermal tracking. It makes routing the traces awke=ward some times because the best placement electrically is not compatable with the best placement thermally. So if you are trying to layout a small PCB this is one more problem to deal with. Take a look at how one guy solves this: http://www.aksaonline.com/products/...ts_aksa55.html. Notice that the three wires don't even come of the board near each other - this is very cool solution. Obvious and simple once someone else thinks of it. (It's an EF rather than CFB design but the idea would work for both.) |
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| slowhands |
| quote: | Originally posted by tcpip
I'm not sure I understood this correctly, so please can you help me? I was wondering what if I connect eight signal diodes in two series-chains of four each, between input and signal-ground. Each chain of 1N4148 will have four diodes, hence will conduct only when the potential difference will go beyond about 2.4V. Will such diodes also introduce distortion?
And what about the 1N4007 diodes that are used between the speaker output and the supply rails of the power amp? Will those also cause distortion?
I'm really new to all this, so some of my questions may sound stupid. Sorry. :D |
The diode strings will probably work, and with negligible distortion.
The Hitachi MOSFETs have built in diodes, so the 1N4007s are not needed. However, this is what they are intended to do: protect the output transistors from inductive spikes. If you were to wiggle the speaker cables while delivering high output (causing them to make intermittent connections) the inductance of the speaker system would send high voltage spikes back at the amp outputs, possibly causing them to exceed their breakdown rating and short out destructively. Those 1N4007 diodes should never conduct, unless there is a highly inductive load like a typical speaker, and rapidly changing waveform. The diodes are clamps on the output voltage, so it can't spike above (or below) the positive (negative) supply voltage, damaging output transistors.
The diodes are a vestigial holdover from the bipolar version of this amp, where they most definitely are needed since BJTs don't have an intrinsic clamp diode. Like most engineers, Slone leverages known good designs wherever possible. |
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| Nelson Pass |
Not only are the diodes a vestigial remnant of bipolar amps,
they are an artifact created by short protection circuits -
an amp without foldback current limiting is not going to see
enough flyback to break the reverse bias voltage of the BE
diode.
I put them in anyway, 'cause I wear a belt and suspenders.
:cool: |
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| tcpip |
| quote: | Originally posted by sam9
Yes, a bipolar is sub-optimal, but it takes up a lot less space (8mm diameter) which seemed to be an issue. |
Thanks for the answers. Makes sense.
| quote: | | So if you are trying to layout a small PCB this is one more problem to deal with. Take a look at how one guy solves this: http://www.aksaonline.com/products/products_aksa55.html Notice that the three wires don't even come of the board near each other - this is very cool solution. |
That photo really made the whole thing fall into place. Yes, it's a very cool design. I guess Hugh Dean is a cool designer. :D
Seeing the size of his AKSA55 PCB, I now think perhaps I can try doing a "Slone-Fig11.4" PCB within the bounds of Eagle. Or else I'll just edit the layout you did in Vutrax. I'm waiting for it eagerly.
Tarun |
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| tcpip |
| quote: | Originally posted by slowhands
The diode strings will probably work, and with negligible distortion. ...
The Hitachi MOSFETs have built in diodes, so the 1N4007s are not needed. However, this is what they are intended to do: protect the output transistors from inductive spikes. |
So I guess I can begin to insert these diodes in both places, inputs and outputs, in any designs I do. Cool. Thanks. :) |
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| Midficollege |
| I'm very interested in building one of the CF-MOSFET amps that are shown on the Sealelectronics site. Any more information would be appreciated, like what exactly comes with the kit. Are power supplies included? Binding posts? Is this a one channel or stereo amp? Where would one get an enclosure? Etc. |
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| tcpip |
| quote: | Originally posted by Midficollege
I'm very interested in building one of the CF-MOSFET amps that are shown on the Sealelectronics site. Any more information would be appreciated, like what exactly comes with the kit. Are power supplies included? Binding posts? Is this a one channel or stereo amp? Where would one get an enclosure? Etc. |
Your questions are very specific to what the seller of the kit supplies. In that case, why don't you write an email to them? They used to be very prompt in answering email. |
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| lucpes |
| quote: | Originally posted by Midficollege
I'm very interested in building one of the CF-MOSFET amps that are shown on the Sealelectronics site. Any more information would be appreciated, like what exactly comes with the kit. Are power supplies included? Binding posts? Is this a one channel or stereo amp? Where would one get an enclosure? Etc. |
1 Kit includes PCB, heatsink, components for one channel, assembly instructions. You need 2 kits for stereo, obviously :) You can buy PS filter capacitors from Mr Slone, but you'll additionally need (3rd party sourcing): transformer(s) - they're heavy and shipping costs cut in here so get them from a nearby shop, binding posts, RCA connectors and connecting wires. You might also want a case to put it in, unless you're like me and like it naked :) |
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| lucpes |
| quote: | Originally posted by tcpip
And do you really recommend a bipolar cap for carrying the signal? What kind of bipolar is this? Won't it be better to just use two 10uF MKP/MKT caps in parallel?
|
The original value is two series 47uF tantalums which comes out to ~20uF, so it would be nice to use MKPs here. However nothing beats a piece of wire instead of the cap, as unity gain at DC is assured by the cap in the feedback loop. Unless there's any chance to put 5VDC or more at the input I'd leave those out.
If you decide to use MKP then try to get lower voltage ones to save some space... 10uF/100V is kinda huge :) |
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| sam9 |
DC coupled input has a certain logic but I remain nervous about it, nonetheless. Reliance on just the NFB return to protect you takes more faith than I've got.
On the other hand preamps often have output caps and it seems to me that having a cap at thr preamp output and another at the amp input is redundant. In the commercial world it makes sense as you don't know what you customer is going to do. For diy where you know (or think you know:D ) the environment in which each piece of gear is operating, you can safely eliminate some redundancies. If I had built both the preamp and the amp or was building an integrated amp, direct coupling the stages would not bother me.
I would also want to be sure that both were plugged into the same mains circuit to be sure they saw an identical grond potential. If there were a difference in potential seen by each unit that would cause a DC offset that is as real as connecting a battery to the amp's input. |
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| tcpip |
| quote: | Originally posted by lucpes
If you decide to use MKP then try to get lower voltage ones to save some space... 10uF/100V is kinda huge :) |
And Randy says that if you really want to go first-class, you should use a 250V MKP cap at the input, to protect the rest of the circuit against accidental high-voltage DC. He recommends this not for sonic reasons, but for protection.
I guess you've seen the sale of GE MKP caps on Madisound.com? They're at really low prices. |
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| sam9 |
| Appearently he built quite a few custom amps for musicians. The input connectors are often TRS (1/4" phono) jacks. I've seen a few roadies in my time (the Greatfull Dead used to make appearences near here a couple times a year) some know what they are doing and some sholudn't be allowed to use sissors without supervision even when not "chemically enhanced". Thus I imagine Slone recognizes real need to protect his handiwork from having all kind of thing plugged into the input. |
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| lucpes |
Regarding input caps, I suggested lower voltage MKPs because of the space issues that were previously discussed.
For personal use it's ok to go capless , if you're willing to take the risk (or keep only one cap either at the preamp out or amp in if necessary) :) Sam9 is right about 'plugging' things into the input... you'll never know what will come in there when talking about commercial units. |
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| tcpip |
I guess this bit of Randy's personal life is not known widely, but he plays some musical instruments (I forget which), and he's been part of a travelling band. He loves music, and listens quite a bit, and I believe he still plays for his own pleasure. So I guess he knows very well what the "pro audio" environment is like, at least for performing tours.
Sometimes, audio designers who believe in measurement and objective tests, double-blind comparisons, etc, are branded as dry and lacking the urge to sit and listen. Both Randy and Seigfried Linkwitz are music lovers, though both of them have an engineering approach to audio system design and evaluation. I was told SL likes attending live concerts. Both these people are my inspirations for audio system design and evaluation. |
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| slowhands |
| quote: | Originally posted by sam9
Thoru,
......The 11.4 is a CFB and is subject to mysterious oscillations (benign and otherwise). In addition to board layout two things were a real help to getting it going. 1-well shildieded input lines; I cut up some interconnect cable that has a sturdy woven copper shield and 2- move the output inductor (+5W resistor) and the zobel circuit off the PCB and closed to speaker terminals. If you do this watch the location of the output inductors as they can inject cross talk into the other channel as well as add feedback back into your input. Keeping them at a couple of inches away from anything is a good idea. |
If you can, leave out the output inductor. An amp should be stable without it. It does nothing good, other than make the scope pictures pretty with cables attached.
Definitely move the Zobel net to the output terminals, and use a separate ground return to star ground. All it does on the card is inject noise into the ground system, which can cause big problems. |
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| tcpip |
| quote: | Originally posted by slowhands
Definitely move the Zobel net to the output terminals, and use a separate ground return to star ground. All it does on the card is inject noise into the ground system, which can cause big problems. |
Is the Zobel network necessary, in general and specifically for the Slone amps? From what I read, it seems a lot of good-sounding amps have left it out. In Elektor amp articles, they always keep those components optional. "If you face problems, you can try adding these..." -- type of thing. |
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| sam9 |
Both Rod Elliot sound.au.com and D. Self (in his book on amplifiers)have done some stuff on benefits of both of these (Zobel and output inductor). My interpretation is the the output inductor becomes less needed the shorter the speaker cables and visa versa. (I use it because I tend to have lonish speaker cables.) The zobel is generally beneficial although in some cases ther may already be one at /in the speakers.
One benefit of diy is you can build to your specific situation, whereas when you build for others to use, you have to assume the worst. |
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| sam9 |
| By the way, there is a "rule of thumb" whose accuracy I can't vouch for that says the optimal value for zobel resistor is chosen the same value as the nominal impedance of the speakers. So if you have 4 ohm speakers use a 4 ohm zobel resistor. I would be interested to hear if there is any validity to this. |
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| tcpip |
| quote: | Originally posted by sam9
The zobel is generally beneficial although in some cases ther may already be one at /in the speakers.
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I have heard one set of opinions which say that the Zobel is only needed as an impedance correction facility for the speakers, because the speaker driver's impedance rises with rising frequency. The Zobel is not a stability related feature. Comment? |
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| sam9 |
In Self's "Audio Power Amplifier Design Handbook" he reports expiriments conducted with and without a zobel. He clain HF instability in the output section if omitted even if the the speaker load is even "mildly inductive"
As for the output inductor, he claims that by experiment he found that if the inductor is omiited (or shorted - the same thing) a 100nF of capacatance parallel to the load can result in destructive ocillations. He distingushes this from the dampened ringing seen in the standard capacative load test. ***LET me add that I tried this very thing when building my 11.4 and got the same results - only quickily hitting the off switch saved a pair out output BJTs. At the time I had not read Self's book so I wasn't expecting the such a spectacular result - my scope just went totally bonkers!** Just a speculation-- a CFB output section may be more suseptable than an EF.
Self is as full of opinions as anyone (some contoversial), but one thing I like about him is that he actually checks most of them out at least in simulation and often with a real amp. |
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| tcpip |
| quote: | Originally posted by sam9
He clain HF instability in the output section if omitted even if the the speaker load is even "mildly inductive" |
Does this mean that practically any speaker with a coil and a moving diaphragm will need a Zobel?
| quote: | | ... if the inductor is omiited (or shorted - the same thing) a 100nF of capacatance parallel to the load can result in destructive ocillations.... |
Wow. Actually, Randy Slone's book also talks about how ringing at the output reduces if you put the inductor, but I didn't know it can get this bad this easily. |
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| sam9 |
"Does this mean that practically any speaker with a coil and a moving diaphragm will need a Zobel?"
Unless the spaker itself already has one. ."
"I didn't know it can get this bad this easily"
There a lot of varibles that can have an influence. The parameters vary wildly from one speaker design to the other, some cables can have an influence, and two amps with the same schematic but different PCB layouts can react differently. Thus it is also within the range of possabilities that one combination of factors results in a stable situation while another oscillates readily. I doubt any are "beyond the laws of physics" but there are just a lot of permutations that make predictability hard. One way to deal with this is just to anticipate the worst.
You might want to look at this: Rod Elliots's web site (sound.au.com), the article on "Cable Impedance |
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| tcpip |
| quote: | Originally posted by sam9
There a lot of varibles that can have an influence. The parameters vary wildly ... |
I get at least one message from all this. I'd better retain provision for both of these in my PCB design. I can choose to not populate some of it at the time of building. Too unsafe to drop even the option of these protection mechanisms.
Thanks. :) |
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| thanh |
| I simulated Slone's circuit .It is not linearity at output high level ,about 17-18V,.perhaps that's non-linearity of input or VAS stage |
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| lucpes |
| quote: | Originally posted by thanh
I simulated Slone's circuit .It is not linearity at output high level ,about 17-18V,.perhaps that's non-linearity of input or VAS stage |
Could you post more details on your finds? (graphs, etc) |
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| sam9 |
"I simulated Slone's circuit .It is not linearity at output high level ,about 17-18V,.perhaps that's non-linearity of input or VAS stage"
Are you talking about the "11.4" amp? I set one up in LTSpice and found nothing unusal. More important several here (including me) have built it. Your concern does not seem consistent with experience of actually building and listening to one even when the output is fairly close to the rails which are `30V in my case.
BTW, what do you mean by non-linearity? Frequency response? THD? All amps are non-linear in some respects, at least until someone produces one that truly has zero distortion. |
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| OPTI-MOS PAT |
Update,
I received my power supply parts, and started wiring things up. Here is Randy Slone’s new low impedance power supply board, I’m using 8 10,000uf caps but the board can hold 10 caps. The transformer is an 800VA 50+50. Anyway back to work!! I will let you guys know how it sounds very soon!!!!!! |
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| tcpip |
| quote: | Originally posted by OPTI-MOS PAT
I received my power supply parts, and started wiring things up. |
Looks great! :D
Where did you get your chassis and heatsinks from? Can you give me specific pointers and prices please? |
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| OPTI-MOS PAT |
tcpip,
The case I'm using for now used to be a Kenwood 5 disk CD player that never worked well from new, the aluminum plate is from a car amp, and I added the handles to it. This is a temporary case, as I plan to build a 4 or 5 channel amp in one enclosure. As for the heatsinks they came as a kit, which consisted of PCB all components and heatsinks. This is my first attempt at building an amplifier, so I decided to buy it as a kit form. He does sell things separately at his web site (seal electronics). I just finished setting the bias and it is ready for action! I will be connecting it up tomorrow morning, and see how she performs!!!! It’s too late now kids are sleeping.:bawling: |
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| lucpes |
Good job! Looks great and this just might be a reason for me to start building a case for my amps :)
Make sure that you tighten those blue connectors properly :) , and let us know how it sounds. You may also try to up the bias current a tad bit (have my OPTI-MOS kits running at 80mA instead of 40mA) and everything is better sound quality wise :smash: |
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| OPTI-MOS PAT |
Lucpes,
Thanks for the advice, I will start with it at 40mv first for a bit and then I will try to raise it so I have something to compare it too. Does raising the bias only affect the sound quality or will it affect other things as well? :D I am hooking things up right now!!!!!!!:D |
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| lucpes |
What's your power supply voltage? I have mine on +/-63V and the heatsinks ran warm to the touch at 100mA (around 40-45 deg celcius) so I backed it up to 80mA just to be 'safe'. It also depends on your speakers, mine are 4ohm, 86dB/1W sensitivity and they tend to 'suck up' more power than 8ohm higher sensitivity ones.
The OPTI-MOS highly benefits (sonicly) from the input tantalum caps removal (shunt with a piece of wire here) if your preamplifier permits (does not have any DC offset larger than 5-10mV). The preamp DC offset shouldn't be any trouble because the 470uf/35V in the feedback loop assures unity gain at DC.
Also solder the fuses in their slots (use a 100W soldering gun) to avoid excessive resistance causing rail dropping on heavy bass passages :smash:
The higher bias shouldn't cause any problems except for the 'small' additional heat; the amps are stable as a rock and do not run into thermal problems due to L-mosfets use (of course, if you get to mail Mr Slone about these he will tell you that is totally unnecessary and the fact that everything seem to sound better is just a subjective claim).
Just hook everything up, paying attention to the blue connectors that do not stand much fiddling around (I ended having the PS lines soldered because of this), run the amp a couple of days at 'defaults' and then up the bias/remove the input caps. If you feel there's any difference, leave it like this. If not back it up to 40mV between the two test points and remove the wire :)
Oh, I also tried changing the green mylar caps for metallized polypropylene ones and the sound got more congested in the dynamics department so leave those as they are, they do their job good. |
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| thanh |
Hi!Have you ever tested to know how optimos's distortion is?
I built a slone amp but i haven't any spectrum.I use 2SC1815/2SA1015,its noise is quite high.You know ,2SC2240/2SA978 is qiute expensive ,=3*2Sc1815 |
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| demons_wing |
| i do believe that the CF output is more susceptable to oscillations..now this is just an educated guess..but if you look at the CB junctions of the output sections, you will see that the miller caps and the resistor make a 2 pole circuit...very reminiscent of a phase shift oscillator...just my pennys worth..i could be wrong |
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| Damon Hill |
| quote: | Originally posted by OPTI-MOS PAT
Update,
I received my power supply parts, and started wiring things up. Here is Randy Slone’s new low impedance power supply board, I’m using 8 10,000uf caps but the board can hold 10 caps. The transformer is an 800VA 50+50. Anyway back to work!! I will let you guys know how it sounds very soon!!!!!! |
Very nice power supply board; I may have to order one of
those when I rebuild my Leach amplifier into something that
looks more respectible. Looks like the bridge rectifier solders
into the board, bypass caps on the main caps, bleeder
resistors, etc.
Gotta have one. And two of those heatsinks.
--Damon |
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| lucpes |
Here's a list of 'definitive mods' I performed on my Slone OPTI-MOS amps:
- replace the tantalum input caps with something better or put a piece of wire instead - unity gain at DC insured by C12 so no prob here;
- replace all 100V/100uf caps with 220uf/100V Panasonic FC;
- replace C12 with 680uf/35V Panasonic FC or bigger;
- increase R31&R35 to 100R to allow for slightly more headroom before the limiting kicks in;
- replace the cheap mylar caps on rails/zobel (C4, C23, C24) with WIMA MKS 4 250V/0.1 uf (RM 7.5mm, board has 7mm between holes)
- adjust gain with R22 (larger means less gain, I went up to 680R to allow for hotter preamp signal, no probs in two months)
- remove input diff pair protection diodes (D3/D4), sounds lot clearer now but make sure not to put anything nasty through the amp now (like connecting preamp while the amp is on) or tweeters will go to heaven;
- check for voltage drops on rails when playing bassy passages and re-check all connectors/fuses/so on...
- solder PS wires & fuses in (OK, this is nuts but it really helps with lower impedance speakers) |
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| sam9 |
I'm not totally sure about this, but when you raise C12 to 680uF would it be a good idea to parrallel a lower value cap .1u or 1U.? An electro that size may well start exhibiting inductance (risiinf AC frequency dependant resistance) in the upper audio range. Obviously you are not having any adverse problems but it is something I would think about.
I'm alittle surprised (by Slone) by the film caps to bypass the zobel and rails. Again the bandwidth limitation. I believe it is called "self resonance". I've used good (COG or NPO) cermics for this to be sure the bandwidth extends as far as possible. Again, if you don't have a problem, there is obviously no need for concern. |
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| lucpes |
| quote: | Originally posted by sam9
I'm not totally sure about this, but when you raise C12 to 680uF would it be a good idea to parrallel a lower value cap .1u or 1U.? An electro that size may well start exhibiting inductance (risiinf AC frequency dependant resistance) in the upper audio range. |
IMO By choosing a good quality cap (not so sure that low esr is equivalent to low inductance) you can avoid this issue. Could this be of concern at higher than audio frequencies and lead to amp instability?
| quote: | Originally posted by sam9
I'm alittle surprised (by Slone) by the film caps to bypass the zobel and rails. I've used good (COG or NPO) cermics for this to be sure the bandwidth extends as far as possible. |
Well, the film caps (might) add a coloration of their own which one may like/or dislike :D Agreed on NPO issue, quality high voltage ceramic caps for these positions might fit better. |
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| HiFiNutNut |
Many thanks to you all who contributed your great ideas to this thread. I have gained a lot from your discussions.
I built an Optimos (version 4) 2 months ago. It sounds fabulous. I am building another 5 channels of Optimos - a 3 channel amp is to be used either as a stereo amp when needed or in a home theatre for the centre and rear channels; and 2 mono blocks of 400W will drive either the main speaker or a subwoofer.
I have taken your advice and experimented 2 small mods. Removing the input tants and the diodes across the input transistors DO IMPROVE the sound clarity, image and dynamics. Initially I thought removing the tants would only affect the bass department. But my latest tests proved that it affects mid and high frequencies as well. I am using an active speaker.
I will eventually add in a 20uF polypropylene cap on the input to provide some protection. I guess that it will unlikely degrade the sound to an extent that is audible, unlike the tants.
I have 2 questions:
1. Some of you said that you have not put in the protection circuit. Do you mean Q25, D12, C17, R50, R52 and R53? which is connected to the Integral Overload Output? or do you mean Q19, Q20, D6, D7, D8, D9, C20, C21, R31, R31, R32, R33, R34 and R35? or both. The first set is a late addition to the newer version of the Optimos. In his book Mr. Slone when describing the benefits of MOSFETs said that the only reason that he put in the protection circuit was to prevent from burning the fuse when overloaded. Did he refer to the 2nd set of components? I striped both sets in my new boards (still being built) last night and am wondering if I have gone too far.
2. I read from this forum somewhere that 1N4148 is not good enough. IN4148 is used in a number of places in the circuit. Do you know of any good substitutes? Are 1N5252B and 1N5060 good enough? Substitutes?
Many thanks. |
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| thanh |
| Should I use D5? Can D5 change DC offset? |
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