OPTI-MOS PAT said:
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
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)
- 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)
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.
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.
sam9 said:
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?
sam9 said:
Well, the film caps (might) add a coloration of their own which one may like/or dislike
Agreed on NPO issue, quality high voltage ceramic caps for these positions might fit better.Optimos mods
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.
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.
hi there, I just want to know where should i connect this integral overload output because this one is different from the book i bought.as you have said that randy sloan made some improvements on optimos amplifier and hope you dont mind me asking.I am not an engineer but i could assemble amplifiers inifact i have already finished building 4 optimos amplifier and i just want to try his revised edition of optimos amplifier.thank you so much.
hi,i have read your past thread about the optimos rev 4.0,the modification that you have made.it looks to me that you have built the optimos rev 4.0 because you attached the schematic in it.I'm having second thoughts on building this.but when i read your thread its enough for me, to continue do the pcb layout for this schematic.i have built the older version optimos which is featured in audiophiles project sourcebook and im very amazed how this amplifier sounds.
I have one question about this schematics. what is the purpose of Q25, R52, R50, C17, D12, AND R53?can i omitt this in my pcb design?where does it connect and what is integral overload output?
your reply will be much appreciated.
Good day to you Lucpes
I have one question about this schematics. what is the purpose of Q25, R52, R50, C17, D12, AND R53?can i omitt this in my pcb design?where does it connect and what is integral overload output?
your reply will be much appreciated.
Good day to you Lucpes
I don't have a Slone amp, but I have had some experience building amps and also modifying commercial amps.
Some of the mods suggested by lucpes are very interesting, and I think should be carried on. But by looking at the circuit I would also like to to suggest others:
1) Try a bipolar electrolytic cap for C12, a good one of course. It doesn't need to be high voltage, which is a problem in BPs. If you increase R22 you can use smaller caps for C12 too.
2) Using a DC servo. It might allow completely eliminate C12.
Some 0.1 caps have polarity on the schematic, though I guess they are mylar types, right? Replacing them with same value polypropylenes should be worth trying.
Has anyone tried regulating the low current stages? It might bring sonic benefits, even if using a simple capacitance multiplier.
Some of the mods suggested by lucpes are very interesting, and I think should be carried on. But by looking at the circuit I would also like to to suggest others:
1) Try a bipolar electrolytic cap for C12, a good one of course. It doesn't need to be high voltage, which is a problem in BPs. If you increase R22 you can use smaller caps for C12 too.
2) Using a DC servo. It might allow completely eliminate C12.
Some 0.1 caps have polarity on the schematic, though I guess they are mylar types, right? Replacing them with same value polypropylenes should be worth trying.
Has anyone tried regulating the low current stages? It might bring sonic benefits, even if using a simple capacitance multiplier.
optimos rev4.0
is this schematic correct?because the capacitor c4,c24 and c23 have polarity
because right now im doing the pcb foil pattern for this schematic?
is this schematic correct?because the capacitor c4,c24 and c23 have polarity
because right now im doing the pcb foil pattern for this schematic?
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just add mosfet and make it 6 pairs and increase the voltage up to 85 volts dc.i have already tried it.you just need to increase the size of the of your heatsink.and for sure use 1/2 watts resistor. Randy use 1/4 watts as much as possible because he doesnt want to use bulky resistor if he cannot avoid it he makes it in series connection.my optimos is from the audiophile project sourcebook and not the version 4.also put heatsink on pre driver transistor
Drowranger
Although i'm a newbie in simulation, i thought i'll make an attempt on Optimos. Recently, i got Bob's book on amp design and started following the tutorials on spice simulation. Optimos performed well in 20k transient sims, square wave tests etc., as expected. However when i probed the VAS input for current and voltage, the waveform looks out of place.
Similar waveform appeared, while probing inverted input for current, but waveform for voltage looks good.
Is this behaviour normal or else do i miss something....
can you throw some light on this...?
Although i'm a newbie in simulation, i thought i'll make an attempt on Optimos. Recently, i got Bob's book on amp design and started following the tutorials on spice simulation. Optimos performed well in 20k transient sims, square wave tests etc., as expected. However when i probed the VAS input for current and voltage, the waveform looks out of place.
Similar waveform appeared, while probing inverted input for current, but waveform for voltage looks good.
Is this behaviour normal or else do i miss something....
can you throw some light on this...?
Attachments
Hello everyone,
I know this is an old thread, but I wanted to share my experience with you.
I have recently built the Revision 4 OPTI-MOS amplifier by Randy Slone, as posted by lucpes. Here it is:
The Schematic:
I made a few small changes:
1. I replaced the tantalum input caps for MKPs;
2. As I couldn`t find a reliable source for the K1058/J162 output transistors, I used the EXICON ECX10N20/ECX10P20R, which have similar specs and are still manufactured nowadays.
I designed the PCBs myself, and it ended up big. The size is 210 x 110 mm. It is double sided, 2 oz Cu, 2mm thick. I ordered the PCBs from a chinese manufacturer. The gerbers are attached, and you are allowed to produce PCBs for non comercial use.
Gerbers: View attachment Revision 4 OPTI-MOS Gerbers.zip
This amplifier really surprised me. It is a solid amp, and sounds really great! I measured 175W RMS per channel using 1kHz sine wave and 8 ohms dummy load.
I am still to perform frequency response and THD tests, and I will get back with the results.
Regards!
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Hello. The PDF files are attached. Just remember that all holes are plated.
View attachment Slone_PCB_Pdf.zip
Regards,
Hello Mitchel,
I am toying with the idea of building the v4 of the Optimos amp that you crafted PCBs. Do you have a BOM that you could share?
I am particularly interested in knowing where you bought those T0-220 heatsinks.
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