PICS: "Optimos" 140W Monoblock Amps!

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Finally Pics of my so called "Optimos" amps. Almost finished.
Still to do is the aluminium cover, Blue LED potential divider circuit and an aluminium plate between the PSU and the amp...

Hope you like them - they sound great!

P.S. Sorry about the long wait! I wanted to keep the image quality.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


If you can't see those pics use link: http://www.diyaudio.com/forums/showthread.php?s=&postid=92074#post92074

Thanks,

Gaz
 
Looks nice.

Have you figured out if is the OptiMOS you've built? We've had
some discussion about this previously, and I got the impression
you weren't sure about this then. The OptiMOS is one of the
designs I am considering, so it interesting to hear opinions about
it.

Do you really need those large heatsinks? Judging from the
photos it should be the standard 120W version, so I guess
you could manage with quite smaller ones. Not that it hurts
with overkill on the heatsinks, of course. I also see that you
have quite long leads to the output transistors. I would have
preferred a different board layout to avoid that, but if the amps
work well it probably doesn't matter in practice.

Edit: Just saw that it says 140W in the title. I suppose you
just increased the supply voltages a little bit and kept the
number of output devices (if it is the OptiMOS, that is)?
 
Hi,
I had just written a reply when my PC crashed so here goes again!

BrianGT:
I am using Aluminium Sheeting to cover the Top, back and front with a 3mm blue LED. The PCBs are 125x175mm, but the actual circuit on the board is slightly smaller... more like 90x170mm.

jgwinner:
The boards are by my own fair hands! They are by a system called Press 'n' Peel which I highly recommend avoiding!!! Much better to get a UV light and photo-sensetive PCB. The heatsinks were £10 each from Jakeh on this forum. He is very approachable an are stunning quality! There are no extras on the circuit.

Christer:
I do not believe it to be the OptiMOS circuit. The schematic is slightly different, but the OptiMOS is certainly the closest version to the one I built. It says in the book that it is rated at 140W into 8Ohms and 200W into 4 Ohms when the Power supply is at +- 55V. Since my power supply is at +- 63.1V it will be slightly more. The book says 200W into 8Ohms at +- 68V, so you can do the maths! :)

The sound is fantastic, but until I build a preamp, I cannot test it with anything but a very dodgy CD player! As I said above, the heatsinks were cheap and allowed me to fit everything in. I'm really happy with the way it's all worked out!

Thanks for the comments, and keep them coming! ;) If you want pics of anything in particular, just ask!

Thanks again,
Gaz
 
Rarkov said:
I do not believe it to be the OptiMOS circuit. The schematic is slightly different, but the OptiMOS is certainly the closest version to the one I built. It says in the book that it is rated at 140W into 8Ohms and 200W into 4 Ohms when the Power supply is at +- 55V. Since my power supply is at +- 63.1V it will be slightly more. The book says 200W into 8Ohms at +- 68V, so you can do the maths! :)

OK, then I see the reason for the big heatsinks.

Any chance you could post the schematic? It would be interesting
to compare it to the OptiMOS and the designs in Sloanes
power amp book.
 
Press n peel

I have used it a few times and it works fairly well but...
It can be a bit tricky. It does not work well at all for large masking areas and wise traces, I always have to fill those in using nail polish. All the problems I ever had with it were in the peel part. If you are peeling and a trace dosen't stick, stop peeling and iron some more. Never peel it all the way off unless you are happy with the result. Getting it to work right can be difficult but is not impossible. The instuctions are not kidding about a band of copper around the project edge, this holds it down so you can be sure that you get all the traces down.

If I am not using chips and the circuit is small (like power supplies) I usually make a few drawings, then sit down with the board and use an engraving bit to seperate the traces. Not the sexiest but much faster than drawing it up and etching it.

Also congrats on the amp! Looks great
 
Thanks Rarkov,

I would definitely say it is the OptiMOS. As far as I can see it
is exactly the same topology with just a few component values
differing slightly. I suppose the version on the web page is
newer and Sloane has done some tweaking on the exact values
of some resistors.

As I said, I might choose to build the OptiMOS myself, so its
good to hear your positive report on how it sounds. (On the
other hand, considering the weather right now I should perhaps
go for a huge class-A amp instead :) ).
 
Hi,
Sorry...That's my fault...Didn't mean to step on anyone's toes!

Therefore, to see the image, you must buy The Audiophile Source Book (Which I highly recommend [grovel grovel!]). You can gt it from Amazon - and is quite cheap. Loads of interesting circuits - not just amps. but protection, preamps, crossovers, equalisers, balanced-unbal convertors etc etc.

Please forgive me! ;)

Gaz
 
I was quick enough to see the schematic before it was removed,
so it served my purpose of comparing it to the OptiMOS schematic.
As I said before, it is the same design, except for one or two
resistors having a slightly different value. For anybody else who
is interested but didn't see the schematic in time, it is indeed the
same one as the OptiMOS published on the Seal Electronic
web page (except for those one or two resistors).
 
Rarkov said:
Apart from the drawing layout, it does turn out to be the same, but quite why the output ratings are rated so differently, I have no idea!

I don't know if the ratings are that different. Your figures from
the book said 140W at +-55V and 200W at +-68V, assuming
8 Ohm speakers. The web page says 150W at +-56V and
200W at +-63V. OK, the latter figure differs a bit, but maybe
he makes different assumption about whether the rail voltages
are at full load or not. I did some SPICE simulations and got
the following figures: 140W at +-55V and 230W at +-68V,
assuming these are the full-load rail voltages.

BTW, what is the VA-rating of the transformers and how big
resevoir caps do you use in your amps?
 
Hi,
I'm really interested in your simulations. What package do you use? I have access to Orcad 9.1 and Protel at uni so if they are compatible, maybe you could post the files?

Would you check the output power for +- 63.1V? This is what my power supply puts into the amp whilst it's running. I have a 500VA toro transformer per amp. Each power rails uses two 6800uF, therefore 4x6800uF per amp. The amps (as you saw) are in monoblock configuration.

Like I say, I'm really interested in what your simulations have to offer. What about THD+N?

Thanks,
Gaz
 
I use SwitcherCAD 3 which is a freeware implementation of
Spice. I don't think any other SPice implementations can read
these files, but I could extract an ordinary Spice netlist for
you. Or you could download SwCAD3. It is true freeware with
no limitations. You can find it at http://www.linear.com/software/
Although it is intended primarily for design of switching PSUs it
is a real Spice implementation so it can be used for any type of
circuit.

I tried with +-63.1V and max peak input voltage without clipping
is about 1.45V which gives just under 190W in 8 Ohms. Bear in
mind that there are a number of uncertainties in a simulation,
especially regarding transistor models which are not very
accurate. The simulation also assumes that the rails are at
+-63.1V at this output power.

I haven't run any distorsion analyses on the OptiMOS yet, but
I could do that. It is rather time-consuming however, so don't
expect any immediate results. Running distorsion analyses
in Spice is of questionable value, as was discussed in another
thread, and I use it mainly for comparisons between different
designs, to get some idea of their relative behaviour.
 
I could try lower impedances too, but I am not sure to what
extent it is possible to predict stability problems here. BTW, I
should have mentioned that I have not incorporated any
protection circuitry in the simulation model, so the real amp
may cut the MOSFETs at lower power levels.
 
Protection? What's that?!

That's alright...Apart from fuses, there isn't any! ;)

I'm not sure how an unstable amp reacts to an input - or at least how you would view this on a spice sim. I am interested in the 4 Ohm power output though. Thanks for this BTW! And I highly recommend this amp. When I first turned it on, I was quite disappointed. There was no bass and the whole show seemed to be played in a cubic concrete room...There was no sense of space.

Given a few days running it has totally opened up. The bass seems to gain more extention each day and I'm finding it easier to pin point voices and instruments. I am untrained in the art of listening, but I am loving the learning process! ;)

This is one fantastic circuit, but I suppose it is just as much about the circuit bedding in, as it is about me getting used to the amp.

Have a go and see what you think.
Gaz
 
By request, some distorsion results from Spice. I've used
Rarkovs raíl voltagees of +-63.1V, input 1.45V peak, which is
about max before clipping with this rail voltage. Output is
c:a 190W into 8 Ohms.

Minor notes: I use 2N5401/2N5551 also for the diff pairs. Perfect
current and voltage sources are used for biasing the diff pairs
and the cascodes.

Major note: This is just a Spice simulation, so don't trust the
results to have much to do with reality.


Figure 1:
Output spectrum for 1kHz sine wave. Both 2nd and 3rd
overtones are down between -75 and -80dB.
 

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