Optimos and Totem Pole amplifiers
LEDE:
For starters the DIY portion of our website is pretty much a front to a very professional life in music, radio and television broadcasting. I make little if any money out of the website.
Anyway I promised Randy I would be associated with his work as long as I could because I believe his design work is truly awesome. I don’t know of any audio amplifier in the world that can outperform the Optimos and Totem Pole amplifiers. This is my 40th year in the business. In short I support anyone interested in his designs as much as I can. The results [i.e. completed projects] have made a lot of people more than very happy.
There are not many ZUS [note Z] circuit boards left but Randy has given us permission to go on with our own [without performance compromise] when we run out.
In short the ZUS boards will probably not be available. These boards were manufactured in Canada and are now subject to serious copyright laws.
This means, that since I have permission from Randy to build any boards here I like, this will become the norm. The only downside is our boards are single sided and not tinned. This means after soldering they need to be laquered or coated with resin to protect the copper. The upside is our boards will be very rugged and reliable FR4 fibre glass and some $ dollars lower in cost than the ZUS boards. I am currently finalizing a board for the Totem Pole. Performance specs. will NOT be compromised. I have promised people the Totem Pole will be ready around New Year. The Optimos will follow after. A few months I expect. BTW I would not recommend the TP for home use.
Q: Regarding the Opti Mos ver 4, I assume the 400 watt kit is 200 wpc into 8 ohms. Is this the circuit on page 354, Design 12, in Randy Slone’s book, HP Audio Amp Construction Manual?
LEDE: The circuit on page 354 is very much like but not the same as the Optimos V4.
The Optimos V4 and the Totem Pole are basically the same except for the output stages.
Q: However, I am not clear as to what is included your amplifier kits. Are the circuit boards already populated with components as shown in the photos, say of the Opti Mos ver 4? The power supply is not included? The enclosure is not included? Are there any instructions or a manual with suggestions on how to put together?
LEDE:The Optimos delivers full power [and the same power] into 8 or 4 ohms. It is also a soft clipper.
The power output of the Optimos is determined by the rail voltage. 200W version nominal rail V = +/-63V. The 400W version uses +/- 84V rails, and at this voltage the larger double die Mosfets should be used.
We don’t normally supply transformers and power supply bits for international orders. Builders can save big $’s by getting those heavy parts locally. We are happy to advise of known US suppliers.
My logic is simple [like me]. The performance is worth building for,,, but the boards should be assembled before planning chassis. Thes are big amplifiers, and they need to be to deliver what they are easily capable of.
Q: After mounting the PCBs inside the enclosure one of my Opti-mos modules doesn’t work properly. I had tested it OK but maybe I touch accidentally some parts with the multimeter and I damaged it.
Now it has an output DC offset (-150mV) and I cannot find the problem. Can you help me?. Is it possible to know which stage is not working?. Maybe you can tell me some test points in order to find the fault.
I soldered both modules at the same time, so they are identical.
Looking forward to hearing from you. I cannot sleep.
Thanks for you co-operation.
LEDE: There are many things that can cause this in a DC coupled amplifier but because the offset is a relatively low voltage I suspect something near the front end.
If you feel that the module was O.K. then I suspect a resistor may be damaged in the early stages.[be wary of any low value resitors in emitter leads] If you can power both amplifiers,,,, voltage comparisons between the two amplifiers may get your problem into a stage. In the worst case you will have to test as many components as you can on board and remove any you are not sure of for testing. If there is nothing obviously wrong you may have to check beta matching of the input MPS….. pairs.
Another thing worth doing is to see if audio goes through the amplifier at a few watts. Clipping or bad distortion on one half of the signal will help you localize the fault fairly quickly.
Q: Some questions about grounds. My enclosure is metallic. The HQG will be connected to the enclosure. The AC ground will be connected to the HQG via chassis.
LEDE: That’s fine
Q: Must I connect the input connectors ground to the chassis or it’s is better to isolate them?
LEDE: Always better to isolate them. Probably best to ground the inputs with a wire straight form the PCB.
Q: Must I connect the speaker output ground to the chassis or to the HQG and isolated?
LEDE: The speaker ground can go straight to the H.Q.G..I prefer to isolate the speaker common but it is not essential to do so.
*{Wire from the speaker common and reservoir capacitor common should be quite thick} i.e. easily 15Amp rating
**The common wires to the PCB’s does not have to be very thick Thick wire will have less inductance that could improve RF stability in the entire system.
Some people save a bit of wire and believe they get better noise figures gounding any pre-amplifier boards from the power amp P.C.B. common [i.e. the pre-amp board has no direct connection to the HQG but is grounded via the power amp PCB
***Most builders tend to put in too much grounding rather than not enough.
For main power supply I always run about two soldered wires from the input mains connector I.E.C. One goes to the H.Q.G. The other goes to any panels I think could come loose or not grounded very well through the chassis system.
Q: I have almost finished the amp. I have decided to solder the MOSFET without wires. I need to make four holes and M2.5 thread in the heatsink.
One question more. I don’t know how to use the integral overload output.
LEDE: Thank you for your email! I don’t believe you will have any problems mounting your Mosfets ‘off-board’ so to speak. I am a fan of running wire from the leads back to the board in some applications because it reduces the physical stress on the actual Mosfets. The problem that can creep in is when the leads [particularly to the gate] are long. To help,,,, some add cylindrical inductors over the gate very close to the Mosfet case. I would only recommend this as a last resort because a resonant circuit will be formed by the use of any inductor.
So I think all you have to worry about is H.F. stability and heat transfer. I’m sure you will be O.K.
Q: I want 200 + 220 Watt (200 Watt/channel) amplifier , so I think single die Mosfet are right. I will have “On Board Status” Version if it is available(can you specify the functions of the aux board?).
LEDE: The Totem pole uses a total of 8 output Mosfets per channel, [i.e.4 devices per rail]
The Optimos uses 4 output devices per channel,[ i.e. 2 devices per rail].
This may be confusing. The Totem Pole can handle higher rail voltages in single die application than the Optimos but this is only recommended where speaker Z is 8 ohms minimum.
If you intend to use more than a total of 30,000uF filters per rail, per channel I would recommend a softstart system.
The AUX board has a softstart circuit, D.C. speaker protection which includes switch on speaker muting.
It requires a small transformer to supply it with 24V a.c. @ 150mA continuous.
The ‘onboard status’ amplifiers do not have a softstart circuit on board. We do have a softstart board available.
Q: The AUX kits provide ‘Softstart’?
LEDE: The AUX kits provide ‘Softstart’ and also protect against speakers being hit with destructive DC in the remote chance that something causes the amplifier to ‘blow up’. They are a bit big,,, PCB dimensions = 4.2″ x 6″, but very rugged.
Another point; the Seal Aux boards I intend to send for speaker protection also have a ‘soft start’ system which controls inrush current to the power transformer [at switch on only] using ‘ballast resistors’. In Australia we use 230V mains so I use 330R resistors in the ballast section lieu 220R. [6 in parallel]. used originally by Randy.
I don’t regard this as an issue at all,,, but you may,,, so please let me know if this is a problem for you and I will get hold of some 220 ohm jobs.
***Please note they require a 24V AC @ 250mA [of course a higher current rating is O.K.] supply to operate. I don’t normally export such transformers.
One AUX board is fine for 2 channels.
Q: In the aux control unit building notes you say “Remember to install only the ‘HOT’ {ACTIVE} line in series with the TB6-1 and TB6-2 connection terminals”.
In Spain you cannot control this. The position of the hot line in the sockets is not standarized and the wires can be inverted depending on the way the appliances are connected. Should I mark where is the hot in the amp and detect where is the ‘hot’ in the socket after connecting it?
LEDE: The logic of the ‘active’ being on the resistor group is that if the relay does not operate full dagerous voltage is not applied to the power transformer. In Australia the mains neutral is joined to earth at the house so the only dangerous wire is the ‘active’.
Anyway it should not cause much problem if you connect either of your supply wires to the resistor group. Having said that please take care not to go up in smoke. I always cover dangerous voltage with heatshrink or teflon tube.
Randy’s Aux control board which has muting, protection and sofstart [suits one channel or stereo use] requires 24V a.c. at approx 200mA. Max speaker current 30A per channel continuous.
* Our own ‘stand alone’ soft start [requires 15V a.c. at approc 120mA]
* Our own stand alone speaker ‘on-delay’ and protection board [requires +/- 15V d.c.] Max speaker current 30A continuous.
* Our own +/- 15V regulated supply kit. Max current approx 800mA with heatsink mounted to main chassis.
Q: Wondering if you offer any free help or advice concerning projects based on Randy Slones designs. Here is my problem…
I am wondering if you or anyone else has had trouble getting distortion from the modules. I have built a number of them and bought and used top grade parts from different manufacturers through the years only to have the same results. What I get is a popping distortion some times, and other times I get a distorted crackly sound in the midbass. All this happens from anywhere of 60W on up.
Recently I have been on the forums polling people for clues. One area I thought of possibility was in the setting of quiescent current. Many replies were stated that the Semelab double die devices needed a much higher current setting than what was stated in the design sheet that Randy had provided. Since then I have tried all the way up to 240mV and had no real change in results. The setup I have for test is one pair of double die Semelab devices each with .5 ohm source resistors, 75V no load rails.
I plan to use one more pair following some sort of success.
Can you offer any advice or help?
LEDE: There are conflicts with Randy’s design in that the capacitors across the source and drain are 10pF in Randy’s design and 22pF in the above and that the gate resistance in Randy’s plan is 680 ohm. The other capacitors listed are not even listed in Randy’s design.
I have across my gate and drain pins the listed 10pF value of Randy’s design and have upped my gate resistances to 750 ohm and then up to 1k ohm with not much headway. I will not have a chance until tomorrow to explore the use of additional caps from drain to ground. As well, I am not sure if I have any 22pF caps in my supply and these may prove necessary.
Thanks for your time, I would love to get this sorted out.
By the way, what should I have the Quiescent current and voltages set at??
Please tell me a lot about your power supply and your load and the design you are working on.
Q: The power supply is 50V+50V secondary @750VA, 33,000 mF Caps. Load I would say is no lower than 4 ohm. I have tried another in parallel with worse results.
I am totally lost with the Quiescent current thing now. I have read of so many differing opinions. I realize that in the project description, one recommends 18mV @ .1 ohm source resistor, but I am using .5 ohm source resistors. In the book Randy states that the goal is to reach 40mA across the resistors. 40mA over a pair of .1 ohm resistors would result in a mere 8mV. If I just branch off of the 18mV target with my resistors, I would need 90mV and this would seem that 90mA is the current target.
Just as a final note, these fixes are a result of 3 years R&D and many of these amplifiers built with these dual die devices.
Others may have confilicting advice which may help, but these fixes have been developed based on my topologies and PCB layouts and may not apply to your pcb layouts or Randy slones designs.
LEDE: I won’t spend much time on your problem before first excluding the most probable cause. If you are using the foldback protection circuit used in most of Randy’s designs this is most likely what is being triggered. This can happen when the load impedance goes below expected or when say a 0.5 ohm resistor is carrying all of the load current.
There are several ways to sort this out. Using double dies you can temporarily solder another 0.5 across each source resistor to make the source resistors about 0.2 ohms. You can also use different values in the foldback resistor divider to reduce the threshold level reaching the foldback stage. You can also bight the bullet and remove the foldback stage completely. Providing a bit of common sense is used nothing will get damaged. The last option is to use a load which has a constant impedance over the audio spectrum. If your problems do not show up on say a 15 ohms load I would say the foldback circuit is definitely being stirred up by a non linear load.
I’ll tell you how I adjust quiescent current when I can’t be bothered getting out the big test gear. I play a female vocal track I know is good and reduce the quiescent current at low audio level until I can hear crossover distortion. Then just increase quiescent until the distortion disappears. Measuring very low voltages across the source resistors is full of traps because of noise and meter accuracy at low levels. If you or a mate have a CRO and a sine wave generator you will see that not much current is needed through lateral mosfets to get rid of crossover distortion. DMOS
[Hexfets etc.] is another ball game.
Q: I’ve no idea why Jeff Gehring/ Weber Re-Vibe decided to use a 16R of all values. Are they common in the USA or something?
LEDE: Copyright laws are highly enforced in the US. One way to get around it is to use values either hard or impossible to get. This way the user can argue that he improved the design with his special value, making prosecution extremely remote.
Q: the information, how expensive your amplifier 25W is, and which housing it has.
Can you please also tell me, which connectors are in the kit.
LEDE: The board is basic, not tinned but rugged reliable FR4 professional board.
To save money for people we recommend you buy power supply, case and heatsinks locally.
In a nutshell the kit comprises only the PCB + all onboard components. The board terminals are all high quality turrets. Mr. Prinz built one of these kits in Germany which was a topic of discussion by Flavio Dellepiane from www.redcircuits.com
The amplifier exceeded all expectations.
Q: Hi with the 800 watt power amplifier what value capacitors would you go for for example 80 volt 10,000 uf or a smaller value if you could give me your view please.
LEDE: Unless you are very experienced with heat sink design and systems forget the 800W. 600W would be a realistic target. For 600W you will need at least 84V rails. The main reservoir capacitors should have at least a 100V rating. The actual capacitance value per rail is determined entirely by application. I recommend absolute min of 20,000uF per rail per channel. For professional
[paticularly sub woofer systems] 50,000uF per rail per channel would be a nice system.
Q: The 25W Mosfet layout.
LEDE: The component designations will be very close to the Redcircuits schematic documentation. I suggest you get cracking on the power supply as per the Redcircuits schematic. You will need to build your chassis. Aluminium is great. You can join panels with small angle using bolts or pop rivets.