Micro computer speaker and amplifier build/design

[Operandi]

Jed,

What do you think of using the Dayton RS100 vs. the Peerless. By Zaph's tests it looks like really nice small mid-woofer. Assuming it goes into production of course.

[Jed]

That Dayton looks excellent as well. It's a larger cone with more low end and doesn't have the 3rd order rise the Peerless does at 1k. Both are very useable. I'd have to do a controlled comparison at the same time with the same setup to really do the comparison justice though.

Jed

[JonP]

[QUOTE=Jed]You mean something like this? 8O

Heh, but you'd need a reeeeeeal skinny woofer!

Yep, that's pretty much it, with a widened base section. Or, the narrow top as a separate cab, sitting on a taller wider box. Or, tapering out, like Curt C's Cinderellas... Possibilities are endless.

I have one other idea, that I might actually do, so I'll hold off now in case that happens. It'd be called the "Available Parts", due to the construction philosophy as well as parts used. It might just be made from "available projects" as well.

[megamuel]

I can't say enough good things about the TB W6-1139. That little sub really impressed me. It can fit in a tiny box (neo motor is a big help here) and has 13mm of linear excursion! It's well behaved even when driven past xmax. For a high quality sub/sat system I think the 8" would be the obvious choice, but the 6.5" is perfect for moms.

I think that Peerless SLS is cool, if it has lower distortion than the TB I could see using them in compact 3 way maybe. But if you are only using one woofer for sub duties I think the excursion of the TB wins out. Just my .02


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Sorry to hijack the thread but does anyone know any more about these speakers? Who's are they and are there any links to the design? Which driver is used in the surrounds? Cheers,

Sam.

[Jed]

Maybe Brandon (Augerpro) can post more about it, but the design can be found here:

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AND the thread/post:

https://www.htguide.com/forum/showpost.php?p=372360&postcount=89

It's called the Bose Buster II.

Brandon, feel free to reveal the details of this speaker as it fits the thread topic perfectly.

[Johnloudb]

I working out details on a BOM and a detailed schematic for this computer speaker amplifier, to post this design. I'd really like to build this myself, but I just can't do that right now. I have too much going on right now.

This amp should be extremely quiet, the gates of the mosfets are driven directly by the low output impedance of the very low noise op-amp. Also, the noise path to gate of the mosfets is a very high impedance. This is the exact opposite of my preamp circuit which has mosfets referenced directly to ground, thus amplifying the noise.

So, I'll be posting the design, instructions, and BOM in next couple days. I just had to get that noise issue worked out in my head.

[Johnloudb]

Amp Gemini

Ok, I'm getting this amp design drawn up. I hope it's clear enough ... I really tried. But I'm not the artist. Eventually, I may go back and redo the schematic with some schematic drawing software I have (which I did do). I'll keep updating this post till I get finished, BOM, etc..

Here is the schematic for one channel of the 15 watt, class A amplifier. The bias voltage is adjusted by varying the value of potentiometer Rp2. The DC offset is adjusted by varying the value of Rp1.

This amp uses only 6dB of global feedback. Some people say adding any feedback is bad and this amp can be used with no feedback by eliminating R6 and changing R1 to 20k ohms. But, this amp measures better with feedback, and I'm not afraid of feedback myself. The Op-Amp of course uses lots of feedback by default.

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Here is the unregulated power supply. L1 and L2 are just ferrite beads with a couple turns of wire. C10-C13 are 4700uF caps. The transformer is a 230VA Avel with dual 15VAC secondary windings. (click on pictures, then click + to enlarge):

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Here is the regulated power supply. I think it looks a lot better than my hand drawings, ya think? Anyway, I can't have a shabby looking amp so I'm redoing all my schematics on the computer.

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Below is the BOM for the 2 channel amp. But, Don't Anyone, Buy Anything Yet. This post is under construction.

Digikey Parts (click on pictures, then click + to enlarge):

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Below are the pin out for the MOSFETs. Don't worry that my schematic drawings look different than those on the Amp Schematic. The source of each MOSFET connects to a pair of output resistors (Rs). The N-channel MOSFET drain connects to the positive (+21v) power supply rail and the P-channel MOSFET drain connects to the negative (-21v) power supply rail.

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More very soon.

Below is the pontentiometer I'm using for Rp1 and Rp2. It is a multiturn to allow fine adjustment. Turning the screw moves the wiper, and varies the resistance between the wiper the two outer pins. Rp1 is used for to adjust the DC offset, and Rp2 is used to adjust the bias voltage, and bias current. The bias current should be adjusted to 550milliamps (0.55A). You measure the voltage across one of the Rs resistor pairs and divide it by the equalivent resistance (0.235 ohms) of the paralleled resistors.

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[Johnloudb]

Okay, I have to seriously focus on some other work for a month. I'll gradually finish work on the post above. Don't try to build it yet though - not done. I'll wait on posting the crossover and sub portions till we see what Jed comes up with for a speaker. I think he may leaning toward a 3-way Tower of Computer Speaker Power? which this two channel amp could drive if it's 90+ dB in sensitivity. That might need a sub too though.

[Johnloudb]

I just want to add, that I really can't recommend that anyone build this amp until I've built and tested it. That would be very irresponsible. I think I just got a bit too excited about finishing up this amp. I'll get to doing that but it may take a while.

[Jed]

Okay, I have to seriously focus on some other work for a month. I'll gradually finish work on the post above. Don't try to build it yet though - not done. I'll wait on posting the crossover and sub portions till we see what Jed comes up with for a speaker. I think he may leaning toward a 3-way Tower of Computer Speaker Power? which this two channel amp could drive if it's 90+ dB in sensitivity. That might need a sub too though.

I've been sorta feeling things out with this one. Waiting to see if people really want a speaker like I've posted in this thread. I like the 2.5way concept. A 3.5way tower would be cool and work well for a computer speaker and HT or as a bedroom speaker. Although the crossover would get pretty expenisve unless we could go active for the woofer LP.

For really small speakers, it seems that most folks are building microbe's or one of zaph designs. Now that the Aura NT1 is out of stock maybe it'll peak more interest in my proposed design with the peerless 3" and Vifa D26. Otherwise one could just build a Lineup F4/D4 or something for a computer speaker to go with your amplifier.

[impala454]

I am digging your drawing in post #213...

[Gir]

I'm definitely interested.

[Johnloudb]

Either of those designs would be really nice, I think. Having an active crossover in the 3.5 way certainly makes life much easier for the 15 watt amp. And like you say it's less expensive since adding a chip subwoofer amp, and crossover is only about $25.

I need to really focus on some other work right now, so it will be a month or so before I can build and test the amp. The amp is done from a design standpoint, although there could be problems, and I'd have to change things obviously. The BOM does have errors. It's just there to look at. :B

[Operandi]

I've been sorta feeling things out with this one. Waiting to see if people really want a speaker like I've posted in this thread.

I'm interested. Personally I'm building two sets of Microbes but thats simply because I bought all the drivers before this thread had started.

Still, I have at least one other friend that's looking for some high-end PC speakers so I may end up building these (whatever they end up being).

I think this thread is a great idea, a lot of people are not happy with the not so good options they have for desktop speakers.

[Johnloudb]

Nelson Pass designed cute little push/pull 50 Watt class A amp called the F5! So, my work is done! :demon:

Just kidding, I plan on testing both amps to see how they compare. If my amp works (?) it will run a bit cooler - not by much. Might even build the Pass amp to power my Lineup R44s, used along with my preamp. I'll use the 150 watt output MOSFET transistors Pass used for both designs.

The F5 is featured in audioXpress this month (May 2008 issue).

In other news I recently solved the noise problem with my preamp. It uses 5 Linthium coin cell batteries to set the bias voltage for the circuit. That was the source of the high frequency noise.

I had a 220uF cap in parallel with it, so I just add a 221 series resistor between the cap and battery. So thanks JonP, for bringing up battery noise as a problem.

It's still going to be a few weeks before I can start on the amp, though.

[Hdale85]

50 Watt Class A amp? Cute little? Have you gone insane A 50 watt Class A amp would be HUGE! Not to mention not cheap! And of course extremely power hungry.

[Johnloudb]

Have you gone insane

The jury is still out :lol:

A 50 watt Class A amp would be HUGE! Not to mention not cheap! And of course extremely power hungry.

Usually that'd be the case. The F5 is 50 watts peak, or 25 watts RMS. His designs are usually single-ended with 25% efficiency or less, but this is a simple push/pull and about 40% efficient, with a unique design and low distortion (<0.002% below 1 watt).

F5 --> Idle Power Dissipated = Ibias*(2*Vrail) = (1.3amps)(2*24v) = 62w/ch

My amp --> Idle Power Dissipated = Ibias*(2*Vrail) = (1.1amps)(2*21v) = 46w/ch

Any other thoughts on this? Sound good?

[Hdale85]

Hmmm.... I couldn't find any info on an F5 on the passlabs website. Got some links? It sounds like an interesting amp especially if its truly Class A. Of course I think all of Nelsons amps are Class A. Other question is how much are the parts on the F5 going to be lol.

[Johnloudb]

To see it now you'd need to buy an audioXpress magazine, and I'm not trying to push the magazine or anything else. It'll probably show up on www.passdiy.com sometime after this issue. I just think the F5 might interest more people and likely sound better.

[Hdale85]

I might be interested for my main system. Class A for computer speakers sounds a bit extreme. Although right now my main speakers are my computer speakers .

[Johnloudb]

Yep, I tend to agree. I guess trying to squeeze a class A amp and sub amp onto one heat sink is asking for trouble, too. I'll still be testing both amps with the same power supply, in the near future though.

[Hdale85]

Guess you don't have an idea of how much it would cost to build the F5? I have heatsinks already at least

[Johnloudb]

It's a very simple amp, Pass didn't add up the parts though. Heatsinks, transformer, & filter caps cost the most. I think about $150 would easily cover it, not including your enclosure. And you've got the sinks, like you say.

[Hdale85]

Well.... I have the PSU board from the Aleph 30 I was building so probably just use that. I still need the filter caps for it which were going to be like 80 bucks.

[Hdale85]

Found the schematic.

[Johnloudb]

Yep, where'd you get that? If it's copied from aX your probably violating copyright laws by posting. Not that people don't do it all the time.

If your PSU has Pos. and Neg. rails, it should work with the right transformer. It can output lots of current. Be a good amp for the Max, I think.

[Hdale85]

No Nelson posted it over at DIYaudio. I'd like to do a balanced amp though. Not sure if that ones setup for that .

More then likely they will have a PCB groupbuy for this amp over there.

[JoshK]

Class A for computer speakers sounds a bit extreme.

I don't know why that would be. For computer speakers I can't see any reason to need more than say 5 watts. You are sitting so close, let's not forget. For 5 watts, or thereabouts, class A is reasonable, I'd think.

I plan to use my PP 6V6 amp for computer duties...its around 11 watts unless I triode strap them and then its like ~6 watts iirc.

[Hdale85]

Very true. I don't know chances are if I build some computer speakers I will just use a T-Amp or something. I'd like the F5 for my main system.

[Johnloudb]

No Nelson posted it over at DIYaudio. I'd like to do a balanced amp though. Not sure if that ones setup for that .

More then likely they will have a PCB groupbuy for this amp over there.

Glad it's not an aX copy. Just saw that post at DIYaudio. Too bad about Pass lifting that XA200 amp and getting hurt. Hope he has a fast recovery.

Balanced configurations are way overrated. In many systems it provides too much gain making the sound worse, because the volume is turned way down. Noisy, and puts more series resistance at the gate, base, or grid of applicable gain device.

[Hdale85]

Well my DAC benefits greatly from balanced and I also don't use a preamp so it goes directly to the DAC and then to the amp. The F5 has a lot less gain then my Chipamp so I don't think it would be a problem. The chipamp has something like 30dB of gain the F5 has like 15dB of gain.

The F series from Nelson usually needs a high gain preamp as they only have one gain stage. At least this was the case with the F4 and would think the F5 is similar.

[BobEllis]

Looking at the F5 Schematic posted above, there isn't a way to convert it to balanced input. It looks like current feedback - note the low values of the feedback resistors.

A mini Aleph would be a more appropriate project if you need balanced in - at low rail voltages you could build it with fets for the input stage with little modification. I haven't followed the F series too closely, but I bet there's a balanced input version somewhere along the line, too.

Check surplus houses like www.apexjr.com for big capacitors. (no affiliation, just a happy customer) I picked up a bunch of 50,000 uf/50V caps there for $4 each a while ago. He may have something else suitable.

[Hdale85]

There are a couple people making balanced versions. Balanced isn't mandatory would just be nice I could just get the Ballsie which is a bal to se converter for my DAC. I think Nelson has a balanced schematic as well he just hasn't shown it yet. The Mini Aleph is only like 10-20 watts of power as well and I know its probably enough but I'd like to keep it close to what I have now which is 54wpc. I think the F5 would really be suitable for me. Also the Mini-A is not as efficient. Thinking about trying to make my own PCB for this we'll see. I would order some but small quantities is expensive.

[Johnloudb]

Well my DAC benefits greatly from balanced and I also don't use a preamp so it goes directly to the DAC and then to the amp. The F5 has a lot less gain then my Chipamp so I don't think it would be a problem. The chipamp has something like 30dB of gain the F5 has like 15dB of gain.

The F series from Nelson usually needs a high gain preamp as they only have one gain stage. At least this was the case with the F4 and would think the F5 is similar.

You know your system :T This circuit converts from balanced to unbalanced. It accepts both balanced and unbalanced inputs. With a toggle switch at the input you can even invert polarity. You could make a preamp with it or maybe use it in you DAC. If you need it.

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[Hdale85]

Yeah I need to build something like that. So basically the opamp and some resistors it looks like. Would this work just as well as the Ballsie from Twisted Pear? Nelson said I should just get some prototype board from radio shack for the amp since its so simple. So I guess I need to put together a parts list...not something I've always been good at

[Hdale85]

Anyway that BAL to SE converter would work with my PSU thats in the DAC? It's rated at 7.5v right now. Not sure how much that thing needs. I priced out the parts with a few extras just in case and comes out to about 12 bucks for 2 channels lol. Pretty good if you ask me.

[Hdale85]

I just did a parts list for the Schematic that Nelson posted up. And of course this is just for the amp board but I'm getting about 22 bucks per channel. So 44 bucks for 2 channels minus the PSU and what not. Thats really cheap. And since they only use 2 mosfets (IRFP240 and IRFP9240) they don't have to be matched.

[Hdale85]

This is the PSU they recommended to use for the F5.



A bit complicated. I have to remember what all these parts are as its been a while since I've used a schematic. The amp is easy only uses a few parts.

[Johnloudb]

Anyway that BAL to SE converter would work with my PSU thats in the DAC? It's rated at 7.5v right now. Not sure how much that thing needs. I priced out the parts with a few extras just in case and comes out to about 12 bucks for 2 channels lol. Pretty good if you ask me.

It needs positive and negative rails (i.e. +/- Vr) +/- 7.5v could work but it's a bit low. Op-amps are said to sound better with higher rails like +/- 15v.

peter_m found a nice inexpensive power for his crossover. I'll go dig that up.

Here it is:

http://sound.westhost.com/project05.htm

It needs a 16-18 VAC wall wart power supply. Check www.allelectronics.com

[Johnloudb]

To choose resistance values to adjust voltage gain for this:

gain (Vin/Vout) = R2/R1, where R1=R3 and R2=R4.

keep R1,R2 between 10k - 25k.

Also put a 12pf - 24pf cap in parallel with R2 and R4.

This circuit needs modification to be used as a preamp, but makes a good Bal ot unBal converter and polartity inverter.

You know your system :T This circuit converts from balanced to unbalanced. It accepts both balanced and unbalanced inputs. With a toggle switch at the input you can even invert polarity. You could make a preamp with it or maybe use it in you DAC. If you need it.

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[Hdale85]

Yeah Russ said to use 2k and 2.2k for the resistors. He said the Wolfson WM8740 has a schematic for one that includes a filter.

[Johnloudb]

This circuit is just a converter used outside the DAC. It isn't a filter or I/V converter. This is used after all the DAC circuitry. To convert Bal. to Unbal..

Values less than 10K will load the DAC ouput too much. So, I'm not sure what you're refering to. Unless your changing the filter circuit for unbalanced output.

[Hdale85]

Thats what Russ White and Brian Donegan told me to use (they are the creators of the DAC) so I'm not sure. They said 10k would be to high. Something about distortion.

[Johnloudb]

I just looked at the "Ballsie" schematic on twisted pair. It depends on which op amps they're using I suppose. Some op-amps are put out more current, like the opa2134. They used 1k in their converter circuit which is really low, but they designed it and took distortion measurements so they would know. The "Ballsie" has single ended and balanced outputs, so you might want to do that.

[Johnloudb]

He said the Wolfson WM8740 has a schematic for one that includes a filter.

Yep, page 22, figure 22 in the wm8740.pdf