Slick little Chip-Amp Kit and Other Project Ideas

[slipperybidness]

I like the styling, wish they posted some measurements.
https://www.boxedkitamps.com/gobo-stereo-audio-amp-kit

I may end up building this as a class project this semester (Linear IC). But, the teacher may not let me just slap together a kit. If the kit doesn't fulfill the project requirements, then I may take this kit and put a filtered sub output on it. That should definitely fulfill the project requirements.

Anybody have any other IC class project ideas?

 

[ImcLoud]

Amazon.com : FMOD Crossover Pair 70 Hz Low Pass : Vehicle Audio Video Accessories And Parts : Car Electronics low pass done, lol...

I would make something super use full, I think you are on the rite path with the filtered sub out put idea..

Put together a device that handles high and low pass and splits the input with individual gains on each of the 4 outputs....
In other words 2 rca's go in and 4 come out, a left and right have a high pass dial and each has a gain dial, and then the other left and right have a low pass dial and a gain dial for each, I would also install a switch that makes the sub outputs summed mono...

Shouldn't be too hard but it would be awesome to have a little analog box like that for integrating subs into a 2 channel system with out needed a special preamp, fmods, or dsp...

Another idea would be to build a no power needed preamp, just well made switches and a really nice volume control...

 

[slipperybidness]

Amazon.com : FMOD Crossover Pair 70 Hz Low Pass : Vehicle Audio Video Accessories And Parts : Car Electronics low pass done, lol...

I would make something super use full, I think you are on the rite path with the filtered sub out put idea..

Put together a device that handles high and low pass and splits the input with individual gains on each of the 4 outputs....
In other words 2 rca's go in and 4 come out, a left and right have a high pass dial and each has a gain dial, and then the other left and right have a low pass dial and a gain dial for each, I would also install a switch that makes the sub outputs summed mono...

Shouldn't be too hard but it would be awesome to have a little analog box like that for integrating subs into a 2 channel system with out needed a special preamp, fmods, or dsp...

Another idea would be to build a no power needed preamp, just well made switches and a really nice volume control...

LOL!

Yeah, get a little project box, add the F-Mods, call it a day, easy A

Unfortunately, I'm a little too honest to try to pull that one off.

But, yeah that kit could be really interesting with some bass management added in. I could see that thing making a nice little desktop system paired with a pair of DT SM350s (that I already own) and a sub. And, you can't beat the price!

I know you are a fan of keeping it simple and a short signal path. It really doesn't get much simpler than a chip-amp like this.

And, the other idea about the little box isn't such a bad idea either, but that's probably a bit more work than I want to do for this class. And, being an IC class, I will almost certainly have to do a project using active components.

 

[GIEGAR]

Anybody have any other IC class project ideas?

Slippery, there's more project ideas here than you poke a stick at: ESP Projects Pages - DIY Audio and Electronics.

There's a good chance something will meet your needs, or at least plant the seed.

 

[lsiberian]

Could you pull off dsp + amp combo board?

Mind you I have no idea how much work the dsp part would be.

 

[slipperybidness]

Slippery, there's more project ideas here than you poke a stick at: ESP Projects Pages - DIY Audio and Electronics.

There's a good chance something will meet your needs, or at least plant the seed.

Thanks! I haven't seen that site before, can't believe it's slipped under my radar!

I peaked ahead at the next few chapters for this semester, and we are coming up on ACTIVE filtering pretty soon. Should be interesting.

 

[BoredSysAdmin]

or more idea:
https://www.mayflowerelectronics.com/shop/diy-products/diy-objective2-kit/
This a reference quality level headphone amp kit, optionally with dac

 

[slipperybidness]

Quick update. The kit was ordered late last Wed, and I received it this Tuesday. ~6 days from order placed to item recieved! Already off to a good start on that.

I pretty much just opened the box and said "Yup". But, it was packaged well and double-boxed.

I will start working on it next week. I might just be ready to test it out next weekend.

I will be building it and measuring it. Seeing if it meets the advertised specs (at least as much as I can with the equipment that I have available), and also doing some thermal analysis. After all the measurements and subjective stuff is done, I will start looking into useful mods/upgrades. Why? Why not At $100, there isn't much to lose, as long as I don't kill any speakers.

Since this is a class project, it should end up being a fairly thorough review. I will try to post that in a couple months once it is complete.

 

[slipperybidness]

or more idea:
https://www.mayflowerelectronics.com/shop/diy-products/diy-objective2-kit/
This a reference quality level headphone amp kit, optionally with dac

Thanks! Well, I already purchased the GOBO, but we all know that has never stopped us from the next purchase anyway.

 

[BoredSysAdmin]

Good luck. It shouldn't take you more than one weekend to build it Unless you don't know how to solder

 

[slipperybidness]

Oh, I'm a solderin fool.

Projects under my belt:
Quickie Pre-amp with the Constant Current upgrade
Quickie 1.1 Battery Powered Directly Heated Tube Preamplifier Kit | Bottlehead
PJCCS Upgrade for Quickie | Bottlehead

Dynaclone ST70
tube4hifi ST70 page

This little drum machine
http://bleeplabs.com/store/bleep-drum-midi/

And this analog synth! Man, this was ~40 hours of work!
PAiA - Fatman Analog Mid Synth

Probably at least 1 other that I have forgotten. Plus, I have a few electric RC cars with plenty of mods and upgrades. Dang, what a rewarding and fun hobby those are, and keeping them running keeps your mind sharp for troubleshooting on mechanical and electrical problems.

Obviously, I'm about at the point that I don't have much to learn from a kit. Next step is to mod some kits and build from schematics. After that.....I guess it's time to try designing and building circuits from scratch. I've got some ideas, and some ideas that I could turn into a little side business of selling modular kits. Of course, electronics repair can be a nice little side business too. Probably just as important as income would be the tax breaks you can get as a small businessman.

 

[slipperybidness]

So, the GOBO is built and I am certainly impressed!

It drives my Infinity 363 (4 ohm as measured by AH) to high volumes with no problems and without putting out a lot of heat. I will measure the temp at the heat sinks in the near future via IR thermometer and post the results.

I have it with me to take to class tonight. I should be able to get some measurements tonight. In/Out Z, freq resp, gain, AC ripple on the P/S output, load regulation on the P/S.

I'm not sure if I will be able to do power measurements today, need to find some appropriate resistors. And, a friend just purchased a distortion analyzer. He doesn't even know how to use it yet, but now is a good time to learn.

 

[lsiberian]

Yeah chip amps are quite capable.

 

[slipperybidness]

OK. First round of measurements are done! Let me re-state: I am nothing but impressed with this little amp! The more I dig into it and measure and learn, the more impressed that I am. It is obvious that these guys have a clue about what they are doing. It is well engineered and thought out and laid out. For the current US price of about $120 with shipping, it is a dang tough amp to beat.

My only real complaint is that the kit is made for complete noobs, and has several areas where the original design uses crimp-connectors. We don't need no stinking crimp connectors! All solder over here!

I certainly hope that my continued measurements don't uncover any flaws, because I like what I hear and see and I want to like this little amp too. Tomorrow, I plan to try to get some THD+N measurements and In/Out Z, and maybe a 2 ch driven power measurement. I will also borrow some resistors to get a 4ohm dummy load for early next week.

First round measurement results, with 8 ohm resistive dummy load:
*26Wpc peak power (1 ch driven)
*1.3V input to reach full power
*Av = 27dB
*-2.6 dB @ 13Hz and +0.15dB from 10kHz to 20kHz
*AC ripple on the output of P/S = 200mV peak-to-peak

I am now considering looking into this chip a little deeper (LM1875). I may end up ordering another kit and doing a souped-up hot-rodded version of this kit, assuming that the chip can handle it.

So far, I have only run this on my P363s. I may hook it up to the Philharmonitors in the near future. Obviously, risk the cheap speakers first. I also have a speaker protection circuit in the works to help play it safe.

It barely got warm when playing the P363s. However, driving it with a sin wave for measurements certainly heats it up quite a bit more than real music ever did.

 

[KennoMonkey]

We are thinking about advertising here and I just saw your post. So, cool! (Ken from Boxed Amps here, we make the Gobo)

I've also thought about the hot-rodded version. The LM1875 can handle up to +/-30 volts. We need a list of components that need to be upgraded. I'm thinking caps, possibly, but they are all over-sized. My biggest worry would be how to get rid of the extra heat.

As for the crimped terminals ;^) I wanted to make it so you could disassemble the amp after you made it, so you could make mods. The concept is for each wire, one end is soldered, the other detachable. Mostly screw terminals, but yeah a couple of crimp-ons. Besides, it's only in the 120VAC circuit path. If anyone's got ideas for a better solution there, I'm all ears.

Anyways, I'm looking forward to your other measurements. Thanks for the props. -Ken

 

[slipperybidness]

We are thinking about advertising here and I just saw your post. So, cool! (Ken from Boxed Amps here, we make the Gobo)

I've also thought about the hot-rodded version. The LM1875 can handle up to +/-30 volts. We need a list of components that need to be upgraded. I'm thinking caps, possibly, but they are all over-sized. My biggest worry would be how to get rid of the extra heat.

As for the crimped terminals ;^) I wanted to make it so you could disassemble the amp after you made it, so you could make mods. The concept is for each wire, one end is soldered, the other detachable. Mostly screw terminals, but yeah a couple of crimp-ons. Besides, it's only in the 120VAC circuit path. If anyone's got ideas for a better solution there, I'm all ears.

Anyways, I'm looking forward to your other measurements. Thanks for the props. -Ken

Hey, nice to see you following along and posting over here on AH!

Good info on the chip and what it can handle.

Any chance that you have already done some THD measurements? And, any chance that you could post those or send them my way via email or PM?

My friend is an electronics tech and just purchased a distortion analyzer. He hasn't used it yet, so we have a learning curve on that. If I had the THD measurements from the vendor, it would help me to be sure I'm doing it correctly. If you don't have the measurements, or don't feel comfortable releasing them, then I completely understand.

I have to say that I have learned a LOT from this build and the associated measurements! It fit right in with my Linear IC class this semester too! Keep up the good work!

 

[slipperybidness]

Well, as far as a hot-rodded amp:

I was considering a separate P/S. Over-built and more than it could possibly need, then pigtail the DC power over to the amps.

And, what is your opinion on Liquid Cooling? I know some computers use it, I just dunno if it's a good idea for an amp, and how noisy is the liq pump?

Yeah, yeah, yeah, these things are "over the top"......but that's the point

 

[slipperybidness]

Just a few items to add.

Slew rate @ 20kHz = 12V/us

Also, the amp was stable and linear freq response up to ~75kHz.

 

[slipperybidness]

No posts in this thread for a while, so I wanted to give an update.

I have been using this gobo amp built from a kit (I paid $100 for the kit, less than the current asking $160)
https://www.boxedkitamps.com/gobo-stereo-audio-amp-kit

With a Parasound ZCD in silver (used off ebay for $225)
http://www.parasound.com/img/zcustom/zcd_angle_silver.jpg

And the DT SM350 (new from newegg, I paid $200)
http://www.newegg.com/Product/Product.aspx?Item=N82E16882325059&cm_re=definitive_350-_-82-325-059-_-Product

For $525, this is an incredible little desktop setup! I actually use it at my workbench where I work on electronics projects and repairs, where space is at a premium.

I can turn this system gain up to max with the cd paused, and I get absolutely no hum or hiss from the speakers, even with my ear right up to it. I can also turn the volume down to min and put my ear up to the ZCD and just barely hear the disk spinning. That is no trivial feat!

The Parasound ZCD: A FINE CD player! Small so it is easy to move between amps or rooms, and that is important if you build audio gear, or have limited space. It also has the option of fixed or variable outputs, another great option for an amp builder. It is completely QUIET. I can BARELY hear it spinning when I mute the audio and put my ear right up on it. If I had to nitpick, slot load drives aren't my favorite, but I'll let it slide for everything else that it does right. A great deal for the $225 that I paid!

The GOBO from BKA: A great little amp! Small and it looks snazzy and it puts out a real ~20Wpc (8 ohm). It's not a beast or anything, but it does its job well and has no hum or hiss! There are 2 nitpicks to add: 1) It could use a subwoofer out. 2) There is a "thump" through the speakers when it powers down. That has kept me from running the Philharmonitors on this amp. It needs soft-start / shutdown. I am currently working on an external speaker protection circuit that should solve this problem. For the $100 that I paid for this amp, good luck finding anything better at that price point (it aint gonna happen).

The DT SM350: Good, small speakers. Sure, they are probably not the most accurate out there. For the $200 that I paid for them, they are worth every penny! Even if not the most linear FR, they do sound good to my ears, and they are an easy load to drive, and they have better deeper bass than I expected (room placement helped on that).

I will most likely be moving the GOBO to take on duties for my drum machine / synth setup, feeding P363 towers. The ZCD will move to my Parasound 1206, and eventually to my reference level LM4780 amp (once it is completed), driving the Philharmonitors. That leave the DTSM350 as "floater speakers" for a while, and will eventually be paired up to a LM3886 build.