DIY amplifier
« on: December 30, 2018, 01:39:48 PM »
Sup GDIY,

just yesterday I started putting together a power amplifier.





I've never built an amp before.. the design is based on a VCA/limiter from ESP. (I've built one for a crossover)

Technically it runs off a rectified ~38VDC PSU I pulled from a defunct Akai cassette deck ,the one I built earlier used a 12VDC wall wart. (edit : the transistor circuitry sees roughly a 24VDC voltage. I measured the signal inputs and outputs for leaks as well as the voltage applied to transistor drain, ideally I'm looking to either add another transistor for more gain and/or add another amplifier channel for stereo operation. It uses an IRF520 MOSFET, and slightly different components than the xover limiter, such as a homebrew cap and one from a hairdryer so it's mostly made from unobtainium/handwavium parts and as such almost impossible to clone)

I can't make a CAD drawing for the time being because my desktop PC is suffering from thermal breakdowns.

This is purely a test to see how a DIY amp would perform, and if it's worth the trouble (most cabinet builders use/buy off-the-shelf or custom it seems).

Essentially I'm looking to use them (and my earlier DJ mixer & crossover builds) in a PA system I've been building (it's still a work in progress, link to build thread in Speakerplans)



Any thoughts/advice/ideas?

-ef

EDIT : tested with a driver.. it works I guess. To clone it I'd need to reverse-engineer the PSU and find a similar cap to the one it has now, luckily I rolled those capacitors in pairs.. rest of the parts are off-the-shelf.
« Last Edit: January 01, 2019, 03:20:19 AM by efinque »


JohnRoberts

Re: DIY amplifier
« Reply #1 on: December 30, 2018, 03:30:09 PM »
Big efficient speakers are easier than big amps, but modern amps are cheaper these days... I remember when $1/watt was considered cheap.

I attached a picture of my first DIY amp circa early 70s (and last so far) while I did design one amp for Peavey (AMR PMA 70+). My big DIY amp was 4x200W and quite heavy. The transformer alone was 65# total weight was something like 125#. It worked the last time I fired it up. The box right above it was my surround sound kit from 80s.

I am considering cobbling together some  Hypex modules, probably should just do it... I need 6 channels for my living room, but don't need hundreds of watts. https://www.diyclassd.com/audio-amplifiers/

These look a bunch cheaper than the last time I looked (sweet).

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: DIY amplifier
« Reply #2 on: December 30, 2018, 03:50:10 PM »
Big efficient speakers are easier than big amps, but modern amps are cheaper these days... I remember when $1/watt was considered cheap.

That's my main concern.. a T.Amp E-800 costs 159e on Thomann.

Quote
I am considering cobbling together some  Hypex modules, probably should just do it... I need 6 channels for my living room, but don't need hundreds of watts. https://www.diyclassd.com/audio-amplifiers/

Those modules look actually quite nice spec-wise (and in general). There's no price though?

JohnRoberts

Re: DIY amplifier
« Reply #3 on: December 30, 2018, 05:27:01 PM »
That's my main concern.. a T.Amp E-800 costs 159e on Thomann.

Those modules look actually quite nice spec-wise (and in general). There's no price though?
I just ordered some... one 4x70W and and one 2x30W.. with shipping to US and conversion to dollars still comfortably < $200 ( a bunch cheaper than last time I looked, back then I had to source a PS separately, now included, and more.)

Bruno Putzey the brains behind those amps is one of the few truly great design engineers in the game today.  I am pleased to finally buy something he engineered.

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: DIY amplifier
« Reply #4 on: December 31, 2018, 06:44:14 AM »
I just ordered some... one 4x70W and and one 2x30W.. with shipping to US and conversion to dollars still comfortably < $200 ( a bunch cheaper than last time I looked, back then I had to source a PS separately, now included, and more.)

The PSU is another concern as I doubt it was designed to drive any loads in the first place.

Analog Metric has a nice catalog of amp modules/kits too.. at one point I was thinking of ordering one for testing purposes.

JohnRoberts

Re: DIY amplifier
« Reply #5 on: December 31, 2018, 10:05:45 AM »
The PSU is another concern as I doubt it was designed to drive any loads in the first place.

Analog Metric has a nice catalog of amp modules/kits too.. at one point I was thinking of ordering one for testing purposes.
I have long been a fan of Bruno's particular approach to class D, the high efficiency is finally delivering a cost saving from the reduced heat sink and power supply requirements compared to conventional analog amps. For decades class D was too complex (expensive) to actually enjoy those cost savings. These are not cheap amps but good bang for the buck, with high performance.

Sorry to hijack your thread... pimping Hypex

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Rob Flinn

Re: DIY amplifier
« Reply #6 on: December 31, 2018, 10:12:19 AM »
The Hypex amps are great.  I use the UCD180 for my studio monitors.  They are very simple to get going, just bolt to a suitable heatsink & put them in a box with a suitable PSU.  I built a PSU just usinga a Torroid & some caps. Works great.

The reason you can't see prices on the HYpex website is that there are 2 sites.  One is wholesale for companies (with no prices) & the other for DIYers & other consumers (with prices).

Look for prices here

 https://www.hypexshop.com/shop/shop.jsp?groupID=116
regards Rob

Re: DIY amplifier
« Reply #7 on: December 31, 2018, 10:50:07 AM »
For decades class D was too complex (expensive) to actually enjoy those cost savings. These are not cheap amps but good bang for the buck, with high performance.

Yes I had a hunch that high-end amps/class D have their complexities.

The reason you can't see prices on the HYpex website is that there are 2 sites.  One is wholesale for companies (with no prices) & the other for DIYers & other consumers (with prices).

Look for prices here

 https://www.hypexshop.com/shop/shop.jsp?groupID=116

Thanks for the link!

Atm I'm weighing options what's worth building and what's not.. for example power amplifiers sold off-the-shelf have features like limiters/DSP etc, and the option for bridging.

EDIT : and I don't mean playing it at war volumes.. maybe use it for the tweeters or something.
« Last Edit: December 31, 2018, 11:29:14 AM by efinque »

JohnRoberts

Re: DIY amplifier
« Reply #8 on: December 31, 2018, 11:05:35 AM »
The Hypex amps are great.  I use the UCD180 for my studio monitors.  They are very simple to get going, just bolt to a suitable heatsink & put them in a box with a suitable PSU.  I built a PSU just usinga a Torroid & some caps. Works great.

The reason you can't see prices on the HYpex website is that there are 2 sites.  One is wholesale for companies (with no prices) & the other for DIYers & other consumers (with prices).

Look for prices here

 https://www.hypexshop.com/shop/shop.jsp?groupID=116
The link I provided is for the DIY site and includes prices... 

How else could I just buy some?

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: DIY amplifier
« Reply #9 on: December 31, 2018, 11:32:16 AM »
Another idea I got from the Hypex site is a soft-start module which could be handy.


JohnRoberts

Re: DIY amplifier
« Reply #10 on: December 31, 2018, 12:04:08 PM »
Yes I had a hunch that high-end amps/class D have their complexities.
Price performance has been the albatross hanging around class D's neck for decades. Peavey was already selling class D amps before I started working there (1985). They were premium price points and less than premium performance. It was more of a novelty than an effective amplifier topology.

As an engineering manager at Peavey I supported an active engineering project under my group to develop a class D amp module for use in top box powered mixers. This could have been a very high volume application, but despite promises, the technology never got down to a competitive price point against analog.  I wasted a couple man-years of one junior engineer working full time on that one project without success.

Another decade later I became the product manager in charge of all Peavey power amps, one of which was a one rack space 1000W class D amp.. Still a relatively expensive, medium performance novelty.

Now more decades later the Class D technology has matured to the point where most lower price value power amps are Class D because it is finally cheaper than analog. (Where was that technology*** last century when it could have done me some good? ).   

JR

*** I actually know what the technological hurdles were back then but too much of a veer...
Quote
Thanks for the link!

Atm I'm weighing options what's worth building and what's not.. for example power amplifiers sold off-the-shelf have features like limiters/DSP etc, and the option for bridging.

EDIT : and I don't mean playing it at war volumes.. maybe use it for the tweeters or something.

Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: DIY amplifier
« Reply #11 on: December 31, 2018, 12:21:42 PM »
Now more decades later the Class D technology has matured to the point where most lower price value power amps are Class D because it is finally cheaper than analog. (Where was that technology*** last century when it could have done me some good? ).

I've seen those 1U class D amps giving +1kW but I'm skeptical as the average class AB/B amps with the same power rating are usually 2-3U and weigh around 10-15kg.

EDIT : btw, I have a L293DNE quadruple half-h driver IC that came with the Arduino Starter kit.. wonder if it could be used as an amplifier? According to the spec sheet it's a motor driver.
« Last Edit: December 31, 2018, 02:40:11 PM by efinque »

Phrazemaster

Re: DIY amplifier
« Reply #12 on: January 01, 2019, 12:26:52 AM »
Big efficient speakers are easier than big amps, but modern amps are cheaper these days... I remember when $1/watt was considered cheap.

I attached a picture of my first DIY amp circa early 70s (and last so far) while I did design one amp for Peavey (AMR PMA 70+). My big DIY amp was 4x200W and quite heavy. The transformer alone was 65# total weight was something like 125#. It worked the last time I fired it up. The box right above it was my surround sound kit from 80s.

I am considering cobbling together some  Hypex modules, probably should just do it... I need 6 channels for my living room, but don't need hundreds of watts. https://www.diyclassd.com/audio-amplifiers/

These look a bunch cheaper than the last time I looked (sweet).

JR
Time to dust!  ;D :P
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** * Kablooie!

Rob Flinn

Re: DIY amplifier
« Reply #13 on: January 01, 2019, 09:23:18 AM »
I've seen those 1U class D amps giving +1kW but I'm skeptical as the average class AB/B amps with the same power rating are usually 2-3U and weigh around 10-15kg.
 

That's because the class D amps are far more efficient & quite often are running from SMPS which are more efficient too.    I had an HH 700W per channel power amp that was normal amp someone gave me that weighed like an AMPEG SVT.  Most of the weight was a huge torroidal transformer for the linear PSU.   The class D amps don't get as hot.    The 180W Hupex amps I'm using for monitor are very ballsy.   The class D amps are far more tolerant of load changes in speaker impedance that you get with varying frequency program content too.   I have 2 in a 2U box with a linear PSU, but could easily fit another pair for my Auraclones.
regards Rob

JohnRoberts

Re: DIY amplifier
« Reply #14 on: January 01, 2019, 10:48:25 AM »
Time to dust!  ;D :P
I am waiting for my wife to dust.... but since I am not married I will have to keep waiting.   ::) I have two big air cleaners with micron filters with one or the other running 24x7. About once a month or so I vacuum accumulated dirt off the outside of the air filter element. Despite this I still have to dust visible build up from flat surfaces.

That old power amp has been collecting dust since the 70s. Back then it was sand blasted and had a nice fresh coat of paint.

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: DIY amplifier
« Reply #15 on: January 01, 2019, 11:00:33 AM »
Well, the transformer I pulled from an intercom doesn't show any secondary readings.. it's a 20VA laminated core.

JohnRoberts

Re: DIY amplifier
« Reply #16 on: January 01, 2019, 11:12:12 AM »
I've seen those 1U class D amps giving +1kW but I'm skeptical as the average class AB/B amps with the same power rating are usually 2-3U and weigh around 10-15kg.
You would become less skeptical if you had to carry them around, set up and tear down for every live sound gig.  I just had to hump them around for display at trade shows and that was enough lifting for me.

The superstition that somehow amps need to be heavy to make big power has surely faded by now.. Back when I was still product manager for all power amps at Peavey I had a series of old school class A/B power amps to sell. The biggest topped out at 2x1000W, was heavy and large

I even wrote an ad touting the "heavy iron" transformer and heatsinks hoping there were a few would be customers out there who were thinking like you.  ;D (I wasn't lying, the amps were big and heavy.)
Quote
EDIT : btw, I have a L293DNE quadruple half-h driver IC that came with the Arduino Starter kit.. wonder if it could be used as an amplifier? According to the spec sheet it's a motor driver.
Looks like its designed as a saturated switch (either on or off), and modest output current for an amplifier.
=======
I have watched the evolution of amplifier technology play out over the decades.  I even got sound to come out of a crude couple watt class D amp I built on my bench in the 70s. It also shut down radio reception in the immediate area.  :o

Here is an article I wrote in another lifetime... https://peavey.com/support/technotes/poweramps/classact.cfm You can date the article from all the Peavey amps I was pimping in the article. The basics are still true, but Class D in the decades since has become cheap (and good) enough to eclipse several categories.

JR
Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: DIY amplifier
« Reply #17 on: January 01, 2019, 01:41:17 PM »
I have watched the evolution of amplifier technology play out over the decades.  I even got sound to come out of a crude couple watt class D amp I built on my bench in the 70s. It also shut down radio reception in the immediate area.  :o

Haha.. I think radio brownout here can get you in prison in the worst case if it's intentional.

PRR

Re: DIY amplifier
« Reply #18 on: January 01, 2019, 04:06:03 PM »
> 1U class D .... I'm skeptical .... AB/B amps with the same power rating are usually 2-3U

Size is not about sound quality. It is mostly about heat.

100 Watt class B will dissipate 25W to 50W. Plus 50/60Hz power transformer losses (many Watts) and weight.

100 Watt class D will dissipate 15W to 5W. And is commonly used with a switcher supply using 40KHz "iron" and much lower losses (heat).

Re: DIY amplifier
« Reply #19 on: January 01, 2019, 04:13:59 PM »
Size is not about sound quality. It is mostly about heat.

100 Watt class B will dissipate 25W to 50W. Plus 50/60Hz power transformer losses (many Watts) and weight.

100 Watt class D will dissipate 15W to 5W. And is commonly used with a switcher supply using 40KHz "iron" and much lower losses (heat).

Yes the heat is a concern.. which is why I'm skeptical.

Usually when things warm up they begin to sound different too.

EDIT : I was thinking a thermal fuse but meh.. I don't think it's necessary. Reworking the PSU is something I've considered (it IS an Akai casette deck PSU, after all)
« Last Edit: January 01, 2019, 04:53:36 PM by efinque »


 

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