Looking for a little power amp project (spoilt for choice on here)

Puggie

Member
2004-10-11 5:21 pm
Hi All

Looking for a bit of advice. I want to step up my diy audio game, I've done nothing for the past 10 years apart from a bit of car audio and stuff prebuilt boards in to enclosures on rare occasions (currently listening to an ebay TPA3116 board in an ebay DOUK aluminium enclosure).

So I'd like to build up something akin to the Sugden Bijou system:
RPi based streamer with Allo BOSS DAC (currntly running this into an old A&R A60)
DIY Stereo headphone amp or Sugden Headmaster if I can find one (3ip pre-amp)

I want to build a nice small footprint power amp, I'd quite like something small and class-a (no real logic to this decision so feel free to try and sway me)

I listen at home at low levels so I do not need reference level power, and my speakers are small mini monitors (troels Graavessen Seas w15 and fountek ribbons).

So there are the JLH amps, various Pass amps, Rod Elliots stuff etc etc, where on earth do you start? I want a foot print of 250x280mm (ish), im happy to build it quite tall (4-5U is no problem). This is what I'm building in the style of (hopefully):

DSC_0022.jpg


can anyone suggest a suitable start point for me. This will hopefully be a nice winter project.
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
I think the current ACA from Nelson Pass has to be a real contender if you want small and Class A. Its a modern tried and tested design. Using an SMPS overcomes any problems of ripple on the supply (as with conventional PSU's) although of course yoy can go down that route with the JLH.
 
Unless your Troels Graveson speakers are 91dB or more sensitive, an ACA is simply not enough power to satisfy. You might look at the Aksa Lender Pmos Hybrid Aleph (ALPHA) 20w version. Very simple to make (7 actives) and no adjustments of any kind. Sound is fantastic and needs no preamp as has 29dB gain. ACA is 14dB gain, so probably needs a preamp.

Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
 

Puggie

Member
2004-10-11 5:21 pm
Thanks everyone for your thoughts:

The ACA looks interesting, I'm concerned 5w will not be enough, but its so simple looking and I like the use of SMPS, it strikes me as an intelligent design cutting all the right corners. So I might build one anyway if I can find a suitable heatsink kicking around, I know I have 19v laptop PSUs courtesy of the WEEE bin. Could make for a very cheap (mostly scavenged) amp for my desk at work.

My speakers are well into the 80s dB so despite not wanting a lot of power I think 10-15w would be needed rather than 5w. I'm not afraid of a more complex build, my assembly abilities are pretty good (I'm certified for space flight hardware assembly). I have a half built Greg Ball SKA150 somewhere, but not seen it since moving house. The ALPHA look interesting, I need a shortlist to properly go through the threads of each, a 280+ page thread is a bit daunting when you look and find at lease a dozen suitable candidates on here for builds to research.

Which Pass, there are so many, hence me asking on here :)
You assume I'm happy with the 3116, it makes a pleasant noise at my office desk, but I wouldn't use it at home (my old A&R A60 is nicer now I've re-capped it). This thread is about making something to properly eclipse both the TPA and A60 for my home listening. It has to be a properly WAF approved system, so no bare MDF speakers, no massive Krell KSA50 clones with exposed mains for the children to lick when I'm no looking, nothing that requires 4 different remotes to operate (pre-amp will be needed to switch between the RPi streamer and tv, and have control volume all off the existing samsung TV remote). I want something fairly compact, but quality hence I'm using the Sugden Bijou for inspiration, If I could fine their music master at sensible money I'd probably just buy one and I'm still considering the headmaster pre amp to run all this from (as it just uses a regular ALPS motor driven volume and simple relay source switching, all that control is on separate PCBs and ripe to be hacked into what I need).

My rough chassis design is looking like 0.4-0.45 deg c/W of cooling available per channel (250x150x40mm deep finned heatsink) Is this in the ball park for a 15-20w class A? looking at the ALPHA somewhere in the box of bits in the loft have an old Scythe ninja heatsink which would look cool hanging out of a build (its bloomin massive), not what I want to do here though.

thanks again for the thoughts, keep em coming.
 

huggygood

Member
Paid Member
2011-03-19 8:42 am
france (bretagne)
I know the whole jewel of sugden, I got it and I still have the CD player.
the chassis is entirely aluminum and very thermal conductor.
it lends itself perfectly to the assembly of a class A amplifier of 10/15 W with 2x1.5 / 2A of dissipation.
me, I would be you, I will not start a JLH69 as simple as possible with a good CRC power supply and the right components for the amp.
the best would still be a JLH in P2P.
or so but with a little more work, a No. 217 NRDS 2x30W from JM Plantefeve, the only amp I have been keeping for over 15 years in class AB with a big part of class A

30W_nrds.gif
 
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My rough chassis design is looking like 0.4-0.45 deg c/W of cooling available per channel (250x150x40mm deep finned heatsink) Is this in the ball park for a 15-20w class A? looking at the ALPHA somewhere in the box of bits in the loft have an old Scythe ninja heatsink which would look cool hanging out of a build (its bloomin massive), not what I want to do here though.

This is a tad undersized for a 20w-25w Class A amp with +/-25v rails and 1.25A bias. However, if compactness is what you look for, simply adding a 120mm PWM fan set to lowest speed (silent operation) will let this heatsink have perhaps only a 10C rise over ambient. I know so many treat fans on Class A as anathema and are the work of the devil... But they really are the way to go for keeping the amp small and compact (also smaller heatsinks cost a lot less).

A small heatsink like this (costs $15) can dissipate 100w no problem. Our computers do this routinely. Imagine the size and cost of a slab of finned aluminum needed to dissipate 100w.

659378d1517198709-aksa-lender-mos-hybrid-aleph-alpha-amplifier-alpha-prototype-02-jpg
 

Puggie

Member
2004-10-11 5:21 pm
Thanks for your input, I was thinking about this earlier the whole compact heating issue and yes I would rather avoid fans, maybe I'm a snob, maybe I see it as 'cheating' maybe I should give them a chance. Would this fly:

take the basic Sugden chassis concept in post 1, take the heatsinks and in each 'trough' between the fins, drill a row of 3-4mm dia holes maybe 20mm apart through the base of the heatsink (I have access to a CNC mill to make this a bit more sensible a job). Now mount a large fan in the base of the casing drawing the coolest air from under the amp and giving a very low volume of airflow through the case and out between the fins. Nothing on show to suggest fan cooling. PSU parts may be mounted on a mezzanine in the case or hung from the top.

my intention is to make the construction similar to the sugden but anodised black, so I may get away with it, but its always nice to have a plan B. I may even have a couple of 'silent' 120mm fans in the loft from my media PC building days.
 
Perhaps go with the PASS F4. Here's why,

It is a complimentary output stage which operates in Class A up to a point and then switches to Class B. This allows you to have your cake and eat it. Set the Class A bias for the first few Watts and provide enough rail voltage so that it can swing into Class B on the peaks. You get higher peak and average power capability with less heat.

The F4 is proven, has a strong track record. There is a version of it without the JFET input stage which is further advantageous because the JFETs are hard to come by.

It needs a decent pre-amp to provide voltage gain and drive. This gives you a fun excuse to make a PASS pre-amp too.

If you want to go even simpler, search up the Susan Parker Zeus amplifier.
 
Perhaps go with the PASS F4. Here's why,

It is a complimentary output stage which operates in Class A up to a point and then switches to Class B. This allows you to have your cake and eat it. Set the Class A bias for the first few Watts and provide enough rail voltage so that it can swing into Class B on the peaks. You get higher peak and average power capability with less heat.

The F4 is proven, has a strong track record. There is a version of it without the JFET input stage which is further advantageous because the JFETs are hard to come by.

It needs a decent pre-amp to provide voltage gain and drive. This gives you a fun excuse to make a PASS pre-amp too.

If you want to go even simpler, search up the Susan Parker Zeus amplifier.

The Susan Parker transformers cost 450 pounds,way too expensive.
 
Puggie,
Good luck trying to choose which amp to build!!!
Once you start it's a bit like eating peanuts. Any of the Pass amps and variations M2 has Quite a few New flavours.
The Aksa Alpha 20 sounds Great easy to build No adjustments using easy to obtain parts. Also has Pass Tech in the design.
Most people on this Forum don't just stop at building one amp.
Build the case and a power supply ( The Expensive Part) and try a few different amp boards from the diyAudio Store.
GOOD LUCK!!!!
Steve.
 
If you want a superb quality amplifier with excellent construction documentation and after sales support, don't look past the : Neurochrome Mod-86 You will struggle to find an amplifier anywhere that will offer lower distortion and noise performance. The power output is about right for your application too. Check out the build threads HERE and HERE.

There are lots of small chassis on Ebay that will house this amp nicely. I used the 2107 chassis for my build, you would probably prefer THIS.
 
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Digital or a class amp!

Or a more modern digital amp complex over Aca (someday) LTspiced better than zetex ddfa.

Direct DFA with independent digital audio input ports/I2S/TDM , wireless multiroom /hard drives or the cloud, into one easy-to-use control app for smartphones, tablets and laptops option (combined with dirac 2 live) room correction system . Today // tomorrows VR sound technology.

Both(N.P class A push pull and, ddfa use FET output .

Nelson pass "quote": The academic paper approach has its place, but it seems intended for people who mostly understand the stuff already.

If you want to communicate with DIYers, you depend more on colorful analogies, a little hand waving, and very little differential calculus.

But a class or where to start building amps . A valid question ?

As aca was recommended by mooly and xrk 1st then

IC,discrete,hybrid,tube amps . Topologies . Compesations eg. http://jultika.oulu.fi/files/isbn9789514261770.pdf

You didn't mention your know how about electronics so basics "A standard EE handbook" for starters.

http://hguywilliams.net/images/documents/library/Elec/dee.pdf

Have fun while building & trying diffrent audio amps , may "jhl with igbt class a amp from exp." ,randy S. bob.C & self D. electronics world,elektor,esp,hifisonix for starters too help you on your journey to come , your amplifier build .

2018 hifi expo today/tomorrow/sunday :xmas: Cheers. Toni