Pass ACA Class A Power Amplifier Review

[amirm]

Thanks. I did not know about that type of tea. Will have to seek it out some day!

 

[MRC01]

I don't want to disparage Nelson uniquely. He's part of a cadre or clique that includes the 'high end' press, dealers, and naive customers who do argue (one cannot deny it) that these designs are magical.
...
Again, I don't want to single Pass out. Other names can be included, such as John Curl, Bascom King (PS Audio) et al. Men who can be contrasted with names such as David Hafler, Stu Hegeman, Gordon Gow (off the top of my head)--men who represented the opposite.

Nelson Pass is hard to paint with a single brush. He's designed some "high end" boutique stuff, but also designed the Adcom 555 and 58xx series amplifiers, which are of conventional high bias class A/B design, well engineered with great measurements and priced for blue-collar audiophiles.

 

[MRC01]

Be very careful, the coffee rabbit hole is nearly as deep as the audio one. ... Now I own more than a dozen grinders, the least of which cost $2000. A grinder is a grinder you say, well, isn't a loudspeaker a loudspeaker. It plays music, what more do you want? Ha. ...

Is there any coffee grinder that does better more perfect/even grind than a hand crank conical burr?
That doesn't scale to mass production, I can understand coffee shops needing something more industrial. But for personal use, what could be better?

 

[almico]

Is there any coffee grinder that does better more perfect/even grind than a hand crank conical burr?
That doesn't scale to mass production, I can understand coffee shops needing something more industrial. But for personal use, what could be better?

I have several hand grinders. The best are from Orphan Espresso, the Pharos and Lido family. The Pharos is a dedicated hand espresso grinder. It works very well, but it takes a consistent cranking motion. Stopping and starting, or varying cranking speed will not do the cup any favors. Motors add consistency.

 

[bluefuzz]

The best are from Orphan Espresso, the Pharos and Lido family.

I have a Lido II. While I can't fault the grind quality (if and when you get it dialled in), the adjustment mechanism is fiddly and unreliable. And the plating on the lower adjustment ring started peeling off after a month. Can't say I'm too keen on the neo-brutalist design æsthetic either ...

I prefer my Knock Hausgrind which grinds every bit as well as the Lido but looks nicer and works reliably every time.

Much of the charm of 'boutique' manufacturers, whether coffee gear or audio gear, is the personal touch – being able to communicate directly with the manufacturer etc. However, niether Orphan Espresso nor Knock seem to have grasped basic 21st century communication skills like answering emails. I tried umpteen times to contact Orphan about the peeling plating on the Lido and never got a reply. I also tried through the British dealer where I bought it, but to no avail. And Knock are famously incommunicative. You send your money – no receipts or acknowledgments are given – and maybe in a few months, or a year, you might get a grinder back. Sometimes it may even be the one you ordered!

Boutique manufacturers - caveat emptor ... ;-)

 

[almico]

I have a Lido II. While I can't fault the grind quality (if and when you get it dialled in), the adjustment mechanism is fiddly and unreliable. And the plating on the lower adjustment ring started peeling off after a month. Can't say I'm too keen on the neo-brutalist design æsthetic either ...

The only issue I've ever had with my Lido 2 is traveling with it. The "neo-brutalist" design makes TSA x-ray techs' heads pop off. Between that and 2-3 pounds of coffee in my overnight bag, I have to get to airports earlier than most.

 

[MRC01]

I have several hand grinders. The best are from Orphan Espresso, the Pharos and Lido family. The Pharos is a dedicated hand espresso grinder. It works very well, but it takes a consistent cranking motion. Stopping and starting, or varying cranking speed will not do the cup any favors. Motors add consistency.

I'ved used a Peugeot Bresil coffee mill for the past 10 years or so. Quite happy with the results, nice consistent grind. And very simple, durably constructed, wood & steel, no plastic, like something you'd make yourself in wood shop. Easy to disassemble & clean too.

 

[almico]

FWIW, Amp Camp monoblocks with Klipsch R51m (Best Buy $144) fronted by an Apple TV playing the Radio app through an Su-9 DAC running balanced outputs. Recorded on my iPhone.

And a taste with the Borg K1 pre and no DAC on the ALTECS. Still on the iPhone which attenuates the mic when the dBs increase. Lovely.

That's Leo doing some critical listening on the left. He doesn't care how they measure either.

 

[HornJunkie]

Hello guys,

I would like to build my first amp.
so the amp camp kit is very easy and cheap (from China) and I need in sum 4 channels.

i have an active loudspeaker system and want to use the amp with my horns (mid- and high frequencies).
The efficiency is above 100db/1watt, I think 105db/1watt.
both are 8 Ohm speakers.

i think the amp camp amp is perfect for this operation or not?

best regards,

Florian

 

[MakeMineVinyl]

Hello guys,

I would like to build my first amp.
so the amp camp kit is very easy and cheap (from China) and I need in sum 4 channels.

i have an active loudspeaker system and want to use the amp with my horns (mid- and high frequencies).
The efficiency is above 100db/1watt, I think 105db/1watt.
both are 8 Ohm speakers.

i think the amp camp amp is perfect for this operation or not?

best regards,

Florian

Sure it would work, but I'd go with a low power tube amp if your budget allows.

 

[HornJunkie]

Yes great idea with tubes, but not yet.
They are often not so cheap and the ACA is very cheap to build.

best regards,

florian

 

[MakeMineVinyl]

Yes great idea with tubes, but not yet.
They are often not so cheap and the ACA is very cheap to build.

best regards,

florian

If you go the ACA route, might I humbly suggest that since you are going active, you place a capacitor in the speaker line to the HF horn in order to protect it if there is any DC failure in the amp. Has been known to happen. Don't ask me how I know this.

 

[HornJunkie]

If you go the ACA route, might I humbly suggest that since you are going active, you place a capacitor in the speaker line to the HF horn in order to protect it if there is any DC failure in the amp. Has been known to happen. Don't ask me how I know this.

Thanks for the information
And yes, I think it’s better not to know why

the capacitor in row (as 1. order butterworth filter) or parallel?


best regards,
Florian

 

[MakeMineVinyl]

Thanks for the information
And yes, I think it’s better not to know why

the capacitor in row (as 1. order butterworth filter) or parallel?


best regards,
Florian

It needs to be a larger value bi-polar capacitor in series with one of the speaker terminals. I hook the capacitor right on one of the driver's terminals and run the other end of the cap to the speaker wire coming in. The value of this capacitor should be selected to have a pole at half (or lower) the crossover frequency. If I remember correctly, I think I have 200uF in series with my 16 ohm drivers. There is a tradeoff between a too-large capacitor which could allow a momentary pulse of DC in the event of failure verses a too-small value which would interfere with the crossover slope.

In one instance of stupidity before I used this method, the driver's diaphragm was damaged by a surge while connected to a tube amp. In input cable got jerked out of its socket which, since my tube amp has good LF response, sent a nice long pulse to the voice coil, which slammed the delicate aluminum diaphragm against the phase plug and got embossed with the phase plug's pattern. Not nice.

 

[Sal1950]

We all have our own opinions but instead of putting tone, distortion, and noise generating amps in front of a highly revealing horn, I would look to get a modern transparent SS amp for your use. For something inexpensive, Off the top of my head I've heard good things about the Emotiva BasX A-100. At 50wpc into 8ohms it would fit the needs perfectly. Only $229 to your door.
https://emotiva.com/collections/basx-series/products/a-100
Used you can find a Adcom GFA-535 II on ebay for $100. I've been using them for 25 years and currently I got 2 powering my Atmos channels.
Great F--- Amplifiers designed by Nelson Pass before he got into voicing his designs.

 

[HornJunkie]

It needs to be a larger value bi-polar capacitor in series with one of the speaker terminals. I hook the capacitor right on one of the driver's terminals and run the other end of the cap to the speaker wire coming in. The value of this capacitor should be selected to have a pole at half (or lower) the crossover frequency. If I remember correctly, I think I have 200uF in series with my 16 ohm drivers. There is a tradeoff between a too-large capacitor which could allow a momentary pulse of DC in the event of failure verses a too-small value which would interfere with the crossover slope.

In one instance of stupidity before I used this method, the driver's diaphragm was damaged by a surge while connected to a tube amp. In input cable got jerked out of its socket which, since my tube amp has good LF response, sent a nice long pulse to the voice coil, which slammed the delicate aluminum diaphragm against the phase plug and got embossed with the phase plug's pattern. Not nice.

thanks for your answer, I will do that with the caps

best regards,

florian

 

[HornJunkie]

We all have our own opinions but instead of putting tone, distortion, and noise generating amps in front of a highly revealing horn, I would look to get a modern transparent SS amp for your use. For something inexpensive, Off the top of my head I've heard good things about the Emotiva BasX A-100. At 50wpc into 8ohms it would fit the needs perfectly. Only $229 to your door.
https://emotiva.com/collections/basx-series/products/a-100
Used you can find a Adcom GFA-535 II on ebay for $100. I've been using them for 25 years and currently I got 2 powering my Atmos channels.
Great F--- Amplifiers designed by Nelson Pass before he got into voicing his designs.

yes you are right, but I want to build my own amp.
But just as the beginning the ACA amp.
I buy a bigger enclosure with internal 250mm x 250mm x 80mm, so there is enough space for a bigger project later.

best regards,

Florian

 

[MRC01]

yes you are right, but I want to build my own amp. ...

Does Hafler still sell kits?
If so, the Hafler is a well engineered, clean, powerful amp that would have performance far exceeding the Pass ACA amp.

 

[Sal1950]

yes you are right, but I want to build my own amp.
But just as the beginning the ACA amp.
I buy a bigger enclosure with internal 250mm x 250mm x 80mm, so there is enough space for a bigger project later.

best regards,

Florian

There's a ton going on in the DIY world building SOTA measuring and sounding class D amps. Check out a couple other sites like DIY Class D, and Ghent Audio. You could then build a amp that will give you decades of accurate listening pleasure.

 

[ta240]

Used you can find a Adcom GFA-535 II on ebay for $100.

Every time I look they are about $250 with shipping, they seem to have gone up in the last few years.

There's a ton going on in the DIY world building SOTA measuring and sounding class D amps. Check out a couple other sites like DIY Class D, and Ghent Audio. You could then build a amp that will give you decades of accurate listening pleasure.

Great suggestions. I'll add that if you are dead set on soldering the components on the amps I'd search out a good LM3886 design or TDA7293.

I like what I've seen of Nelson Pass as a person and I built his M2 design that aside from a slight hum that the transformers in the audio circuit picked up I really enjoyed the sound of it but the ACA that I built left me completely underwhelmed. I just never listened to it; every time I tried to sit down and listen after a very short time I'd turn it off and go do something else. It never pulled me into the music. I think his name being attached to it has upped the mythical nature of it from a super simple class A design with a low danger power supply designed so that it could be built in a several hours by complete amateurs to an amazing sounding amp that outshines most anything else.