[mlundy57]

I ran across the Amp Camp Amp (ACA) DIY kit designed by Nelson Pass over in the Cheap and Cheerful thread. They looked easy enough even for me to build and I wondered how they would work with the Wedgies so I decided to give them a try. These are two mono blocks that were originally designed to put out 5wpc but have been upgraded and now put out 6wpc.

This is how the kit arrives




Here are a couple of pics of the build in progress and nearing the end





I strayed from the kit a little. I used Cardas RCA jacks and binding posts instead of the ones that come with the kit. I had to enlarge the holes for the binding posts but it was very easy to do with a reamer and drill.




Once I got them finished I crossed my fingers and flipped the switches (after all, this was the first time I soldered up a PCB). No smoke    Since they worked and didn't blow up it was time to see what they sounded like. I swapped out the PrimaLuna and hooked the ACA's up.



Here's a pic of the system




So, how did they sound? Underwhelming to say the least. With the volume control all the way up the Wedgies could only manage a little over 70dB at the listening position (subs off). With the subs on I would only get a little over 80dB. Additionally the wedgies sounded thin and anemic. Some questioning on the ACA forum at DIYaudio identified the problem. It came down to differences in gain and input sensitivity (voltage needed to drive an amp to full power) between the Prologue 4 and the ACA's.  The ACA's are monoblocks with 14dB of gain and an input sensitivity of 1.5V each (3V total needed to drive to full power). The Prologue 4 is a stereo amp with 29dB of gain an input sensitivity of 600mV.  This created a mismatch in my system.

My DAC puts out 2V which is more than enough to drive the Prologue 4 so the Dodd Audio Tube Buffer with 0 gain is a good match. However, since the ACA's only have 14dB of gain (vs 29) and the DAC cannot put out enough voltage to fully drive the ACA's the Dodd Tube Buffer is not a good match. So I borrowed a Jolida JD-5T preamp (10dB of gain and 7V max output) from another system and used it in place of the Dodd




Now the ACA's get enough voltage and the additional 10dB of gain allow the Wedgies (sans subs) to hit over 100dB at the listening position. The ACA's no longer sound anemic. They have a full and pleasing sound. At this point they only have a couple hours on them so I will see how they do after they get some more playing time. 

I cannot evaluate bass extension when using the Wedgies so later on I will move the ACA's into my office and see how they do with the LGK 1.0's in the desktop system. I may also see what they sound like with the N3's

Mike

[nickd]

Love pass designs
I Keep a Forte 1A on hand just to supprise folks that think their $20,000 mono blocks are the hot ticket.
The older Pass A40's are jaw dropping too.

[poseidonsvoice]

 

Best,
Anand.

[HAL]

Built one of Nelson's Son Of Zen SE MOSFET DIY amps many years ago and loved it.  These look like a great kit!   



 

[lacro]

Nice work Mike! You do realize you are starting down the rabbit hole of building your own electronics  It looks like your ready to build that stack of Folsom Amp PCB's you have stashed. With your great looking speaker builds, I can't wait to see what you come up with for enclosures to house the results of your new found hobby of solder slinging 

[pslate]

Can't concentrate on post, just staring at the wedgies  Those are amazing.

[mlundy57]

nickd and Rich,

These little things sound surprisingly good and at only $269 for the complete kit are a steal of a deal.

Best,
Anand.

Anand,

Thanks for your help in figuring out what was going on with these.

Nice work Mike! You do realize you are starting down the rabbit hole of building your own electronics  It looks like your ready to build that stack of Folsom Amp PCB's you have stashed. With your great looking speaker builds, I can't wait to see what you come up with for enclosures to house the results of your new found hobby of solder slinging 

Larry,

Getting there. I still want to get some tutored experience with power supplies, troubleshooting and fixing problems before I tackle the Folsom amp and Antipole boards.  As for rabbit holes, I'll withhold judgement until I see how the Folsom amp(s) turn out.  When it comes to wood enclosures I need to do some investigating. Heat, especially uneven heat and solid pieces of wood do not tend to play nice together. I need to figure out how to build the enclosures so they don't warp, crack, or split.  Especially with class A amps.

Can't concentrate on post, just staring at the wedgies  Those are amazing.

pslate,

Thanks. They sound even better than they look.


Mike

[gmurray618]

Excellent!   I built Nelson's F5 and love it.  You'll get lots of help at diyaudio

Looking forward to hearing about your ACA with the LGKs.  Bet its a sweet combination. 

[planet10]

I am using a pair of these and find that they are very good.

dave

[bfs21]

How long did it take to build them?
 

[mlundy57]

Excellent!   I built Nelson's F5 and love it.  You'll get lots of help at diyaudio

Looking forward to hearing about your ACA with the LGKs.  Bet its a sweet combination.

George,

I listened to three different pairs of speakers with three different sensitivity ratings this weekend in the 11'x13'x8' room whit the listening position 8' from the speakers this weekend. The speakers were GR-Research LGK 1.0 desktop monitors @ 85dB & -3dB @ 70Hz, PSB Image B6 bookshelves @ 90dB & -3dB @ 45Hz and Klipsch RB-81 II bookshelves @ 97dB & -3dB @ 44Hz.

Here are the LGKs




The PSBs




and the Klipschs (the subwoofers were not on)




At the listening position, the ACAs were able to drive the LGKs to 85dB, PSBs to 90dB and the Klipschs to over 100dB.  Bass response was obviously different with the LGKs being thin, the PSBs mediocre and the Klipschs decent.

Later on this week I'll bring the ACAs downstairs and see how they sound with the N3s in the living room (20'x25'x8') and with the LGK 1.0s in the office.

How long did it take to build them?
 

bfs21,

I built them in a weekend on and off. Probably 4 hours or so each. However, this was my first time building anything like this so I was slow. If you know what you are doing you could probably build both of them in an afternoon.

Mike

[poseidonsvoice]

Mike,

How warm are your heatsinks? You can tell me with a temp gauge on the Mosfet itself, or on the heatsink or how many seconds you can place your hand on the heatsink.

Just a general idea.

Thanks,

Anand.

[mlundy57]

Mike,

How warm are your heatsinks? You can tell me with a temp gauge on the Mosfet itself, or on the heatsink or how many seconds you can place your hand on the heatsink.

Just a general idea.

Thanks,

Anand.

Anand,

They are back driving the Wedgies. I ran them for an hour putting out 75-80dB at the listening position and the heat sinks were just warn. You could hold your hands on them for as long as you wanted. So I cranked 'em up to 90-95dB at the LP for another hour (I was NOT in the room) then went back and checked the heat sinks, Again they were just warm to the touch. You could hold your hands on them as long as you wanted.

Mike

[Folsom]

They would never put out more than 50w of heat.

Bass is bad, and your input on them isn't limiting it? I could probably make it better. At least it would be fun to try.

[mlundy57]

They would never put out more than 50w of heat.

Bass is bad, and your input on them isn't limiting it? I could probably make it better. At least it would be fun to try.

You have to take into account the size of the speakers vs the size of the room and distance to the LP. For example, the LGK 1.0s use a single 3" full range driver in a 4-1/2" x 12" x 8" ported enclosure and are -3 around 70Hz. Also, they were designed for nearfield listening as desktop monitors.

Then you have to realize what I am using as a reference for bass response, especially in this room. Compared to the dual 12" OB subs, decent is about the best any bookshelf speaker is going to do.

The real test for the ACA's bass response will be when I put them in the living room system driving the N3s. I normally do not use a sub with the N3s when listening to music so it will be a much better comparison. The ACAs against a Marantz SR5007 playing in stereo mode.

Mike

[Folsom]

5w is enough to gain 6db on top of the sensitivity of the speakers. But I'm sure you're losing 3db from distance. So a 3db increase is about all you can expect. That doesn't mean bass response shouldn't be good.

[gmurray618]

Thanks Mike, you gave us some nice quantitive loudness comparisons, have you put the ACA with the LGKs in their natural environment (on a desk, near-field) and how do they sound?  I'm looking for a qualitative impression.  If you don't need to crank it up too much, how does the comb sound?

I'm not sure how easy it is to camper the ACA's 5W of class A to a more powerful amp class A/B (I'm a Nelson Pass fan  ).  Bottom line is would you recommend these amps for a Laptop -> ACA -> LGK (on a desk top) setup?  I their were a preamp before the ACA might that help?  Would it even be needed?

Picture someone who appreciates fine high quality sound working at her laptop, no need for super loud. 
Thanks, George

[mlundy57]

Thanks Mike, you gave us some nice quantitive loudness comparisons, have you put the ACA with the LGKs in their natural environment (on a desk, near-field) and how do they sound?  I'm looking for a qualitative impression.  If you don't need to crank it up too much, how does the comb sound?

I'm not sure how easy it is to camper the ACA's 5W of class A to a more powerful amp class A/B (I'm a Nelson Pass fan  ).  Bottom line is would you recommend these amps for a Laptop -> ACA -> LGK (on a desk top) setup?  I their were a preamp before the ACA might that help?  Would it even be needed?

Picture someone who appreciates fine high quality sound working at her laptop, no need for super loud. 
Thanks, George

George,

I'll try to get the ACAs set up in the office tonight to check this scenario out. I'll start by feeding them directly from the DAC Whigs is an iFi micro iDSD. Then I'll add the Jolida preamp to see if it makes a difference.

Mike

[mlundy57]

ACA listening update with the LGK 1.0 speakers in a desktop system

In the office system I normally run an iFi micro iDSD DAC which feeds a Rotel RA12 60wpc integrated amp which powers the LGK's. The Rotel has preamp outputs so this allowed me to evaluate three conditions: 1) the DAC connected to the ACAs which drove the LGKs, 2) the DAC feeding the Rotel preamp which was connected to the ACAs which drove the LGKs, and 3) the DAC connected to the Rotel which then drove the LGKs.

The micro iDSD DAC has three output power settings. The specs list the line output voltage as >2V but doesn't give any more info than that. Eco is for driving highly sensitive IEMs, standard is for driving normal headphones and turbo is for hard to drive cans and speakers. When connected directly to the ACAs the DAC's standard power mode was underpowered. Sound from the speakers was weak and noisy. When the turbo mode was used the noise was gone and volume was more than sufficient for being only 3ft from the speakers (70-75dB). However, bass response was thin.

When the DAC was connected to the Rotel preamp the sound was clean up to 80dB. Also, the sound was fuller, more fleshed out and bass response was deeper.  The ACAs are a pretty good amp for this type application and I could live with the bass response, especially since this system is used to play relaxing music while I work, not for critical listening.

When the Rotel amp was used to drive the LGKs the bass response was even more extended and full than with the ACAs. I don't know if this is a function of the Rotel being 60wpc vs the ACAs 5wpc or what. Logic would say that since I am using less than 1/8 watt for these SPLs it shouldn't make a difference but something does.

To check it out I used another 5wpc amp, an OddWatt PoddWatt Dual Mono Block (a preamp and two 5wpc monoblocks housed in the same chassis). Unlike the ACAs, the PoddWatt is an EL34 based tube amp. However, the bass output of the PodWatt was very similar to the ACAs. The PoddWatt may have had just a tad more bass extension compared to the ACAs but still not comparable to the Rotel. I have no idea whether the extended bass response of the Rotel is a function of it's additional power availability or something else  .

However, when comparing the two 5wpc amps the ACAs stacked up favorably and preformed well in a desktop application with the LGK 1.0s. The ACAs provided the best sound when used with a preamp just as they did in the larger system/room.

Mike

[poseidonsvoice]

Mike,

I do not believe your subjective conclusions are necessarily due to the differences in the power output between the Rotel and ACA.

The mu follower output stage in the ACA has a relatively high DC impedance, but it is an active component with an AC negative resistance. It contributes to raising the apparent output impedance of the amplifier. Mu followers are popular in the tube world but typically in preamps. Pass' use is both unusual and creative which is what is wonderful about him!

Pass in his Amp Camp article stated that the damping factor of this amplifier is about 3. So output impedance assuming a vanishingly low speaker cable impedance (in addition to the wire in your crossovers), is going to be 8 ohms/3 or 2.66 ohms on the best day (i.e. short thick/beefy speaker cables). Various fellas have already confirmed Pass' output impedance measurements as true. Of course a higher output impedance and/or low damping factor all things being equal will contribute to a 'looser bass.' Usually, these designs are more compatible with woofer drivers that have very low Qts. But that doesn't mean it sounds bad as you have heard.

It's likely that the Odwatt unit has a similarly low damping factor.

Just my $.02.

Enjoy!

Anand.