To significantly improve the sound in this amplifier, you need to do the following: put a 2N5089 transistor at the input (the gain of this transistor varies from 400 to 1200), put an IFR250 at the output, put a 10 microfarad audiophile film capacitor at the input, put 3300 microfarads at 25 Volt Nichicon KA or FG. All electrolytes can be shunted with 100pf Vima + silver-mica 100-820pf. But I can see that the sound is no better than the modified amplifier on the TRA3255. The Pass amplifier requires good cooling so that half of the voltage does not drift, but is stable, which takes up a lot of space and heats up like a battery. The modified amplifier on the TRA3255 has an excellent stereo panorama, good sound detail, clean operation, takes up little space and the radiator is a small, more powerful amplifier. In terms of sound, they are approximately the same, even if Pass is worse ... The revision of the PASS amplifier is working, the sound becomes of high quality.
Is the bias setting correct on your amp? Bias is adjusted with the blue potentiometer on each amplifier board. You could also check that the power supply is running at correct voltage. How efficient are your speakers?
Nice video of a test of a cheap eBay pass Labs clone knock off at 5 Watts 88db speakers are not considered a easy load but it will work that circuitry was not designed for an 88 DB speaker it's recommended 90 and above it really starts singing after a 92 to 96 DB speakers and above and mr. Nelson's a c a design and that particular amplifier was designed to be driven with a pre-amplifier with the specific recommended gain and voltage if not the performance will greatly suffer
Yup, other designs can have lower noise and distortion. Different designs types can sound different that just noise and distortion specs cannot fully explain IMO. Maybe there is something to the Class A single transistor working with both positive and negative portions of the waveform sounds better than an AB with N channel working on 180 degrees and a P channel working on the other 180 degrees?
@@DanPattenAudioG33k hi thank you for the very kind and helpful advice Yes sound quality perception is a very tricky thing The only way to decide is by listening with our speakers Not always easy to do Kind regards gino
@@ChicagoRob2 hi thank you for the very helpful advice I am a little worried by heat It can shorten parts life in the amp I wonder if class AB amps can't be smooth sounding as well
@@gino3286 I think they can come close, but they tend to be quite expensive. I used to have a Bryston 4B, which I thought was very smooth for class AB.
There are a lot of factors that can contribute to the overshoot. I did not investigate it thoroughly. The overshoot can be a result of: - Non-deal impedance/loading (which is probably some of it). - Simple transistor /feedback design. - Capacitive coupling. I have measured a couple class A designs with somewhat similar designs and they have all had relatively high overshoot on that leading edge. I am planning on taking a look at the "official" ACA and will investigate it further. Thanks
@@DanPattenAudioG33k I think the most important is the current plot as this is proportional to the cone movement in the speaker, and the speaker doesn't have a resistive characteristic.
I believe it would be difficult to modify the design to accomodate a bridged design. However, it would be simple to add an external circuit to provide a non-inverted and inverted signal to the unbalanced inputs to do so.
Hi Dan , another question , what would prevent one from changing the transformer to 24v secondary to raise the rail voltage like the later aca's getting 8 watts out of the amp ? Then copying the method used in the pass 1.8 to bridge . The aca's are about 400$ shipped with brick ps.
It can be done but might be more work than initially thought :) You would need: - Find appropriate transformer - Make sure bias points are still good - Make sure all the supply capacitors have proper voltage rating - Make sure thermal capability of heatsinks are still ok
That is a good idea, I can do it. The speaker is my own design and construction. Even built the planar driver myself :) Could probably get to it in a couple of weeks. Thanks.
Thanks for review, it seems this clone biased little less then original and less psu voltage ..and therfore little worse THD...interesting which type of jfet they use instead of sk170..(j112 or other? But they also increase thd according to diyaudio)
Your welcome. I did not really look at the input FET to determine manufacturer and model. I should have. Sorry. Overall, I was impressed with the build quality.
Have you compared it side by side with a real ACA? Are the parts inside the same as the original amp? Nelson Pass is very adamant about the quality of the parts that he uses in all his amps.
I did not do a side by side comparison of parts. The schematic/design appears similar but did not check all components. Did specifically notice that the Pass ACA uses IRFP240 parts for the output and this amp used IRFP250. Technically the IRFP250 is the "better" part for current rating but may not sound better than the IRFP240 :) I should have looked at the input transistor but forgot. Sorry. Only had the amp for a short time so did not spend a long time reversing the design. Thanks
Hi there hope u gd. Is it pure class A. I Just read that it’s not gd for strings n j would imagine jazz which I listen to s lot it’s meant to go with my full range drives It is said that class A works well with those kind of drivers Any other classA can you recommend
Yes, the amp is pure class A. Possible issue is that the design operates from a single rail power supply so the output must be capacitive coupled. There are some DIY versions of the Pass Aleph series, such as Aleph 3.
Interesting video! I just subscribed to your channel. Tip: for the audio clip you can use music from the RU-vid library which is pre approved and copyright claims free.
It is an audio analyser made by Audio Precision. Model: Portable One Plus (P1+). No longer made. Modern/Current unit manufactured my Audio Precision is APx515.
Thanks. My AP P1+ has been a real work horse :) Have had it for more than 20 years and I fear the day it finally fails. FYI, I made a parallel port to USB adapter so I can print to electronic file. What type of work are you doing with the P1+?
@@DanPattenAudioG33k , my P1 is the Dual Domain but I don’t do anything digital, yet, it is new to me and my use is just as a hobbyist, I’m one of the Nelson Pass greedy boys that builds his DIY designs and also repair any of his ADCOM designs that I find in the wild that are broken and at a good price. I’ve been thinking about that adapter you made but there are a few very pricey ones in the market that I’m not even sure if they’ll work, how did you make yours? My printer works with USB or Ethernet.
I have admired many of Pass designs and also a fan of single ended class "A" designs. My Audio Precision unit does not have capability to store test results other than a printed copy. I made a printer emulator with a FTDI parallel to USB converter IC and custom code in a companion microcontroller. This device looks like a printer to the AP P1+ and the printer data is streamed to a serial (USB) port on a Windows box.
Have never listened to the Quad amps and preamps. Have listened to Quad ESL speakers and have always been impressed with them. Just googled the Quad 34 and that would be an interesting test / evaluation.
I do not know why one would say that it would not be good for a particular type of music. IMO, if you are running within the amplifier's power capability, you should be fine.
@@DanPattenAudioG33k Gotcha thanks. Would like to try this Pass clone as my first class A amp before jumping into the fire. Do you recommend it? or should I just get the real thing?
Yes, I would recommend the amplifier as a first time single ended class A amp. Cost is not too great and it can easily be re-sold without losing a lot of cash.
I did not notice any instability during measurements or listening. I do agree that the over/undershoot in this amp is not ideal :) I have measured other amps that are capacitive coupled and have noticed similar issues on some of them.
@@DanPattenAudioG33k thank u. yes i dont need that much power but i love to diy and heard many good reviews about the amp. so i just have to modify the speaker output to a headphones jack the?
Correct. You could just make an adapter from the amps outputs to your headphone jack. The amp's outputs are not bridged and the ground is common so this should be safe to do.
Seller is: zhufan2015 Link is: www.ebay.com/itm/Finished-HIFI-PASS-ACA-Stereo-single-Ended-Class-A-FET-MOS-power-amplifier-5W/133079032717?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
@@DanPattenAudioG33k How is the sound? some people say that with the original ACA, A ton of detail in the treble is lost with these. Do you feel it happens with the chinese clon as well?
Are you referring to diyaudiostore.com? I was considering this ACA but was out of stock when I checked. Maybe when they are back in stock, I will give it a try. Thanks.
@@DanPattenAudioG33k yes. That is correct. They do tend to sell out fast. Probobly one of the most popular kits there. If it is just register yourself there for the next batch. Just keep in mind they will be powered by a wall wart power supply. But one of neslons choosing. They of course get better with linear power supplies as well. These kits serve as a good starting point for other diy kits or projects there such as the first watt,aleph j, f5, f6, f4, m2, etc. I apologize if I seemed not nice in my response as I have had some success for some Chinese made amps and kits. If your a handy diy you will find some great projects there!
@@DanPattenAudioG33k glad to see you get one of these terrific amps! I have the 1.6 monos (2 aca). Hope you have fun building it and listening to it! What speakers you plan to try with them? Thanks!
I am somewhat amazed that you feel this is a good amplifier. The THD is probably the worse I have ever seen, much worse than a cheap one tube amplifier where 5% distortion is typical. Why class A? A cheap class B amplifier with loads of crossover would measure better. As for the square wave, that over shoot is un believable. This amplifier with it's low power, very poor THD and poor square is really just junk, very far from HIFi and a -60dB S/N ratio is only fair. If I was Mr Nelson I would be ashamed to put my name to such a poor amplifier. Nice video however!
Class A amplifiers of this type/design usually do not measure well. To be clear, this amplifier is not an official Nelson Pass amplifier. It is a clone. I'll have to get my hands on the official ACA unit and give it a whirl :). Years ago, I measured a Pass Aleph 0s amplifier, its measurements were not that great but it did sound good :)
Having just built two Pass ACA Class amplifiers in the past two weeks, I can tell you that this thing doesn’t look anything like the two that I built. Anywhere...front panel is different, the original doesn’t have a transformer inside, there is a XLR input for bridging on mine, and the circuit boards and interior are not remotely the same. Who is this guy kidding...Clone???
I agree that this amplifier is not a 100% replica, specifically, there are several mechanical and electro/mechanical differences. However, the circuit topology is very similar and I would consider that portion of the amplifier a clone. An interesting part of this implementation of the ACA is the power supply. It could be argued that this amplifier's power supply might be better than the original. There are many audio purists :) that will not use a switching type power supply.
I am an admirer of Nelson Pass' work and designs. IMO, he specified the switching power supply for "Safty's Sake". A beginning amplifier builder working with 120VAC input can be dangerous.
A 22 minute video with no sound demo is useless. Its like looking at a race car with no engine revving to back up its horsepower. And the worst part....hooking this up to a preamp and attaching speakers takes 2 minutes to accomplish while he spent so much time telling us how much heat it will emit. My cable box gets hot too when its left on for a few hours.
Sorry that I did not show it connected to my system. I thought about it. My concern is that by the time: the amp plays through my speakers, conversion from acoustic to electrical through my mic, analog conversion to digital on my computer, encoded to lossy compression format in my video editor, re-encoded to lossy compression format on RU-vid, digital to analog conversion on your computer, played through your amplifier and lastly through your speakers... You are not hearing the amplifier but a summation of all of these other links in the chain. There are just too many variables to demonstrate good sound over RU-vid. IMO. Thanks for watching the video. I am working on a video idea on a LM3886 amplifier which I hope will be interesting.
@@DanPattenAudioG33k Hi Dan, I agree making a video from hifi music does not make much sense but you should listen to the video I made from my DIY Little Nautilus. It sounds pretty convincing! My experimental system consisted of a MiniDSP 4x10HD, tube amp for the tweeters, Marantz for the midwoofers and a Rotel for the woofers I mounted in a cabinet. Unfortunately I had to move to a smaller house so I can't DIY anymore. The video below was made with my old iPhone 6 but sounds decent. Enjoy! Music video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-6R6_3WJpoTc.html Closer Look at Little Nautilesses: ru-vid.comjvfitD7KszE Bytheway, I hope you will test some more "cheap" clones around $350-600! But then you will need to spend some money unfortunately. Would be great if you reach enough subscribers and views so you can buy clones with youtube earnings. I will subscribe so you are one closer! You can probably attract a lot of views by showing which parts you can upgrade. I am not very technical but I am always wondering if you could spend another $50-100 on parts to make a clone really great. The youtube revenue system values instruction videos highly so the revenue should be nice! Maybe something like $3-5 per 1000 views. There are a lot of fun clone amps out there! On the site below the same you find everywhere but sometimes with a little more info. With this one below it's interesting they mention _"4 wheat original SPRAGUE or BC 75V39000UF capacitor filter arrays, (these new capacitors are very expensive, we have not way to put new capacitors, so it's four 2nd hand capacitors)"_ If these 2nd hand capacitors still test good I don't care. At least they are honest about it! hifi-exquis.com/pure-power-amps/503-weiliang-a100-full-replica-nhb-108-amplifier.html#/165-output_power-1_pair_power_chip/151-version_levels-with_volume_knob
