re: the sound - I'm the last to comment, in fairness. Some people say that the sound can seem more "dry" or with less life when using a balanced signal with some amps. Me... I don't necessarily view it that way. I happen to really like a lot of the amps when run balanced / bridged. With that said, the ACP+ definitely has its own character (IMO) that I fear may be lost when running a pair balanced / bridged. Without getting into too much detail, if you've read at all about how Nelson Pass (and many others including me) find a 2nd order harmonic distortion pleasing... that 2nd order harmonic will cancel. This amp may get it's lovely character from that 2nd harmonic distortion. The equal and opposite signals will result in the 2nd harmonic cancelling out when summed at the output. If we enjoy the "character" of a particular amplifier, it certainly could be lost when taking two of them and running them bridged / balanced. Will it be lost? Who knows? Could it be lost; yes.
Overall, the most compelling reason to try running them balanced would be the need / desire for more power, IMO,
Personally, I haven't looked at running this particular amp with a balanced/differential input / bridged output. If you've built one already as a "stand alone" unit as an open-top project, then just the simple / practical act of getting the positive and inverted (AKA negative) signals to the respective amps would be interesting. Could it be done... sure. Should it be done for fun in the name of DIY... maybe. Would it be the project that I'd personally try myself ... not really. But... that's just me. However, I may be missing a super-simple solution.
There are so many other amplifiers to choose from that are inherently designed to be run balanced / bridged or at least allow it to be done a little more easily. I'd consider trying the ACAs or another ACA variant like the MinMax if that may be your cup of tea.
Hope that helps.
Overall, the most compelling reason to try running them balanced would be the need / desire for more power, IMO,
Personally, I haven't looked at running this particular amp with a balanced/differential input / bridged output. If you've built one already as a "stand alone" unit as an open-top project, then just the simple / practical act of getting the positive and inverted (AKA negative) signals to the respective amps would be interesting. Could it be done... sure. Should it be done for fun in the name of DIY... maybe. Would it be the project that I'd personally try myself ... not really. But... that's just me. However, I may be missing a super-simple solution.
There are so many other amplifiers to choose from that are inherently designed to be run balanced / bridged or at least allow it to be done a little more easily. I'd consider trying the ACAs or another ACA variant like the MinMax if that may be your cup of tea.
Hope that helps.
Thank you. You may have answered my question without really answering what I thought was my question. And, yes, that is a good thing. Both my ACP+ and the ACAs are plain vanilla builds...no upgraded components or modifications, so far. One of the things I particularly like about the ACA is the opportunity to easily try different output options. I've obviously used one in stereo mode, and have tried the pair in both parallel and bridged mono. It's been fun hearing the different characters. Right now, I'm running bridged mono and I think it is my favorite. I think the parallel mode gives a little more bass punch, but there is just something about the bridged mode that appeals to me, and I think that may be those 2nd order harmonics.
I appreciate your thoughts!
I appreciate your thoughts!
To get balanced output from an existing ACP+, you can use either active circuit or transformers. A good transformer is not inexpensive, and will need to be mounted carefully to avoid hum pickup due to external power transformer and choke fields. But no power needed so may be easier to implement in existing gear.
Any time - I tend to type too much ... and go in circles. I'll try to keep it 'tidy'.
Mainly..
- for trying balanced out to go into a balanced amplifier. @Halauhula has outlined a fairly common thing to try out.
- for doing a "fully" balanced ACP+ from in to out... it's doable, but ... do ya wanna?
- if you really want a "fully" balanced pre-amp, then something like the Iron Pre or Wayne's pre would be fun.
- for experiencing what "balanced" sounds like (if it has a sound at all), you could also do it with an amp vs. a pre-amp. If you want to compare SE to balanced using the same amplifier, the ACA "family" makes it really easy, IMO. Those amplifiers have that same "H2" style you see talked about. So, you can tell if you like the exact same circuit run balanced or SE. Sure, it varies, but it may give you an idea. You can even run an SE input from the pre-amp (like the ACP+) to bridged output using a really neat inverting trick in the ACA to get a feel for it.
Hopefully my opinion is a tad more clear. LOL! Mainly have fun. You'll see all sorts of cool ideas.
Cheers.
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For Jfets in this preamp can an IDS of around 10ma be ok?
The recommendation is for 6-8ma but the ones I have on hand show B-stock on the package. I measured them on a jig and with 12V and 100 ohm resistor to D and SG tied to ground I get a little over 10ma.
The recommendation is for 6-8ma but the ones I have on hand show B-stock on the package. I measured them on a jig and with 12V and 100 ohm resistor to D and SG tied to ground I get a little over 10ma.
If you mean the LSJ74 or 2SJ74? They operate around 5mA each in this design. So they should be at least 5mA. 10mA will be fine.
I know it's probably old news now but I have taken a step back from projects the last few years and the parts just sat in a cupboard. I have finally started building my ACA+ into a Galaxy enclosure and I'll be using one of my Artemis PSUs to provide clean power to it. There is also a small relay board mounted as I will be using a piezo switch with white LED ring for the power on and off function.
A few pics attached. 😊
A few pics attached. 😊
Attachments
I just bought a similar one to this and while it's not the best built in my collection, it is extremely handy and has very nice features!
(oh and well it's stupid cheap so I figured why not)
Built one of these as my first DIY audio project (having only taught myself to solder a few weeks ago) and while it won't win any prizes for solder or assembly I'm delighted to report it worked as soon as I plugged it in with no issues!
The only issue I had was that the nuts that came with it didn't fit the screws on the outside of the board (it's possible I mixed up the nuts for the two boards and the nuts for the MOSFETs, but the nuts don't look like they'd fit those either), so I had to go to the hardware store and buy some different nuts. But they seem to work fine. (The hardware store also didn't have the k-lock nuts that come with the kit so I just used regular nuts, hopefully that won't cause any kind of problem.)
Probably going to be digging into this thread about mods in the future and it seems like a better power supply might be a good follow up project, but for now I'm just listening and enjoying...
The only issue I had was that the nuts that came with it didn't fit the screws on the outside of the board (it's possible I mixed up the nuts for the two boards and the nuts for the MOSFETs, but the nuts don't look like they'd fit those either), so I had to go to the hardware store and buy some different nuts. But they seem to work fine. (The hardware store also didn't have the k-lock nuts that come with the kit so I just used regular nuts, hopefully that won't cause any kind of problem.)
Probably going to be digging into this thread about mods in the future and it seems like a better power supply might be a good follow up project, but for now I'm just listening and enjoying...
down the memory lane - BAF 2019, building camp
I remember repairing one of those, one of Boyz had helping Gremlins during assembly; I also remember fighting with brain-fog while repairing ... it took me trice time than usual..... beauty of Jet-Lag
Later I did wonder how I didn't even ruined it even more
I remember repairing one of those, one of Boyz had helping Gremlins during assembly; I also remember fighting with brain-fog while repairing ... it took me trice time than usual..... beauty of Jet-Lag
Later I did wonder how I didn't even ruined it even more
ericrosenfield
I like the SMPS DC Filter P089ZB Kit for $ 14.00 USD if you use the power supply that came with the ACP+.
Thanks @JMD3254! I just ordered one of those cheap Jameco LPSes so hopefully that'll obviate the need for the filter. What I'd really like to do is get one of those Modushop cases for it and build a quality LPS with an IEC jack in there, but that's still for the future (and I have to figure out how to punch holes in cases and things for inputs and outputs which I've never done before, and of course I've never built an LPS either. So, baby steps).
Hi all,
So the first modification I want to do: I primarily use HD6XX and ZMF Atrium headphones which both have an impedance of 300 ohms. If I'm understanding Ben Mah's post (here: https://www.diyaudio.com/community/...headphone-amp-acp.344836/page-17#post-6206707) I need to use two 36 ohm resistors across the joints as shown in his post here: https://www.diyaudio.com/community/threads/amp-camp-pre-headphone-amp-acp.344836/page-8#post-5996388
I just want to make sure I understood everything correctly before I order the resistors and solder them in. Thanks!
Edit: reading again it seems like I also have to change the resistors at R16 and R17 to 300 ohm resistors too?
So the first modification I want to do: I primarily use HD6XX and ZMF Atrium headphones which both have an impedance of 300 ohms. If I'm understanding Ben Mah's post (here: https://www.diyaudio.com/community/...headphone-amp-acp.344836/page-17#post-6206707) I need to use two 36 ohm resistors across the joints as shown in his post here: https://www.diyaudio.com/community/threads/amp-camp-pre-headphone-amp-acp.344836/page-8#post-5996388
I just want to make sure I understood everything correctly before I order the resistors and solder them in. Thanks!
Edit: reading again it seems like I also have to change the resistors at R16 and R17 to 300 ohm resistors too?
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It's a good mod, however it's not strictly necessary. If you are getting enough volume with your headphones without the mod, it may not matter. The volume knob may need to be turned up more than lower impedance headphones, but that's not big deal at all.
Is it worth trying? Yes, of course. Let us know your results!
No
An audio engineer friend of mine suggested that I swap the input caps with film and bypass the output caps. I'm wondering if anyone has any experience with that mod and what the results were? Also wondering if there's other suggestions for things like different capacitors that might improve/change the sound quality? It seems like part of the fun of DIY is the ability to experiment, but I don't really know where to start...
You’re welcome to try all sorts of stuff. Some things might even make a difference. Please tell us what you do and if there are any changes!