Amp Camp Pre+Headphone Amp - ACP+

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#821
It will not sag to 24v as you’ve bought the wrong transformer... you need an 18vac (or 20vac) transformer as you gain 40% when you rectify ac to dc.

18*1.4=25.2

And then subtract about 1.4 volts for the two diode drops in the bridge, and maybe another .7 for the pass transistor. Leaving 23.1
 
#823
6L6 said:
It will not sag to 24v as you’ve bought the wrong transformer... you need an 18vac (or 20vac) transformer as you gain 40% when you rectify ac to dc.

18*1.4=25.2

And then subtract about 1.4 volts for the two diode drops in the bridge, and maybe another .7 for the pass transistor. Leaving 23.1
Click to expand...

Another option is to add a regulator at the end of the supply to bring it down to 24vdc. Of course, make sure the input voltage doesn't exceed the limits of the regulator or you'll let the smoke out! I also built a Sigma 22 regulated linear supply using a 24vac or 25vac secondary. That is another option if the secondary starts out that high, and is needed to start that high in order to hit 24vdc on the output side. Or just set it aside for another project and try the 24vdc@10A meanwell with Mark's filter. 🙂

--Tom
 
#824
pinkfloyd4ever said:
Don't take the thread's collective silence personally, it's the most craziest time of this already insane year.

Sounds cool...what are you using for remote volume? Is it remote input selection as well? Looks like maybe not, I think I see a manual rotary switch there.

What phono stage?

In the future I'd like to do a maxed-out full-featured preamp with remote-controlled volume and input selection, tone controls, and possibly phono...not sure about phone though, I may want to keep that in a separate chassis. I'll need to find a turnkey remote kit though because that is way over my head.

Oooo and is that one bag labelled "VU Driver"? Does that come as a kit too? Cause that's also something I'd love to implement in my dream DIY pre but don't have the knowledge to design on my own.
Click to expand...

The Phono is a Hagerman Bugle 2, Manual selector and I have yet to decide how to control the volume pot, I think it needs +/- 3v controlled from the remote. Yes the VU controller kit came from ebay.
 
#825
waam68 said:
I built the ACA way back in 2012 as one of the first projects I ever did (recuperating from serious illness) and after some time away from diy saw Nelson had created a matching preamp. I’d recently dug out the ACA from its hibernation to perform as office/spare bedroom duties as I’ve spent the better part of the last year working in there. The build went well once I’d got the parts together...pretty straightforward. The trickiest bit as I only had a couple of J113’s was playing around with r4 values in circuit to get 10ma per channel. After some experimentation with a dvm and breaking out the calculator I ended up with 33r getting me just a shade over 10ma. All check out voltages were bang on straight off the bat which was a relief. It’s sounding very promising from the get go but I haven’t spent long enough listening (like half an hour) to properly evaluate. The naked form factor matches my ACA which for me was part of the appeal. I couldn’t find any nichicon gold in the right values so went for Panasonic’s which I’m sure are just as good or better. My favourite bit is the knurled volume knob which was like a fiver from China (ebay). The only thing to do is pick up a better power supply as I just used a cheapo I had to hand. Anyway that’s it another triumph of perseverence over knowledge :0). Thanks to Nelson for the design and the forum for the boards and fets. PS no idea why the one photo is rotated on upload.
Click to expand...

Nice Quad gear there too.
 
#826
What's the difference between Alps model 516G and 906G? I can't find the info on the web. I ask since parts express is sold out of the 516G, but Parts Connection has a 20kohmx2 audio taper that is part 906G. I can't seem to find the differences, even on Alps site. I imagine the differences are tolerance-related, or body size, or something similar. I imagine the 906G will work just fine, but I'm curious about the details. Thoughts?
 
#829
Jim, I have the 906g part left over from a tube ampwhere I used something else. I got it from either Parts Connection or Hifi Collective. PC calls it an audio/log taper (in contrast to what @LUX35 writes above) and it fits PM’s breakout board. I’m guessing that it is in the RK27 family. The back of the part calls out 20kx2. I’m trying to understand the specs differences since I’m being cheap by using what I have on hand if possible. That is, assuming baby ever let’s me solder again. Thanks
 
#830
Can you post a photo? I cant find anything on the datasheet that says 906g to verify if it’s appropriate or not. Photos show that code on the back of what are certainly RK27s, so it seems like it’s right, but a quick photo will verify.
 
#833
Zen,
you are right, master
I had a 906 G which was linear (so) or antilog.

I don't know if it was linear or log neg anymore but it didn't work very well
It should have been more linear because the antilog are quite rare because if not use little for gain adjustment
 
#834
Like I said, the supplier calls it log/ audio taper. While my experience is somewhat limited, I’ve never seen a base 10 potentiometer. Does 10^x even make sense? In any case, I’m still guessing the number defines some thing about the parts such as tolerance or shaft length or whether it has a split shaft or something similar. Thoughts, or links to specification sheets, are appreciated. Thanks,
 

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#838
After simulating and playing around with the ACP+ driving an 8ohm speaker load, I've come to this conclusion:

What the audiophile world needs now is a nice, high sensitivty (>92dB), 32ohm, full range speaker.

I know it's asking a lot but, please Santa bring us this for next Christmas. 🙂
 
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#840
Quoting this means I’m not off topic! Is it OK to put woofers in series to get higher impedance? I’ve always thought so, but started thinking about putting 4 8ohm woofers in series to get 32 ohms. I’ve heard the ACP+ driving Nelson’s Tannoy’s (which I think are 98dB efficient) and while it’s quite listenable, it wasn’t very loud. Probably Great for a desktop system, but gonna be very very hard to fit the Tannoys on a desk! I’d say the speaker would have to be at least 101dB efficient, So would need 4 96dB 8 ohm drivers in series per speak!

Cinco said:
After simulating and playing around with the ACP+ driving an 8ohm speaker load, I've come to this conclusion:
What the audiophile world needs now is a nice, high sensitivty (>92dB), 32ohm, full range speaker.
I know it's asking a lot but, please Santa bring us this for next Christmas. 🙂
Click to expand...
 
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