Amp Camp Pre+Headphone Amp - ACP+

[codyt]

I have a question. I'm building a couple ACA amps and I need a preamp. I see the Korg Nutube B1 and the ACP+ are very popular. The Korg kits are out of stock but I can wait if needed as I'd prefer a complete kit vs. sourcing parts for an ACP+ build.

Thoughts on the difference? Ease of build? Sound differences? I'm assuming neither do balanced output xlr based on what I'm seeing (not a deal breaker). Thanks.

I’ve built both, and truth be told, you can’t go wrong. The B1K is a bit more syrupy/tube-like, but not over the top IMO. That said, I’ve built a lot of preamps over the past six months, and I always come back to the ACP+. I think it’s my favorite.

 

[SuppersReady]

Another completed ACP+.

I posted some internal photos a page or two back. I've used an eBay sourced relay based potentiometer. At just over £50 it was worth taking a chance. It even has remote volume control. The chassis is a Hifi2000 unit. I haven't got the gear for milling recesses in the 10mm front panels, so I settled for the 3mm front instead. Not quite as classy but not too bad.

I know I'm preaching to the choir here but the amount of detail from this device is incredible. I've been using it as a headphone amp mostly but tried it in the office setup earlier today. In both applications I can turn the volume up without any sense of stress or distortion in the sound.

Pilk, it works well with the ACA, not surprisingly, even through the little Q Acoustic speakers I have in my office. I'm looking forward to trying it in the main system when time allows.

My thanks to Nelson Pass, once again, for giving such excellent circuits to the DIY community.

Cinco, I hope the situation is improving for you in Texas and the power is still on at home.

 

[Pilk]

I’ve built both, and truth be told, you can’t go wrong. The B1K is a bit more syrupy/tube-like, but not over the top IMO. That said, I’ve built a lot of preamps over the past six months, and I always come back to the ACP+. I think it’s my favorite.

Appreciate the feedback. Since the Korg is out of stock maybe I'll try to source the parts for the ACP+. Where in the midwest?

 

[codyt]

I think you’ll like it, and it’s a pretty simple bill of materials to put together. I’m in Columbus, IN, about 35 miles south of Indianapolis

 

[Pilk]

I think you’ll like it, and it’s a pretty simple bill of materials to put together. I’m in Columbus, IN, about 35 miles south of Indianapolis

I'll see what BOM's are listed in the thread. Thanks again.

 

[docjrev]

Hello,
I built both the ACP+ and the Wayne LS. In my honest opinion anyone with ACA amps should hear the synergy of the ACP+ preamp with them. The drive provided by the ACP+ on my ACA monos is unbelievable. My Wayne LS resides with my Aleph J. My ACP+ will be exclusively driving my ACA with premium parts monos from now on.

If you are still in the process of building your ACA monos, please research the thread called "ACA with premium parts". The improvement on them amps with these premium parts, on my ears, is immense!

When time comes, mate your ACA with premium parts monos and ACP+ and drive a single driver crossover-less speakers (mine are BIBs with Foster 168EZ), heavenly. Godspeed.

 

[Pilk]

Thanks for the feedback. My kit just arrived and I checked out the premium parts thread....seems like another rabbit hole I'm probably going to go down. I'm also building some Elsinore speakers which are xover heavy but reportedly a very easy load to drive. We will see. I've followed some of the single speaker designs and find them very interesting.

 

[Pilk]

Another completed ACP+.

I posted some internal photos a page or two back. I've used an eBay sourced relay based potentiometer. At just over £50 it was worth taking a chance. It even has remote volume control. The chassis is a Hifi2000 unit. I haven't got the gear for milling recesses in the 10mm front panels, so I settled for the 3mm front instead. Not quite as classy but not too bad.

I know I'm preaching to the choir here but the amount of detail from this device is incredible. I've been using it as a headphone amp mostly but tried it in the office setup earlier today. In both applications I can turn the volume up without any sense of stress or distortion in the sound.

Pilk, it works well with the ACA, not surprisingly, even through the little Q Acoustic speakers I have in my office. I'm looking forward to trying it in the main system when time allows.

My thanks to Nelson Pass, once again, for giving such excellent circuits to the DIY community.

Cinco, I hope the situation is improving for you in Texas and the power is still on at home.

Thanks for the feedback!

 

[Cinco]

Another completed ACP+.

Looks fantastic SuppersReady!
I guess you tracked down the hum issue.

Cinco, I hope the situation is improving for you in Texas and the power is still on at home.

We were very fortunate to have our power stay on during that whole deep freeze. I know someone who lost power for 3 days in an all-electric home, frozen water pipes too.

Nice and sunny now, 53°F (12°C) back to normal temps.

 

[IntheBatCave]

Parts list

I was wondering if someone a little more knowledgeable than myself would mind taking a look at my parts order prior to me actually placing the order?
This isn't all of the parts, I've already ordered the volume pot and knob, as well as the LSJ74 JFETs through the diyaudio store. All of the rest is what I am sourcing through mouser.com Aside from the hardware and the PSU, the only thing left I need to source are the Q3 J113s, they are backorderd on Mouser, so I'm going to try and find them someplace else.

I'm mostly concerned about my capacitor selections, I've done some reading on capacitors, and it seemed like I would be wasting money to use UFG capacitors, anywhere other than C3, so I instead went with Nichicon UVR "for general applications".

I couldn't find a 10pf cap in an aluminum electrolytic, and went with a Multilayer Ceramic made by Kemet.

71-CMF551K0000FKEB CMF551K0000FKEB Vishay R1, 10, 14, 15 Metal Film Resistors - Through Hole 1/2W 1Kohms 1%
71-CMF55150K00FHEK CMF55150K00FHEK Vishay R2, 3 Metal Film Resistors - Through Hole 1/2W 150Kohms 1%
71-CMF55125R00BEEB CMF55125R00BEEB Vishay R4 Metal Film Resistors - Through Hole 1/2W 125ohms .1%
594-SFR16S0003322FR5 SFR16S0003322FR500 Vishay R5, 6, 7 Metal Film Resistors - Through Hole 1/2watt 33.2Kohms 1%
594-SFR16S0001000FR5 SFR16S0001000FR500 Vishay R8, 11 Metal Film Resistors - Through Hole 1/2watt 100ohms 1%
594-5053HD1K500F SFR25H0001501FR500 Vishay R9 Metal Film Resistors - Through Hole 1/2W 1.5Kohms 1% SFR25H series
594-SFR25H2.21%TR SFR25H0002208FR500 Vishay R12 Metal Film Resistors - Through Hole 1/2 WATT 2.2 OHM 1%
594-5053HD6R810F SFR25H0006818FR500 Vishay R13 Metal Film Resistors - Through Hole 1/2W 6.81ohms 1% SFR25H series
594-SFR16S0003329FR5 SFR16S0003329FR500 Vishay R16, 17 Metal Film Resistors - Through Hole 1/2watt 33.2ohms 1%
71-CPF3-D-1 CPF31R0000DKB14 Vishay R18, 19, 20, 21 Metal Film Resistors - Through Hole 3watts 1ohms 0.5%
782-4N35-X006 4N35-X006 Vishay Q4 Transistor Output Optocouplers Phototransistor Out Single CTR>100%
844-IRF610PBF IRF610PBF Vishay Q5, 6 MOSFET 200V N-CH HEXFET
647-UVR1E100MDD UVR1E100MDD Nichicon C1 Aluminum Electrolytic Capacitors - Radial Leaded 25volts 10uF 5x11 20% 2LS
647-UFG1E102MHM UFG1E102MHM Nichicon C3 Aluminum Electrolytic Capacitors - Radial Leaded 25volts 1000uF 85c 16x25 7.5LS
647-UVR1E102MPD UVR1E102MPD Nichicon C2, 6, 7, 8, 9 Aluminum Electrolytic Capacitors - Radial Leaded 25volts 1000uF 10x20 20% 5LS
647-UVR1E332MHD UVR1E332MHD Nichicon C4 Aluminum Electrolytic Capacitors - Radial Leaded 25volts 3300uF 16x25 20% 7.5LS
80-C321C330K3G5TA C321C330K3G5TA KEMET C5 Multilayer Ceramic Capacitors MLCC - Leaded 25V 33pF C0G 10% LS=6.35mm
490-RCJ-041 RCJ-041 CUI Devices RCA Phono Connectors RCA Connectors
490-RCJ-042 RCJ-042 CUI Devices RCA Phono Connectors RCA Connectors
568-NYS216G NYS216G REAN Phone Connectors 1/4" STEREO JACK .322" GOLD REAN
490-PJ-037B PJ-037B CUI Devices DC Power Connectors Power Jacks
612-100-F2461 100DP1T2B4M6QE E-Switch Toggle Switches DPDT ON-ON PC MNT
532-551002B00G 551002B00000G Aavid Heat Sinks Channel Style Stamped Heatsink for TO-220, High Performance, Folded Back Fins, Horizontal Mounting, 12.4 n Thermal Resistance

Thank you for any help in advance.

 

[codyt]

That 10pf cap should be 10uf. Elna Silmic is a good choice for that one.

*nevermind. I see that you meant the 33pf

 

[vconsumer]

C5 Multilayer Ceramic Capacitors Capacitors MLCC - Leaded 25V 33pF C0G 10% LS=6.35mm.

Not that it makes much difference, but most of the builds I've seen use this Wima film cap.

 

[Dline]

More gain possible?

Using ACP+ to drive F4. Sounds great but a bit more volume would be nice. Source is a Bifrost 2. Are there any simple mods that can be done to get more gain?

 

[Zen Mod]

increase R7 slightly

for 50% or 100%,choose standard values - say 47K, say 68K

 

[SuppersReady]

Now that have my ACP+ in a case, I don't need the ground plane board. It's free to the first responder, I will only ask for the cost of shipping it.

 

[Zen Mod]

frame it (or not) and hang it on the wall

 

[thomasnadeau]

Though I do not understand why this would be I understand what to do now. Thanks again for explaining. So I will get different resistors and see if R4 current then will be closer to 1.2V.


Thanks to all of you for your quick support! It's much appreciated. Once I learn a bit more, I'm sure I will build more Pass stuff 🙂 already super happy with my ACA mono blocks. Next step might be a F5 one day 🙂

You have a Jfet (J113) providing constant current to your signal/gain jfets (J74’s). 6L6 is suggesting that your constant current jfet (j113) is not providing adequate current to the J74s. Remedy is to lower the resistance from the J113, thus providing more current.

This is something that I unexpectedly stumbled on when I was building the ACP+ kits (which are done now save 1 dang resistor I expect this week). While it is clear Q1 and Q2 must be "matched" from Nelson's article, it is not clear that Q3 must also be "matched" to R4 in order to produce the 10 mA specified in Nelson's design.

The reason why you have to do this is the combination of the variation of J113s and the value of R4 to achieve the desired CSS value. While you can build a simple test rig to use for "binning" the J113s into 4 batches, you don't need to get a bunch of J113s and resistors; what you can do is ensure that the CSS part of the circuit is generating 10mA of current so play around with R4 to get to that point with the J113s you have installed. That is 6L6 just recommended above by trying different values for R4.

--Tom

 

[thomasnadeau]

IRFP610 was a typo. IRF610PBF is good. PBF stands for lead free and that is what is available as the non-PBF IRF610 are now obsolete.

Choose a 33pF film cap. Here is one:

https://www.mouser.com/ProductDetai...EpiMZZMukHu%2BjC5l7Ya09z%2BPFYd21tjAO0570ANE=

Those are indeed one of the IRF610Ps that will work. We ordered these IRFP610BPFs (Mouser# 844-IRF610PBF) for the forthcoming kits.

--Tom

 

[thomasnadeau]

IRFP610 was a typo. IRF610PBF is good. PBF stands for lead free and that is what is available as the non-PBF IRF610 are now obsolete.

Choose a 33pF film cap. Here is one:

https://www.mouser.com/ProductDetai...EpiMZZMukHu%2BjC5l7Ya09z%2BPFYd21tjAO0570ANE=

So it happens with both supplies. It is probably unlikely that both supplies are defective.

You earlier mentioned that it is a 3V rhythmic surge and it is constant. So at the power switch it is cycling between 24.8V and 27.8 V constantly? But at the power supply entry point it is a constant 24.8V?

I've seen SMPSs behave this way before when the internal limiting/shorting protection is tripped either due to a real short or trying to push through too much capacitance. This happened originally on the Amp Camps where sometimes the little SMPS would take 2 or 3 tries to push through the input caps (and they'd make that whining noise).

I recently had this happen with a pretty decent sized Meanwell supply (24v@6amps) that was accidentally shorted on its output and it would try to come on for about 3 seconds, then shut off, pause for a few seconds and try again.

I see you have tried two of the same, but have you tried a *different* 24v SMPS - or just another 24vdc supply ? It might just be the type you are using trips too soon?

--Tom

 

[anystereo]

My headphones are 16 ohms, should I put a 16 resistor in series at the output jack? Or is there another way that'll improve the performance and not burnoff output?

David