Started on the front panel. First drilled 3 holes for the locations of the 2 switches and the volume knob, then drilled out the switch holes to tap the holes with a 1/4 40 tap. I want to mount them from the inside of the chassis, and make 2 vertical sleeves on the front for the switches. That will be for next week when I find some time 
Have some time to kill until my chassis is finished so I tried the film caps for the input. These are 4.7uF instead of the original value of 10uF.
I soldered them in this morning and have listened through the day a bit and have mixed feelings. First impressions were that at higher volumes, let’s say when you really want to do critical listening, it sounded great, noticed a slight increase in soundstage depth perhaps.
But listening at lower volumes I have the impression that it sound a little less dynamic. Maybe a tiny less of low frequencies, or the mids and highs are a bit more pronounced.
It could be between my ears.
Could this be about the value of the cap, or just that is is a film cap instead of electrolytic.
Did someone made the change from the original cap to a smaller film cap and had a similar experience?
I will give it a couple of days, and then maybe switch the muse UES 10uF caps back in
After a long, dark covid period, I'm back
What a nice preamp this is, it has a lot of potential.
My goal is to pimp this ACP+ just like Patrick, EUVL mentioned: with dual rails, no in and output capacitors, linear regulated quality PSU, balanced and single ended inputs, balanced Muse attenuator or a 4-gang motorised Alps potmeter, passive cross feed and a nice casing, probably the Galaxy 330-280 from Modushop with nice machined frontplate.
I build it two times as a matching preamp / HPA for my kids VFET pt2 amplifiers. I have all the time, kids won't be leaving the house soon, because of the shortage of houses in the Netherlands.
Maybe I should open a new thread for this?
Any advice on the balanced Muse attenuator? Is there anywhere a current open thread for this? Where to buy PCB's?
The schematic I made, is a mix of the BA1 frontend, the J2 and this ACP+.
I made on experimental board first the original version and rebuild it to the schematic below, all works fine, output offset of the original was from 40mV to zero in few minutes, this version is from 10mv to zero in a few minutes. Maybe I'll experiment with a simple servo to keep it at 0 volts at the output.
JFET's are 10.0mA 2SK170BL and two perfectly matched 2SJ74BL's of 8.3mA. I will be playing with the 3 specified output transistors. And maybe degeneration of them, that's why I put in the 0 Ohm resistor.
What a nice preamp this is, it has a lot of potential.
My goal is to pimp this ACP+ just like Patrick, EUVL mentioned: with dual rails, no in and output capacitors, linear regulated quality PSU, balanced and single ended inputs, balanced Muse attenuator or a 4-gang motorised Alps potmeter, passive cross feed and a nice casing, probably the Galaxy 330-280 from Modushop with nice machined frontplate.
I build it two times as a matching preamp / HPA for my kids VFET pt2 amplifiers. I have all the time, kids won't be leaving the house soon, because of the shortage of houses in the Netherlands.
Maybe I should open a new thread for this?
Any advice on the balanced Muse attenuator? Is there anywhere a current open thread for this? Where to buy PCB's?
The schematic I made, is a mix of the BA1 frontend, the J2 and this ACP+.
I made on experimental board first the original version and rebuild it to the schematic below, all works fine, output offset of the original was from 40mV to zero in few minutes, this version is from 10mv to zero in a few minutes. Maybe I'll experiment with a simple servo to keep it at 0 volts at the output.
JFET's are 10.0mA 2SK170BL and two perfectly matched 2SJ74BL's of 8.3mA. I will be playing with the 3 specified output transistors. And maybe degeneration of them, that's why I put in the 0 Ohm resistor.
Gate Stopper on Mosfet2?
I am thinking of creating my own mono APC+ boards as has WalterW in the above comment. But I have a question of why Mosfet2 on the ACP+ article by Nelson has no gate stopper resistor. Based on experience with Mosfet output power amplifiers, such as the various Zens, F4, F5, and BA 1, 2, and 3, the output Mosfets have gate stopper resistors in the range of 100 to 221 ohms to control oscillation.
There appears, in fact, to be a fairly stout gate resistor on Mosfet1 of the ACP+ of 1K ohms, but nothing on Mosfet2. Nelson says that the APC+ “resembles a miniature version of the First Watt J2 amplifier.” If I’m not mistaken, from the picture of the J2 boards below, they appear to have gate stoppers. I also note that in WalterW’s schematic in the prior comment, a gate stopper on Mosfet2 which is symmetrical with the 1k ohm on Mosfet1.
I would appreciate input on this before I finish laying out my mono boards.
I am thinking of creating my own mono APC+ boards as has WalterW in the above comment. But I have a question of why Mosfet2 on the ACP+ article by Nelson has no gate stopper resistor. Based on experience with Mosfet output power amplifiers, such as the various Zens, F4, F5, and BA 1, 2, and 3, the output Mosfets have gate stopper resistors in the range of 100 to 221 ohms to control oscillation.
There appears, in fact, to be a fairly stout gate resistor on Mosfet1 of the ACP+ of 1K ohms, but nothing on Mosfet2. Nelson says that the APC+ “resembles a miniature version of the First Watt J2 amplifier.” If I’m not mistaken, from the picture of the J2 boards below, they appear to have gate stoppers. I also note that in WalterW’s schematic in the prior comment, a gate stopper on Mosfet2 which is symmetrical with the 1k ohm on Mosfet1.
I would appreciate input on this before I finish laying out my mono boards.
Attachments
Put the resistor into your PCB layout while you wait for Nelson Pass to answer your question "Is This A Design Error?".
Then when you build the boards you can either populate that resistor position with a 1Kohm resistor, or with a jumper wire, whichever makes you most comfortable at the time.
Then when you build the boards you can either populate that resistor position with a 1Kohm resistor, or with a jumper wire, whichever makes you most comfortable at the time.
Hello,
I have a question on how to wire up a different power supply to the store's ACP+ board. I am going to use a Salas Ultrabib, and I want to bypass the RC filter on the ACP+ board. I am thinking that the way to do it is leave C6, C7, C8 and C9 unpopulated, jumper R18 through R21, and bring in the positive and ground from the Ultrabib to the usual area where the power input jack would normally go. Is this correct?
Thanks,
Alan
I have a question on how to wire up a different power supply to the store's ACP+ board. I am going to use a Salas Ultrabib, and I want to bypass the RC filter on the ACP+ board. I am thinking that the way to do it is leave C6, C7, C8 and C9 unpopulated, jumper R18 through R21, and bring in the positive and ground from the Ultrabib to the usual area where the power input jack would normally go. Is this correct?
Thanks,
Alan
I finally got my chassis parts back from the metal workshop at my work, they did a good job, except for nicking the front plate a little bit near the volume knob. still happy with the the result.
I will try to finish the build this weekend, but before I do that, the conversation above got my thinking about the filter caps on this pre amp. The R-C filter will benefit from a good quality cap, with, I assume, a low esr, high ripple value. The caps that are on the board now are 1000uF 35v UKW.
Specs are:
I ordered 4 UHW caps but decided to use the above caps, cause I saw a lot of builds with audio grade caps in this position.
The UHW specs are:
On paper these are much better, should I try these ones in the power supply? Or is there any benefit using audio grade caps?
I read that C8 and C9 provide local decoupling between channels, will the UKW provide any benefits? Or still better use the UHW with better ripple rating, lower ESR and DF?
I will try to finish the build this weekend, but before I do that, the conversation above got my thinking about the filter caps on this pre amp. The R-C filter will benefit from a good quality cap, with, I assume, a low esr, high ripple value. The caps that are on the board now are 1000uF 35v UKW.
Specs are:
I ordered 4 UHW caps but decided to use the above caps, cause I saw a lot of builds with audio grade caps in this position.
The UHW specs are:
On paper these are much better, should I try these ones in the power supply? Or is there any benefit using audio grade caps?
I read that C8 and C9 provide local decoupling between channels, will the UKW provide any benefits? Or still better use the UHW with better ripple rating, lower ESR and DF?
article said this preamp draws 300mA of current with 24v dc
is it possible to use 3x 9v (27v) 700mAh battery to power them?
(i think it will last about 2 hours)
and also any possibilities to modified it into 9v dc rails?
so batteries can be paralleled into 9v 2100mAh (longer life, 7hours)
thanks
is it possible to use 3x 9v (27v) 700mAh battery to power them?
(i think it will last about 2 hours)
and also any possibilities to modified it into 9v dc rails?
so batteries can be paralleled into 9v 2100mAh (longer life, 7hours)
thanks