This is a question I hope to answer similarly for myself once I finish these F2J amps.
I am currently using a pair of ACA mono blocks with my Oris 200 front horns loaded with Lowther DX3. They are very nice sounding.
I use the ACAs solely for the fullrange front horns.
I have a B5 active crossover that splits the signal and I supplement the bottom end with dipole bass panels that are powered by some bridged Rotel amps. The very bottom is filled in with a subwoofer.
The only modification done to the ACAs is that I turned them into a “J” version by substituting Semisouth 100A at Q1 position. The ACAs use a revised version 1b pcb which had a few changes made in the circuit that were carried on to the current ACA version.
I thought about some of the upgrades in the “Premium” thread including the power supply, but left them running on the laptop bricks and moved on to the F2Js.
I suppose once I’m done I will get about as close to an “apples to apples” comparison as could be had regarding the ACA vs F2 circuits. They will both be mono blocks and have comparable components except for the Semisouth being substituted in both.
I am currently using a pair of ACA mono blocks with my Oris 200 front horns loaded with Lowther DX3. They are very nice sounding.
I use the ACAs solely for the fullrange front horns.
I have a B5 active crossover that splits the signal and I supplement the bottom end with dipole bass panels that are powered by some bridged Rotel amps. The very bottom is filled in with a subwoofer.
The only modification done to the ACAs is that I turned them into a “J” version by substituting Semisouth 100A at Q1 position. The ACAs use a revised version 1b pcb which had a few changes made in the circuit that were carried on to the current ACA version.
I thought about some of the upgrades in the “Premium” thread including the power supply, but left them running on the laptop bricks and moved on to the F2Js.
I suppose once I’m done I will get about as close to an “apples to apples” comparison as could be had regarding the ACA vs F2 circuits. They will both be mono blocks and have comparable components except for the Semisouth being substituted in both.
Attachments
Interesting. I didn’t know that the ACA circuit and the F2 circuit were closely related. I’ve always thought ACA must be similar to a FW model. I guess it’s the F2J.
I’ve built the ACA 1.6 as monoblocks with TungstenAudio’s mods. Still running the switching power supply, though. I’m curious to see what you think of the sound comparison. I do have a set of Kinku’s F2J boards for a future build.
Finally got my first F2J monoblock fired up today.
I roughly adjusted the bias with my DMM to half my rail voltage and then tweaked it to 11.65V after about an hour of cooking when things seemed to settle down.
I have a used DSO Nano pocket scope someone gave me, but even after finding a manual for it online I can’t figure how to use it. I downloaded an iPad App called ToneGenerator that allows you to generate a variety of tones including square and sine waves. Maybe I can use that in conjunction with the Nano if I can figure it out. I only have a couple of 10 Ohm 10 Watt wirewound resistors lying around to use as a dummy load.
I was a bit paranoid about heat dissipation with this case design and my raw Heatsink USA heatsinks and went through a bit of trouble squeezing a cooling fan with a separate transformer and adjustable voltage regulator in the back of the amp only to find that the fan was making more noise than I wanted and the amp didn’t really get all that hot. I could easily keep my hand on the heatsink indefinitely even after dialing the fan voltage all the way back to 6V to make it quite enough. I may just try disconnecting it.
I hooked up a couple of cheap Aura fullrange drivers I have for testing and pumped some music through the amp from my favorite Down Tempo Apple station on my iPhone.
I was very surprised at how nice the music sounded from those cheap little speakers plopped down on the bench. I’ve used them several times before and have always just said to myself “OK it works...they make noise.”
I am really looking forward to getting the second monoblock running and getting them into my system. I just hope they have enough juice as the ACAs are supposedly putting out 8 Watts compared to 5 Watts of the F2J into 8 Ohms.
I roughly adjusted the bias with my DMM to half my rail voltage and then tweaked it to 11.65V after about an hour of cooking when things seemed to settle down.
I have a used DSO Nano pocket scope someone gave me, but even after finding a manual for it online I can’t figure how to use it. I downloaded an iPad App called ToneGenerator that allows you to generate a variety of tones including square and sine waves. Maybe I can use that in conjunction with the Nano if I can figure it out. I only have a couple of 10 Ohm 10 Watt wirewound resistors lying around to use as a dummy load.
I was a bit paranoid about heat dissipation with this case design and my raw Heatsink USA heatsinks and went through a bit of trouble squeezing a cooling fan with a separate transformer and adjustable voltage regulator in the back of the amp only to find that the fan was making more noise than I wanted and the amp didn’t really get all that hot. I could easily keep my hand on the heatsink indefinitely even after dialing the fan voltage all the way back to 6V to make it quite enough. I may just try disconnecting it.
I hooked up a couple of cheap Aura fullrange drivers I have for testing and pumped some music through the amp from my favorite Down Tempo Apple station on my iPhone.
I was very surprised at how nice the music sounded from those cheap little speakers plopped down on the bench. I’ve used them several times before and have always just said to myself “OK it works...they make noise.”
I am really looking forward to getting the second monoblock running and getting them into my system. I just hope they have enough juice as the ACAs are supposedly putting out 8 Watts compared to 5 Watts of the F2J into 8 Ohms.
Attachments
@twitchie...Thanks very much. It’s been a long road. I started fabrication of the cases some time in July of this past year.
Well I finally got the second monoblock together and powered up today. I spent some time this morning letting it cook on the bench and checking the bias several times over a few hours.
I was checking temps in the case and on the heatsink while adjusting the voltage regulator for my cooling fan. This fan was making a small ticking noise now and again for some reason even though it is brand new. It became very faint along with fan noise in general once I dialed the voltage back to 6V. It is inaudible at any more than a few feet. Still, once you hear it you tend to focus on it.
Ill have to keep an eye on it as I don’t know if the fan might die prematurely. I seriously doubt the amp will over heat even if it does as the temps were barely reaching 140 F even on the heatsink right next to the IRFP9240 which generates a bit more heat then the Semisouth.
Everything else went pretty smoothly. Just had to play around with cables a bit to hook things up and squeeze them in where I had my ACAs. I attached some pics for fun.
I was able to listen probably for an hour or so after I had let the the amps come up to operating temp while I had my afternoon coffee. I put on my favorite Apple Down Tempo station on an older iPad I use to stream music through my system often. Not a great source, but one I am very familiar with.
The volume level on the iPad was set to its maximum and as soon as I brought the volume of my preamp up I heard distortion. I lowered the iPad level and tried bringing up the preamp again and all was good.
I never had that issue with the ACAs...they really needed the max output of the iPad going into the pre and the pre volume dialed up to about 50% to make the horns sing.
After playing around with the volume level on the iPad and the preamp I would say that I reached a nice listening level with the iPad at 75% and the pre at only 25%. That is a bit lower than what I expected and experienced with the ACAs.
My listening with the F2Js has barely begun. There is always a smile during the honeymoon.
I’ve tried to figure out a way to verbalize my first impression of them. Nelson talks a lot about 2nd harmonics and how they relate to the sound of amps. There definitely is nothing harsh sounding about these amps, yet they don’t sound dull or syrupy either. There is good detail as well as a broad and defined sound stage when the recording has that information to offer. It is easy to identify lousy recordings.
I want to say that there appears to be better low frequency response, but I’m not sure that is what I’m experiencing. Especially when one considers that the B5 is cutting things off around 150Hz and sending it to my dipole bass panels through the bridged Rotels.
I actually found low bass response lacking on some of the electronic music I was listening to and decided to up the gain on my subwoofer a tiny bit. I don’t know if this is because at the lower levels my source and preamp were set at the horns were playing more efficiently with the F2Js and the gain wasn’t enough for the rest of the system. Some testing and more listening will definitely be needed.
If I were to try sum up my initial impression of these amps in my system with a few adjectives I would say they are “polite” and “elegant” yet they have “authority” about them.
Well I finally got the second monoblock together and powered up today. I spent some time this morning letting it cook on the bench and checking the bias several times over a few hours.
I was checking temps in the case and on the heatsink while adjusting the voltage regulator for my cooling fan. This fan was making a small ticking noise now and again for some reason even though it is brand new. It became very faint along with fan noise in general once I dialed the voltage back to 6V. It is inaudible at any more than a few feet. Still, once you hear it you tend to focus on it.
Ill have to keep an eye on it as I don’t know if the fan might die prematurely. I seriously doubt the amp will over heat even if it does as the temps were barely reaching 140 F even on the heatsink right next to the IRFP9240 which generates a bit more heat then the Semisouth.
Everything else went pretty smoothly. Just had to play around with cables a bit to hook things up and squeeze them in where I had my ACAs. I attached some pics for fun.
I was able to listen probably for an hour or so after I had let the the amps come up to operating temp while I had my afternoon coffee. I put on my favorite Apple Down Tempo station on an older iPad I use to stream music through my system often. Not a great source, but one I am very familiar with.
The volume level on the iPad was set to its maximum and as soon as I brought the volume of my preamp up I heard distortion. I lowered the iPad level and tried bringing up the preamp again and all was good.
I never had that issue with the ACAs...they really needed the max output of the iPad going into the pre and the pre volume dialed up to about 50% to make the horns sing.
After playing around with the volume level on the iPad and the preamp I would say that I reached a nice listening level with the iPad at 75% and the pre at only 25%. That is a bit lower than what I expected and experienced with the ACAs.
My listening with the F2Js has barely begun. There is always a smile during the honeymoon.
I’ve tried to figure out a way to verbalize my first impression of them. Nelson talks a lot about 2nd harmonics and how they relate to the sound of amps. There definitely is nothing harsh sounding about these amps, yet they don’t sound dull or syrupy either. There is good detail as well as a broad and defined sound stage when the recording has that information to offer. It is easy to identify lousy recordings.
I want to say that there appears to be better low frequency response, but I’m not sure that is what I’m experiencing. Especially when one considers that the B5 is cutting things off around 150Hz and sending it to my dipole bass panels through the bridged Rotels.
I actually found low bass response lacking on some of the electronic music I was listening to and decided to up the gain on my subwoofer a tiny bit. I don’t know if this is because at the lower levels my source and preamp were set at the horns were playing more efficiently with the F2Js and the gain wasn’t enough for the rest of the system. Some testing and more listening will definitely be needed.
If I were to try sum up my initial impression of these amps in my system with a few adjectives I would say they are “polite” and “elegant” yet they have “authority” about them.
Attachments
Thanks Zen.
I spent part of my morning re-reading Papa’s papers on current source amps and crossovers as well as the factory F2 manual while the amps played in my system.
Pa calls the F2 “a tinkerer’s amplifier” in the manual. I’m trying to formulate a strategy for my tinkering.
I think the first thing I will need to do is pull out my UMIK again and fire up REW to try and get an idea of what’s going on with the response.
I’m pretty sure I have a shelf filter active on the high pass section of the B5 from the last time I tinkered with the system. I’ll probably try resetting everything to a baseline or even pull the B5 and take measurements first.
I’ve not attempted any other kind of active or passive correction network with the DX3s in the Oris horns. I’m not sure how I’ll approach that if there seems a need.
For now I’ll just continue to let them cook and listen while I clean up my work space and think things over.
I spent part of my morning re-reading Papa’s papers on current source amps and crossovers as well as the factory F2 manual while the amps played in my system.
Pa calls the F2 “a tinkerer’s amplifier” in the manual. I’m trying to formulate a strategy for my tinkering.
I think the first thing I will need to do is pull out my UMIK again and fire up REW to try and get an idea of what’s going on with the response.
I’m pretty sure I have a shelf filter active on the high pass section of the B5 from the last time I tinkered with the system. I’ll probably try resetting everything to a baseline or even pull the B5 and take measurements first.
I’ve not attempted any other kind of active or passive correction network with the DX3s in the Oris horns. I’m not sure how I’ll approach that if there seems a need.
For now I’ll just continue to let them cook and listen while I clean up my work space and think things over.
Its been a while, but I used the info that kinko posted at beginning of thread...post #9.
I didn’t have a proper signal generator...I suppose I could have used REW...but I can’t even figure out how to use the pocket scope someone gave me.
I set it to half my supply voltage, let it cook and readjusted it a few times over a few hours.
I think the pot was just centered on its range as it was shipped from Mouser.
I most definitely had my DVM hooked up before I fired it up so I would see if there were any crazy voltages.
Zen probably held my hand a little...he might chime in.
I didn’t have a proper signal generator...I suppose I could have used REW...but I can’t even figure out how to use the pocket scope someone gave me.
I set it to half my supply voltage, let it cook and readjusted it a few times over a few hours.
I think the pot was just centered on its range as it was shipped from Mouser.
I most definitely had my DVM hooked up before I fired it up so I would see if there were any crazy voltages.
Zen probably held my hand a little...he might chime in.
Setting P1 to a particular value on F2 prior to power up is not necessary (but if someone knows a theoretical value that would be convenient). Just adjust it to create symmetric clipping once the amp is up and running. Looking at my F2J build notes I see that I replaced the originally specified 5K pot with a 10K.
There is a small improvement in quality with F2J which I believe is from less distortion charecterestics of output device aka JFEt.
I made the F2 first to experiment and I loved it and hence proceeded to making F2J, which is still being used until something killed it.
It is easy to convert on to other with just three less than 3$ parts changed ( except semisouth jfet) and that’s how my boards are designed.
I will also try 10 K pot this time when I repair it.
I made the F2 first to experiment and I loved it and hence proceeded to making F2J, which is still being used until something killed it.
It is easy to convert on to other with just three less than 3$ parts changed ( except semisouth jfet) and that’s how my boards are designed.
I will also try 10 K pot this time when I repair it.