I'm not an expert but here goes.
It will have some increased distortion over the optimum grade. The explanation is a bit complicated and is best explained on many web pages that are available. Search for information on "loadline". Once you understand loadlines, it may help for you to know that the circuit has about 4.75ma going through the jfet.
There is of course more to it than just getting an optimum loadline, but then my head starts to hurt.
Jim
Two ACA newbie questions
First Pass build and I have a couple of questions (since boards are all that is available, not full parts kits):
1. Are 2SK170 GR (Toshiba) OK?
2. Given the PSU requirements, are there any issues (e.g. noise, etc.) that would result from using a single Dell 19.5V / 6.7A power brick instead of the two smaller 19V / 2A bricks? I have a freebie in my parts box.
Thank you,
-Derek
First Pass build and I have a couple of questions (since boards are all that is available, not full parts kits):
1. Are 2SK170 GR (Toshiba) OK?
2. Given the PSU requirements, are there any issues (e.g. noise, etc.) that would result from using a single Dell 19.5V / 6.7A power brick instead of the two smaller 19V / 2A bricks? I have a freebie in my parts box.
Thank you,
-Derek
Well, according to Pass, leaving out the R15 mod cost you about a watt I believe, and that's like losing 20% !
Is it possible to add an Aikido tube mono pre in the same build as the ACA? I am trying to biamp my speakers. I have a Music Reference RM-10 with 35db of gain. I thought I could combine an ACA (14db) and an Aikido pre (20db) to match the Music Reference. I would control both amps with a Intact Audio AVC.
Well, given the high B+ requirements of an Aikido tube mono (assuming you are talking about the octal or noval dual-mono board), that'd be a bit weird as there would be a significant disparity between the two with regard to power requirements. On the other hand, if you built an Aikido LV, you can run it on approximately 22VDC - in theory, if you built a good linear power supply (Aikido may not like the ACA switching PSU), you could give the Aikido LV the full 22VDC and then regulate down to 19VDC for the ACA.
-D
Someone stated that it needs to have an IDSS of 6ma or more. The 2SK170 grades are GR: 2.6~6.5 mA, BL: 6.0~12 mA, V: 10~20 mA, so it seems that only a limited percentage of the GR grade would work. If the DIYAudio Store has a long wait time for the correct B grade you might want to go for the D's. I ran a quick simulation in LTspice. I get that the V grade gives about 10% more distortion than the BL grade. As we are down in the hard to hear the distortion levels, 10% of hard to hear probably does not matter. If you already own the GR jfets, test the IDSS.
Jim
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Thanks for the reply and great info!!
There is also the Aikido 12v that can also run on 18v. Do you think that is more suitable? Is it a problem is the Aikido runs off a power supply that is 1v higher as in the ACA's wall wart?
Thanks
I don't think you'd need to drop the voltage for the ACA - my ACA seems perfectly happy running on a 24 volt (regulated) supply as an 'interim measure'.
Enochrome,
Doesnt the Aikido 12V version you are talking about runs on 12V AC??. There are on board rectifiers, specifically a sextupler circuit that converts the 12V AC to 80 to 120V DC depending on what tube you end up using.
New Aikido 12Vac PCB and part kits
The Aikido LV is a different design and the one that uses the nearly unobtanium 6GM8 tube (and variants) runs on 24V DC. Indeed, the ACA can run on 24V DC as well as long as the drain of the output mosfet is set to about 12-12.5V, assuming you are using the latest ACA 1b circuit/schematic as is sold in the diyaudio store.
Aikido LV
http://www.diyaudio.com/forums/pass-labs/215392-amp-camp-amp-aca-287.html#post4836994
You also need to determine/decide if you really need an overall gain of 35dB for your system/speakers/source/room/listening habits. That's a lot of gain. The passive Intact AVC is an excellent unit, the balanced version is my reference.
Best,
Anand.
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Anand,
Yes, you're correct the 12v is AC, I forgot about that. Good catch.
I wanted to add more gain to ACA so as to match the gain of my other amp that has a gain of 35 (which I agree I think is too much). I thought that if I bi-amp that two amps, the ACA and the other, that I would need to get the gain/power as close as possible. You can tell that I do not have a lot of technical knowledge
If biamping is truly is what you are after, then yes, matching the gains would be best advised.
Of course, you do not need to use a tube stage ahead of the ACA to get your extra gain. You could use solid state right? And that might be much easier as there are a multitude of solid state designs out there.
I surmise that you plan on using the RM-10 tube amp for the mid/highs and the ACA for the lows. Or is it the other way around? Remember the RM-10 has a damping factor of 12.5 which means the output impedance is 0.64 ohms. The ACA on the other hand has an output impedance of 2.67 ohms! So perhaps the ACA should be for the highs and the RM-10 be for the lows. The ACA has an overall power output of 6-8 watts while the RM-10 is about 35 watts.
The overall gains of 35dB is still an issue from an SNR standpoint (Have you double checked that spec from Roger Modjeski?). You might want to contact Roger about any modifications that could be done to the RM-10 to drop that gain. I imagine you really do not need more than the usual 26dB given a 2V source. Of course, that might change a little if you use vinyl mostly or if your speakers are inefficient.
The next question is why you want to biamp in the 1st place
This is getting off topic, sorry folks! Rob, we can continue this via pm if you would like.
Best,
Anand.
Of course, you do not need to use a tube stage ahead of the ACA to get your extra gain. You could use solid state right? And that might be much easier as there are a multitude of solid state designs out there.
I surmise that you plan on using the RM-10 tube amp for the mid/highs and the ACA for the lows. Or is it the other way around? Remember the RM-10 has a damping factor of 12.5 which means the output impedance is 0.64 ohms. The ACA on the other hand has an output impedance of 2.67 ohms! So perhaps the ACA should be for the highs and the RM-10 be for the lows. The ACA has an overall power output of 6-8 watts while the RM-10 is about 35 watts.
The overall gains of 35dB is still an issue from an SNR standpoint (Have you double checked that spec from Roger Modjeski?). You might want to contact Roger about any modifications that could be done to the RM-10 to drop that gain. I imagine you really do not need more than the usual 26dB given a 2V source. Of course, that might change a little if you use vinyl mostly or if your speakers are inefficient.
The next question is why you want to biamp in the 1st place
This is getting off topic, sorry folks! Rob, we can continue this via pm if you would like.
Best,
Anand.
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PASS ACA amp camp amplifier project. diyAudio Store's ACA kit for 8w monos and a pair of 24v torroidal power supples. Chassis based on the power supply boxes, raised with heat sink from diy for the amp stage. Silver hookup wire in the signal path. Poplar faceplate and top with tea soak to bring out the grain and add black to the brown (it really works!) then Minwax ebony stain and gloss poly.
Thanks to all here for the help along the way for this total newbie. The sound is really way above what I expected. I did this to learn and just get a bit of a sense of the First Watt sound. Impressed with the stock build, I moved to a 24v switching supply. The sound improved noticeably. So I went for the linear supplies. I didn't expect to make these keepers, but they surely are!
And say hi to Andy, our 13 year old Rottweiler/German Shepard mix.
Thanks to all here for the help along the way for this total newbie. The sound is really way above what I expected. I did this to learn and just get a bit of a sense of the First Watt sound. Impressed with the stock build, I moved to a 24v switching supply. The sound improved noticeably. So I went for the linear supplies. I didn't expect to make these keepers, but they surely are!
And say hi to Andy, our 13 year old Rottweiler/German Shepard mix.
