Hi Jim and many thanks! You are always there when we need you and you are much appreciated here. I have that Antek in my Cart already��
When stating 4 - 15000 I was referring to per side, which I didn’t specify. Are you saying a total of 8 capacitors for the power supply, 4 for - and 4 for + = 8 ?
When stating 4 - 15000 I was referring to per side, which I didn’t specify. Are you saying a total of 8 capacitors for the power supply, 4 for - and 4 for + = 8 ?
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Hi 6L6,
I plan to listen to it long term before messing with anything. I do have a good feeling about this amp as it is rare to see 100uV noise at the outputs on a big Class A amp like this with a simple CRCR PSU with linear trafo.
I do have a question about the trim pot for the LTP bias current. I set the pot at the recommended value before soldering. Is it necessary to check the actual current value and what adjustments should be made to eek out all the performance of the system?
@naturalmystic:
All I can say is that, if you are going with a linear PSU, follow the FW PSU plan to the "T". Each detail makes a difference in ensuring no ground loops and reducing hum/noise, and do get the CL60 power thermistors - they make a huge difference in hum reduction and allow a graceful startup.
This was one of the most straightforward builds as far as big Class A amps go, and the initial power-on and adjustments were pretty uneventful (good).
I plan to listen to it long term before messing with anything. I do have a good feeling about this amp as it is rare to see 100uV noise at the outputs on a big Class A amp like this with a simple CRCR PSU with linear trafo.
I do have a question about the trim pot for the LTP bias current. I set the pot at the recommended value before soldering. Is it necessary to check the actual current value and what adjustments should be made to eek out all the performance of the system?
@naturalmystic:
All I can say is that, if you are going with a linear PSU, follow the FW PSU plan to the "T". Each detail makes a difference in ensuring no ground loops and reducing hum/noise, and do get the CL60 power thermistors - they make a huge difference in hum reduction and allow a graceful startup.
This was one of the most straightforward builds as far as big Class A amps go, and the initial power-on and adjustments were pretty uneventful (good).
I built my PSU following the diagram in the F6 article: http://www.firstwatt.com/pdf/art_f6_baf.pdf
It's slightly different than the standard FW PSU, I believe it has better filtering and channel separation as the outputs are separated onto their own CRC.
I am not sure if the DIYA store PSU board is wired this way (note where the output taps are located vs the one on the F6 build guide thread):
Here is what I built to:
vs. the one on F6 build guide thread:
I am using the Antek 400VA 18v toroidal trafo btw, and CDE 33mF 25v (85 deg C) caps x 8 for the PSU.
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xrk971 thank you for the information. I really appreciate hearing from those who are willing to share their experience. Though I will stick with the 300v transformer I’ll pull out the DIYAUDIO PSU board to see what is what. The DIYAUDIO board is pretty flexible in some aspects and my guess is working in the thermistors is doable.
XRK - Re: LTP bias, if you set the pot properly on assembly, leave it.
I shouldn't have included a pot in that position, when I have the next revisions on the PCB done, I'm removing that and a few other things that were added to give builders flexibility in building and troubleshooting, and those things have essentially never been used.
naturallmystic - yes, (8) caps in total.
Thermistors and line cap for 120V wiring -
I shouldn't have included a pot in that position, when I have the next revisions on the PCB done, I'm removing that and a few other things that were added to give builders flexibility in building and troubleshooting, and those things have essentially never been used.
naturallmystic - yes, (8) caps in total.
Thermistors and line cap for 120V wiring -
I used a pair of AudioCap Thetas I had lying around, and they work well. Otherwise my favorites are Dynamicaps, Obbligato Gold and Russian military K75-10. Clarity Caps are nice too, though the top of the line gets pretty pricey. I've never used K42-Y2 in a position like this but they would probably be a very good (and cheap) possibility as well. Of course you can do better if cost is not an issue......
I used Mundorf Evo Silver Gold Oil ... HUGE improvement over the WIMA and not terrible expensive. I chose them because they are shorter than most others and fit the hole spacing easy.
This is interesting:
Aleph J input capacitor (C1)
I wonder how large the initial offset might be without C1.
Dennis
Aleph J input capacitor (C1)
I wonder how large the initial offset might be without C1.
Dennis
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John: Does it matter if you are running a balanced or single ended input in order to hear the impact of the C1 cap? I've been gathering some Russian PIO and Teflons lately... I was thinking a big, fat PIO might be interesting with the M2.
Scott: Guess it's time for a nice amp to go with your new Pearl! I hope you are enjoying you vinyl collection!
I have all of the parts for an Aleph-J and a VFET2 build, not sure which one to go for next... Also have critical parts for a CSX1 and M2, but need to order the balance of more mundane parts. If only chassis and transformers were cheaper
If it doesn't last long you could just use a relay to ground the output and open the relay after a time with a timer circuit. Then it wouldn't matter how big the offset was.
I have the Aleph J connected to my main system now. ScanSpeak 10F/8424 and RS225-8 FAST speakers in a transient perfect alignment. Pretty low sensitivity speakers but the Aleph J has enough guts to drive it nicely. Using an Aksa CFP SE Class A preamp to drive the Aleph J. Will listen long term for a week or so and report back. Bass duties below 100Hz augmented with a FLH sub with separate Class AB amp.
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I built my PSU following the diagram in the F6 article: http://www.firstwatt.com/pdf/art_f6_baf.pdf
It's slightly different than the standard FW PSU, I believe it has better filtering and channel separation as the outputs are separated onto their own CRC.
I am not sure if the DIYA store PSU board is wired this way (note where the output taps are located vs the one on the F6 build guide thread):
Here is what I built to:
vs. the one on F6 build guide thread:
I am using the Antek 400VA 18v toroidal trafo btw, and CDE 33mF 25v (85 deg C) caps x 8 for the PSU.
I have stared at these two power supplies for a few minutes, could you point out the difference? I am not finding it! Old eyes...other than slight difference in the way "TH" drawn in schematic....and line cap.
Russellc
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There are independent outputs for Left and Right channels on the newer one. Meaning that they don’t share the exact same power rail which gives better stereo separation and imaging. The newer one has has a “y” shaped CRC (look at the resistor array - it’s dicided into two sections on newer one) Look for +V_A and +V_B etc.
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I see that, but ( and I am far from the brightest bulb on the DIY porch) it appears to be minutia to me....if I were that concerned, I would just use two power transformers and dual mono the power supply, albeit at greater expense.
Does taking this power out before the last capacitor stage somehow help this separation? Not to be nit-picky, but I have had the completed AlephJ boards ready to go since 6L6 first offered the set, and am getting ready to buy a deluxe 4 chassis and rear parts kit to finish it at long last....never noticed this difference before!
Russellc
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