I got rid of 2 mounting holes and added C20 and C21 adding caps to the power rails on the amp boards. These can be 5 or 7.5 lead spacing up to 16mm caps, one per rail. I'm going to run with this on GB#2. I also fixed EBC/CBE on Q4&5.
I'll update the build docs for these changes after the GB2 is finalized.
C20 and C21 need to be rated for rail voltage or greater. There should be plenty of options for 1000+uF choices from your favorite suppliers: Panasonic, Nichicon, Elna, etc.
I'll update the build docs for these changes after the GB2 is finalized.
C20 and C21 need to be rated for rail voltage or greater. There should be plenty of options for 1000+uF choices from your favorite suppliers: Panasonic, Nichicon, Elna, etc.
Hi Randy,
just to be sure, the latest version is no CRC network, just one 1000+ uF cap per rail?
just to be sure, the latest version is no CRC network, just one 1000+ uF cap per rail?
Istvan, Correct. I'll add that C20/21 to the next rev.
It's a similar concept to a Juma F5 "mini" I'll be building soon with rail caps on the local board. I like the concept, and AddiDub's comment made me think about how to add it to the Aleph board. I think CRC will be a bigger effort and will result in dropping a pair of MOSFETs. I opted to keep it simpler...
It's a similar concept to a Juma F5 "mini" I'll be building soon with rail caps on the local board. I like the concept, and AddiDub's comment made me think about how to add it to the Aleph board. I think CRC will be a bigger effort and will result in dropping a pair of MOSFETs. I opted to keep it simpler...
That would work.
Connect positive rail from Q7 center pin. Negative rail from R41, just follow the trace from V-. Or spare rail pins.
Make sure you orient the negative rail cap correctly. + to gnd, - to PSU V-
I need to check my stash of spare caps to see if I have some extras that will meet the rail voltages. I have a huge stash of resistors, but I tend to order caps as-needed. So some spares, but not a lot... If I have some I'll try this mounting concept this weekend.
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Did some final adjustments of the AC current gain of the Aleph current sources this weekend. At first turn-on I had dialed down the Iq Bias to ~0.7 A per Fet, resulting in a total bias of ~2.1 A. I also checked carefully for equal distribution of the Bias current through the three parallel MOSFETs. Everything looked fine. DC Offset at the output was dialed down to 1mV. I suggest to let the amp warm up for one or two hours to let it reach its thermal equilibrium before doing any adjustments.
Until today I did not find the time to set the AC current gain of the Aleph current sources. I only measured R42 in both channels because of the perfectly equal distribution of the current between the parallel devices. I followed the procedure described on page 4 in the perfect build notes that Randy provided to us. I had printed them for convenient work flow. During the procedure I noticed, that after step 5 the signal level of the signal generator has to be adjusted to reach the same level as set during step 1. I used two 8ohm loads in parallel, so I got 4 ohms. I did my adjustments with 20W of output power = 9V AC into 4 ohms.
During the procedure I realised that my AC current gain percentage was way off the specs. In step 3 of the procedure I measured 350 mV through R42 (on both channels), while In step 6 I measured only 135 mV through R42, so I dialed P2 until I got 175 mV, an AC current gain percentage of 50%. Iq Bias current and DC offset stayed spot on after the setting of the AC current gain.
Now I am listening again and I am convinced that the amp sounds way better then before. I fear that I won't make it to bed early today.
Until today I did not find the time to set the AC current gain of the Aleph current sources. I only measured R42 in both channels because of the perfectly equal distribution of the current between the parallel devices. I followed the procedure described on page 4 in the perfect build notes that Randy provided to us. I had printed them for convenient work flow. During the procedure I noticed, that after step 5 the signal level of the signal generator has to be adjusted to reach the same level as set during step 1. I used two 8ohm loads in parallel, so I got 4 ohms. I did my adjustments with 20W of output power = 9V AC into 4 ohms.
During the procedure I realised that my AC current gain percentage was way off the specs. In step 3 of the procedure I measured 350 mV through R42 (on both channels), while In step 6 I measured only 135 mV through R42, so I dialed P2 until I got 175 mV, an AC current gain percentage of 50%. Iq Bias current and DC offset stayed spot on after the setting of the AC current gain.
Now I am listening again and I am convinced that the amp sounds way better then before. I fear that I won't make it to bed early today.
Regarding rail voltages and temperature, some data of the hot amp after two hours of listening to music.
Calculated values according to "Aleph Power and Dissipation Spreadsheet" by wuffwaff:
- Aleph 30 Stereo build as per build notes, set to 50% AC current gain
- boxed in a 4U 300mm Deluxe UMS enclosure
- Transformer: toroidy.pl Audio Supreme Grade, 2x 18V, 400 VA
- positive rail: + 22.35 V
- negative rail: - 22.28 V
- total DC Bias ~ 2.1 A
- DC offset: next to 0 mV
- AC Ripple 100Hz on output: ~1.5 mV
- Temperature Heatsinks: next to X*?@! hot (~60°C)
- Temperature Transformer: Blimey hot (~45°C - 50°C)
Calculated values according to "Aleph Power and Dissipation Spreadsheet" by wuffwaff:
- Output power into 8 ohms: 23W
- Output power into 4 ohms: 35W
- Heat Dissipation for each Channel: 93W
- Dissipation per FET: 16W
- calculated Heatsink Temp: 56°C
- calculated FET junction Temp: 77°C
Excellent results and thank you for correlating the subjective with the objective.
Enjoy the music!
Best,
Anand.
Aleph 60 Mono, Deluxe 4U chassis. Antek AS-4225 Donut per monoblock. ~31.5V rails, 2.2A bias. After 24 constant run with the top on the hottest I measure on the heatsink is 47C. 4U Deluxe seems to be a perfect match for the A60.
I expect a toroidy or other donut with a little higher secondary voltage that gets rails up to 35V would get temp a little higher.
So with the 4U/500 I should be just fine, as predicted/calculated. Your temps were actually a bit lower than I expected. Thanks for confirming, Randy! Actual data is way better than my back-of the matchbook calcs.
Just signed up for an Aleph 30 stereo build, and starting to plan buying parts. Thinking about power supply caps, a couple of things are bothering me.
First, the PS rails will be close to 25V, and yet 25V rated caps seems to be the standard recommendation. Isn't that a bit risky? Having said that, I know that the factory Aleph 3, back in the day, was fitted with 25V rated caps. So maybe I'm worrying about nothing?
Secondly, over time, I've gleaned a few 'rules of thumb' for CRC supplies, including the following: the first bank of caps should have high ripple rating; the second bank should have low ESR; the first bank shouldn't be too big, to avoid stressing rectifiers etc; the second bank should be no smaller than the first bank, and can be bigger.
On the "New Original" F5 power supply PCB, however, which is recommended for the stereo build, the second bank of caps is split into two separate channels. So each channel/rail is seeing a first bank of 44mF, and a second bank of 22mF. Isn't that less than optimal? Or are the 'rules of thumb' above really just myths?
First, the PS rails will be close to 25V, and yet 25V rated caps seems to be the standard recommendation. Isn't that a bit risky? Having said that, I know that the factory Aleph 3, back in the day, was fitted with 25V rated caps. So maybe I'm worrying about nothing?
Secondly, over time, I've gleaned a few 'rules of thumb' for CRC supplies, including the following: the first bank of caps should have high ripple rating; the second bank should have low ESR; the first bank shouldn't be too big, to avoid stressing rectifiers etc; the second bank should be no smaller than the first bank, and can be bigger.
On the "New Original" F5 power supply PCB, however, which is recommended for the stereo build, the second bank of caps is split into two separate channels. So each channel/rail is seeing a first bank of 44mF, and a second bank of 22mF. Isn't that less than optimal? Or are the 'rules of thumb' above really just myths?
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Thanks both. Yes, that's pretty much what I was thinking.
Thanks for the link, Anand - I'd missed that thread. What a mess that Aleph 3 was in! My own factory Aleph 5 has 34V rails and the caps are rated at 50V. It looks like new inside. (I'm about to recap it anyway, though.)
I'm thinking I'll supersize the caps for the second bank - if I get 47kuF caps then the second bank will effectively be about the same size as the first bank. The 47kuF caps I've found have lower ESR than any of the smaller ones, too.
Thanks for the link, Anand - I'd missed that thread. What a mess that Aleph 3 was in! My own factory Aleph 5 has 34V rails and the caps are rated at 50V. It looks like new inside. (I'm about to recap it anyway, though.)
I'm thinking I'll supersize the caps for the second bank - if I get 47kuF caps then the second bank will effectively be about the same size as the first bank. The 47kuF caps I've found have lower ESR than any of the smaller ones, too.
For the second bank, split for two channels, you could also use 33 mF caps. Combined with the new C20 & C21 on the channel boards, you can make a good low impedance supply.
The first bank absorbs the surge current from the bridge rectifiers, the second bank needs to provide a low impedance supply of current. I suggest 2200 uF, 35V audio grade caps for C20 and C21.
The first bank absorbs the surge current from the bridge rectifiers, the second bank needs to provide a low impedance supply of current. I suggest 2200 uF, 35V audio grade caps for C20 and C21.
I hooked the amp to a 4 ohm load, a signal generator and did some scope measurements. I wanted to check for funny sine waveforms like reported in other threads about other aleph projects here on diyaudio.
Up to an output voltage of about 8.8V RMS (19.5W into 4 ohms) the sine wave looked fine from 20Hz to 20kHz.
To observe severe clipping I had to crank the output up to 12.7 V RMS (40W into 8 ohms). Noob question: is this voltage clipping? Would a higher rail voltage cure this limit?
Last picture is a square wave with a reasonable low signal level. There is a little HF overshoot, but to me it looks well damped.
Conclusion: my Aleph30 build delivers clean sine wave with 20W into 4 ohm, acceptable, slightly distorted sine wave up to 32W into 4 ohm (not shown). That should be enough for my speakers and small room, I think most times only need 1W to 5W for modest SPL levels with my setup.
Square Wave test shows only moderate HF overshoot on 10kHz at low levels. Now I am asking myself if I should try to dampen the overshoot further through enlarging C8 from 10pF to 15pF. I would loose some bandwidth and maybe get some remarkable phase shift in the upper audio band, don't know if it's worth a try.
Regards, Addi
Up to an output voltage of about 8.8V RMS (19.5W into 4 ohms) the sine wave looked fine from 20Hz to 20kHz.
To observe severe clipping I had to crank the output up to 12.7 V RMS (40W into 8 ohms). Noob question: is this voltage clipping? Would a higher rail voltage cure this limit?
Last picture is a square wave with a reasonable low signal level. There is a little HF overshoot, but to me it looks well damped.
Conclusion: my Aleph30 build delivers clean sine wave with 20W into 4 ohm, acceptable, slightly distorted sine wave up to 32W into 4 ohm (not shown). That should be enough for my speakers and small room, I think most times only need 1W to 5W for modest SPL levels with my setup.
Square Wave test shows only moderate HF overshoot on 10kHz at low levels. Now I am asking myself if I should try to dampen the overshoot further through enlarging C8 from 10pF to 15pF. I would loose some bandwidth and maybe get some remarkable phase shift in the upper audio band, don't know if it's worth a try.
Regards, Addi
That is actually a good looking square wave - what I would call critically damped.
Time to stop messing with the amp and enjoy music. 🙂
Time to stop messing with the amp and enjoy music. 🙂
I randy, I just want to double check with you.
BOM v.1.0d doesn't mention R16.
in a replay to Plott you say R16 = 221R but in the schematic R16 = 392R
Which one is the correct value for R16 ?
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