| xavier1000 |
After some months working quite hard on them (specially for the metal hardware), my Aleph X's are both up and running.
Voltage at the fets: Between 17.5v and 18v
bias: 7,2A
AC Gain: 54%
Number of fets: 8
The DC offset between the outputs is between 18 and 25 mV and the absolute DC offset 350mV after two hours of use. The temperature is fine: after two hours, I still can touch them with the hands without problems.
The sound is really amazing. They are driving a pair of B&W 803 and the preamp is an Aleph P1.7
Xavier |
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| xavier1000 |
| More pictures... |
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| xavier1000 |
| The chassis... |
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| xavier1000 |
| The transformer... |
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| xavier1000 |
| And finally, the inside. |
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| Zen Mod |
| quote: | Originally posted by xavier1000
The transformer... |
front plate isn't on par with chassis(make it thicker and especially bigger-to hide bottom plate edge).......but :
:worship: |
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| wuffwaff |
Hi,
nice amp! Very easy way to make a chassis with those edge connectors. Where did you buy those? Do they come in different sizes?
William |
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| xavier1000 |
I bought them in a local hardware store. They are supposed to be use for making glass tables or shelves.
The width of the square tubes is 25mm and you can get the tubes cut at any lenght. They have several different edge connectors (3 or 4), feets, etc.
The structure can be mounted without any screw. |
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| Stefanoo |
Hi!
i noticed that you used mills resistors...isn't it?
Another thing.....on your picture i can see just a part of your loudspeakers...are your speakers B&W?! they really look like!
I don't know if oyu gave the necessary time to the amp to burn in all the new components.....how does it sound like so far?
What stereo parts do you have?...cables...source....speakers....?
Best,
Stefano. |
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| Apogee |
Very clean!
I also like those corner connectors. Very handy...
I'd be interested in your comments regarding the sound.
Great work! :) |
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| carpenter |
Beautiful, clean job, Xavier. Clever approach.
John:) |
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| Luke |
nice idea with those connectors. Soon well be debating the sound of various plastic connectors:D
Heatsinks are really nice too, where are they from? |
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| kiwi_abroad |
Great amp,
Can you give some spec's on the heatsinks. Dimensions, thermal coefficient etc.
Thanks, Adrian |
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| Peppe |
| Very nice job, Xavier! What's about pcb? |
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| sinuko |
Bravo Xavier.
with 18 V rail voltage Which is the maximum voltage swing at +- ouput connector on your aleph-x before (voltage) clipping?
Wichi value of McMillian resistor have you use?(4.7k?)
Thanks Paolo
x Beppe: about the pcb http://www.diyaudio.com/wiki/index....h-X+Compact+PCB
Ciao Paolo |
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| Stefanoo |
i didn't know there could be all this "compaesani" on this DIY forum!
NICE!
Ciao,
Stefano. |
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| Peppe |
Grazie Mille, Paolo!
Mmmmm.... the GB was 2 years old :eek: at that time I did know nothing about Mr. Pass and this forum! :(
| quote: | Originally posted by Stefanoo
i didn't know there could be all this "compaesani" on this DIY forum!
NICE!
Ciao,
Stefano. |
Yep Stefano, in Italy we like the beautiful things! :D The Pass projects are a very elegant way to approach audio electronics! ;)
How do not love them?!
Nice to meet on this forum :cool: |
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| xavier1000 |
Thank you guys! And, specially thanks to Grey and Nelson. It is a great design!
Let me try to answer some of your comments and give some more details:
The heatsinks are Fischer SK157 0,22šC/W. Their size is 300x200x83mm.
The PCBs come from Carondimonio. Sinosuko is right, that link points the GB that I joined quite late.
Regarding the psu, I am using one transformer Amplimo 2x15v 625VA for each channel. CRC for filtering, using 4 100mF capacitors, i.e. a total of 400mF per channel.
I am using 8 IRFP044 per channel and the value for the source resistors is 0.27R (yes, they are Mills). The McMillan resistors are 4.75k, R1/R45 68R and I am not using caps at the input.
Regarding clipping, this measurement is still pending. However, I would say that the voltage at the fets is not as high as 18v, is more between 17.6 and 17.7v.
My initial impression on the sound is very positive. The sound is really good. Bass is tight and controlled, the midrange is sweet and extremely transparent. The highs are a little brighter than my tube amplifier but less than commercial transistor amplifiers.
Xavier |
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| xavier1000 |
| quote: | | front plate isn't on par with chassis(make it thicker and especially bigger-to hide bottom plate edge)....... |
You are right, Zen Mod. I thought nobody would notice that... :) |
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| yup |
Great work! It is good to see more people complete the Aleph-x sucessfully
What type of tube amplifier are you comparing it to?
Does the absolute DC offset stay fairly steady at 350mV? or does it drift slightly?
Also, can you notice any hum at your speakers? I am going through final tweaks on my pair and have a faint hum at the speaker still, however I still plan to eliminate it completely (and post some pictures) when I get some free time. It is definatley a slow process
Jeff |
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| xavier1000 |
| quote: | | What type of tube amplifier are you comparing it to? |
My tube amplifier is a 4 KT88 PP per channel in triode mode
| quote: | | Does the absolute DC offset stay fairly steady at 350mV? or does it drift slightly? |
When I connect the amplifier I have around 4v of absolute DC offset that goes down quickly to less than 1v and then needs one hour to go downto around 350mV. It stays between 340 and 360mV.
However, these numbers are only for the second channel. The first channel I did was not as good. The DC offset between outputs is about 60mV and the absolute DC offset about 900mV. I plan to change the input differential fets for this channel. In fact, for the second channel, I used a socket so I could try some of them in real conditions. I will definately do the same for the first channel.
| quote: | | can you notice any hum at your speakers? I am going through final tweaks on my pair and have a faint hum at the speaker still, however I still plan to eliminate it completely (and post some pictures) when I get some free time. It is definatley a slow process |
I only notice some hum at the speakers if I am closer than 2 meters. The ripple I measured was about 80mV.
I am also in the process of fine tunning the amps, but I want to stay some weeks just listening music and enjoying the amp. Then I'll start the tweaks.
I agree with you it is a slow process, but it pays when you just have finish the amp and you enjoy it with your favourite music drinking your favourite red wine!
Xavier |
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| Stefanoo |
| quote: | Originally posted by Stefanoo
Hi!
i noticed that you used mills resistors...isn't it?
Another thing.....on your picture i can see just a part of your loudspeakers...are your speakers B&W?! they really look like!
I don't know if oyu gave the necessary time to the amp to burn in all the new components.....how does it sound like so far?
What stereo parts do you have?...cables...source....speakers....?
Best,
Stefano. |
Still waiting to know the things quoted above :) ... |
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| xavier1000 |
Hi Stefanoo,
I forgot to answer your questions in the first page. Sorry about that!
| quote: | | i noticed that you used mills resistors...isn't it? |
Yes. The source resistors and output resistors are Mills. The rest are Dale CMF-55-143.
| quote: | | Another thing.....on your picture i can see just a part of your loudspeakers...are your speakers B&W?! they really look like! |
You are right. They are B&W Nautilus 803. Although they are marked as 8 Ohms, their minimum impedance is 3 Ohms. That is the reason for having quite high bias (7.2A per channel).
| quote: | | I don't know if oyu gave the necessary time to the amp to burn in all the new components.....how does it sound like so far? |
Not yet, but I don't expect too many changes in the quality of the sound. In fact one of the channels was up two weeks before the other and they sound the same.
| quote: | | What stereo parts do you have?... |
Speakers: B&W 803
Amplifier Aleph X
Preamp Aleph P1.7
CD Rotel rcd991 modded
Phono preamp Aleph Pearl (with MC pre and differential output)
Turntable Michel Syncro + cartridge Shelter 901
Ciao,
Xavier |
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| Netlist |
Split thread can be found
here.
/Hugo |
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| xavier1000 |
After some days of listening, I did some fine tunning to the amps:
1- I reduced the relative DC offset of both channels by changing the differential pairs (I have sockets on both channels). Now I have 7 mV in one channel and 25mV in the other.
2- I noticed that when puting the cover to the enclosure, there is an increase of the temperature that produces changes. The absolute offset increased about 1v so I had to re-adjust V2 through the holes of the cover, without removing it.
The cover was also reducing the bias. I had to re-adjust V1 and V3. Doing so through the cover was quite easy. Measuring the voltage at the source resistors was more difficult. I had to remove the cover and measure each resistor immediately since once the cover was removed, the voltage drifted very quickly. Any alternative ideas on how to measure the bias of each side of the channel without removing the cover would be appreciated!
3- In order to reduce the remaining hum, I added two capacitors in parallel (1000 + 10000 uF) right at the mosfets for each side, i.e. a total of 22000 per channel (see the picture). Each pair is connected to the drain of the current source (V+) and the source resistor of the output devices (V-) for each side of the monoblock.
This totally removed the remaining hum in the left channel while for the right channel, you have to put your ear almost against the speaker to hear some noise.
Xavier |
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| xavier1000 |
I did some measurements for 8R and 4R loads.
The measured peak voltage before clipping was 32v (22,6v RMS) for 8R and 28v (19,8v RMS) for 4R. I measured +17,54 and -17,58 from psu and bias about 7.2A
The voltage before clipping for 4R is a little bit less than expected for 4R (98W instead of the 105W according to the excel sheet). I tried to increase the bias to see where was the limitation but I was having 28v consistently, so probably the voltage loss at the fets and the source resistor is higher than expected.
Clipping at 1KHz and Z=8R |
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| xavier1000 |
| Clipping at 1KHz and Z=4R |
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| xavier1000 |
| Now without clipping |
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| sinuko |
Dear Xavier,
thanks for your data.
Can you check if the sine wave at 10kHz (or hihger is better) is correct just before the clipping?(On my Aleph-x (I hope to post it in the next fews weeks), I notice same strange shape (not clipping) at high frequency before the clipping (3-4V).).
My power supply is -21 + 21, and I notice this "strange" shape at 22Vrms output (on 8R).
Thanks Paolo |
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| xavier1000 |
Paolo,
I tried with 20KHz and I have exactly the same thing.
First picture, the signal is still OK: |
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| xavier1000 |
| Second picture, a strange shape can be seen: |
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| xavier1000 |
And 3rd picture, when clipping is even worse.
Could it be caused by the feedback cap (10pF)?
Anyone can tell us what is happening?
Xavier |
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| sinuko |
Thanks Xavier,
I have the same problem.("Second picture, a strange shape can be seen").
A picture is better than 1000 words.
(Just for refernce I used 12 mosfet for channel and Coromandimonio PCB, DC offset is 20mV, Diff Offset 10mV).
Thanks Paolo |
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| xavier1000 |
I couldn't find too much information about phase shift or distortion at high frequencies. I found this post from Neson Pass refered to Aleph 3
| quote: | Originally posted by Nelson Pass
When you deviate from the 50% figure for current gain
on the current source, you get more distortion at the
highest output, either because you are current-starved,
or because the current source is shutting off on negative
peaks. The cure in both cases is more bias.
Come to think of it, more bias is almost always the cure
for any limitations of Alephs. ;)
|
So I tried to decrease the AC Gain from 54% to 49.6% while I increased the bias from 7.2 to 7.4A to maximize the power at 4R.
The resulting waveform at 20KHz (just before clipping) was very similar to the one I showed before.
So, no improvement in that, but the sound was better now. I don't know how to describe it. The sound is even more clear now. The piano Sounds more like a piano.
Anyway, I would like to understand what is happening between 10KHz and 20KHz at high output voltages. Anyone could help? |
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| jupiterjune |
Try comparing the output to the output (drains) of the input devices. If you see the distortion there, then it is probably in the input stage (although, I am unsure as to what effect the feedback would play).
I have seen a lot of different distortion signatures with the BZLS, where the tops of the output sinewaves start to flatten off or do other strange things, like curling to the right or left ever so slightly.
JJ |
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| xavier1000 |
Hi JJ,
I checked the output between the drains of the input devices for different frequencies and levels:
100Hz: the wave was perfect at low levels and high levels
1KHz: the wave was perfect at low levels and less perfect at high levels
20KHz: the wave was perfect at low levels and really distorted at high levels, much more than the wave at the output when using the same input level.
Now I am a little bit lost. :whazzat:
Could it be that when measuring there I am introducing more distortion or interfering the signal in any way?
Xavier |
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| carpenter |
| Perhaps you should keep adjusting the gain down and the current up. You mentioned that the sound improved and that there was "some" change in the scope reading. |
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| jupiterjune |
| quote: | | 20KHz: the wave was perfect at low levels and really distorted at high levels, much more than the wave at the output when using the same input level |
Well I think that definitely tells us something -- but I don't enough about the circuit to interpret what is happening there. I wish I did.......
My scope is dual trace -- I never saw any effect on the outputs of my aleph mini when I connected probes to the drains of the input devices.
JJ |
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| xavier1000 |
I took some more measurements:
First picture: square wave 1KHz at input (Vpk= 2.9v) |
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| xavier1000 |
| Second picture: same square wave 1KHz at output (Vpk=28v) |
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| xavier1000 |
| 3rd picture: sinus wave 1KHz (both sides referenced to GND) at output |
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| xavier1000 |
| 4th pic: the same wave adding both signals (having one of them inverted) |
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| xavier1000 |
| 5th: sinus wave 20KHz (both sides referenced to GND) at output |
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| xavier1000 |
| The same wave after adding both signals |
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| xavier1000 |
Sinus wave 20KHz after increasing a little bit the level.
It seems to be clipping at the positive only. |
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| xavier1000 |
And finally the same wave after adding both signals. Here we can see the strange shape at the output.
The asymetrical clipping that can be seen in the previous picture could be causing this behavior but then, why is only happening with high frequencies (10-20KHz) and not for 1KHz? :confused:
Thanks for your help.
Xavier |
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| wuffwaff |
Hi,
Iīve noticed the same problem in my AlephJ-X thread. It always happens when thereīs current limiting (in my case only at 4 ohms).
Did you notice that thereīs a build in time factor?
The signal is ok for a second or two and then goes into severe distortion. I think it has something to do with the bootstrap capacitor losing itīs load and the two resistors connecting it to the rail and the bjt.
It got worse when lowering the value of the upper resistor (connected to the rail). I will experiment further when my Jfet input is ready.
William |
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| xavier1000 |
The following image summarizes three cases (1KHz, 20KHz and 20KHz. All measured using an 8R wirewoud resistor between
out- and out+, but was the same for 4R and without load)
1 and 2: Normal behaviour
3 and 4: for high frequencies, the positive part of the wave is thiner and taller than the negative. This gets hidden in pict 4 since one side compensates the other.
5 and 6: If we increase the output level, the amp goes into clipping at the positive way before than the negative since the wave is much taller at the positive.
So the problem seems to be the behavior in high frequencies.
Xavier |
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| xavier1000 |
| quote: | posted by Wuffwaff
Iīve noticed the same problem in my AlephJ-X thread. It always happens when thereīs current limiting (in my case only at 4 ohms).
Did you notice that thereīs a build in time factor?
The signal is ok for a second or two and then goes into severe distortion. I think it has something to do with the bootstrap capacitor losing itīs load and the two resistors connecting it to the rail and the bjt.
It got worse when lowering the value of the upper resistor (connected to the rail). I will experiment further when my Jfet input is ready. |
William,
I think the problem could be similar. Not sure I understood what you are refering to when mentioning "build in time factor" though.
The two resistors connecting the rail, cap and bjt I am using are 520R for the upper (R14 in original schematic) and 1k for connecting to the bjt (R15). The "high-powered" version uses 1.5k and 1.5k. Do you think that using these values could improve things?
(note that my rails are aprox. +/- 17,6v). |
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| wuffwaff |
Hi,
with time factor I mean that first the signal is OK for a second or two and then suddenly goes into distortion.
Just try to set it at a level where it just distorts and then turn off the signal generator, wait a few second and turn it on again.
In my case the signal will then be OK for a few seconds , then return to itīs distorted form.
Iīve used 1k2 / 1k2 and changed this to 1k5 / 1k5 wich was a bit better.
Looking at older Alephs (2, 4, 5) the upper resistor is even 4k75
William |
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| EUVL |
William,
May I suggest you try taking out the 2 resistor and replace the cap with a 9V battery ? The experiment will cost you 2.50 Euros at most (and an hour or so for testing).
You would probably need to trim the CCS again because of the difference in voltage (across what was the cap).
Patrick |
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| sinuko |
I use 1.5k/1.5k for r14 r15, with 12 fet for channel, rail voltage +21-21 and 6 amp. bias... and I have the same problem that xavier.
In your test, have you used a balanced signal test? I used unbalaced signal test.
Thank Paolo
p.s. with pspice I can't see any of these distortions. |
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| EUVL |
> May I suggest you try taking out the 2 resistor .....
Correction, I meant only remove the resistor to the +ve rail.
Patrick |
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| xavier1000 |
Today, while I was I checking this ...
| quote: | Originally posted by Wuffwaff
with time factor I mean that first the signal is OK for a second or two and then suddenly goes into distortion.
Just try to set it at a level where it just distorts and then turn off the signal generator, wait a few second and turn it on again.
In my case the signal will then be OK for a few seconds , then return to itīs distorted form. |
Today I checked this and I found that the wave was not OK from the first second. So, it seems to be a different problem.
But, while I was checking with the scope I discovered a 2MHz/100mV amplitude oscillation. The attached image shows this wave when connecting the probes between the 100k feedback resistor and gnd.
So, the problem I am facing could be produced by an oscillation. This could explain why Sinosuko, who is using the same PCB, is facing the same problem.
I did the following:
1- I moved the 68R resistors to ground from the back of the pcb to the output connectors to minimize loops at the output. No changes
2- I increased the feedback caps from 10pf to 20pf by adding one 10 pf cap in parallel. I could not detect any change
3- I added one 2.2n cap between base and collector of each CCS bjt (BC550C). Bingo! Now the wave at 20KHz has improved a lot. The shape is normal until Vpk=30v. The oscillation has been reduced about 25%, but it is still there.
One thing that I detected from step 2 (I didn't checked before) is that the oscillation is not present immediately when I switch on the amplifier. It starts after about 15min suddenly.
I might try with a bigger cap tomorrow.
Xavier |
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| Netlist |
Xavier,
This comes from Nelson himself, written somewhere in the big AlephX thread:| quote: | | 0.001ĩF RF compensation caps can be added between Collector and Base of Q3, Q8 or 0.01uF caps between Collector and Emitter of the same transistors. |
/Hugo :) |
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| wuffwaff |
Hi Patrick,
will try this in due time. Iīm not shure this is a problem in real live and I will have a look at my Aleph5 first.
Still havenīt changed my drain resistors cause I was on holiday and probaly wonīt in the next two weeks since Iīm away on bussiness.
William |
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| sinuko |
me too find that the wave was not OK from the first second.
Very good Xavier,
next week-end I hope to find same time to make the same tests.
Thanks Paolo |
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| xavier1000 |
I've been doing some more testing to remove the 500KHz oscillation (yesterday I mentioned 2MHz by mistake):
1- First of all I removed all the compensation caps I added yesterday and changed the two drain resistors from 520R+1k to 1k+1.5k. This should decrease the current going through the bjt and change the frequency characteristics. It might get rid of the oscillation without any additional cap.
The result: the oscillation was there and the shape of the 20KHz wave was bad again.
2- Added a 10n compensation cap between emitter and collector of the two bjt's. Result: same as before.
3- Removed the 10n caps and I put 1n cap between base and collector. Results: great improvement in the 20KHz sinus wave but the oscillation was still there.
4- I tried with 2.2n and 4.4n and the sinus wave was getting worse and the oscillation was still there.
5- Then, tried 150p. This got rid of the oscillation and the 20KHz is like case 3. It is almost perfect until an amplitude of 30v
So I will leave this channel with this configuration for some days to check how it sounds.
BTW I had to readjust everything, even the AC Gain (now it's 50,4%)
Xavier |
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| wuffwaff |
Hi Xavier,
very interesting. Will have a look at my amp too. Maybe the same thing is happening here (with a slight delay.....). I never tried smaller values than 1n in the active current sources (without cap I had an oscillation at the output).
William |
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| sinuko |
I checked for oscillation but I did't found anything. I can see aoly the "bad distortion" at high frequency (>10khz).
After Xavier suggestiom, i tried to put a cap between B-C of q3 and q8 (Grey Rollins schematic), 3.3nf and the sinus wave is quite better, (no improvement with the cap between E-C), I'll trie with othe cap but (lower) but today :
I have the time but the shop are CLOSED :bawling: :bawling:
Paolo |
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| sinuko |
Dear William,
in my tests I obtain the best results witn 3.3nf between B-C of q3 and q8.
Now I can see a residual of "the strange distortion" just before the clipping.
Paolo |
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| wuffwaff |
Hi,
with 3n3 itīs gone but then the other problem is present (heavy distortion into lower impedances at high frequencies).
William |
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| sinuko |
Hi,
Which is a "lower impedances" for you? 6R 4R or lower?
in any case I'll try next week.
Thanks Paolo |
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| wuffwaff |
Hi,
4R and lower. I only test at 8, 4, 2,8 and 2R because thatīs the way my power resitor bank is build.
William |
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| RoboMan |
It seems there is no discussion on the situation in posting 39. I think this is a parasitic oscillation (not ringing).
I saw this in my Aleph5 and this can be cured by adding a 1000pF (1nF) cap across the gate resistors of the gain MOSFET and the output, i.e. -out and C of Q4 ; +out and C of Q9 (Grey's version dated 5/24/02).
The waveform is reproduced here: |
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| CheffDeGaar |
Hi Xavier
Just curious about your generator...
Do you use a CD player with a recorded square wave on a CD ? Your waveform looks like truncated Fourier series attempting to reproduce a square signal, or if you prefer, the Gibbs phenomenon.
If its ringing, it is damped as it begans to decrease until half the high or low levels of your squre wave. But then, why does it begin to re-rise agian after ? The ringing must follow a level change, not precede it :) Or get a patent on time reversal;)
If it's oscillations, why are they damped in the middle of the high and low levels ? And why is it so symmetrical ? The duration of a level is an exact multiple of the oscillation frequency. Seem to be too much luck...
Just have a look at the pictures here : http://en.wikipedia.org/wiki/Gibbs_phenomenon
Pretty the same, hu ?
May be I'm completely mistaken, but it strongly reminds me a digital problem... Just tell us where your square signal comes from :)
Cheers |
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| RoboMan |
| Cheff, you may be right. It was labelled as 1KHz and made me thought it was oscillation. I think it is actually a 10KHz signal (5 X 2 uS per cycle). |
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| xavier1000 |
| quote: | Originally posted by CheffDeGaar
Just tell us where your square signal comes from |
You are right, Cheff. The signal is generated by a PC from a wav file and then feeds the preamp. It already has this shape at the input of the AX.
Xavier |
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| macka |
Hi guys,
This link may help with understanding what is a happening.
http://stereophile.com/solidpoweram...***/index4.html
As I recall the review samples were not biased correctly but the clues are perhaps there. In that respect take the absolutes with a grain of salt but there is a trend with lower load impediances. In any case amp reviewed impressively compared to the Halcro on a subjective basis as one would expect.
Note the tests were done at 2 watts.
At 20 kherz the output impediance is relatively higher and given a 4 ohms load this has an effect on the FR response tests particularly at high power levels when doing such test.
With that increase in output impediance I suspect the voltage drop is converted to heat and you get the effect you have been discussing. I doubt if this is an issue in normal operation.
This is only my educated theory and I hope it facilitates some productive discussions.
best
Ian |
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| xavier1000 |
I tried removing the McMillan resistors and the behavior improved quite a lot. As a drawback, absolute offset starts with +12v and goes downto -9v after two hours. I will post some picts of the measurings I did in some minutes.
Ian,
Thanks for the link. I am trying to digest all this information and the additional information I got after removing the McMillans.
Xavier |
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| xavier1000 |
The attached image shows some scope measurings. Now I have to leave. More comments tonight.
Xavier |
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| Nelson Pass |
| quote: | Originally posted by xavier1000
I tried removing the McMillan resistors and the behavior improved quite a lot. As a drawback, absolute offset starts with +12v and goes downto -9v after two hours. |
Are you loading the output stage with resistance to ground?
:cool: |
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| xavier1000 |
| quote: | Originally posted by Nelson Pass
Are you loading the output stage with resistance to ground?
:cool: |
I am currently using 33R to ground for each side. |
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| xavier1000 |
I didn't have the chance to describe the pictures I post some hours ago.
Pict 7: this picture shows a 20KHz sinus wave just before removing the McMillan resistors. The distortion can be seen just before clipping.
Picts 1, 4, 8: after removing the McMillans and removing the caps between BC of Q3 and Q8. Pict 4 shows some distortion for 10KHz. Pict 8 shows no distortion because there is some attenuation of the signal.
Picts 2, 5, 9: same as before, but adding a 150p cap between B-C of Q3 and Q8. Pict 5 and 9 shows some distortion, but the amp had been working only 15 minutes. After some minutes, this behavior changed.
Picts 3, 6, 10: everything the same but after 15 minuts. The shapes improved and apparently almost no distortion can be seen. The text has a mistake since the capacitor is still 150p.
Xavier |
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| sinuko |
Dear Xavier,
at the moment I am using McMilliam resistor (4k75) , and Cap between BC (of q3, q8) of 3.3 nF.
I am currently using 120R (I obtain the same result with 60R) to ground for each side.
With higher McMillian resistor the time to stabilize absolute offset is too long (the DC offset between + and output is 20 mV), I tried using 40R to ground with no apparent positive results.
So now I can note the strange distortion just before the clipping (at high frequency >10kHz) .
Paolo |
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| xavier1000 |
Hi Paolo,
I am not sure if you already tried that but, could you just try to remove the McMillan resistors while using the 40R resistors to ground. Then you switch on the AX (having disconnected the speakers) and, after let's say 1 hour, readjust V2 to have an offset near 0. Then test with the scope and check if you still have that distortion.
And don't forget to report any progress :)
Xavier |
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| macka |
Xavier,
Please can you tell us how is your scope connected to the amp when meauring. Schematic of test rig? Also the signal generator.
regards
macka |
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| xavier1000 |
Hi Macka,
The connection is as follows:
PC Generator --> DIY Aleph P 1.7 (balanced) --> AX
Input A of the scope is connected to out+ of the amp and input B to out-. Ground is connected to ground. Then Input B is inverted in the scope and both signals are added.
Regards,
Xavier |
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| sinuko |
In my case YES, William.
Paolo
(less marked but the shape is quite similar). |
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| sinuko |
Hi William,
I have one photo of my distortion, I hope that you can see samething.
Yes the photo is quite bad.
Xavier,
I tried without McMillan resistor (with 40R to ground), but I foud a residual of distortion (and the time to stabilize the DC off-set is too long) so at the and I decide for 4k74 value.
Paolo |
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| xavier1000 |
William,
I would say so, but in my case everything happens at less voltage since my rails are about +/- 17.5v
The latest images I post shows only the remaining of the initial distortion after some changes (Cap, McMillans, etc), but my initial pictures were quite similar to yours. In my case, I got a similar waveform to the one you posted whenever I used bigger caps for B-C of Q3 and Q8 (more than 1nF).
I also detected after removing the McMillan resistors that the behavior was better after the amp had been switched on for a while, having the offset to ground at about -3.5v. If you compare pictures 5 and 6 from my previous post, the only diference is that picture 6 was taken 30 minutes later, with more negative offset to ground.
Paolo,
You are right, removing the McMillans improved things only apparently but did not removed the distortion. It is not the solution, but helps to identify the causes of the problem.
I am not sure yet about it but, could you guys check if you have some improvement in your wave by adjusting the offset to ground to, lets say about -4v instead of near to 0? (only as a test, I am not saying that you leave your amps with this offset as a solution).
Thanks
Xavier |
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| Nelson Pass |
| quote: | Originally posted by macka
As I recall the review samples were not biased correctly but the clues are perhaps there. |
In that case, the bias current was correct, but the gain of the
Aleph current source was mis-adjusted to less than 50%. Just
shows what happens to review units when the sales
department hijacks them off the test bench.
:cool: |
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| macka |
It must have impressed someone on the production line .....LOL
Well that makes all those measurements invalid I guess.;) |
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| Buzzy |
| Wow ! Ur amp looks beautiful. How thick are those wires ? |
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| Stefanoo |
| Xavier...have you figured your problem with distortion on your Aleph X out? |
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| xavier1000 |
| quote: | Originally posted by Buzzy
Wow ! Ur amp looks beautiful. How thick are those wires ? |
Thanks, Buzzy, but I am not sure which wires you are refering too!
Xavier |
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| xavier1000 |
| quote: | Originally posted by Stefanoo
Xavier...have you figured your problem with distortion on your Aleph X out? |
Hi Stefanoo,
I am quite busy and I haven't much time to test. I just reverted to the previous stable situation to be able to listen music. Anyway the distortion only occurs just before clipping and only for frequencies above 10KHz, so I don't think it is a problem for me for listening music at a normal level.
Xavier |
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