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Old 19th November 2018, 05:45 PM   #531
sakellogg is offline sakellogg  United States
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Quote:
Originally Posted by Pocoyo View Post
Need veteran PCB part list ...
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Old 19th November 2018, 05:48 PM   #532
sakellogg is offline sakellogg  United States
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Quote:
Originally Posted by Pocoyo View Post
Need veteran PCB part list ...


Wait.....?! this is veterans board right?
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Old 20th November 2018, 03:28 PM   #533
carsten.witt is offline carsten.witt  Germany
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Hi,
or take look to here.
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Old 21st November 2018, 01:07 PM   #534
Pocoyo is offline Pocoyo  Indonesia
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Thank you mate

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Old 27th November 2018, 12:41 PM   #535
Pocoyo is offline Pocoyo  Indonesia
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Quote:
Originally Posted by Zen Mod View Post
yeah .....

nothing really to set , except little tweak of P1 , to equalize gain between channels

volume pot originally at output

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Old 27th November 2018, 12:50 PM   #536
Pocoyo is offline Pocoyo  Indonesia
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Quote:
Originally Posted by Zen Mod View Post
boredom to look for bucket pics

anyway , 2K trimpot is definitelly for gain tweaking , while (by value) 50R trimpots are definitely for fine tuning of Iq , left and right side

take proper pictures of trimpot area , so we can see few resistors around, to give you some guidelines how to set it

any other text info , besides Pass P1.7 ?

vol pot - same as in original schematic , on output

I would use 4k7 log pot there ........ 10K max.
Dear ZM

Where we put vr2 & vr3
Hope this work

Rgds
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Old 20th January 2019, 07:36 AM   #537
albertNL is offline albertNL  Australia
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Pass Aleph P 1.7 preamp builders thread
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Originally Posted by Bfpca View Post
Hi folks

Just a heads up. I powered up my boards and did some basic DC checks. The basics looked Ok. I shorted one input to ground and hooked up my signal generator. It seemed to be working but I had a large imbalance (10%) in the +and_ outputs. The 20ma current sources also seemed to be imbalanced.
I had to leave it until I got home tonight. I had a suspicion that the circuit could be oscillating. Sure enough, I got out the scope and found the output had RF riding on the 1khz sine wave. The oscillation frequency was about 8mhz. It was more on one phase then the other, depending on which input was grounded. I found that the 20ma current sources Q12 and Q14 were oscillating. The Fets and transistors both have stopper resistors of 221 ohms. I took a second 221 ohm resistor and placed it in parallel with these resistors. Lowering the value of the gate stopper caused the oscillation to stop while lowering the base stopper resistor caused the oscillations to increase. It seemed counter intuitive to lower the gate stopper so I replaced the base resistors R52 and R67 with 499ohms and the problem was fixed. I now have a balance within .01volts with an output of 10volts on each phase.
If anyone experiences a similar imbalance it should be a symptom of an oscillation. A scope is very handy to have for situations like this!
Hi Bfpca,

You may remember I have Aleph P1.7 that a friend of mine built with KK boards. I was having trouble with the Dantimax RelVol3 (distortion when changing volume). Since then I have moved to Australia and all my gear was packed up for qute a while.

I had given up on the Dantimax problem and a DIY Audio member gave me an Aleph P1.7 board with integrated volume control (looks the same as SE MOSFET full balanced +128 step volume control PCB ! | eBay ) that he was not using. I populated the board and used my own design arduino based board to control the volume relays on the board as well as control input selection I designed.
I just completed the preamp and after initial testing hooked it up single ended to a Squeezebox Classic as source and a diy F4 with some old speakers. It sounds OK as far as I can judge using these speakers :-)

After re-reading your post I checked the amp using ARTA, REW and DiaNa and an old M-Audio Audiophile USB soundcard (never used them before so not sure if I am measuring things correctly) and noticed I had different distortion patterns on the + and - part of the amp on the channel I tested.

I have a Rigol scope (again, hardly any mileage and still working out how to use it) and was wondering what to look for (and how!) to see if I may also have the osciallation problem you mentioned.

Thanks,

Albert
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Old 20th January 2019, 12:10 PM   #538
Bfpca is offline Bfpca  Canada
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Quote:
Originally Posted by albertNL View Post
Hi Bfpca,

You may remember I have Aleph P1.7 that a friend of mine built with KK boards. I was having trouble with the Dantimax RelVol3 (distortion when changing volume). Since then I have moved to Australia and all my gear was packed up for qute a while.

I had given up on the Dantimax problem and a DIY Audio member gave me an Aleph P1.7 board with integrated volume control (looks the same as SE MOSFET full balanced +128 step volume control PCB ! | eBay ) that he was not using. I populated the board and used my own design arduino based board to control the volume relays on the board as well as control input selection I designed.
I just completed the preamp and after initial testing hooked it up single ended to a Squeezebox Classic as source and a diy F4 with some old speakers. It sounds OK as far as I can judge using these speakers :-)

After re-reading your post I checked the amp using ARTA, REW and DiaNa and an old M-Audio Audiophile USB soundcard (never used them before so not sure if I am measuring things correctly) and noticed I had different distortion patterns on the + and - part of the amp on the channel I tested.

I have a Rigol scope (again, hardly any mileage and still working out how to use it) and was wondering what to look for (and how!) to see if I may also have the osciallation problem you mentioned.

Thanks,

Albert
I figured out what was happening with the attenuator relay switching noise. I had the same issue when I built a hand wired logic controlled output attenuator. When you are switching from one volume level to another several relays can be switching at one time. The output impedance is high due to the current source output. During the relay switching period all the relays can sometimes be open circuit and the full unattenuated output goes out of the preamp. In other words, big noises at certain volume control transitions. There are ways to deal with this and I tried a few but because I was not using Arduino but 4000 and 7400 series gates to do the logic it was very difficult to make changes. While I was dealing with this problem I discovered some more serious oscillations a higher output levels. Everything would be fine until a certain level and then a large oscillation that is easy to see on the scope would occur.
At that point I packed it in on the Aleph P. I could not invest any more time on it.The oscillations may be caused by the board layout, the parts used, temperature related, my particular chassis layout, etc. If I had used an Arduino based attenuator solution then I would have been much better off when it came to making changes.
If you look at the unattenuated output of the preamp and feed it a large sinewave ( the level of most sources which could be as much as 4v rms) you should easily be able to see if you have the same issues. Make sure it is up to full temperature. Hopefully you do not find the same issues.

Brian

Last edited by Bfpca; 20th January 2019 at 12:13 PM.
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Old 20th January 2019, 12:29 PM   #539
albertNL is offline albertNL  Australia
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Thanks for your reply Brian. I will try to find the source of my trouble. I assume I should see identical (or close to identical) FFT graphs on + and - of the outputs? I noticed amongst other things that the 2nd/3rd ratio is not the same. This does not seem normal to me.

How do you see a high frequency oscillation? I assume the scope will use the primary (say 1 kHz) signal as trigger and display it.

Thanks,

Albert
Scope-noob
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Old 20th January 2019, 09:54 PM   #540
chede is offline chede  Germany
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Pass Aleph P 1.7 preamp builders thread
Hi Albert,


when I look for oscillation using my Rigol scope, I display the signal from the signal generator (the 1 kHz going into the amp / pre-amp under consideration) on one channel, and the output of the amp on the second channel.

The first channel (input) should show a clean, sharp 1 kHz sine wave.
Ideally, the second channel (amp output) also shows a clean sine wave of higher amplitude.

If you have oscillation, one hint would be that the sine wave of the amp output would look hashy (not a thin line, but broad).

You can also see it on a 1kHz rectangle, where the horizontal top / bottom of the amp output looks like painted with a broader brush ...


You can the go searching for the oscillation frequency by triggering on the second channel (amp output), and switching the time base to higher and higher frequencies. In my case, the amp under consideration (a Sony V-FET 4650) oscillated (even with inputs grounded) at about 6 MHz with a nice sine wave of around 150 mV rms amplitude ...


Successful measuring,
best regards,
Claas
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