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Old 5th November 2013, 04:55 PM   #3061
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The board is excellent. As for adjustment of the modulated CCS, i am not at all convinced the modulation is an improvement with normal loads. It will certainly be interesting to test switching the modulation off.

My "tongue in cheek" post related to the optimal resitor values and bias. Probably won't make any difference but i just have to give it a go

Already raised the bias of the output from 13 to 18mA and cannot hear any difference.
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Old 5th November 2013, 05:25 PM   #3062
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Originally Posted by analog_sa View Post
Oh, cool. So instead of building it once we can build it twice. Any further radical updates anticipated?
Not-lol.... Lol.
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Old 6th November 2013, 08:31 AM   #3063
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by analog_sa View Post
...........Already raised the bias of the output from 13 to 18mA and cannot hear any difference.
It will depend very much on how much capacitance is mixed in with your nominal load and how much interference is picked up and transmitted with the signal to be attenuated at the next RF filter.

If you have low capacitance and low interference, then you will not be able to measure the effect of the unused excess current capability.
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Old 7th November 2013, 10:35 AM   #3064
Marra is offline Marra  United Kingdom
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A big thanks to all for there advice I am now in a hum free Paradise.
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Old 7th November 2013, 05:31 PM   #3065
hesener is offline hesener  Germany
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... except the birds and the bees on your records, I hope
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Old 7th November 2013, 05:34 PM   #3066
RCruz is offline RCruz  Switzerland
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A big thanks to all for there advice I am now in a hum free Paradise.
Cool... that is the way it should be
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Old 7th November 2013, 06:28 PM   #3067
FdW is offline FdW  Netherlands
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A big thanks to all for there advice I am now in a hum free Paradise.
Enjoy it
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Old 10th November 2013, 01:04 PM   #3068
Paulski is offline Paulski  United Kingdom
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Default Not quite Paradise yet....

Finally got around to putting my Paradise boards (boards and parts from the original GB plus BC327/BC337 that I sourced for matching) together and I have a few issues. I'm using the 'official' pre-regulator boards to power and these were built up first. These produce around +/-43.8V with no load which seems about right. I hadn't measured the rails for noise until now but we'll come back to that later...

I built up the Paradise boards using bi-polars that matched to 1% or better across the board (all measured at hFE 492 +/-2). The input trannies were the very best matches although I don't think the accuracy of my meter (Peak DCA55) is better than about 2%. On power up of just the regulator sections it all looked good, all LEDs shining and, after trimming, a nice stable +/-18.2V on both boards. A good start.

I inserted the bridges to power the amplifier and did a little initial trimming of the input offsets then left to run for a few days to let any necessary cap forming happen. I then added a 47R resistor across the input and re-trimmed for 0mV, both channels seem very stable in this respect. I then checked the output for DC and found an offset wandering from roughly +100mV to -100mV but I also found about 14V of AC voltage! At that point I had no RIAA caps so added these and the AC on the output (as far as my Fluke 179 reads) was gone. Clearly though that level of AC on the output was not right so I got the scope out and found that both channel had an output of around 150mV RMS at about 73 to 77MHz. For good measure there's also some much higher frequency components in the output, up in the low GHz region albeit at a lower level.

I decided to focus on one channel to start with and did the following. Checked the power rails after the regulator, these looked very noisy with around 50mV of crap in the high MHz region. I added the compensating caps to the regulator section and this improved matters a little but the noise remains. I measured the voltages around the board and they're all very close to what they should be. The only 'imbalance' being +.6V -.54V either side of the 82R resistor, R5. Where I do have an 'issue' is the output from the servo as this floats from around +5V to +8V which seems high although not entirely out of spec.

I put the scope on the output from the pre-regulator and, perhaps unsurprisingly, there's noise present. Now I'm not saying I expected to see perfect DC but surely there shouldn't be much noise after the pre-regulator has done its job. There’s an even higher level of noise on the power rails coming out of the regulator, ground is also similarly noisy when measured at the regulator-amplifier bridge.

Here are shots of the ‘scope screen:

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Old 10th November 2013, 03:54 PM   #3069
hesener is offline hesener  Germany
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Quote:
Originally Posted by Paulski View Post
At that point I had no RIAA caps so added these and the AC on the output (as far as my Fluke 179 reads) was gone. Clearly though that level of AC on the output was not right so I got the scope out and found that both channel had an output of around 150mV RMS at about 73 to 77MHz. For good measure there's also some much higher frequency components in the output, up in the low GHz region albeit at a lower level.
The "wandering" of +/-100mV is quite normal and due to the thermal variations of the input stage. Others have reported that when they put a shield or heatsink there this stuff is gone. The high frequency stuff you are seeing is the amplifier oscillating, not the power supply (that would be a couple MHz).

Quote:
Originally Posted by Paulski View Post
I decided to focus on one channel to start with and did the following. Checked the power rails after the regulator, these looked very noisy with around 50mV of crap in the high MHz region. I added the compensating caps to the regulator section and this improved matters a little but the noise remains. I measured the voltages around the board and they're all very close to what they should be. The only 'imbalance' being +.6V -.54V either side of the 82R resistor, R5. Where I do have an 'issue' is the output from the servo as this floats from around +5V to +8V which seems high although not entirely out of spec.

I put the scope on the output from the pre-regulator and, perhaps unsurprisingly, there's noise present. Now I'm not saying I expected to see perfect DC but surely there shouldn't be much noise after the pre-regulator has done its job. There’s an even higher level of noise on the power rails coming out of the regulator, ground is also similarly noisy when measured at the regulator-amplifier bridge.
The servo output variation is due to whats described above, not unusual. Check the assembly guide, there is some information on the compensation caps for the amplifier as well. BTW, did you put the SMD caps on the bottom side of the PCB?

If that fixes it, this will be the second confirmed case of Paradise amplifiers oscillating, not too bad I think.....
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Old 10th November 2013, 04:50 PM   #3070
Paulski is offline Paulski  United Kingdom
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Quote:
Originally Posted by hesener View Post
The "wandering" of +/-100mV is quite normal and due to the thermal variations of the input stage. Others have reported that when they put a shield or heatsink there this stuff is gone. The high frequency stuff you are seeing is the amplifier oscillating, not the power supply (that would be a couple MHz).

The servo output variation is due to whats described above, not unusual. Check the assembly guide, there is some information on the compensation caps for the amplifier as well. BTW, did you put the SMD caps on the bottom side of the PCB?
I'm not too worried about this, as you say it's quite normal and the boards are in free air currently. Yes, I have fitted the SMD caps.

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If that fixes it, this will be the second confirmed case of Paradise amplifiers oscillating, not too bad I think.....
Well, I suppose that depends on your perspective After all the transistor matching and careful stuffing it's pretty depressing from where I'm sitting. I'm going to take a break from it for now, I'll have a hunt for some suitable compensation caps and try that later in the week.

I'm wondering how many working Paradise builds are out there now, it seems odd that I've run into the same issue that analog_sa had all those months ago. I find it really frustrating when there's no obvious reason for something like this, it all feels a little too 'random' and that makes no sense to me. That said I'm very appreciative of all the design efforts that went into this and for any help given.
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