M. Wright,
I don't understand what you mean by 'the triode in the cascode section'. Do you refer to the triode in the slcf of the rtp5? If so the anode is at about 150V, cathode at about 60V and grid at about 66V. R2 in the schematic of the rtp5 of the cookbook is 1K2.
I'm very bad at math and have tried to calculate gain a number of times but get lost. R1 in the schematic of the cookbook is 470R now but I have also tried 1K2 which made no difference.
The F5 has a gain number of about 15, so does the aleph-x. Speaker sensitivity is about 87db/W.
I am using one of your supperreg kits. This is fed from a rclc supply where the choke is 10H. Supplies for +15V and -24V are LM317/337 based, the heaters supplies are standard crc's and lifted to +20V (input) and +80V (slcf).
Yes I used the layout posted ( I found another little mistake, bias of the upper fet of the slcf, in the layout posted but that is not there in the actual circuit board). Indeed it seems the layout might be the culprit. Shame but at least i'd like to know why so i don't make such a mistake again next time.
Thank you for taking the time to help me.
grtz
Joris
I don't understand what you mean by 'the triode in the cascode section'. Do you refer to the triode in the slcf of the rtp5? If so the anode is at about 150V, cathode at about 60V and grid at about 66V. R2 in the schematic of the rtp5 of the cookbook is 1K2.
I'm very bad at math and have tried to calculate gain a number of times but get lost. R1 in the schematic of the cookbook is 470R now but I have also tried 1K2 which made no difference.
The F5 has a gain number of about 15, so does the aleph-x. Speaker sensitivity is about 87db/W.
I am using one of your supperreg kits. This is fed from a rclc supply where the choke is 10H. Supplies for +15V and -24V are LM317/337 based, the heaters supplies are standard crc's and lifted to +20V (input) and +80V (slcf).
Yes I used the layout posted ( I found another little mistake, bias of the upper fet of the slcf, in the layout posted but that is not there in the actual circuit board). Indeed it seems the layout might be the culprit. Shame but at least i'd like to know why so i don't make such a mistake again next time.
Thank you for taking the time to help me.
grtz
Joris
Sorry,
I haven't looked at the RTP-5 circuit in 10 years, so I thought it used a cascode in the gain section.
Repeat question, what voltages do you get on the gain triode, BEFORE the SLCF?
And when I asked about how much gain do you have, I do NOT expect you to calculate it - I expect you to have measured it with a sig gen and a scope.
Calcs are irrelevant, IMO.
Regards, Allen
I haven't looked at the RTP-5 circuit in 10 years, so I thought it used a cascode in the gain section.
Repeat question, what voltages do you get on the gain triode, BEFORE the SLCF?
And when I asked about how much gain do you have, I do NOT expect you to calculate it - I expect you to have measured it with a sig gen and a scope.
Calcs are irrelevant, IMO.
Regards, Allen
Umm, don't think the grid should be more positive than the cathode. Possible sign of oscillation or a serious wiring mistake nearby.
Hi,
I did some measurement. Don't have a sig generator so used the laptop and software. Not ideal but it's what i've got now. I let the preamp warm up for about 30 minutes before taking measurements and the scope for an hour.
Input tube:
Anode +65V (+/- 1V)
Cathode +1V
Grid 0V
SLCF tube:
Anode +143V (+/- 1V)
Cathode +68V
Grid +65V (+/- 1V)
The indications of +/- 1V are the differences between the various triode sections in the tubes. I have not focused on getting those as close as possible yet because i'd like to solve the noise issue first. I figured differences of < 5% are ok enough to start with.
For the gain measurement i set the input voltage at 1V PP at 1KHz and fed that to the positive phase input (+IN) of the channel. The negative phase
(-IN) is grounded on the input side of the grid resistor. Output was measured at the anode of the input tube.
Gain:
Positive phase input triode: 16V PP at 1 KHZ, which is 16 times or ~24dB?
negative phase input triode: 1,6V PP at 1 KHZ, which is 1,6 times or ~4dB?
Both channels measure near identical for the gain factor.
I am wondering about the gain of the negative phase halve of the circuit. I thought the differential (or LTP or are those indeed the same?) would function like a phase splitter with one input grounded. Should i not see the same gain for both halves of the circuit?
The signal voltages at the cathodes are:
Positive phase input tube: 0,4V PP at 1 KHZ
negative phase input tube: 0,06V PP at 1 KHZ
I have not been able to swap the inputs yet and take measurements. Due to my assumption about the input stage I connected the negative phase input channel to the power amp (+out). This means gain is low and the noise is easier to hear. I have not tried connecting to the -OUT yet. I will do both next week if i can.
grtz,
Joris😱
I did some measurement. Don't have a sig generator so used the laptop and software. Not ideal but it's what i've got now. I let the preamp warm up for about 30 minutes before taking measurements and the scope for an hour.
Input tube:
Anode +65V (+/- 1V)
Cathode +1V
Grid 0V
SLCF tube:
Anode +143V (+/- 1V)
Cathode +68V
Grid +65V (+/- 1V)
The indications of +/- 1V are the differences between the various triode sections in the tubes. I have not focused on getting those as close as possible yet because i'd like to solve the noise issue first. I figured differences of < 5% are ok enough to start with.
For the gain measurement i set the input voltage at 1V PP at 1KHz and fed that to the positive phase input (+IN) of the channel. The negative phase
(-IN) is grounded on the input side of the grid resistor. Output was measured at the anode of the input tube.
Gain:
Positive phase input triode: 16V PP at 1 KHZ, which is 16 times or ~24dB?
negative phase input triode: 1,6V PP at 1 KHZ, which is 1,6 times or ~4dB?
Both channels measure near identical for the gain factor.
I am wondering about the gain of the negative phase halve of the circuit. I thought the differential (or LTP or are those indeed the same?) would function like a phase splitter with one input grounded. Should i not see the same gain for both halves of the circuit?
The signal voltages at the cathodes are:
Positive phase input tube: 0,4V PP at 1 KHZ
negative phase input tube: 0,06V PP at 1 KHZ
I have not been able to swap the inputs yet and take measurements. Due to my assumption about the input stage I connected the negative phase input channel to the power amp (+out). This means gain is low and the noise is easier to hear. I have not tried connecting to the -OUT yet. I will do both next week if i can.
grtz,
Joris😱
You have some major problem, becaue you should have near identical gain from both outputs. The noise could be the result of this problem.
I would inspect carefully the jfet CCS in the cathodes of the diff pair.
Regards, Allen
I would inspect carefully the jfet CCS in the cathodes of the diff pair.
Regards, Allen
I'm with Allan on that one, but would also add that you should swap the inputs if you have not done so already and see if the gain mirrors the behavior you described previously - if it doesn't then it means it is not something common to both phases. If the behavior is mirrored then it does point at the CCS specifically.
silence is golden...
Hi,
Thank you for pointing me to the ccs mr Wright and Kevin, it was indeed the cause. I just ripped the ccs's out and replaced both of them. This solved the problem. And now everything is dead silent and working. One of them still wasn't stable and led to LF instability but i managed to solve that. The unit has been stable for about 10 hours now with intermediate switch on and off's in the meantime.
I'll keep it running in the test system for a while and try to do some more measurements to make sure it keeps stable and has enough stability margin to be trusted.
Replacing the ccs's made gain go down to about 10X and both channels measure more alike, current through the input stages is now about equal.
For now i'm going to listen to it a bit and ponder about the fact i did not look at the ccs earlier...
Regards and Thanks!,
Joris
Edit: did swap inputs before replacing the ccs
Hi,
Thank you for pointing me to the ccs mr Wright and Kevin, it was indeed the cause. I just ripped the ccs's out and replaced both of them. This solved the problem. And now everything is dead silent and working. One of them still wasn't stable and led to LF instability but i managed to solve that. The unit has been stable for about 10 hours now with intermediate switch on and off's in the meantime.
I'll keep it running in the test system for a while and try to do some more measurements to make sure it keeps stable and has enough stability margin to be trusted.
Replacing the ccs's made gain go down to about 10X and both channels measure more alike, current through the input stages is now about equal.
For now i'm going to listen to it a bit and ponder about the fact i did not look at the ccs earlier...
Regards and Thanks!,
Joris
Edit: did swap inputs before replacing the ccs
Last edited:
You ripped out the CCS's and replaced them with WHAT?
Your posts are hard to follow, if I may say so.
Regards, Allen
Your posts are hard to follow, if I may say so.
Regards, Allen
Hello mr. Wright,
Apoligies if I was not clear enough, maybe the joy of the moment.
I used the schematic from the chapter 'Mod's and maybe's in the preamp cookbook (nr4 best) with 2n5459 fets with the source resistor set to 1K2. Don't know what i did wrong with them but i replaced the fets for j309's and the caps as well. Also checked the resistors and those where ok. I did not bother to check which component was faulty and just replaced because i was getting a bit impatient. The 309's where what i had at hand.
Does this help?
Regards,
Joris
Apoligies if I was not clear enough, maybe the joy of the moment.
I used the schematic from the chapter 'Mod's and maybe's in the preamp cookbook (nr4 best) with 2n5459 fets with the source resistor set to 1K2. Don't know what i did wrong with them but i replaced the fets for j309's and the caps as well. Also checked the resistors and those where ok. I did not bother to check which component was faulty and just replaced because i was getting a bit impatient. The 309's where what i had at hand.
Does this help?
Regards,
Joris
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