As Starcat said, the PSU does not change. You also do not need to alter the bias current. The general operating characteristics of the amplifier modules are not changing. You simply have double the number of them, and you wire them a bit differently to the inputs and outputs along with making (to some) relatively tedious adjustments to ensure that your relative and absolute DC offsets are minimized reasonably and that your distortion profiles match between the positive and inverted phase signals along with between the left and right channel monoblocks (if you care for such things). Then, if you really want... choosing the overall distortion characteristics of both amps, and keeping them the same (if you're using P3) will be an additional challenge.
There is no additional heat or higher voltages seen anywhere in the amps. The only higher voltage is the swing at the output b/c you are running a differential signal. The PSU caps are totally fine. No need to change them.
If that's incredibly confusing, I'd suggest brushing up on some basics of how the differential signal is run from input to output. It might help you understand what you're considering... and perhaps you'll be better informed as to if it's worth doing in your situation.
Example - You had 1 amp with two amplifier "modules".
Module 1 - Left Channel
Module 2 - Right Channel
You are considering new monoblocs (or similar) to work with a differential signal. Most people might build an amplifier identical to the one they have already built. Using the same PSUs, components and everything will help to minimize discrepancies. Then... with a bit of rewiring on the first amp, and the second amp built for a differential input and output, you might have...
Amp 1 Module 1 - Left Channel Positive Signal
Amp 1 Module 2 - Left Channel Inverted Signal
Amp 2 Module 3 - Right Channel Positive Signal
Amp 2 Module 4 - Right Channel Inverted Signal
You're really just considering building another amp and wiring each of them a bit differently for all intents and purposes.
Yes, that's a bit oversimplified, but it's for illustration vs. being dead on accurate in terms.
Hope that helps.
There is no additional heat or higher voltages seen anywhere in the amps. The only higher voltage is the swing at the output b/c you are running a differential signal. The PSU caps are totally fine. No need to change them.
If that's incredibly confusing, I'd suggest brushing up on some basics of how the differential signal is run from input to output. It might help you understand what you're considering... and perhaps you'll be better informed as to if it's worth doing in your situation.
Example - You had 1 amp with two amplifier "modules".
Module 1 - Left Channel
Module 2 - Right Channel
You are considering new monoblocs (or similar) to work with a differential signal. Most people might build an amplifier identical to the one they have already built. Using the same PSUs, components and everything will help to minimize discrepancies. Then... with a bit of rewiring on the first amp, and the second amp built for a differential input and output, you might have...
Amp 1 Module 1 - Left Channel Positive Signal
Amp 1 Module 2 - Left Channel Inverted Signal
Amp 2 Module 3 - Right Channel Positive Signal
Amp 2 Module 4 - Right Channel Inverted Signal
You're really just considering building another amp and wiring each of them a bit differently for all intents and purposes.
Yes, that's a bit oversimplified, but it's for illustration vs. being dead on accurate in terms.
Hope that helps.
Hi:
I am interested to build F5T V3 (100W mono blocks), however I will start with the F5T V2 (50W stereo) first and want to the fill the V2 boards to be capable of reconfiguring to V3 at a later date. I have a number of questions:
1) If I fill the V2 configuration FE boards with Q1.1, Q2.1, Q7 and Q8 would that be ok to use on the 50W stereo configuration?
2) Looked at various F5T V2/3 builds, some of them use the power thermistors before the transformer and no Soft Start board. Are the power thermistors sufficient to deal with the inrush current? I plan to use a 800VA 24X2 transformer.
3) Also noticed some F5TV2/3 builds did not use the Speaker Turn ON Delay / DC Protector board. Any turn on thump on the F5T V2/3?
4) I plan to use the Universal Power Supply V3. Since F5T V2/3 is a class A power amp, are the snubber resistors (R11, R12, R20, R21, RS 1, RS2) and snubber capacitors (C17, C18, CX1, CX2, CS1, CS2) required on the Universal Power Supply V3?
5) For the bias is the target 350mV for 0 VDC the same independent of the rail voltage and (50W stereo or 100W mono)? If not, any formula for the target bias in relation to the rail voltage?
6) After biased the D5 chassis heat sinks reaches about 50 deg C. I think this is the temp of the heat sink when amp is at idle. How much hotter do the heat sinks get when music is playing?
Thanks in advanced for the answers.
Regards,
Phil
I am interested to build F5T V3 (100W mono blocks), however I will start with the F5T V2 (50W stereo) first and want to the fill the V2 boards to be capable of reconfiguring to V3 at a later date. I have a number of questions:
1) If I fill the V2 configuration FE boards with Q1.1, Q2.1, Q7 and Q8 would that be ok to use on the 50W stereo configuration?
2) Looked at various F5T V2/3 builds, some of them use the power thermistors before the transformer and no Soft Start board. Are the power thermistors sufficient to deal with the inrush current? I plan to use a 800VA 24X2 transformer.
3) Also noticed some F5TV2/3 builds did not use the Speaker Turn ON Delay / DC Protector board. Any turn on thump on the F5T V2/3?
4) I plan to use the Universal Power Supply V3. Since F5T V2/3 is a class A power amp, are the snubber resistors (R11, R12, R20, R21, RS 1, RS2) and snubber capacitors (C17, C18, CX1, CX2, CS1, CS2) required on the Universal Power Supply V3?
5) For the bias is the target 350mV for 0 VDC the same independent of the rail voltage and (50W stereo or 100W mono)? If not, any formula for the target bias in relation to the rail voltage?
6) After biased the D5 chassis heat sinks reaches about 50 deg C. I think this is the temp of the heat sink when amp is at idle. How much hotter do the heat sinks get when music is playing?
Thanks in advanced for the answers.
Regards,
Phil
6. Highest stress for Class A amplifier is at idle.
5. 350mV is the voltage indication of the bias, and will change a bit due to resistor tolerance. You want a max of about 30W dissipation per device, so the target bias current (Ibias = 30/Vsupply). Vsupply is per rail, not the whole supply. The 350mV target is for those using the diodes and the recommended 0.5 ohm source resistance, as the diodes begin to take off around 400mV (at 25C). For a build without diodes, you can set the bias as high as your devices and heatsinks will allow.
3. The amplifier has no turn on or turn off transients that I can notice on any of my builds.
2. A inrush limiting thermistor that is not bypassed is a fire waiting to happen. If you aim a thermometer at it after a half hour, you will see the case temp hit in the low 90s. And when thermistors go, it isn't pretty. The relays are meant to bypass the thermistors after the inrush surge, so yes, the thermistors can deal with the current at turn on. But they should not be used in continuous mode ever. Nelson's original recommendations do not have a thermistor bypass, but he's using them for a ground breaker, not to deal with the inrush surge. Completely different application. I suspect what you've seen is the ground breaker.
Cannot answer the rest of the questions as I don't use the store boards.
5. 350mV is the voltage indication of the bias, and will change a bit due to resistor tolerance. You want a max of about 30W dissipation per device, so the target bias current (Ibias = 30/Vsupply). Vsupply is per rail, not the whole supply. The 350mV target is for those using the diodes and the recommended 0.5 ohm source resistance, as the diodes begin to take off around 400mV (at 25C). For a build without diodes, you can set the bias as high as your devices and heatsinks will allow.
3. The amplifier has no turn on or turn off transients that I can notice on any of my builds.
2. A inrush limiting thermistor that is not bypassed is a fire waiting to happen. If you aim a thermometer at it after a half hour, you will see the case temp hit in the low 90s. And when thermistors go, it isn't pretty. The relays are meant to bypass the thermistors after the inrush surge, so yes, the thermistors can deal with the current at turn on. But they should not be used in continuous mode ever. Nelson's original recommendations do not have a thermistor bypass, but he's using them for a ground breaker, not to deal with the inrush surge. Completely different application. I suspect what you've seen is the ground breaker.
Cannot answer the rest of the questions as I don't use the store boards.
You don’t need Q1.1, 2.1. These are used only if you plan to use more than two output boards per channel in stereo or per n/p side in mono. Don’t use any snubber on store power pcb. Don’t need them. Only crc component. Absolutely no turn on/off thumps in my F5v3t mono’s build. A class A amp at idle is dumping all its wattage into the heat sinks, so highest temp is at idle. All power that is not being used for music program is being wasted as heat, so heat sinks actually get a bit cooler when amp driven hard playing music.
Sangram, are you saying that the cl30 in series with transformer primary, as depicted in Nelson’s F5 turbo article, is unsafe? What are alternatives? can you parallel more cl30 for dissipation? Don’t want to complicate things with relays.
Sangram, are you saying that the cl30 in series with transformer primary, as depicted in Nelson’s F5 turbo article, is unsafe? What are alternatives? can you parallel more cl30 for dissipation? Don’t want to complicate things with relays.
I forgot about the second thermistor. You're right about the series thermistor being there.
Yes, it's not advisable to run a thermistor without bypass. You can bypass manually by using a switch on the front panel.
Long-run current of a couple of amperes will heat up the thermistor to very high levels. I remember reading 105C on the thermometer before turning it off, and this was 320VA on 240V mains - just over an ampere.
For the exact same reason, thermistors should not ever be used in parallel, the standard practice is to use them in series to get more voltage drop when the inrush current is too high. Raytheon (?) had a nice article on usage of thermistors, and this is what I remember the overall recommendation being.
Yes, it's not advisable to run a thermistor without bypass. You can bypass manually by using a switch on the front panel.
Long-run current of a couple of amperes will heat up the thermistor to very high levels. I remember reading 105C on the thermometer before turning it off, and this was 320VA on 240V mains - just over an ampere.
For the exact same reason, thermistors should not ever be used in parallel, the standard practice is to use them in series to get more voltage drop when the inrush current is too high. Raytheon (?) had a nice article on usage of thermistors, and this is what I remember the overall recommendation being.
I assume you are getting this reference from post #1 and/or #2. It's recommended to quote or directly say where you are finding information b/c there multiple sets of test points; one set for the front-end boards and one set for the output boards.
My guess within the context that seems most relevant ... TP2 and TP3. Those test points, I believe, should be the equivalent to measuring across a pair of source resistors on the output boards. Someone with more direct knowledge can confirm. If you have the boards already, you can measure for verification.
Two 1R resistors in parallel => 0R5 - See schematic.
My guess within the context that seems most relevant ... TP2 and TP3. Those test points, I believe, should be the equivalent to measuring across a pair of source resistors on the output boards. Someone with more direct knowledge can confirm. If you have the boards already, you can measure for verification.
Two 1R resistors in parallel => 0R5 - See schematic.
Hello RF Phil,
in the schematic aren't the testpoints. You measure the bias over a pair of 1 Ohm resistors (=0,5 Ohm - as IAIMH pointed out). You measure
the voltage from one leg to the other leg of the bias resistor - or you use the testpoints on the outputboards of the F5T.
And check the resistance between the testpoints of your frontendboard - very important before start-up. This is all described by 6L6 on the first page of this thread.
I hope the pics help?
Cheers
Dirk
in the schematic aren't the testpoints. You measure the bias over a pair of 1 Ohm resistors (=0,5 Ohm - as IAIMH pointed out). You measure
the voltage from one leg to the other leg of the bias resistor - or you use the testpoints on the outputboards of the F5T.
And check the resistance between the testpoints of your frontendboard - very important before start-up. This is all described by 6L6 on the first page of this thread.
I hope the pics help?
Cheers
Dirk
Hello, can anyone assist me in troubleshooting my F5Tv2. About 2 weeks ago, I powered it up and there was no sound from either channel. After a few different attempts of wtf is going on here, I remembered I had swapped some cables and possibly I had then plugged in the wrong outputs on the back of my preamp which is exactly what I found. I thought I had the power switch off on the F5T but I didn’t and when I swapped the one cable on the back of the pre, I let the smoke out of one of the MOSFETS on the P channel board. At some point I was planning on converting the F5Tv2 into a V3 minus this diodes as well. I purchased a full matched set of MOSFETS and changed them all. This amp is built as dual mono. I powered up one side at a time with the variac. The P1 & P2 pots are set down to 0 ohms on the FE board. The problem in having is the left channel, the one I smoked is so far so good. I was able to power it up and bring the bias up to roughly 250mv/0v offset and it’s been pretty stable. When I am bringing up the power on the variac, I’m noticing I’m getting over 150 mv bias on the N channel board and 0 mv on the P channel board and my AC voltage is only at 30/35v. There was nothing smoked on this channel but now it’s nop. Can anyone point me in a direction of what to look for. Thank you in advance.
I'm having a bit of trouble following... perhaps others are also.
Is this generally correct in terms of sequence and what you're saying?
Is that how far you get on the Variac when you're seeing 150mV at the bias test points for the N board of B channel?
Here's where I'd start if above is correct. Leave Channel A disconnected from the PSU. Do below for Channel B.
Edited to remove any confusion re: biasing the FE. After reviewing... that's not helpful.
Is this generally correct in terms of sequence and what you're saying?
- Hot plugged an input. => Smoked a P channel MOSFET of that channel. We'll call this channel A moving forward.
- Replaced ALL MOSFETs (both channels?)
- Why?
- Did you remove the diodes already in anticipation of the V3 conversion?
- Channel A works now, but you wanted to tell us the story. Channel A is now irrelevant.
- Channel B is not working
- Did it ever work?
- Were there any symptoms and or are you now just trying to power it up for the first time after swapping the MOSFETs and/or removing the diodes?
Is that how far you get on the Variac when you're seeing 150mV at the bias test points for the N board of B channel?
Here's where I'd start if above is correct. Leave Channel A disconnected from the PSU. Do below for Channel B.
- Turn P1 and P2 back to where you have 0V at the test points. You can measure the resistance prior to power up also. See biasing procedure posted by 6L6.
- Start the biasing procedure again. Report back.
Edited to remove any confusion re: biasing the FE. After reviewing... that's not helpful.
Last edited:
ItsAllInMyHead, Yes, the above is pretty much correct. You got it for the most part but I’ll clarify the confusion:
Replaced ALL MOSFETs (both channels?)
Channel B is not working
Is that how far you get on the Variac when you're seeing 150mV at the bias test points for the N board of B channel?
The 30/35 volts is how far I can turn the variac up to where I’m getting 150mv on the N channel board test point.
Replaced ALL MOSFETs (both channels?)
- Why?
Channel B is not working
- Did it ever work? Yes, B channel worked fine prior to plugging in while amp was hot 2 weeks ago.
- Were there any symptoms and or are you now just trying to power it up for the first time after swapping the MOSFETs and/or removing the diodes? No symptoms, yes powering up for the first time after replacing MOSFETS this morning. There are no diodes, they’ve been cut out from after the initial build.
Is that how far you get on the Variac when you're seeing 150mV at the bias test points for the N board of B channel?
The 30/35 volts is how far I can turn the variac up to where I’m getting 150mv on the N channel board test point.
- Turn P1 and P2 back to where you have 0V at the test points. You can measure the resistance prior to power up also. See biasing procedure posted by 6L6.
- Start the biasing procedure again. Report back.
^ Awesome. Thanks for the clarifications.
So both channel A (blew a P channel MOSFET) AND channel B stopped working when you plugged in hot?
THEN
You replaced all MOSFETs and removed the diodes on both channels.
NOW
Channel A has not been powered up at all after the modifications. Channel B is giving you a fit.
Is that right?
If so....
Are you getting that 150mV across the test points with 0 ohms measured across all appropriate test points or did you begin turning the pots?
So both channel A (blew a P channel MOSFET) AND channel B stopped working when you plugged in hot?
THEN
You replaced all MOSFETs and removed the diodes on both channels.
NOW
Channel A has not been powered up at all after the modifications. Channel B is giving you a fit.
Is that right?
If so....
Are you getting that 150mV across the test points with 0 ohms measured across all appropriate test points or did you begin turning the pots?
Channel A smoked and after replacing mosfets is now biased to 320mv where I’m going to let is run for a couple days.
Channel B, I don’t know if it Channel B blew originally or not. There was nothing charred but not after replacing mosfets is now not operating/giving me a fit lol.
Yes, I am getting 150mv on the test points on the output board before I even try to adjust the pots AND they’re not even seeing my rail voltage because the variac is throttle way back.
The amp blew (2) weeks ago and there were no diodes in it. I removed them based on the recommendations from you and many others in the group at the time of build.
Channel B, I don’t know if it Channel B blew originally or not. There was nothing charred but not after replacing mosfets is now not operating/giving me a fit lol.
Yes, I am getting 150mv on the test points on the output board before I even try to adjust the pots AND they’re not even seeing my rail voltage because the variac is throttle way back.
The amp blew (2) weeks ago and there were no diodes in it. I removed them based on the recommendations from you and many others in the group at the time of build.
^ Same page now, I think.
Great news re: channel A.
If ... when you started off the biasing process for Channel B you had 0 ohms measured across the test points AND before turning the pots you have 150mV across the test points on the N channel board (at such a low supply voltage), then I'm reasonably certain you have an issue with the N-channel board.
There should be no current flowing through the MOSFETs yet.
I'd start with just that board.
Check all pins on the N-channel MOSFETs for shorts to the heatsinks and to each other.
Others may have a better step-by-step, but at the lowest power you can put to it with the Variac, I'd check the voltage at the gates of all the N-channels.
Also, you can try to see if it's one or all of them conducting by checking each pair of source resistors vs. checking at the test points. (I think)....
It's doubtful I can get you through all of it... but now that the issue is clearly spelled out... wiser people will likely contribute to getting you across the line. I'm far from an expert.
Good luck!
Great news re: channel A.
If ... when you started off the biasing process for Channel B you had 0 ohms measured across the test points AND before turning the pots you have 150mV across the test points on the N channel board (at such a low supply voltage), then I'm reasonably certain you have an issue with the N-channel board.
There should be no current flowing through the MOSFETs yet.
I'd start with just that board.
Check all pins on the N-channel MOSFETs for shorts to the heatsinks and to each other.
Others may have a better step-by-step, but at the lowest power you can put to it with the Variac, I'd check the voltage at the gates of all the N-channels.
Also, you can try to see if it's one or all of them conducting by checking each pair of source resistors vs. checking at the test points. (I think)....
It's doubtful I can get you through all of it... but now that the issue is clearly spelled out... wiser people will likely contribute to getting you across the line. I'm far from an expert.
Good luck!
I appreciate all your help this far. I’m really not sure what the jerk is going on. I pulled the board and it looks like one of the leads to the thermistor may have been touching one of the MOSFET pins. I pushed it out of the way, remounted the board and fired up the variac. Got it all the way up to line voltage with 0mv on either board. Started adjusting pots and now I’m close to bias. These boards have could be compromised from the initial build. I’m considering purchasing another set from the store and starting from scratch with the output boards. I’ll keep posted but that you for your help again.