I'm so jealous nonetheless... I have some F5 boards I bought from Peter Daniel GB, but cant seem to find the time to begin the actual build 
wife's pregnant (8th month) so for now is DIY my 1st born son nursery 😉
wife's pregnant (8th month) so for now is DIY my 1st born son nursery 😉
carcass said:I'm so jealous nonetheless... I have some F5 boards I bought from Peter Daniel GB, but cant seem to find the time to begin the actual build
wife's pregnant (8th month) so for now is DIY my 1st born son nursery 😉
You'll have plenty of awake time soon enough. Of course I would not be playing with electricity after being woken up 5 times a night.
Best of Luck!
carcass said:I'm so jealous nonetheless... I have some F5 boards I bought from Peter Daniel GB, but cant seem to find the time to begin the actual build
wife's pregnant (8th month) so for now is DIY my 1st born son nursery 😉
Parabens! Espero que tudo anda bem quando o dia chegar... E realmente, o quarto do nenem tem que ter prioridade, nao e? Pelo menos, lembro que quando nosso primeiro estava chegando, minha esposa insistiu que tinha prioridade...
Hope you have more 😴 😴 😴 than
(We were pretty lucky in that regard...)Cheers
Nigel
Progress update
Well, I've done a fair bit on the F5 - here's the state of play, for anyone interested.
1. Decision is taken for a pair of monoblocks, external power supply (already built) feeding both monoblocks by a pair of umbilicals. Final design of monoblocks to be determined, but most likely will have the big heatsinks on the front, with wooden sides (Some tropical hardwood... we'll see what I can find...) and a minimal back, to guarantee good ventilation. (I'll worry about EMI and so forth later...)
2. I have put everything together to test (photo below) and had a go at adjusting the bias. On the one amp this went fine, after a false start, and I now have it up to 0.56 V across R11 and R12, with negligible DC offset (less than 3 mV - I don't trust my multimeter to be accurate so low...). The other was less successful... Smoke came up from the power resistors at one point, which doubtless means I did something wrong (probably rushed things too much...) I will have to start the adjustment from scratch, after checking to see no obvious harm was done to anything. Unless I'm mistaken power resistors are pretty tough, and I have the current limiting circuitry in, so I hope nothing too essential turned its toes up.
3. I tried the amp that works with a test speaker, which sounded fine - no obvious distortion or problems, but the speaker really isn't good enough to judge the sound. We'll have to try that later.
4. One thing I noticed was how sensitive the whole thing is to position. I was adjusting things with the heatsink on its front (to avoid knocking it over accidentally and crushing the board...) and when I put it on it's end the voltage across the resistors dropped from
about 0.5V to 0.4V. I presume this is due to the thermistor reacting quickly to a change in convection patterns. This leads me to wonder - how are people fixing the thermistors? Glued to the mosfets, or just "touching", as I have them?
We have family arriving shortly, so I have to interrupt all this fun stuff... 😡
Cheers
Nigel
Well, I've done a fair bit on the F5 - here's the state of play, for anyone interested.
1. Decision is taken for a pair of monoblocks, external power supply (already built) feeding both monoblocks by a pair of umbilicals. Final design of monoblocks to be determined, but most likely will have the big heatsinks on the front, with wooden sides (Some tropical hardwood... we'll see what I can find...) and a minimal back, to guarantee good ventilation. (I'll worry about EMI and so forth later...)
2. I have put everything together to test (photo below) and had a go at adjusting the bias. On the one amp this went fine, after a false start, and I now have it up to 0.56 V across R11 and R12, with negligible DC offset (less than 3 mV - I don't trust my multimeter to be accurate so low...). The other was less successful... Smoke came up from the power resistors at one point, which doubtless means I did something wrong (probably rushed things too much...) I will have to start the adjustment from scratch, after checking to see no obvious harm was done to anything. Unless I'm mistaken power resistors are pretty tough, and I have the current limiting circuitry in, so I hope nothing too essential turned its toes up.
3. I tried the amp that works with a test speaker, which sounded fine - no obvious distortion or problems, but the speaker really isn't good enough to judge the sound. We'll have to try that later.
4. One thing I noticed was how sensitive the whole thing is to position. I was adjusting things with the heatsink on its front (to avoid knocking it over accidentally and crushing the board...) and when I put it on it's end the voltage across the resistors dropped from
about 0.5V to 0.4V. I presume this is due to the thermistor reacting quickly to a change in convection patterns. This leads me to wonder - how are people fixing the thermistors? Glued to the mosfets, or just "touching", as I have them?
We have family arriving shortly, so I have to interrupt all this fun stuff... 😡
Cheers
Nigel
Attachments
this one in papa's amp looks like free standing ! 😀
http://www.6moons.com/audioreviews/passlabs/open2_big.jpg
http://www.6moons.com/audioreviews/passlabs/open2_big.jpg
carcass said:
That appears to be one of the CL60´s from the PSU circuit... The ones I am in doubt about are the 4.7k thermistors that adjust the bias on the mosfets.... If I dig around in the big F5 thread a bit more perhaps I can find a photo that helps.
Cheers
Nigel
max426 said:
Aha!! Thanks.
carcass said:
Yes, I had seen this, and may try the amplifier "without".... My concern is that the thermistors, which were from a place I don't normally use, and have no markings on them at all, may not be the right values. Can anyone enlighten me as to whether "without" means *with* the 2.2k resistors, and just short the thermistors (which is my guess), or do I take out the 2.2k's as well, as I think someone showed on a circuit in the big thread? ,
Thanks!
Nigel
not having shure of this, normally the resistors are placed in series with the thermistors to take some of the heat from them, ie to alleviate the burden
... so I think that you can take it all, but I would wait for a more insight post 😉
... so I think that you can take it all, but I would wait for a more insight post 😉Hi,
the series pair of resistor and thermistor are removed.
The pots 1&2, then do the trimming.
If you add in the 2k2 with the thermistor location shorted it would change the total parallel resistance too low and allow too much current to flow in the FETs to generate the necessary Vgs for the output device.
the series pair of resistor and thermistor are removed.
The pots 1&2, then do the trimming.
If you add in the 2k2 with the thermistor location shorted it would change the total parallel resistance too low and allow too much current to flow in the FETs to generate the necessary Vgs for the output device.
AndrewT said:
The first part is clear - if I decide to do this (and I may, at least to see what will happen) then as a practical instruction I now understand what to do. Thanks.
But if I understand what to do, I don´t really understand why. When the thermistor is hot it has a low resistance, so the combination of 2.2k plus thermistor (in series) is more or less the same thing as the 2.2k by itself (??). So why would the 2.2k by itself give a total resistance too low, where the amp in a steady state with a hot thermistor does not? To explain my question in a little more detail, if the thermistor is excluded (or shorted) then presumably P1 and P2 would be at different settings without the 2.2k than with it, to compensate for it´s presence/absence, but it seems to me that their settings would be the same with the 2.2k and without the thermistor than with both, making the hot resistance the same in the two cases... Or have I misunderstood something? I realise that the resistance would be different while the amp is heating up, but isn´t the hot resistance what really interests us?
😕 😕
I left them out.
It works just fine, but I should mention I used jfets with much lower moo than the stock Toshibas.
JJ
njepitt said:
So the Thermistor never acts like a wire, the impedence changes from ~3.8K to 4.7K. The warmer the FET is, the more the bias wonders up. So the thermistor compensates for this.
I dont see any reason to put one 7K resistor or somthing there. I would leave it all out and adjust slowly or keep it in there, and the amp will bias higher quicker. In other words, sound better faster.
Tea-Bag said:
As I understand things, then, since either increased resistance or increased heat raise the bias, the thermistor lowers resistance as heat rises, trying to maintain the bias at as close to a constant level as possible. (Have I got that part right?)
The thermistor goes the other way, right? At room temp it´s 4.7k, decreasing to 3.8k or so as the amp heats up? In any event, I think I understand things better now: Leaving the thermistor out but keeping the 2.2k resistor is less resistance than the 2.2k together with a *hot* thermistor, which would be 6k or so. Putting a fixed 6k resistor instead of the 2.2k/thermistor pair is a waste of time, since adjusting P1 and P2 will compensate anyhow. (How´s that?)
I think I will try leaving the thermistor out; as I mentioned above I am a little worried they are not "right".... (I can always put it back later if I change my mind.) Unlike JJ I am using standard Toshibas: can anyone give me an idea of how much warm-up time we are talking about until things "sound better"? 10 min? or 2 hrs? (JJ: Out of interest, what Jfets did you use? I have 2N5457/2N5460s on hand also, and I have used sockets, so it is easy to switch them in and out...)
Thanks
Nigel
Hi Nigel,
I see only one digital multi-metre from the picture in your post #86.
In my opinion, adjusting P1 and P2 with "two" digital multi-metres is the best way for trouble-free adjustment. Therefore, I recommend to have two DMMs by borrowing or buying another one.
If we do not have the thermistors, it will take longer time for us to arrive at the final bias and offset adjustment, depending on the time taking for the thermal stability of the amp. But, if we have them, it will help the final adjustment with respect to the adjustment time. As far as I understand, this is the only role of the 4.7K thermistors.
I really would like to recommend at least two DMMs for better fun of DIY.
>>🙂<<
I see only one digital multi-metre from the picture in your post #86.
In my opinion, adjusting P1 and P2 with "two" digital multi-metres is the best way for trouble-free adjustment. Therefore, I recommend to have two DMMs by borrowing or buying another one.
If we do not have the thermistors, it will take longer time for us to arrive at the final bias and offset adjustment, depending on the time taking for the thermal stability of the amp. But, if we have them, it will help the final adjustment with respect to the adjustment time. As far as I understand, this is the only role of the 4.7K thermistors.
I really would like to recommend at least two DMMs for better fun of DIY.
>>🙂<<
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