214mA is OK, 87 mV across R11/R24 is normal too, in the post earlier I neglected the total ~27mA bias current: 214-27=187, ./.2 =93.5mV
The difference can be down to resistors tolerances (nothing to worry about) or offset: if a 4 ohm speaker is connected, the 14mA difference amounts to 56mV, which begins to be excessive.
So, check with and without load, and check the DC offset.
The drivers do dissipate quite an amount of power, even under quiescent conditions, so a decent heatsink is preferable
There is no simple way to do that, since the selling argument of the Circlophone is that it is adjustment-free.
There are lots of amplifiers where this adjustment is not only present, but absolutely crucial and finicky, and if you miss that kind of sensation that's probably you best option.
140mA could happen with a particular combination of resistors tolerances and Vbe's mismatches, but is not easy to reproduce on purpose.
You can shift the center design value from 180mA to 140mA, by increasing R8, R11, R24 in the same ratio.
But on a particular amplifier, you could still end with 210mA (or 100mA).
Anyway, it will not make any difference. But going below 100mA will begin to unveil non-normalized differences, the usual class AB artifacts, and it is preferable to stay well clear of that value.
But, I repeat, there is no single point where the quiescent current can be adjusted. That is old thinking and is completely irrelevant here.
Measure the voltage, divide by the resistor value, if it's 1.5mA +/-50%, it's OKP.S.
The question I'd actually meant to ask is how to measure for R21 value to confirm that the correct value was/wasn't installed.
The drivers Hfe will influence mainly one aspect: the capability to drive Lo-Z loads, under 1 ohm to full power.
Other than that, it is completely transparent.
Thank you so much for all of your answers. It does turn out that one would not want to alter the resistor values more than a slight difference off spec. But, then I do wonder about some other creative way to increase efficiency instead.
The driver question didn't work but I can ask that question upside down: Which output devices is expected to have the finest quality audio?
MJE3055
TIP41
TIP33
BD911
TIP3055
2SD1047
BD249C
2N3055
MJL21194
MJW21196
MJ15015
MJ21194
MJ21196
MJ15022
MJ15024
MJ15003
The deal is: For the builder's thread I would like really good representatives of the useful sizes and current ranges (small, medium, medium-HV and large), but the builder's thread and constructor's chart doesn't need to promote a vast list that includes non-optimal devices. Can we remove the poorest sound quality third of that list, and thus create a shorter list of better quality?
Thanks Elvee. Speakers are 8 ohm and offset is 24mV. Sounds like alls well.
The MJ15003's barely get warm.
There is some part of subjectivity in assessing the "quality" of the transistors.
We can try to minimize it by computing a figure of merit based on the transition frequency and the Hfe constancy vs. collector current (within their normal range of power).
Here is the league table based on this criterion (based on original manufacturer's data):
Code:
1/ 2SD1047 1.76
2/ MJ(L)21194 1.6
3/ MJ(W)21196 1.45
4/ MJ15022,4 1.2
5/ BD249C 1.04
6/ MJ15003 0.94
7/ MJE3055 0.46
8/ TIP41 0.43
9/ 2N3055 0.35
10/ TIP33 0.34
11/ BD911 0.29
12/ TIP3055 0.16The "best"...
I would not venture that far, there are certainly a number of other types equally suitable.
But it is a good shortlist anyway.
I wonder what happened with MJ15015. Did we lose it? Normally, I just lose the SMD pieces as they cannot be found in the carpet.
Me too!
I thought my |00...0> +|11...1> ran away with it. I'll add it back to the builder's thread listing. MJ15015 is mostly unpopular except for authentic--good odds for having an authentic part.I have a few more curiosities. . .
The 2N5551 actually does not work consistently across all builds for Q12/Q13 (HFE and noise differences), and as a result, there is some variety of troubles, like suddenly blown output devices, extra heat, or just a sonic signature difficulty. Is there, by any chance, a better commonplace device "just like" BC546B that could manage Q12/Q13 with up to 40+40vdc rails?
And, there's two more curiosities from the prototype photos. . .
Those two big yellow 22uF caps? Are they inbound of the Shottky's or is it simply 22uF//100uF per rail?
That ST-BD140 driver pictured has the extension obscured by the mounting screw and I was wondering if it is BD140-10 or BD140-16, since whichever device was actually used during measuring is a nice point of reference.
The 2SC(or KSC)1845 is a perfect substitute, commonly available and suitable for up to +/-60V supplies
No they are 2.2µF rail decouplings (mylar), but this was an early prototype, and I don't recommend doing it: they resonate with the supply leads and cause ringing.
Good electrolytics like in the schematic are preferable, they provide decoupling and damping
Neither, they are unsorted, suffixless.
I have just tested the 2SA1930/2SC5171 pair as drivers and VAS.
The samples kindly provided by Daniel are authentic, and they perform remarkably well in the Circlophone.
The all-plastic construction makes mounting on a heatsink very easy, and the case has a low enough thermal resistance of its own for the VAS to be left without heatsink.
In summary, an excellent choice: high availability, good performances and ease of use: a dream.
The samples kindly provided by Daniel are authentic, and they perform remarkably well in the Circlophone.
The all-plastic construction makes mounting on a heatsink very easy, and the case has a low enough thermal resistance of its own for the VAS to be left without heatsink.
In summary, an excellent choice: high availability, good performances and ease of use: a dream.
Today I have done more upgrades to the Circlophone Builder's Thread so it can be faster to read.
The information is presented tight and compact.
It also has example schematics, a verified parts shopping feature, many pcb layouts, a perfboard method, a build/art gallery, and accessories.
Circlophone has a live sound characteristic.
There are many available parts and perhaps you already have most of them.
What do you think of these?
MJ802G 30a,
MJW1820G 30a,
MJE13009G
FJA13009TU
While I was working on it, some of the program code on the builder's thread found those devices automatically. So, temporarily, I have constricted the search to omit them, because I do not know if they are suitable.
Good news for the MJ802. Thanks.
MJW1820? Sorry for the typo. It is MJW18020G, a 250w plastic.
The links below open datasheets.
Here are the stragglers:
MJW18020G 30a, 250w HFE14
MJE18008G 8a, 125w, HFE14
FJP13007H1TU 8a, 80w, HFE15
MJW18020G 30a, 250w HFE14: 2.36
The 2.36 figure is excellent, but unfortunately since it is a high voltage transistor, the useful Hfe is low, around ~30, and this will demand hefty drivers.
These two have a really too low gain (<10) to be of any use:
MJE18008G 8a, 125w, HFE14
FJP13007H1TU 8a, 80w, HFE15
Indeed: its figure of merit is 6.
With this transistor, a good layout, good bypassing and optimum compensation is compulsory: with the 50MHz Ft, any imperfection will result in oscillations.