DIY Audio Projects Forum

Thank God we don't sit around listening to square wave.

_________________
Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic

Stefan , Mark


Well , just was an observation . but , I accept jokes , and I need perfect square wave because my home-room is square.

Apart . I test k40y-9 still in process break-in and works less brilliant but more natural . I was hearing 716p and works very fine too , finally I think each one is fine depends that music you are hearing


Regards .

Hi all!

It's probably not the most gentle way to start in a forum with a post asking some questions in a six-month old discussion, but maybe this is stil interesting, also for other users..
First of all - I really appreciated reading this discussion and I'm very curious how the MCA will perform driving a three-way transmissionline I designed and build some month ago.

But let me start with some questions regarding the circuit.

1) In the power supply schematics of the ZCA, you start the C-part with a 'low'-capacitance low-ESR-cap, that I don't really understand at this position.

2) The supply ends with a 100nF cap, that I basically know from catching hf-spikes directly at a switching transistor. I don't know if this guy really makes sence. Somebody compared with and without this one? Partly, this discussion in the neighbour-forum ( http://www.diyaudio.com/forums/power-su ... -caps.html ) deals with this topic..

3) A general thing - is a symmetric pi-filter (CLC) usually prefered over an asymmetric one? More precise - is it preferable to set C1 = C2 or do you focus just on their separately seen low-pass-capability?

4) Next to the input-signal, there is a 100k resistor in parallel - does this guy defines the input-impedance? Should it be set relative to the used preamp-output-impedance to get best results? If I read correctly a user in this discussion left it away, so it's a non-crucial component? By leaving it away, one could design an Even-More-Minimal-Component-Amplifier (EMMCA) :-p

5) What is the idea behind the 100µF-cap attached to the 1M-resistor and the 100k-Poti?

6) As in point 4, a user in this discussion left away the 1Ohm resistor attached to the emitter. How would this influence the circuit? Would somebody recomment keeping or leaving this one away?

I'm looking forward to hear from somebody. Thank you guys!
Cheers,
Jannis

Firstly design the PS however you think it would be best. Each big electrolytic cap should have a 100nf poly across it.

The cap associated with the 1m is to hold that basis voltage steady.The input resistor, 100k, help set the the input impedance and stops the input floating when there is nothing connected to the input.

_________________
Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic

Hi Mark,
good to know, thanks for your quick answer!

The 100nF poly should shunt some ac ripple to increasy lifetime of the electrolytics or what's the idea behind these? I guess it's nothing audible..?!
Do you set the 100k-input resistor with resect to the preamp you are using or is such a value in general a good choice?

And regarding the 1Ohm emitter resistor.. what is the consequence of having it or leaving it away? Sure, I could make my own experiences by putting him to the emitter, short circuit it and compare. But I can imagine somebody here already did this.

Best, Jannis

Supposedly electrolitics are noisy, the smaller cap removes that noise. You could make the input resistor smaller or a little larger. I use tube preamp so a high out impedance is best. Re is to provide a little negative feedback. It also helps balance transistors.

_________________
Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic

Thank you Mark!

I oversaw the effect of feedback adjusted by Re. Here is an article about exactly this topic:
http://www.electronics-tutorials.ws/amp ... tance.html

"You could make the input resistor smaller or a little larger" is a bit meaningless, but I think I got the point -> just try

I'll post pictures when the design is finished.

Just another short question - I have plenty of different 2N3055 transistors and I attached a picture of them:
After reading a bit, it came up, that over the years the quality changed significantly (also from company to company).. So is here anyone having a recommendation with which to go (without just saying to measure them all)?
I also have four 2N3055 specifically designed (whatever this means in detail) for audio applications, called 'BDY20 2U50'. Somebody with experiences about these ones?

Cheers,
Jannis

I never used them but I have some high frequency 3055s and I have some ultra low distortion ones. Never used either.

I'd go for the ones designed for audio if I was you.

_________________
Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "retro-Hiraga" - Jean Hiraga Le Monster
Website: retro-thermionic

I will make an emphatic suggestion here:

Use 2N3772G from ON Semiconductor, but from a reputable supplier as there are *lots* of counterfeits out there.

http://www.mouser.com/ds/2/308/2N3771-D-43368.pdf

I have replaced 3055s successfully (100% of the time with only very minor bias adjustments in some cases) for items from AR, Dynaco, HH Scott and others. The transistor is more rugged, sounds better and heats up less, all good things.

Thanks for your inputs regarding the choice of transistors. I decided to go for the BDY20 2U50 and I dont regret - it sounds very nice!! Highly recommendable for as an amp for daily indoor use. Depending on the input device (in my case a Focusrite Scarlett 2i2 (max. output voltage: 1.2V pk-pk @ 1kHz)) it's easily loud enough to disturb neighbours

The housing just contains the amplifier and a small RC input-filter with 1 Ohm and 10mF on each side. Very handy! A mid-size fanless CPU-chiller sinks the heat of both 15Ohm resistors:



For the moment, I use my switching mode lab power supply and there is no hum at all. A CLC-supply (20mF-50mH-20mF) is close to be ready to use, too.
By driving the input at 28V, I burn almost 50W.

Playing with the input voltage, I only observe a clip in the positive half wave. Is this normal?

Because the MCA shows an amplification which is over a wide range independent on the input DC-driving voltage, I think I reduce it to say 15VDC, reset the bias and burn only a bit more than 10W all the time. Does this change the overall performance drastically (sure, I will shift the Q-point by some volts, but is this a 'serious' thing?)? My ears and my oscilloscope say it's fine as long as the input voltage is restricted by the preamp such as in my case to a relatively small value of 1.2V pk-pk. Unfortunately, I don't really have a detailled idea about the distortions and how to measure them..

In general, I'm curious how to calculate/estimate the damping factor, that will be provided by this circuit. Anyone an idea?

Thank you!