C5 and C6 will see 20 volts, so 25 volt rating will be fine. For C4 and C24 I would go with 35 volt, but If I had good quality 25 volt rated caps, it wouldn't bother me for this design. If you had a regulator fail shorted you would be over voltage, but you would have other problems at that point?
Hi guys, question to the freq. Compensation of R16 in parallel with C9: how big is the Influence on the linearity?
I want to reduce R16 to 70k or 80k and add R15 (20k or 30k) so that I can reduce the gain a bit by Shorting R15 easily.
Thanks a lot
Thorsten
I want to reduce R16 to 70k or 80k and add R15 (20k or 30k) so that I can reduce the gain a bit by Shorting R15 easily.
Thanks a lot
Thorsten
Two capacitors to consider, C9 across the 100k and the gate-to-source on the output MOSFET.
If you reduce R16 to 10K from 100k you will reduce the gain by 20dB.
At the same time, you move the frequency of the pole. C9 is there for stability
Jackinnj, thanks. But I want to reduce R16 only to 70k and wanted to know, if there Would be any influence on linearity or stability as you mentioned..
any idea? thanks
any idea? thanks
You will raise the frequency of the pole by 100k/70k (neglecting the effect of the MOSFET capacitor). I don't think it will have a major effect upon stability.
Hi, what values do you use for C12 in parallel with C16: 0,2µ total or more for more bottom end?
How high can I go? Would 1µ still be okay?
Thanks, Thorsten
How high can I go? Would 1µ still be okay?
Thanks, Thorsten
The capacitor in conjunction with the resistor R13 100K form a -3dB high pass filter. With the specified values the cut-off frequency is 8 Hz. Changing the capacitance to 1uF lowers the cut-off to 1.6 Hz. I don't think there is any benefit to such a low cut-off frequency. Note that unwanted low frequencies such as turntable rumble, warp wow, etc. could be issues if too low of a high pass frequency is used.
I'm just starting another Pearl II. I've checked Mouser, DigiKey, Newark and RS and they are out of stock on ZTX450. I prefer not to purchase from eBay and risk counterfeit devices. I've read that BC550 or MPSA18 is a working substitute, but not necessarily in the Pearl II. Any suggestions for sources or substitutes will be appreciated, thanks.
I do realize that the pinout on the alternate transistors may be different from the ZTX versions
As long as you take care of the difference in pinouts, you can use BC550 in place of the ZTX450 in the Pearl 2.
If I understand things correctly, the Q6 ZTX450 is a cascode and the other two are set up as current sources.
So any known good part will be fine.
If I understand things correctly, the Q6 ZTX450 is a cascode and the other two are set up as current sources.
So any known good part will be fine.
Octopart shows some ZTX450 in stock at Arrow, Newark, Future Electronics, etc.
https://octopart.com/ztx450-diodes+inc.-13152700#PriceAndStock
Thanks. I'll look into it. Newark doesn't have any as of last night so it might be that Octopart's information is a bit dated. For example, DigiKey sold out last night.
Arrow had 29 (slow ship from Netherlands) Future Electronics had 5K+ (and you can buy individuals). Online Components has some, but their price is wonky.
Thanks for the explanation. Will use a 0,47u I have around.
For the output cap C13: I can go down to 1u, right?
Stay safe!