Simplistic NJFET RIAA - Page 175

Salas · 11th May 2009, 08:38 PM

Try easiest wrap way and see in practice if hum goes. If sound worsens or hum field don't go 100%, then we think why. Don't forget to ground the tape to chassis. It must have electrical continuity to GND. Take care of covering secondary exit.

Salas · 11th May 2009, 11:19 PM

Ricardo, I have a mod 4U to try. Instead of just D1, can you use a 3.9V-4.3V Zener plus two or three Leds until you reach about 7.5V on the Cascode transistor base? If yes, tell me if you can hear lower noise or different tone. I don't have this version handy to mod myself, but I wanna know.

RCruz · 12th May 2009, 09:50 AM

I will do that in the weekend.

Thank you Salas

nicoch58 · 12th May 2009, 10:26 AM

Ricardo if you have spare caps you can tray kg-R-Jensen on psu....

RCruz · 12th May 2009, 05:19 PM

Quote:

Originally posted by nicoch46
Ricardo if you have spare caps you can tray kg-R-Jensen on psu....

Hi nicoch46
I did think about it but I do not know if it is needed anymore. The hum is field generated and it is my present focus.

Sound is becoming real magical with the present setup...

Hi Salas

Regarding D1 mod, I use only leds in my 317 based sregs.... Can I do the same here and loose the zener ?

If I must use a zener, can I use two in paralell ? (This tech reduces noise in the sregs).

Ricardo

Salas · 12th May 2009, 08:15 PM

I just put the base voltage of a small Zener in the Vref string there bcs its equivalent almost to a led, so to avoid using many LEDS. But if practically does not bother you, do it all LEDs. Just trim to around 7.5V total. Green or red are OK. The thing is capacitor bypassed, but bcs 6.5-9V is not a best region for Zeners, I wanna see if some noise still escapes. Up to 4V7 Zener must not scare you, or above 12V.

RCruz · 13th May 2009, 05:57 PM

The schematic I am using (Gain 46db for medium MC ~1mv) indicates D1 = 1N4738A (8.2v zener), so I am a little confused.... why use 7.5v instead ?

Also I do not understand the frase : "Up to 4V7 Zener must not scare you, or above 12V." Do you mean zeners generate max noise from 6 to 9 v so 12 volts is ok ?

Sorry for the nube questions but I need to know.

Ricardo

Salas · 13th May 2009, 06:20 PM

Quote:

Originally posted by RCruz

Do you mean zeners generate max noise from 6 to 9 v so 12 volts is ok ?
Ricardo

Yes.

The 8V2Z is bypassed by a capacitor. Generically its noisier than Zeners under 6V or 12 and over. We did not have noise, but lets see if some escapes the bypass.
7.5V I slightly prefer for THD in first stage maybe. And it can be done with LEDs.

RCruz · 13th May 2009, 06:34 PM

I believe this is a must do mod.

I do not know if I can reach exactly 7,5v with leds only.... What is the best voltage [<-window->] or the minimum possible value?

Ricardo

Salas · 13th May 2009, 09:37 PM

7.5-8.5V

12th May 2009, 09:50 AM	#1743
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	I will do that in the weekend. Thank you Salas __________________ RC

12th May 2009, 10:26 AM	#1744
nicoch58 diyAudio Member Join Date: Oct 2004	Ricardo if you have spare caps you can tray kg-R-Jensen on psu.... __________________ Sic58

13th May 2009, 05:57 PM	#1747
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	The schematic I am using (Gain 46db for medium MC ~1mv) indicates D1 = 1N4738A (8.2v zener), so I am a little confused.... why use 7.5v instead ? Also I do not understand the frase : "Up to 4V7 Zener must not scare you, or above 12V." Do you mean zeners generate max noise from 6 to 9 v so 12 volts is ok ? Sorry for the nube questions but I need to know. Ricardo __________________ RC

13th May 2009, 06:34 PM	#1749
RCruz diyAudio Member Join Date: Sep 2006 Location: Saxon Blog Entries: 1	I believe this is a must do mod. I do not know if I can reach exactly 7,5v with leds only.... What is the best voltage [<-window->] or the minimum possible value? Ricardo __________________ RC

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

11th May 2009, 08:38 PM	#1741
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Try easiest wrap way and see in practice if hum goes. If sound worsens or hum field don't go 100%, then we think why. Don't forget to ground the tape to chassis. It must have electrical continuity to GND. Take care of covering secondary exit.

12th May 2009, 08:15 PM	#1746
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	I just put the base voltage of a small Zener in the Vref string there bcs its equivalent almost to a led, so to avoid using many LEDS. But if practically does not bother you, do it all LEDs. Just trim to around 7.5V total. Green or red are OK. The thing is capacitor bypassed, but bcs 6.5-9V is not a best region for Zeners, I wanna see if some noise still escapes. Up to 4V7 Zener must not scare you, or above 12V.

13th May 2009, 09:37 PM	#1750
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	7.5-8.5V

Currently Active Users Viewing This Thread: 2 (0 members and 2 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read