417a line preamp help

kasra · 12th October 2004, 10:20 PM

This is my second tube project and i really would like to hear some opinons from you experienced guys out there, about the schematic i gotten:

Does it look good? Any values that need to be overlooked? Any room for improvments?

analog_sa · 12th October 2004, 10:46 PM

The 1660 is presumably wired 4.5:1, right? Looks fine although i am not particularly fond of non-bypassed cathode resistors. Consider replacing the resistor with a couple of NiCds as well.

kasra · 12th October 2004, 10:57 PM

analog_sa:

yes 4.5:a SE to line output.
What type of NiCd do you reccomend?

The person i got the schematic from used anoher value POT, im going to use as seen 250K, i dont have to change any values because of that? the one i had on mind was the 100k

analog_sa · 13th October 2004, 07:36 AM

Is this a linear pot being log-faked by the 100k resistor? Then you would also need to reduce the resistor value in order to get a smooth pot action. Or just use a log pot and remove the resistor.
The batteries i currently use are NIMH and come from 900mA/h cellphone batteries. I use 2 cells for 2.4v bias.

barossi · 13th October 2004, 09:48 AM

Hi,

i have built this nice pre-amp (called: Euridice) with the LL1660/18mA. In the normal connection the output level is too much. IMHO you don' t need 4,5:1.

Batterie biasing is a good way...

Greetings Barossi

kasra · 13th October 2004, 10:48 AM

analog_sa:

To be honest i dont know the type of the pot, its an alps black beauty marked: 643t 250KX2
I will look it up.

barossi&analog_sa:
As i understood you both are using batteries instead of cathode resistor. What have you compared with and what was the results?

analog_sa · 13th October 2004, 01:42 PM

Quote:

using batteries instead of cathode resistor. What have you compared with and what was the results?

Not me. I generally dislike batteries in the cathode. Better than resistors, just not good enough. As i use a TVC my battery is in series with the input - it does not get recharged very effectively in this position but it also does not pass much (any?) current so it's sonics contribute a lot less colourations.

It's pointless talking about the sonic results if the PS is not shown. I use 83 rectifier with low DCR transformers and chokes (Lundahl) and Cerafine caps.

kasra · 13th October 2004, 01:56 PM

analog_sa:

The potentiometers are logaritmic, perhaps i can just remove the 100k?

analog_sa · 13th October 2004, 03:59 PM

It is not essential. I guess it's only purpose is to keep negative bias for the tube if the wiper goes AWOL.

Bernt · 14th October 2004, 12:11 AM

If you decide to use NiCd battery for this, just make sure it can stand the current. Look in the datasheet what charging current is OK.

It is also possible to use battery for bias and no cathode resistor at all.

For bypassing the cathode resistor, it is good to use tanthal electrolytics I´m told.

12th October 2004, 10:20 PM	#1
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	417a line preamp help This is my second tube project and i really would like to hear some opinons from you experienced guys out there, about the schematic i gotten: Does it look good? Any values that need to be overlooked? Any room for improvments?

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12th October 2004, 10:46 PM	#2
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	The 1660 is presumably wired 4.5:1, right? Looks fine although i am not particularly fond of non-bypassed cathode resistors. Consider replacing the resistor with a couple of NiCds as well.

12th October 2004, 10:57 PM	#3
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	analog_sa: yes 4.5:a SE to line output. What type of NiCd do you reccomend? The person i got the schematic from used anoher value POT, im going to use as seen 250K, i dont have to change any values because of that? the one i had on mind was the 100k

13th October 2004, 07:36 AM	#4
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Is this a linear pot being log-faked by the 100k resistor? Then you would also need to reduce the resistor value in order to get a smooth pot action. Or just use a log pot and remove the resistor. The batteries i currently use are NIMH and come from 900mA/h cellphone batteries. I use 2 cells for 2.4v bias.

13th October 2004, 09:48 AM	#5
barossi diyAudio Member Join Date: Oct 2003 Location: near hamburg	Hi, i have built this nice pre-amp (called: Euridice) with the LL1660/18mA. In the normal connection the output level is too much. IMHO you don' t need 4,5:1. Batterie biasing is a good way... Greetings Barossi

13th October 2004, 10:48 AM	#6
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	analog_sa: To be honest i dont know the type of the pot, its an alps black beauty marked: 643t 250KX2 I will look it up. barossi&analog_sa: As i understood you both are using batteries instead of cathode resistor. What have you compared with and what was the results?

13th October 2004, 01:56 PM	#8
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	analog_sa: The potentiometers are logaritmic, perhaps i can just remove the 100k?

13th October 2004, 03:59 PM	#9
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	It is not essential. I guess it's only purpose is to keep negative bias for the tube if the wiper goes AWOL.

14th October 2004, 12:11 AM	#10
Bernt diyAudio Member Join Date: Jan 2004 Location: Gothenburg	If you decide to use NiCd battery for this, just make sure it can stand the current. Look in the datasheet what charging current is OK. It is also possible to use battery for bias and no cathode resistor at all. For bypassing the cathode resistor, it is good to use tanthal electrolytics I´m told.

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