R vs. RC on secondaries

kasra · 28th March 2005, 10:57 AM

For a WOT preamp ive seen people using both R and RC in order to get better square waves on the output.

What is the difference between the 2 methods?

The transformer is a 4.5:1 LL1660.
Recommended RC: 2k+3nF
Recommended R: 2k

Steve Eddy · 28th March 2005, 04:10 PM

Quote:

Originally posted by kasra
For a WOT preamp ive seen people using both R and RC in order to get better square waves on the output.

What is the difference between the 2 methods?

I don't know that it's so much about two different methods.

A realworld transformer has parasitic inductance, capacitcance and resistance that combine to give the trnasformer a high frequency resonance which can result in response peaking and ringing in the time domain.

For a given transformer there will be a resistive load value that will result in a well-damped high frequency resonance without peaking or ringing. However since transformers reflect the secondary load to the primary, that resistive load may not be ideal in terms of what's driving the transformer's primary.

You may want the driving component to see a much higher impedance. However if you keep the load resistive and inrease its value, then you're going to start running into problems with high frequency resonance.

So usually what's done is the resistive load is increased in order to get the primary impedance in the passband that you want and an RC network is then paralleled with it in order to provide proper damping of the high frequency resonance.

se

PRR · 28th March 2005, 09:11 PM

R loads down everything.

R+C only loads the supersonics.

Steve Eddy · 28th March 2005, 11:31 PM

Quote:

Originally posted by PRR
R+C only loads the supersonics.

I'll try and remember that the next time the Kings play Seattle.

se

Damon Hill · 29th March 2005, 01:56 AM

Quote:

Originally posted by Steve Eddy

I'll try and remember that the next time the Kings play Seattle.

se

Mental note: warn the 'Sonics that the RC has been spiked.

--Damon, who RCs his power supply secondaries

Sch3mat1c · 29th March 2005, 04:24 AM

Pffbt... lucky for you I'm not drinking or eating anything right now!

Tim

kasra · 29th March 2005, 10:43 AM

Thanks guys for clearing things out for me

kasra · 29th March 2005, 04:04 PM

Anyone that could point out somewhere were I can read about this issue - and how to calculate appropriate R load for secondaries?

The setup is like Euridice with 417a tubes biased @20mA, 2200uF cathode bypass, 20kohm input impedance. Trafos are LL1660 4.5:1 wired.

28th March 2005, 10:57 AM	#1
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	R vs. RC on secondaries For a WOT preamp ive seen people using both R and RC in order to get better square waves on the output. What is the difference between the 2 methods? The transformer is a 4.5:1 LL1660. Recommended RC: 2k+3nF Recommended R: 2k

29th March 2005, 04:24 AM	#6
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Pffbt... lucky for you I'm not drinking or eating anything right now! Tim __________________ Seven Transistor Labs Projects and Resources

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28th March 2005, 09:11 PM	#3
PRR diyAudio Member Join Date: Jun 2003 Location: USA	R loads down everything. R+C only loads the supersonics.

29th March 2005, 10:43 AM	#7
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	Thanks guys for clearing things out for me

29th March 2005, 04:04 PM	#8
kasra diyAudio Member Join Date: Nov 2001 Location: Sweden	Anyone that could point out somewhere were I can read about this issue - and how to calculate appropriate R load for secondaries? The setup is like Euridice with 417a tubes biased @20mA, 2200uF cathode bypass, 20kohm input impedance. Trafos are LL1660 4.5:1 wired.