Rogers Cadet III to SY's Red Light District or Gingertubes's Baby Huey - Page 3

jkeny · 22nd January 2007, 07:26 PM

Hey Gingertube,

I posted this before in another thread & was told that this was not the latest schematic for the ECL86 baby Huey amp - can you confirm this?

jkeny · 22nd January 2007, 07:29 PM

I have one other schematic for the BH ECL86

jkeny · 22nd January 2007, 09:17 PM

ping Gingertube

gingertube · 22nd January 2007, 09:20 PM

Been away on holidays for a month so just saw this for the first time.

The second one is the "final" after tweaking circuit I used.

The first one has a missing resistor in the diff amp current source circuit.

The Baby Huey shunt feedback scheme relies on the diff amp swinging extra voltage to overcome the "local" feedback bein applied. There is accordingly a practical limit to how much feedback you can apply which usually will be around 6 to 9 dB (X2 to X3). Without Ultralinear taps some global feedback WILL be required to get output impedance down to a suitable level.

Use SY's LED bias scheme on the outputs, as he says above, this will give much better overload recovery.

Cheers,
Ian

jkeny · 22nd January 2007, 09:28 PM

Thanks Ian,
That was my plan - have no UL tap - will use global feedback. I intend to also try battery bias before LEDs.

John

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22nd January 2007, 09:17 PM	#23
jkeny Banned Join Date: Feb 2007 Location: Dublin	ping Gingertube

22nd January 2007, 09:20 PM	#24
gingertube diyAudio Member Join Date: Oct 2004 Location: Adelaide South Oz	Been away on holidays for a month so just saw this for the first time. The second one is the "final" after tweaking circuit I used. The first one has a missing resistor in the diff amp current source circuit. The Baby Huey shunt feedback scheme relies on the diff amp swinging extra voltage to overcome the "local" feedback bein applied. There is accordingly a practical limit to how much feedback you can apply which usually will be around 6 to 9 dB (X2 to X3). Without Ultralinear taps some global feedback WILL be required to get output impedance down to a suitable level. Use SY's LED bias scheme on the outputs, as he says above, this will give much better overload recovery. Cheers, Ian

22nd January 2007, 09:28 PM	#25
jkeny Banned Join Date: Feb 2007 Location: Dublin	Thanks Ian, That was my plan - have no UL tap - will use global feedback. I intend to also try battery bias before LEDs. John

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