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Old 26th November 2008, 07:26 PM   #601
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Don't forget a 220k/2W bleeder R across the 220uf cap to keep you from getting zapped by B+ when powering down to work on the amp.

Dynamic loudspeakers are a wirewound, inductive load.....
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Old 26th November 2008, 10:11 PM   #602
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Ken (Audio_Idiot) asked if I could post working schematics of the fixed biased Baby Huey Monoblocks.
This is what the amps looked like as of last night - note that I have backed out the change of the shunt feedback from the Ultralinear Taps and shunt feedback is off the anodes again. I felt that the speaker impedance vs frequency curve had too much influence when shunt feedback was taken from the UL Taps and I was loosing too much bass (although I though the fine detail was a bit better) - I may have to try this again. The Source follower CCS loads are "Basic" and can be improved.

Cheers,
Ian
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Old 26th November 2008, 10:13 PM   #603
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And the Power Supply - not absolutely optimal, I made use of transformers I had on hand.
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Old 27th November 2008, 10:01 PM   #604
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And now you see why I'm normally not keen to post working schematics - The feedback from the UL taps mod is back in. Last nights testing showed this is much better. Also pushed up the shunt feedback level for better bass control. It will stay this way for at least a few weeks and maybe forever. Updated Amp schematic attached.
Cheers,
Ian
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Old 28th November 2008, 02:07 AM   #605
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Quote:
Originally posted by gingertube
Ken (Audio_Idiot) asked if I could post working schematics of the fixed biased Baby Huey Monoblocks.
This is what the amps looked like as of last night - note that I have backed out the change of the shunt feedback from the Ultralinear Taps and shunt feedback is off the anodes again. I felt that the speaker impedance vs frequency curve had too much influence when shunt feedback was taken from the UL Taps and I was loosing too much bass (although I though the fine detail was a bit better) - I may have to try this again. The Source follower CCS loads are "Basic" and can be improved.

Cheers,
Ian
Ginger,
This may be another of my idiot-ish question...
I hope this make sense... From what I understand, this partial feedback is a form of Voltage Feedback,it is the voltage amplitude feed into the input that matter the most. a feed back signal taken from UL tap would be smaller (only a portion of the L) as it in essence a voltage divider of the full coil... I also observed that the shunt resistor for the plate is larger then the one from the UL tab. and the shunt resistor will attenuate this signal proportional to its size.

Now my real idiot question, is there any need to play with the UL tap?

Cheers

Ken
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Old 28th November 2008, 02:12 AM   #606
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Hi,

My earlier post

Quote:
Originally posted by Audio_idiot
Hi,

I hope this is relevent
http://www.audioxpress.com/magsdirx/...a/jung2778.pdf
http://www.audioxpress.com/magsdirx/...a/jung2779.pdf

Cheers

the two articles cover lots of detail technical datas of CCS (at least to an idiot like me )

The articles covers the use of LM317 and reference diode for high noise rejection.

I hope we can further discuss this if it is not off topic.

Cheers

Ken
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Old 28th November 2008, 02:35 AM   #607
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Ken I'm not sure what you are asking.
First note that the Feedback pickup from the Ultralinear Taps is back in again.

The Signal voltage at the UL Taps is 40% the signal voltage at the anodes so you don't need to divide the voltage down as much to get the level of feedback voltage you want (as you said).

In addition to that if we say that the output transformer load presented to the output tubes is nominally 8 KOhms anode to anode and that impedance is proportional to the SQUARE of the turns ratio then from Ultralinear Tap to Ultralinear Tap the impedance is 0.4 squared x 8K = 1K28.

When taking the feedback of the anodes I wanted a divider chain (47K + 16K +47K) which was at least 10 times the 8K load presented by the output transformer so that the output tubes are delivering the bulk of their power into the output transformer and not into the feedback divider chain.

When we take the feedback from the Ultarlinear taps the divider should be at least 10 times that 1K28 instead, so the resistors can be smaller and you don't loose as much DC Voltage due to the front end diff amp current flowing through them.

The Feedback from the UL Taps went back in during a marathon test and listen session last night and I posted the moded amp schematic when I got to work about 4 hour ago. It really does sound much better with respect to detail and in particular it has a lovely loping pace and rhythm compared to taking feedback from the anodes.

To get EXACTLY the same level of feedback as before, the divider off the UL Taps should be 10K + 9K1 + 10K. This is what I started with last night but then tried increasing the feedback level by changing that 9K1 cross connect to 10K, then 12K then 13K then 15K and finally to 18K which means I doubled the amount of feedback. This was mostly noticable in better bass control. That last step 15K to 18K did not make much difference and I may go back to 15K but this is just "fiddling at the edges".

The 2 papers you posted links to are probably amoungst the best papers on Current Sources - they are cerainly in my filing cabinet of useful info. They don't cover all the options but give you a good "toolkit".

Cheers,
Ian
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Old 28th November 2008, 02:53 AM   #608
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Ginger,
You understood my question fully.

The UL tap shunt feed back make sense to me now.

I am still looking for excuses to delay my build

I also see that you derive the output tube bias voltage from the -48V rail for the source follower, how would you go about the current balance of the two output tubes? I meant any plans for autobalancing servo?

Cheers

Ken
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Old 28th November 2008, 03:11 AM   #609
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Ken the "bias" is applied to the gates of the source followers via adjustment pots. Each Output Tube has a 10 Ohm resistor in its cathode, the voltage drop across that resistor tells me the idle current. With the input shorted (no signal) - on each side I measure the voltage drop across the 10 Ohm resistor and set the pot for that side to get the idle current I want. For example with the 360V rail I have right now I set for a reading of 0.32 Volts across the 10 Ohms which means 32mA idle current. That means I have about 11.5 Watts of dissipation in the tube. The idle currents are ONLY balanced cause I adjust them to be the same on each side.

A Bias Servo is possible but no plans at this time.

The original CCS biased Baby Huey does not have or need any adjustment and is automatically balanced by the action of the CCS in each output tube cathode (The idle current flows through the CCS). It is one of its "endearing features" but the trade off is that the CCS'es require bypass caps (ALL of the signal current runs through those capacitors) and the sound is influenced by those capacitors.

Best I get back to what I'm meant to be doing (writing a Laser Safety Paper)
Cheers,
Ian
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Old 29th November 2008, 04:29 PM   #610
adamus is offline adamus  United Kingdom
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I have a couple of options for the bypass caps, either silmic 1000uf (i have 4 in the parts bucket) or i have 4 220uf blackgates.

i assume i would lack bass with the 22ouf blackgate?
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