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In the process of building some new amps based on jack elliano's drd design (very similar to this http://www.electra-print.com/300bdrd.php ... but 6n1p input tube and different operating points).
Decided on all parts apart from the cathode bypass on the input tube. Needs to be about 100uF in value. Ive narrowed down my choice to two obbligato options.
1/ 2x Obbligato Gold Premium film 47uF/250V caps. Giving me 94uF. Caps are a bit to the large side but Ive got the room for em.
2/ 4x (or 5x) Obbligato Film Cap 22uF/35V (the little blue ones). Giving me either 88uF or 110uF. Should take up less room, cost about the same amount as option 1.
Are one of the options above clearly better than the other sonically? Has anyone compared the two caps as cathode bypasses and come up with any conclusions on how they compare sonically?
Follow Ups:
Hi,
I know I'm chancing loosing Brian a sale here, but why not upgrading your design to "full monkey" status.
In this case you recycle the output stage current to generate the Driver Bias.
Like this:
Some thoughts about singleended Valve Amplifiers
Just look for the final amplifier circuit...
Here some experiences from a Musician in Spain who build such a "Monkey" Amplifier like that:
My experience building a DRD d3A/300B amp
Also, may I ask WHY ON EARTH the 6N1P must be used? It is really not a very good choice for the job... :-)
Finally, if you really need around 100uF in the original circuit (it may be worth calculating if you really do) and you want to go ahead using the 6N1P even if much better choices exist, I would suggest the small blue 22uF/35V over the other capacitors.
Excessively large (physical size) capacitors in cathodes do seem to sound worse than smaller ones, maybe due to inductance? Who knows.
Nowadays I'm "off" DRD and Monkey Designs and back to rather deceptively simple looking things, but these Amplifiers do manage to sound quite stunning...
Ciao T
Thanks for your help. I probably wouldve gone with your monkey design if I knew about it earlier. I have built your adagio dac which I still use and adore.
Ive already ordered power transformers so its a bit late, the output voltage on them is far too low.
I'll go with the 35v caps, but perhaps try different tubes on the input stage.. thanks!
Hi,
If you have Power Transformers for a "DRD" they will work just fine for an equivalent monkey.
The key to the Monkey Island is to take the same Amplifier as DRD and apply the following changes:
1) Input Tube cathode resistor is "stacked" into the output stage cathode resistor at the bottom, value is adjusted for same bias as before.
2) Input Tube cathode resistor is unbypassed, but the resistor directly above the input tube cathode resistor is bypassed, with a value around 1/2 to 1/4 of the Ultrapath Capacitor in the output stage.
Voila, the DRD has turned into two monkeys on a stick...
BTW, the name "Monkey Amplifier" comes from Brian Clark in London, who said the schematics reminded of a toy from his childhood (which is now WAY BACK), the so-called Monkey on a stick.
I still dimly remember this, but it seems the world wide web is now a Monkeytoy free zone (I guess no longer politically correct or some such)...
Ciao T
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