Cornet2 Output Impedance--reduce?

Yoda · « **on:** 31 Mar 2006, 09:50 pm »

I've been thinking about building a Passive Voltage Amplifier (PVA)Preamp from Electra-Print, but one caveat of using this design is that one's source needs to have an extremely low output impedance (50-150 ohm ideal). Is it possible to modify the output of the Cornet 2 (and potentially chime) for this application?
Matt

hagtech · « **Reply #1 on:** 31 Mar 2006, 11:04 pm »

I suppose it is possible. You'd have to use a low rp tube like a 6H30, then rebias it at a higher current. Not sure off hand if this pinout is compatible, but the concept is valid. You'd also have to reduce the output series resistor. Likely the value of coupling capacitor would have to go way up, maybe by a factor of ten. All depends on the loading of the PVA.

My guess is that the requirements have been exaggerated. What is loading of PVA? If 10k ohms or higher, then Cornet can drive directly.

jh

Yoda · « **Reply #2 on:** 4 Apr 2006, 08:58 pm »

That sounds like far too much work. I don't think the PVA is a good match for my system.

Matt

hagtech · « **Reply #3 on:** 5 Apr 2006, 07:11 am »

Took a quick look at the PVA - not too much info. But if you get the 1:1 ratio you might be ok. Just don't try to get gain out of it! The TX102 and similar transformer volume controls have been used successfully with several Cornets and Trumpets.

I'm sure Jack can make you a nice tranny. Really depends on your system. How much signal does the power amplifier need to reach clipping?

jh

Yoda · « **Reply #4 on:** 5 Apr 2006, 02:24 pm »

2.0v to reach clipping, but plays loud enough when the cornet is hot rodded right into the amps (and sounds great).

Jack really cautions against anything that isn't in the 100ohm range with the PVA. Maybe there is something about the Cornet circuit that might permit this to work?

Maybe there is something with the direct inputs on my amp that connects right to the input tube, bypassing the 100k pot and resistor on the standard input?

who makes the tx102?

Matt

hagtech · « **Reply #5 on:** 5 Apr 2006, 06:53 pm »

The TX102 is from stevens & billington. I think www.bentaudio.com still sells them.

Problem with PVA might be primary inductance. Depends how Jack designed the tranny. Sounds like he was aiming for CD player or opamp type output drive power, so maybe it won't work well. You could lose a lot of frequency extension on both ends.

jh

flocchini · « **Reply #6 on:** 6 Apr 2006, 03:27 pm »

I use the the TX102 set-up from Bent Audio with the Cornet2 and the CHIME. I really like the setup. Great sounstage and detail in my system. I have wired it so I have balanced output to my electronic crossover. In addition to the inputs for the CHIME and Cornet2 I have two balanced inputs. Most of my listening is done between 12 and 2 o'clock postions with 7 o'clock as a "mute" position. This arrangement replaced a DIY 20dB gain preamp which has now become my headphone amp.

Best

Bob

gnnett · « **Reply #7 on:** 7 Apr 2006, 09:36 pm »

If I recall correctly your Cornet2 is an Octal. Does not the octal have a little bit lower out put impedance than the AU7 version?

Cheers

Gn

flocchini · « **Reply #8 on:** 7 Apr 2006, 10:35 pm »

Yes my Cornet is a hybrid using the 6SN7 as the output. Unfortunately I can't answer the question about the impedance. Jim?

hagtech · « **Reply #9 on:** 8 Apr 2006, 06:19 pm »

Yes, the 6SN7 output impedance is a little lower than the 12AU7, but I don't think it's a big deal. We're talking maybe going from 750 ohms down to 500 or so. Something on that scale.

jh