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Old 24th March 2008, 01:27 AM   #111
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Location: Ireland
Nice!

Looking forward to some listening impressions.

Fran
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Old 24th March 2008, 01:39 AM   #112
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Location: Maui, Hawai'i, USA
Awesome!

Put up some circuit values for us.

Poinz
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Old 24th March 2008, 03:30 AM   #113
pchw is offline pchw  United States
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Location: Fremont, California
Measurements were taken earlier today, and they typically vary a little.
The PS consists of:
PT pumps out 141 VAC
--> full wave bridge pumps out 172 VDC
--> 20uF
--> 10H 500R choke
--> 100uF --> 1160R
--> 330uF, the B+ at 137VDC

Heater floats at approx 23.5V above ground
Top cathode: approx 74V
Bottom plate: approx 72.5
Bottom cathode: approx 1.7 (approx 20.5 ma)
Heater voltage: 6.3VAC

There is no exotic parts. Filament and PT are Hammond, and the chokes are Triad. The output cap is Wima MKP 3.3uF 160V which has too low of useful voltage until now.

Already 8 hours into the action, there is apparently more weight at the mid-low and below region. The high was a touch edgy at the beginning. Not sure I've adapted to it or something else. I can no longer hear that. Notice that the power supply is usually cleaner from the evening on in my house. So, I can't say all the improvement is contributed by break in, but the SQ is noticeably better now. It is very quiet. Although my speakers are 86dB ribbon, I can't hear any hum with my ear 2 inches from it. My brother visited earlier today and asked me whether I could build one for him on his way out. That certainly means something of what he heard!!!!
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Old 27th May 2008, 02:51 AM   #114
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Default dB Gain on Poinz's linestage?

Hi folks,

I may have missed it in all of the posts, but what is the dB gain in Poinz's linestage?

I am hoping to pair a nice line stage with a DIY First Watt F1, which apparently works best with a gain of around 10-12 dB.

I saw that the Gounded Grid is around 12 dB, and that Poinz's work posted here is based off of a Rozenblit design, and would rather go with a totally DIY project and can do without any sor to input selector/volume knob since I'm placing it between a HT preamp (in bypass mode) that can handle input selection, provide volume control and convert digital Toslink inputs.
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Old 27th May 2008, 03:06 AM   #115
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Location: Maui, Hawai'i, USA
Nice build, Fred, clean and tiny - my faves.  Are those 6T4s Hitachis?  Nice toob, that.

All your numbers are right on target; what are the values of your cathode (upper and lower) resistors?

You done a good thing, my man.  I have very recently auditioned, with my trombonist/guitarist/band instructor/hi-fi-gooro friend several linestage topologies and devices, and I tell you;  you can take that piece to the very snazziest boutique/ultra audio parties, and she will not be embarassed.

Aloha Kakou,

Poinz
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Old 27th May 2008, 03:11 AM   #116
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Join Date: Oct 2004
Location: Maui, Hawai'i, USA
Sorry, Roscoe,

Gain (Av) is between 6 and 7 (15 - 17dB) depending on the individual tubes, and Zout is ~800Ω.  With a good build, hum+noise will be about 0.02 - 0.04mV (twenty to forty microvolts) on the output jack.

Poinz
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Old 27th May 2008, 07:08 AM   #117
pchw is offline pchw  United States
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Location: Fremont, California
Thank you, Poinz.
Those 6T4's are RCA's. I bought from Jack of www.thetubecenter.com. Including shipping, it averaged $3 per tube, really good deal. The cathode resistors are the exact values as the schematic that you posted, 82 ohms and 75 ohms.
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Old 27th May 2008, 08:21 PM   #118
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Oops, that's what I meant; RCA.  It's all that good medicine I took in the hippie daze.

I like the RCAs a lot, but they tend to have very grungy pins.  Get your pins clean; I use Tarn-X.

Poinz
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Old 28th May 2008, 08:35 PM   #119
JoshK is offline JoshK  Canada
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My audio club heard Poinz's Moebius....everyone was in love with the sound! It rocked. Zero problem driving the difficult SS amps in that gathering.

Its made me take a serious thought about the 6V6/6AQ5 preamps.
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Old 28th May 2008, 09:29 PM   #120
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Thanks for that info Poinz.

Looks like I'll be building a variant of the GG as soon as the DIY Fi gets built.

One question that remains is the tube to use. I've seen a lot on diyaudio about the 12B4, 6SN7 and the 12AU7, but less about the 6AQ5 and the 6T4.

Any one whose heard some combination of these got any comparisons/recommendations?

Poinz, the schematic on your webpage shows the 6AQ5, while what you posted in this thread shows the 6T4. What are the differences in the sound between these two? or between any of the others listed above you've had a chance to hear?

Thanks.
Roscoe
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