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Old 12th June 2011, 10:53 PM   #21
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Thanks for the info. There is one schematic by ZenMod that shows the gate floating and not grounded. It referenced Patrick(EUVL) DAO headphone amp.
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Old 13th June 2011, 10:40 AM   #22
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Would the Arch Nemesis AMp benefit from having a 1:1 OT instead of step down since this would solve the bandwidth issue. The major limitation it seems is the currect rating of the trafos. It would seem that you need a toroid like in ZV7. Would you suspect the R085 would benefit more from a B1 buffer or a cascaded fet? Would the buffer allow you to drop input cap and would it affect the sonic signature of the following stages. Sorry for the questions. Waiting for all pieces of the puzzle to get here and having trouble sitting still.

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Old 13th June 2011, 06:13 PM   #23
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TeaBag,
I looked at the ZV8 and the De-Lite articles again and noticed that in a similar setup, the SS DM Jfet trounces the LU. That is based soley on measurements and not actual listening. Seems I need to send you another PM. I have yet been able to see the connection to the Nemesis article other than a confirmation of similar results with the R085. There is the implication that a higher voltage->higher bias leads to better results.
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Old 14th June 2011, 11:48 AM   #24
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Originally Posted by buzzforb View Post
Would the Arch Nemesis AMp benefit from having a 1:1 OT instead of step down since this would solve the bandwidth issue....
No, probably not. You would not have enough of a load on the transistor. Gain and distortion would suffer.
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Old 14th June 2011, 01:09 PM   #25
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No, probably not. You would not have enough of a load on the transistor. Gain and distortion would suffer.
Could you not put a resistor in series with the trafo? Current seems to be the limitation. I don't know, just learning. More interested in R085 F3 and possible SS PLH.
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Old 14th June 2011, 01:37 PM   #26
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Quote:
Originally Posted by buzzforb View Post
TeaBag,
I looked at the ZV8 and the De-Lite articles again and noticed that in a similar setup, the SS DM Jfet trounces the LU. That is based soley on measurements and not actual listening. Seems I need to send you another PM. I have yet been able to see the connection to the Nemesis article other than a confirmation of similar results with the R085. There is the implication that a higher voltage->higher bias leads to better results.
Yes, the Nemisis is a reference point for an amp that works, we should be able to determine a few points. Mainly there is a a certain amount of voltage and current going through it that works, at least with a trafo on output.

Also agree with the higher voltage and bias - The F3 also benefits from a higher voltage than normal FW PS.
Just have to find time to gut various parts of my F3. Pulling the cascode IRF out will be latter step I think, messing with bias and source resistance first, and tweaking or removal of feedback. As Nelson has noted, and I can say, there have been many people interested in modding there F1 and F2, and can imagine people might want to play with their F3's. A more popular amp I think.

The De-Lite and ArchNemesis don't have a clear path to a good slow start power supply, and I consider that a limitation. For me, no turn on thump is very important.

Of course, I am also wondering if Nelson will pull this part out of the bag as an option for an F6.
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Old 14th June 2011, 01:55 PM   #27
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I ordered extra for my F3 if you need anything. Let me know. If the R085 is indeed more linear with less distortion, then developing a higher power F3 along the lines of what Vladmirk did seems interesting. Might be able to add the BA-1 buffer to the tail end without causing too much change in the sound. I hope to start on the standard F3 this week.
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Old 14th June 2011, 02:54 PM   #28
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Could you not put a resistor in series with the trafo? Current seems to be the limitation. I don't know, just learning. More interested in R085 F3 and possible SS PLH.
Well, I think that might increase the load on the transistor improving gain but effectively throwing away the benifit into the resistor.
let me throw in 2cents here: Why has no one brought up for discussion, or tried, the 550 in the cascoded F3 circuit.
AHHEMMM
Might need a little work to get the EM device bias but...
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Old 14th June 2011, 03:31 PM   #29
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I would lean toward using the 550 in the FE of the PLH. Anything is possible, just leaning towards topology's with similar components in place. The 550 didn't really do as well as the other SS devices in the D-LIte test. Why do you think it would perform better?
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Old 14th June 2011, 05:04 PM   #30
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FE of the PLH is a good idea, maybe with the bigger devices at the output as well?
Also as the VAS of the BA-1 or2?
What de-Lite test of the 550???
Why?
Most of these devices have a rediculous non-linear C curve at low D-S voltages. This messes up the high freq due to the other resistors in the circuit or the available drive current and causes measureable distortion. Remember as the amplifier signal swings D-S voltage up and down, the C load on the circuit driving it is varying widely. Cascoding gets this D-S variation under control to a good degree. Like in the F3. It actually almost gets rid of the capacitance. Remember if there is little or no voltage change between the Gate and Drain or Source, there is no capacitance. The LU device has this problem also as do MOSFETs. Cascoding reduces the voltage difference from Vin vs Vout, to Vin vs cascode voltage. But the cascode voltage does not change so the variation is effectively Vin. 5 times less D-S variation in the cascoded F3 circuit than a non cascoded version.
The power dissapated in the cascoded LU device is only 6-8W at most. The 550 part is a lower power part(very much like the IRF610) but likely capable of maybe 15W max dissapation. So, if you have an F3, you have most of what you need to give the 550 a whirl. You need to add external bias or some bias mechanisim to get the Gate up to +1.0 to +1.2V or so. Note, I said "up to" "+" voltage. Not the self bias method (Source Resistor) as F3 currently usses. You'll need to add an input cap to sheild your source from the 1V bias. You would probably want to make the cascode refrence voltage adjustable and play around looking for the best "distortion spectra" (sound). You probably also want to mess with Source resistor values? And maybe even move the cascode refrence voltage off of ground to the top of the source resistor???
I think thats enough off thread, this is a 085 thread
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Last edited by flg; 14th June 2011 at 05:22 PM. Reason: forgot something
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