F5 Turbo Builders Thread

[Zen Mod]

you're lousy reference for AC , and pray** to stay exactly that.

that's irrelevant

check that you have zillion ohms between xformer primary and case

now , prior to attaching audio gnd NTC to sace , be sure to have same (zillion ohms) between audio gnd and case

**take care , in fact

 

[luvdunhill]

check that you have zillion ohms between xformer primary and case

Check.

now , prior to attaching audio gnd NTC to sace , be sure to have same (zillion ohms) between audio gnd and case

And nope, zero. When PSU isn't connected, I have a zillion ohms. When connected, zero. Brand new board, no soldering - zillion between Earth and Audio Ground. Let me keep disconnecting things.

If I disconnect transformer secondaries, then a zillion ohms between chassis and Audio Ground.

Edit: just the blue/grey secondary causes this. The red/yellow doesn't. I realize this is meaningless, but...

Edit: if I swap the secondaries and plug them both in, then I get a zillion. Hmmm.

 

[luvdunhill]

Ok, well the secondaries were in series, but the phasing didn't match the primaries. Why that matters and creates a short to Audio Ground I have absolutely no clue.

 

[luvdunhill]

Ok, after getting zillion ohms in the right places, replaced TH and powered on - still a smokin'
Hm, scratch that - still seeing low ohmage when the second secondary is plugged in, regardless of phasing. I think time to sleep on it.

Umm, with Trafo disconnected I get low Ohms from Chassis to both sides of the blue/grey winding. I suppose this is what this thingy is supposed to protect against anyways?

 

[luvdunhill]

Waaaaaaaaaa.... look what I found under the mounting washer. This plus the other side of the bolt scratching through the case anodizing created a shorted turn on one of the secondaries!

 

[luvdunhill]

Looking good. So I guess the thing I installed to protect against the thing that I didn't expect to happen was the last thing I thought about checking. Figures.

 

[pchw]

Should any short like this break the fuse?

 

[Zen Mod]

probably not enough voltage at that point of secondary winding , to result in enough primary current

 

[luvdunhill]

I guess? I would have expected something to blow. I guess from now on I won't forget the TH from Earth to Ground!

 

[Blitz]

I am burning my F5Tv2 right now in....so, its a bit early to say where it is going, it is just running now with 33V railvoltage and 0,340V bias with a CLC (30mH, 5a, chokes from AE) PSU (one for both channels). High quality build with texas components/Mills non-inductive resistory, Mundorf Mlytics etc.

My very first impressions:
It sounds from the tone very similar to my Ultralinear El-PP with 6n6P and El34 into Amplimo-OPT with Duelund Cast-caps, no lytics in the amp, amorphous core choke.

Currently the difference is:

- The tube amp is more transparent, people are just "there", more micro-contrast, faster
- Both share the same very natural tone, the F5T is slightly warmer than the tube amp
- F5T seem to paint everything with a bigger brush, the tube amp is finer, more resolution, instruments are smaller.

Both play on 2m high line sources with 12 Fountek ribbons perside and 18 4" Eton-Kevlar chassis, two way system with duelund x-over and actve subwoofers. Certainly 93db sensitivity or better combined with ribbon resolution.

So, for a transistor it plays already VERY good, tonal balance is certainly right, no artificial brightness or harshness at all. If speed and micro-resultion goes up by burning it in (and the tube amp changed as well significantly after a few hundred hours), it might outperform the tube and than I will give it a dual mono-psu. If the fine curtain stays, I am happy to have such a nice amp, but I would stay with tubes for my main system...

...what are your burnng in experiences ? How long and how much improvement to expect ?

 

[buzzforb]

Before making a final decision, I would try two things. Use P3 to adjust harmonic profile. A distortion analyzer will be necessary for this. Secondly, consider dropping the diodes on the output and increasing bias and simply running as a beefy F5

 

[Blitz]

...so did you make the experience that you do hear the diodes on the output ?

I have a 6 ohm speaker, so not shure I need the current delivery ability of v2 anyway....

 

[6L6]

Blitz - listen to the amp for at least a week before even considering any changes.

 

[Blitz]

6L6...I will certainly not touch it now and give it a non-stop-burn-in before changing anything...but what you are saying is: Yes ! There is a noticeable break-in-Periode. - Very promising.

 

[buzzforb]

Without diodes was the implementation I last listened to and preferred. That being said, I think P3 is the place where the most change can be had.

 

[Blitz]

A short update:

The overall impression stays the same currently: The tube amp is more coherent, feels like you have an electrostatic headphone, has a deeper soundstage, much more laser-focussed in comparison.

Neverthess, I do like the F5T a bit more: The tonality is more natural, everythings builds on a much stronger bass/lower midrange-foundation. The F5 shows me the deficits of my tube amp...and vice versa.

So, next steps:
- I will get rid of the thermistors
Get my Laptop up to measure Distortion and play with P3.
- As gate stoppers I have still carbon-resistor in front of the power-mosfets (Kiwame), I guess I want to revisit this as well.
- "Downgrade" to V1, so get rid of the Mur3020...going the Peter Daniel-Path
- Build a separate PSU, so getting Dual-Mono
- Potentially reduce Voltage from 33V to 28, so that I can get rid of the Cascode.
- Drive it with a balanced signal instead of unbalanced....

For sure extremely promising...if you have experiences with these steps...please let me know your observations.

 

[doolav]

"- Drive it with a balanced signal instead of unbalanced...." - how are you going to unbalance the signal?

 

[6L6]

It's already being used unbalanced. He wants to try a balanced source.

If you want to "unbalance" a source, try this -
Balanced to unbalanced

 

[doolav]

"It's already being used unbalanced. He wants to try a balanced source."
- this does not answer my question at all - how is _he_ going to unbalance the signal.
He may use the unbalancer from the link you provided, or use input transformers or something else... Some people don't bother too much, taking just a ground and one phase.

I thought about similar thing - using input transformers to take a balanced signal from bIII dac, hence my interest if anyone had done it and if it's worth doing.

 

[Erlend Sæterdal]

"It's already being used unbalanced. He wants to try a balanced source."
- this does not answer my question at all - how is _he_ going to unbalance the signal.
He may use the unbalancer from the link you provided, or use input transformers or something else... Some people don't bother too much, taking just a ground and one phase.

I use 200 ohm from - to ground.