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Old 22nd October 2010, 11:23 PM   #221
AR2 is offline AR2  United States
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Guys,

Could we please limit our conversation strictly about this project, and avoid pitfalls from many other threads, where conversation gets derailed with personal attacks, and all kind of nastiness. There is enough excitement in this thread about this project, obviously many people are in need, support and of desire to do it, so PLEASE, lets not loose that momentum. We are going for it so please do not derail it with empty rhetoric. . Quite honestly, I could hardly recall any other effort where the complete solution is presented to people - boards, heatsinks and case. Yes, someone might learn some more by etching, sourcing and machining on his own, but there will be many that might get exhausted with the process.

This might be the chance for someone to learn, to assemble on his own and to complete the project. Than to take it to his living room and all happy to stare at it at some cold December night, all proud that he did it. F5 is the jewel of the amps, and balanced will drive many speakers out there with ease. What better project for someone who is starting?

Because of that, lets not make this 150 pages long, lets be open and concise so that anyone could easily get what they need. I will try to document every step, measurement and technic so that even a caveman could do it. Only that way someone will learn instead of spending more time in search and giving up in frustration. Having case and tapped heatsinks is 90% of the amp and that certainly will more than anything encourage people to do it, experience it and and learn from it.

Thank you
AR2

PS Variak, please keep an eye on this thread
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Old 22nd October 2010, 11:33 PM   #222
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Once we have finalised the design and cost, hopefully the moderators will remove all the irrellevant comments.

In my opinioin the Pass forum is the best out of the lot. Lets keep it that way as AR2 has suggested.
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Old 23rd October 2010, 02:25 AM   #223
ichiban is offline ichiban  United States
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Default adequacy of Conrad Heatsink

About April of this year I changed my dual mono F5, Fairchilds on Conrad MF35-151 heatsinks, into a balanced F5. Standard F5 voltage and bias currents. Now the sage advice is that if one can hold their hand on the heatsink, comfortably, for five seconds, then the heatsink is adequate. With the balanced F5 I could hold my hand on for two to three seconds. They were very hot. Ambient was 75F. I did take measurements of sinks at various positions and on tabs of mosfets. I did not save those readings, however I recall the temp on the mosfet tabs was in the safe zone, for longevity, as I found recommended somewhere on the F5 thread.
About six weeks ago I reverted back to the dual mono configuration. Well,
sonically there was more detail overall in the sonic picture. The loss just wasn't apparent for me when I went balanced. I venture a guess, that because of mismatches between the two amps in balanced mode, a veiling resulted.
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Old 23rd October 2010, 03:10 AM   #224
tinitus is offline tinitus  Europe
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with my CD player I can choose between RCA "single ended" and balanced XLR

I decided a long time ago to let it stay in RCA single ended, and to forget about the balanced option

balanced may have some technical advantage
but it sounds too much of "hifi" to me
single ended sounds more natural to me

to me its common basics, and will always be like that
but balanced has to many become the ultimate
to me its way too overrated, and a myth

but Im sure its also about personal preference
a bit like tube amps vs solid state
horns vs dipole
ribbons vs dome tweeters
alu cone vs paper cone
and so on

but if your speakers are a way too heavy load for a 25watt, ofcourse a balanced with twice the power will sound better
but it doesnt mean its a better amp
or it could be just be a simple matter of SPL preferences

its similar with tube flea amps
every(almost) tube amp builder knows that the smaller the better
but speakers become another issue

or you could just say no free lunch
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Old 23rd October 2010, 03:34 AM   #225
EUVL is offline EUVL  Europe
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> Which precision for the feedback resistors?

Closed loop gain should be matched to better than 1% (0.1dB).

The 55R (50R in NP F5) is made up of 4x 220R 1W PRP in parallel.
The 11R (10R in NP F5) is made up of 3x 33R 0.25W PRP in parallel.

Standard PRPs are 1% I believe.
So by paralleling you are automatically getting 0.5% for 55R and 0.6% for 11R.

But since you will need 16x 220R and 12x 33R for 2 channels, you can of course measure and then pair them to get 4 identical sets.
And I bet you will have little problem getting below 0.1% match.
Absolute values are not important.


Patrick
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Old 23rd October 2010, 04:11 AM   #226
EUVL is offline EUVL  Europe
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> I decided a long time ago to let it stay in RCA single ended, and to forget about the balanced option

That discussion we had a long time ago with Aleph and Aleph-X.
It is always a personal choice with audio.

Suffice to say that almost all top of the line Hi-End equipment are balanced from Source to Power amp these days.
Of course it also raise the price & the profit, as a side effect.


Patrick
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Old 23rd October 2010, 04:45 AM   #227
tinitus is offline tinitus  Europe
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I know it may sound strange
but even when I only use RCA single ended, its like it sounds better also having XLR connects connected too(different input switched off)
maybe something with grounding ?
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Old 23rd October 2010, 06:59 AM   #228
EUVL is offline EUVL  Europe
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Have you been using a bridged F5 with a single ended signal ?

If so, the half of the bridge that is connected to the Gnd of the RCA is practically not doing anything and running idle. No wonder .....

F5 is not an Aleph X which has a long tail pair at the input.


Patrick
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Old 23rd October 2010, 07:43 AM   #229
qusp is offline qusp  Australia
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yep, much as I relish the thought of matching power resistors, I think i'll leave the most important ones to Texas components, Zfoil power resistors FTW! though for the really low value ones I will need to stick to SFOIL I think, as I dont think the Z goes down that low.
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Old 23rd October 2010, 10:26 AM   #230
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I would like to know If I can use trafo with 2 x 12 VAC for this project
I will not use regulator
anyone know DC rail value of Clas A amp with 2 x 12 VAC loaded with 4 A

thx
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