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Old 21st February 2013, 08:00 AM   #3701
ianc13 is offline ianc13  United Kingdom
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Quote:
Originally Posted by dimkasta View Post
Nice!! Enjoy man I m so jealous right now

If I had to guess about the hum, I would put my money on those secondaries running so close to the jensens.
Yes the current PSU PCBs are not ideally placed, and are too big to fit how I would like. I am waiting on a new CRC PSU board that will fit better in the chassis and allow me to split up the internal area with some aluminium/mu-metal dividers.

Hopefully it will come soon!!!!!

One thing that I am finding strange at the moment is that the channel imbalance seems to start to correct itself after ~1 hour of playing time. Any ideas? It may be that my brain is just getting used to it and compensating!

Tonight I will flip the power JFETs around to see if the channel imbalance follows them and I'll swap the Cinemag transformers too - really easy with Tea-Bag's transformer daughter board configuration - to see if they are the culprit.
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Old 21st February 2013, 10:35 AM   #3702
Tea-Bag is offline Tea-Bag  United States
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Quote:
Originally Posted by PKI View Post
I thought these are SS, not transformers what give you this signature.
In my experience with it,
transformers and output FETs both leave a strong signature on sound, followed by tweaking the distortion with source resistors, then different quality or brands of resistor parts.
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Old 21st February 2013, 10:50 AM   #3703
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SS definitely have their unique signature, a sort of clarity and crispness. I found this to be true of it when used in the Aleph Jango. Of course you cannot deny the effect of the transformer in this amp. It plays a similiar role to an output cap on a really clean linestage. It can largely define the sound. You will hear the difference in having Rs and not having it. You will hear the difference in AC coupling cap of modulation network. This amp is wonderfully unique in how much and how easily you can change the sound. What is th reason for the change? Parts, distortion spectra, gain, Zo. Who knows. Thats why its fun.
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Old 21st February 2013, 11:17 AM   #3704
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Originally Posted by Nelson Pass View Post
I think it depends one what you mean by "space and depth" on the one hand
and "pinpoint accuracy" on the other. At the very best, I have seen lots of
space and depth and also have been able to drill down to the particulars of
a given instrument in a group and focus on it, somewhat to the exclusion of
the others.

It takes a lot of things working right to get that, but I am not sure that
it represents "pinpoint accuracy"

You are encapsulating my thoughts on this more accurately. 'Pinpoint' suggests a single auditory 'hit' rather than a depth of information. I would substitute 'pinpoint accuracy' with your 'drilling down' (good physical metaphor) quote. Is there a single factor within the circuit which does more than any other to deliver this?
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Old 21st February 2013, 10:21 PM   #3705
ianc13 is offline ianc13  United Kingdom
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Quote:
Originally Posted by ianc13 View Post
One thing that I am finding strange at the moment is that the channel imbalance seems to start to correct itself after ~1 hour of playing time. Any ideas? It may be that my brain is just getting used to it and compensating!

Tonight I will flip the power JFETs around to see if the channel imbalance follows them and I'll swap the Cinemag transformers too - really easy with Tea-Bag's transformer daughter board configuration - to see if they are the culprit.
Well only slightly embarrassing, but at least I have figured out the channel imbalance.

I tried swapping the xformers, swapping around the power JFETs, checking some of the solder joints etc, etc.

Then I thought could I maybe have screwed up one of the components? I did have 2 pairs of Mills 5W resistors kicking around in my parts bin, 100R (for the feedback) and 220R from an older project. Guess what; I seem to have 1 100R and 1 220R still in my parts stash, which means I am running a considerable amount more feedback in 1 channel.

Oh well at least my mystery is solved. Take away - check and double check before soldering everything. Alas in my haste to stuff the boards through sheer excitement I missed that!
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Old 22nd February 2013, 12:24 AM   #3706
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Quote:
Originally Posted by Backbones View Post
You are encapsulating my thoughts on this more accurately. 'Pinpoint' suggests a single auditory 'hit' rather than a depth of information. I would substitute 'pinpoint accuracy' with your 'drilling down' (good physical metaphor) quote. Is there a single factor within the circuit which does more than any other to deliver this?
It starts with good recordings and good front end equipment. Then you
fool around with the amplifier until it does that.

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Old 22nd February 2013, 01:04 AM   #3707
6L6 is offline 6L6  United States
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A good front-end includes the fantastic Pearl or Pearl 2 phonostage from PassDIY...
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Old 23rd February 2013, 08:16 PM   #3708
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Hi!
I'm not a pro in electronics, but I just managed to finish my F6 using Tea-Bags boards.
I build the variable second harmonic version. I soldered all the parts shown in the schematic into the board, but jumpered the source-resistors for the SemiSouth JFETs.
As I forgot to order the 18ohms resistor (R2), I used two 10ohm resistors and soldered them in series to get at least close to 18ohms.

With this setup the sound lacks bass and the amp needs high input-levels, so there is not much gain.
Could this be due to the wrong R2? Or do you think there is an other fault?

Regards
Stefan

Last edited by elfischiso; 23rd February 2013 at 08:24 PM.
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Old 23rd February 2013, 08:27 PM   #3709
Zen Mod is offline Zen Mod  Serbia
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another fault

also - we need more info about your equipment , to understood "lack of bass " and "not much gain " ..... and also "variable second harmonic version" , especially if you're not having Rs-es
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Old 23rd February 2013, 08:48 PM   #3710
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Hi ZM!
I use a double-mono setup:
-2x torodialtrafo 2x18V 300VA each
-16x 33000uF: C-C-R(0,15ohms)-C-C for each rail
-the voltage at the boards is +/-22,6V
- I use the Jenson trafo on the boards
- I soldered all the parts (source resistors and pots) needed for the variable second harmonic version as described in NP's article in the board (except input-stage, this is the buffered version from the article..), for future experiments with degeneration, but i soldered a wire across them to jumper them
Click the image to open in full size.

My speakers are CT250 (CT 250) from the german magazine "Klang und Ton".
In this setup the F6 lacks bass compared to my Symasyms, that I used till today.

What else do you need to know?

Thanks for your help
Stefan

Last edited by elfischiso; 23rd February 2013 at 08:55 PM.
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