Nice!! Enjoy manI 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.
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.
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?
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!
It starts with good recordings and good front end equipment. Then you
fool around with the amplifier until it does that.
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
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
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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
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
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
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
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you need to be sure that both pots (P3 and P4) are on their minimum (or maximum - irrelevant in case when Rs is shortie)
check the gain of amp
whatever - this amp is of relatively highish output impedance , comparing to Symasym ; you can't expect same bass character from these two amps
check the gain of amp
whatever - this amp is of relatively highish output impedance , comparing to Symasym ; you can't expect same bass character from these two amps
Attachments
......make positive k2 by opening your shortcut wire on the negative side... and maybe I would make small wire directly from the sources to the caps not over the 10R pot... at least I have a better feeling to do this.... might be not necessary.
......are the SemiSouth very good matched, so we can suppose you have now k2 at the same level like k3 or even lower...
to have fun with the F6 you must learn to measure distortion....it can sound so different...!
very nice build...!
......are the SemiSouth very good matched, so we can suppose you have now k2 at the same level like k3 or even lower...
to have fun with the F6 you must learn to measure distortion....it can sound so different...!
very nice build...!
OK,
I have my F6 finally up and running from using TeaBags boards.
Xformers are Cinemags
Output devices are IRFP240's
Unbuffered
So overall the sound is very nice and I am biased to 1A per device as of now.
Problem is REALLY bad what sounds like 60Hz hummm.
PSU is Peter Daniel's board stuffed with 22,000uF X 2 per rail and 3X panasonic 0.47 ohm parallel "R" CRC.
Initial startup is very quiet but then after about 1 minute the humm becomes overwhealming.
This PSU has been quiet in other amps - I used it in my F5 for a spell and it was very quiet.
Anything obvious I should try? Could buffering make a difference?
I tried to keep the wiring as simple as possible.
Ground scheme is IEC to chassis star. PSU to chassis star. Each board to PSU. Speaker output ground to PSU.
I have my F6 finally up and running from using TeaBags boards.
Xformers are Cinemags
Output devices are IRFP240's
Unbuffered
So overall the sound is very nice and I am biased to 1A per device as of now.
Problem is REALLY bad what sounds like 60Hz hummm.
PSU is Peter Daniel's board stuffed with 22,000uF X 2 per rail and 3X panasonic 0.47 ohm parallel "R" CRC.
Initial startup is very quiet but then after about 1 minute the humm becomes overwhealming.
This PSU has been quiet in other amps - I used it in my F5 for a spell and it was very quiet.
Anything obvious I should try? Could buffering make a difference?
I tried to keep the wiring as simple as possible.
Ground scheme is IEC to chassis star. PSU to chassis star. Each board to PSU. Speaker output ground to PSU.
Attachments
fat wire from PSU gnd to F6 pcb GND
fat wire from G6 pcb to spk neg. post (NO wire from PSU to neg spk post !)
then bridge made of fat wire between two main GND points of two F6 pcbs
RCA isolated from chassis , coax or twisted pair to pcb
those mains connected NTCs are dangerous - flapping in space and non isolated ; make small pcb for them , place it with screws and extenders on bottom plate
fat wire from G6 pcb to spk neg. post (NO wire from PSU to neg spk post !)
then bridge made of fat wire between two main GND points of two F6 pcbs
RCA isolated from chassis , coax or twisted pair to pcb
those mains connected NTCs are dangerous - flapping in space and non isolated ; make small pcb for them , place it with screws and extenders on bottom plate
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besides all what more competent ZM said.....
I would place the pcb with the Jensen xformer as much as possible the the backside, even if one SS more to the PSU xformer need some longer cables.....
look at the M2 pictures at 6moons......
Nelson placed the small xformer on the board completely on the back side, there is even a piece of Mu metal for shielding......
and on the pcb are long traces to the lonely SS direction PSU xformer...
So cables do the same, the 47R gatestopper of course directly at the gate of the lonely SS......
ZM said.....I would place the pcb with the Jensen xformer as much as possible the the backside, even if one SS more to the PSU xformer need some longer cables.....
look at the M2 pictures at 6moons......
Nelson placed the small xformer on the board completely on the back side, there is even a piece of Mu metal for shielding......
and on the pcb are long traces to the lonely SS direction PSU xformer...
So cables do the same, the 47R gatestopper of course directly at the gate of the lonely SS......