6922

[lohk]

[QUOTE]Originally posted by dice45
[B]Klaus,

did you consider to use the ECC88 as a choke-loaded common-cathode stage?
Provided the signal level is not too high (the tube usually had -1.3 V bias only)
this could work well, but then you have gain 33. For a juicy linestage, i would rather choose a 5687 and an step-down output transformator. Like the pa102 from Simon Shilton. Or a 12B4A ....

Bernhard,

do you have any schematics ready ?
How do I calculate a choke loaded stage ?

Klaus

[dice45]

Klaus,
for a schematic see cheapskates transformer-coupled linestage on Manfred Huber's webpage.
Replace the Talema toroidal trannie by the Shilton pa102 and also replace SS rectification by a decent vacuum diode rectification and there you are. imagehifi raved about a Euro 9000.- British linestage built like this, and i rave about it too, that is the preamp i am currently using, Manfred lent it to me.

Calculation of transformer primary or choke size:
f = r_p / (2*pi*L)
with f being -3dB frequency, L the load inductance and r_p the plate resistance (Innenwiderstand).
our tube has, say, r_p = 1k and the choke has 50H, our -3dB point of the choke-loaded stage is at 3.18Hz; above the stage gain is equivalent to the tube's µ (open loop gain).
An anode choke has to have the same quality as signal transfomers have to have. No point in using PS or swinging chokes. Magnequest, Shilton and Lundahl sell chokes usable as anode chokes. I use Lundahl.

Frank,
i do not use the same stage topology as Selbstzweck (end-in itself), it came out of design considerations. I wanted to get rid of coupling caps, knowing how even the best mess up the sonics. Choke loaded long-tailed pairs have the beauty that AC-wise, they are DC-coupled and high-z towards the PS. DC-wise lower bandwidth is limited by choke size and they are low-Z towards the PS. So if separate PS( voltage)s are used for the stages, stage n's PS voltage determines stage n+1's grid bias voltage and it does so rock-solid, low-Z, without drift. Quite soothing in a DC-coupled amp.
Now the only cause for the amp stages so sit in the corner and not at desired operating point is 1) warmup-effects and 2) tube parameter imbalance (caused by poor matching or by aging of the tubes). So each stage n has a small variable resistor in series with the one of the chokes to balance stage n+1. Has to be done regularly.

[dice45]

Torben,
folowed your link, went into my bookmarks, thanxalot!

I found the L'Audiophile LeTube in it.

to all tube newbies and those planning an integrated tube amp:
the LeTube preamp is incapable of driving nasty loads and/or legnthy and/or highly capacitive interconnects.
As preamp section of an integrated tube amp it is breathtakingly good and simple to implement. Sonics are a blast, just incredible.

I build one once for a friend and tweaked it a bit, non-magnetic resistors and Roederstein MKP 1841 shunted with 1n of mica as coupling cap.

Be aware that RIAA is deviant in the 20 Hz region and it varies with tube aging and change. But then .. who cares, such sonics considered.

High PS voltage: could be seroiusly reduced by replacing the anode resistors by CCSs. Without sonic punishment IMO.

[marjan]

Frank
I understand. Since PS you presented doesn`t reqire some enormes cost to build, and there is no need for any dramatic changes in the basic circuit, I`ll try boath versions of plate load reg. I`m interested what should I do to implement const.cour.sourse using n-fet in original Hampton PS if posible. (BTW sorry about those newbi quest`s, but two years ago I couldn`t tell the diference betwin cap and resistor on a shematic--today my DIY aleph`s and my el34 int.amp are working just fine so, I`m lerning)
What is your sugestion regarding transformers for this kind of aplication, EI, toroid...?

regards Marijan

[fdegrove]

Hello Marjan,

Re yr questions,

Personally I prefer EI core trannies although in case you build the circuit in the same box as the psu toroid will have less stray inductance and would induce less hum.
The Hampton circuit should be built as it is,it would require a complete rethinking job to implement a ccs.
As I mentioned before:I try to keep it simple,there's is no point in going overboard in adding things for the sake of it.
BTW the fets will require some selection for equal idss,the voltage drop should be about 1 V across them,variations will lead to slightly (but audible) differences in gain between channels.
If you have access to a good tube tester select your ECC88's for close matching between channels.
Also if anything will ever die in this circuit it will most likely be the Fets:they are sensitive to heating up too long with a soldering iron.(I speak from experience when experimenting with different coupling caps so be forewarned.)
Anyway this is my personal point of view,others may differ.
Feel free to experiment.
Pls.do not apologise for being a newbie to this.We all started somewhere along the same lines.

Rgds,

[fdegrove]

Hello Bernhard,

This maybe beside the point but still:

-As I understand it your circuit topology requires the user to adjust for drift on a regular basis.I think this is Ok for someone like yourself but surely unacceptable (no offense ) for the everyday user ?

-What I don't understand though is that you try to regulate the PSU on a preamp where hardly any current is flowing.For a choke to regulate sufficient currentflow is required,too much of it and it will swing and saturate it's core.Am I missing something here ?

-My approach to the problem is active valve regulation on a per stage/channel basis : series pass device/comparator/voltage reference tube.
When implemented correctly this is rock solid and has low Z.

-Ok,so you need to adjust things after switch on probably because the tubes need their cathodes to reach operating temperature.If this is the case you're very likely to damage the tubes.
One solution would be to use a valve rectifier EZ81 style and in case you argue about the sonic impact you can still get around it by a timer such as a N555 which would trigger a nasty rectifier bridge once operating voltage have stabilized ?
Active regulation with valves would also give you a slow and natural ramp up of B+.
Most people don't realise this but most components get killed at switch on,valves are even more prone to damage since they depend on their cathodes to operate.If one doesn't respect this cathode "stripping" will occur.

To Torben and Bernhard,

" found the L'Audiophile LeTube in it."

Having lived the haydays of "L'Audiophile" I can add just this :
"Le tube" is a shake and mix of the Dynaco PAS 3 and the Marantz 7C .Not to say it has no merit BUT : it has high output Z so long capacitive (all are by nature) interconnects are a definite "nono" and moreover RIAA correction is not accurate at all and will vary with ageing tubes (Global NFB).
One can circumvent the output impedance by addding a White cathode follower using ECC82 or better still a 12BH7.If you want to keep things really small a pair of 12DW7's would do the trick.
Anyone having compactrons ?
Still it would be a nice starting point for any audiophile with MM cartidge setup and a tight budget.

Let it be understood that I really don't want to step on anyones toes here,just trying to inform.

Keep up the good work,

[analog_sa]

Hi

Does this bring back memories? About 17 years ago i spend quite some time struggling with an ECC88 based step-up. Briefly tried paralleling, but the loss in ambience was not worth the minor s/n gain. Also tried all kinds of active current sources and although they all sounded dynamic and hifiyish at the end settled for tantalum resistors. Anode power came from a string of nicads, everything else sounded like a very poor compromise. I think around 36v. It sounded fairly decent. My only regret being, not having plate chokes to try - today i really love choke loaded line and driver stages.

peter

[dice45]

Frank,
i intended to feed each stage on each channel with a separate shunt reg.

1st stage: 2x EC8010 or 5842, 2x 25mA
2nd stage: 2x 12A4 2x 23mA or 2x 5842, 2x 25 mA
3rd stage: 2x 12B4, 2x 34mA.
I would not call that close to zero current. 164mA per channel, would quite a beast of a shuntreg and then, how do i get each stage's B+ where i want it for DC-coupling.
Better separate regs. And no interstage crosstalk via the PS. And i have the only really expensive thing of those shunt regs already: MKV caps to sit on. I have 120 or so.

Rectifiers will be a quad of fat TV damper diodes like the 6CM3. A Graetz bridge of them will deliver 800mA. That will do.
You point with the heatup are well taken.
I like soft start provided by tube rectifiers and i lave the absence of garbage injected by SS recitifiers in maplifier and wall outlet.

Manual balancing could also be done by a µC and cheap stepper motors. IN the future. But i will have to try out 1st how much imbalance this preamp takes. And how this develops with tube aging.
This is a preamp with DC-coupling over 3 stages and adjsting ablace from time to time will be a small price for that. Dunno if i get this product of insanity running at all, but if i succeed, i will not complain about adjusting the balance now and then.

[lohk]

any comments about this hybrid SRPP circuit ?
Does anybody know more about the ominous "solid source" ?

[gromanswe2]

Originally posted by marjan
I need low noise (as low as possible) 6922/ECC88/6DJ8 double triode for use in MC step up modul. Any recomendation based on expirience with this tube. Whitch one should be the best for that purpouse?
rgds Marijan

What I have found out, just by reading audio tube stuff (be warned, I have not listened to the tube. I gave up listening to my trasistors as well, I couldn't hear a thing)
ECC88 is the most interesting double triode I know of.

It can use and deliver somewhat more current,
and can also be used with a little lower anode voltage
than other triodes.

So if chosing a triode for preamplifiers or even
headphone amplifiers, ECC88/6922 is HIGH on my list.
You can even parallell 2 of them at the output
give more current out.

An alternative for me would be EF86 in TRIODE mode.
It is a penthode with good performance.

That is about what I've learned READING about tubes, so far.
I'll come back if I become any wiser regarding this
special subject in audio circuit design.