• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

basic e88cc line stage ?

Status
Not open for further replies.
Jump to Latest
#61
I can offer you my impressions. I've tried both choke loading and transformer loading, both sound a lot better than resistor/active loads. Of course with choke loading you still have a capacitor to deal with so this may not be such a clean 'iron' solution. First of all the sound is a lot easier to listen to, with better dynamics and detail, yet quite mellow. The music gets a whole lot of new life and energy. Transformer quality is paramount if you want the frequency extremes to be as convincing as the mids though. Lundahl 1660 seems to be the very least worth using. Of course if you want to invest more seriously nothing beats some high nickel content. A friend swears by his amorhous alloy cores but i probably prefer nickel. Keep in mind this stuff is dangerous. Very addictive and once you try it you crave better and better cores. Very unlikely you'd be going back to capacitors.

cheers

peter
 
#62
A MATTER OF SEMANTICS?

Hi,

I've tried both choke loading and transformer loading
Click to expand...

Transformer loading?
Do you mean just for the outputstage?
To me a choke is iron cored by definition.

choke loading you still have a capacitor
Click to expand...

I've never seen it done like that...can anyone explain?
You're suggesting a parafeed?

I'm confused here.

Transformer quality is paramount
Click to expand...

Sure,the transformer's weaknesses are always the frequency extremes.

Very unlikely you'd be going back to capacitors
Click to expand...

When I read the BG hype I start to think no xformer will ever meet this kind of bandwidth.
And you were referring as coupling caps I presume?

Sorry,Peter,no offense but I'm confused by your post.

Cheers,😉
 
#63
Thanks Peter, I'm not confused at all.


Frank,
Have a look at the link I posted earlier on this thread, that's transformed coupled, plus meaning you get an output (secondary coil) you can use for unbalanced or balanced connection (when a center tap is present) to your amp. Sans (output) capacitor.
 
#64
analog_sa said:
Lundahl 1660 seems to be the very least worth using.
Click to expand...

Checked Lundahl LL1660, there is a way to connect it for a 4.5:1 , no center tap provision though for this setup and max 16 mA. Its workable as you said and guess much cheaper than Bartolucci.

I'm looking for a Bartolucci distributor on the US (if there is one) to check prices. I remember that Angela Instruments had some B trannies, I'l look at that.
 
#65
apassgear said:
I'm looking for a Bartolucci distributor on the US (if there is one) to check prices. I remember that Angela Instruments had some B trannies, I'l look at that.
Click to expand...
If you can't find a US distributor, and I don't think there is one from reports I recall reading on other forums, try <a href="http://www.audiokit.it/ENG/Frames/Introduction1.htm">Audiokit in Italy</a>. The other option is to get Jack Elliano at <a href="http://www.electraprint.com/">Electrprint</a> to make you what you want if he doesn't already have one on hs catalogue. NB: I have no experience with Electraprint trans', just going on reputation.
For advice on Lundahl trans, Kevin Carter of K and K Audio (US Lunahl distributor) has a <a href="http://www.audioasylum.com/forums/KandK/bbs.html">forum.</a>

Cheers
 
#70
Yes, Lundahl LL1660 fits the bill for a max 16 mA stage (ECC88 which isn't the best aproach since it has 2/3K RP), though no CT for a balanced output. For the moment I use an Aleph 4 and would like this provision.

As mentioned before I have a pair of 417A's which are the first pick for the Euridice preamp (actually bought them for this purpose) and run best at 20/25 mA.

Did a search on the net and found the following alternatives and prices for ready made trannies for this application:

- Megahertz TL311-Q $210 (Euros) ea. (Audiokit). Originaly used by Ciro Marzio.

- Two options from Bartolucci (www.triodes.nl)
Size M3, 5000 Ohms Prim., 50 mA, 40H $191 ea.
Size M2, 7000 Ohms Prim., 26 mA, 100H $143 ea. I think these are the ones used by Thorsten Loesch for the two Euridice's he made.

- Lundahl LL1660 $71 (Euros I guess).

Even though Bartolucci M2's double the price of Lundahl's these are better suited for the 417A's. Both Bartolucci's have CT.

Think I'l go for the B M2's. Maybe Santa will bring them tonight!

Thank guys for all the input and Merry Chistmas!
 
#71
apassgear said:


I was looking forward to some comments on sound in comparison to a line stage without a coil loaded plate or what are the benefits of this type of loading.
Click to expand...
Describing the intrinsic sound of a particular circuit is really hard, and depends on a lot of variables, but lets just say, when implemented well, it can be very, very good.

Using a transformer as the output allows you to get several advantages over other topologies. Firstly, just like a choke load, it allows you to get the conflicting requirements of decent Ia for the tube (IME 1/3 to 1/2 Ia cont sounds best, for all tubes), high load impedance and sensible supply voltage. For example a resistive loaded 6SN7, with Va=200V and Ia=8mA, and a load of 10x Rp would need a B+ of about 900V. With the same operating conditions, using a choke or OT the B+ is a more reasonable ~220V and with quality iron, the load impedance seen by the tube will be as good or better than the R loaded example. The output impedance of the resitively loaded stage described would be 7k6 (Rk bypassed) or 18k8 (Rk unbypassed) with gains of 19.6 / 26dB and 16.7 / 24.5dB respectively.
In both the bypassed and unbypassed examples, the gain is generally too high for a line stage, as a CDP puts out 2Vrms and most poweramps need 1Vrms for full power, so the gain is usually wasted away in an attenuator somewhere. Lowering the Rl will reduce the o/p Z somewhat, and the gain too, but also increase the distortion. There might be a compromise you're happy with here, but....
An output RC network is required.

With choke loading the choke and the next stage load are in parallel, reducing the load seen by the tube. Using choke loading the gain approaches mu, or about 21.5 / 26.7dB, and the Zout as basically Rp or 8k4 either bypassed or unbypassed. (some approximations made here). Chokes are reactive components and the load presented to the plate will vary a bit with frequency. Not too much of an issue in well designed chokes.
As with resistive loading, an RC output network is required.

With OT loading, the turns ratio of the transformer multiplies the impedance of the next stage load by the square of the TR or 11.7. The o/p Z of the stage will be roughly 1/11.7 Rp (720R), and there is full galvanic isolation between the pre and power, so no earth currents pass between stages. Gain will be 1.85 / 5.3dB which is much more useful, and the reflected load of even a low input Z amp like the 10k Aleph will be nearly 120k, or 14x better than R loded stage would give. If you use the CT on the trans you can have balanced output too.
NB: for a 5842, the Zout will be 1/5 the 6SN7 example and the gain about twice. I did all the calcs for the SN7, before realising I had the 5842 datasheet on this PC.

One last type of topology is parafeed, or parallel feed. It uses the choke loaded stage, which then has the transformer connected between plate and groung, through a cap. Gain and o/p Z are about the same as for the OT setup, but the OPT can be better optimised for signal performance, as it doesn't have DC current flowing through it. The choke and the OPT must be equal *quality*. Disadvantages are two expensive lumps of iron, size, a series cap, weight and two reactances to deal with. The choke can also be replaced with a CCS.
There are lots of proponents of parafeed for it's sonic properties, and I use this topology with a CCS and a transformer volume control in my preamp.

Cheers
 
#72
Brett said:
...the gain is generally too high for a line stage, as a CDP puts out 2Vrms
Click to expand...

That's a maximum value. All cd's do not put out 2V RMS. Most are half that or less, especially older discs from the 80's and early 90's. I have plenty of discs that definitely need gain. It's foolish to build a pre or poweramp with unity gain in any case.
 
#73
Joel said:


That's a maximum value. All cd's do not put out 2V RMS. Most are half that or less, especially older discs from the 80's and early 90's. I have plenty of discs that definitely need gain. It's foolish to build a pre or poweramp with unity gain in any case.
Click to expand...
True the 2V is the Redbook standard for 0dBFS.
Many newer discs run quite hard up against this from what I've measured, although like you say, lots of older discs from the 80's are mastered much lower (and sound the worse for it).

As for it being foolish to have unity gain preamps, 2 points come to mind. First, I never said any such thing. With the Euridice you will get a gain of about 12dB, combined with the 6dB excess you have for Redbook over the average sensitivity of most poweramps (about 1V for full power). Second, you can't know whether the gain is required until you know the gain structure of a particlar system, speaker sensitivity/amp power, average and peak listening levels etc. IME there are plenty of systems out there that burn up 40dB of gain at average listening levels because of too many stages in the system, which is not good for either noise, distortion or resolution.

Cheers
 
#74
Originally posted by Brett

There are lots of proponents of parafeed for it's sonic properties, and I use this topology with a CCS and a transformer volume control in my preamp.
Click to expand...

Just to keep things in balance there are also opponents to parafeed. It's very, very tempting on paper, allowing cheaper/better transformer to be used but it does bring back the dreaded cap. I tried and didn't like the sound.

cheers

peter
 
#75
analog_sa said:
Just to keep things in balance there are also opponents to parafeed. It's very, very tempting on paper, allowing cheaper/better transformer to be used but it does bring back the dreaded cap. I tried and didn't like the sound.
Click to expand...
I never said I liked it particularly, or that it was <i>a good thing.</i> I also mentioned the cap.

My TVCs can't take any DC current or voltage, so parafeed is the only way they'll work. But they're soooo good it's worth it.

Cheers
 
#76
Good Reading - to sort you out

I'd rather consider this article.

It sums it up better then this rather
confusing thread, in which
one doesn'y know who to believe in. :bawling: 😕 😕

THE SUITABILITY OF THE 6DJ8 FOR AUDIO

About The Author

Roger Modjeski received a BS in Electrical Engineering in 1973 from the University of Virginia and was a teaching assistant while studying for his Masters at Stanford in 1975. He has been active in electronics since the age of five watching his dad build a Heathkit Williamson. Prior to starting Ram Tube Works and Music Reference in 1980, he opened a high-end retail store where he met and later worked for Harold Beveridge. His other interests are music theory, piano, singing, building musical instruments, solar energy, architecture, and understanding how things work.

This article attempts to correct a few misconceptions about some of the popular dual triodes used in audio amplification. Through my work developing and running the computer tube tester at Ram Tube Works, I’ve evaluated dozens of each type, from every manufacturer currently in production and many of the classics. I have developed circuits for both home audio and musical instruments. I keep a little collection of these classics to test whether my equipment works with both old and new tubes.

The guitar player seeks to add pleasant distortion, whereas the home audio listener generally requires none. Remember that the solo player can use distortion to enhance that instrument. Yet the same distortion, added again, destroys the reproduction of such a recording.
Click to expand...

/halojoy - do not take all he read all to serious
 
#79
halo,

Thanks for pointing out an interesting article.
Apart from a couple of minor differences of opinion, there is little in there that is different from what's been posted in this thread. For instance, I respect RM's opinion about the max allowable Pa for a 6DJ8, but I've found they sound better at higher currents, and have yet to burn one out. Manufacturers have different priorities and responsibilities than DIYers too, so we can make performance trade off that a manufacturer can't afford to.
 
#80
analog_sa said:
You may have mentioned this before, but what kind of TVC are you using? The relatively high price of S&B has made me desist so far but i really am curious. What amount of dc current do yours take? None at all?
Click to expand...
Hi Peter,

I have the S&B TX1022's (ie 102 mk2). They don't take any DC current at all and aren't even allowed to have a voltage potentiol of any significance across the primary due to the thin insulation layers. I had several long emails with Thorsten about this around the time I bought them.

They are expensive, but a good stepped atten isn't cheap either, esp with decent resistors and a ladder configuration. The 1022's were cheaper then a Shallco switch and Holcos for a balanced ladder atten.

Have you read the app note at the S&B page? It was originally based on a long post by TL on another site, and explains the benefits better than I can.

Cheers
 
Status
Not open for further replies.
Top Bottom