No global negative feedback

LOL

 

Hi,

You could probably just "pull" the capacitor off by force, they come apart and then just remove all the littlke bits they leave behind.

No Volume control range? Having to use the Volume control where it sounds worst, excessive noise....

They are survivable, I mean JC Verdier uses them, but you can do better.

Great. Triode usually sounds much better.

Actually, in Riga you should find an old TV Repair guy who learned his trade under the communists, he should be able to do this easily for you.

Ciao T

 

I will do that as soon as I get home tonight, then report back, thanks...

Will look for the old repair guy when I feel another incontrolable urge to upgrade...

 

Hi,

Just to be clear, I am suggesting to BREAK the capacitor apart (the metal can comes off easily) and to then remove the other bits from the pcb untill you are left with the bare wires out of the capacitor, which cut away. Sounds much more violent as it is.

Ciao T

 

I did exactely that, made sure no bits of wire stayed in the amplifier, connected, and...

There is a lot more crackling noise from both channels, and some hummm only from the right channel...

It is not loud enough to disrupt music listening, but it is much louder than the very slight schhh I had before...

 

Christ if you have to smash it to bits and rip out half it's guts, you have to wonder whether the designer knew anything about audio. Chinese?

I'd sell it and get a decent pair of 300b parallel SE mono's myself.

 

Hi,

The hum indicates a valve with poor Heather/Cathode insualtion (a 12AT7/ECC81) as these valves are run on AC Heaters. Not sure about the "crackling" noise though. It may be again feedthrough from the heaters.

You can get a pair of Elna Silmic or Elna Cerafine 330uF/16V Electrolytics and solder them across the whole of R3 & R4 together, to restore the original condition without too much work.

What are you using as Preamplifier?

Ciao T

 

As I said before, to remove the CAPs properly I would have to remove the PCB, and I didnt want to do that...

Do you think I you be doing this on an expensive amplifier...

I am going to rotate the E81CCs to see if the hummm changes too...

I am using a Linn Unidisc SC player/processor...

 

Hi,

Yup. It is a common failing in these older valves I noticed.

I hope this does not use a digital volume control.

You may find a "passive" preamp using suitable quality components to work better....

Ciao T

PS, I have been interrested in the Classic Range of Amp's, may get one just to fool around....

 

I moved the E81CCs from one side to the other, it seems like the hummm is gone, maybe one was not properly inserted...

The crackle continues, I dont hear it unless I am 1 meter or less from the driver, but it is louder than before...

My friend says that the CAP was filtering AC, now it all is amplified...

 

My friend say they seem to know what they are doing, that they didnt use the cheapest solutions, for instance they use 2 transformer windings and 2 diodes instead of the common cheap bridge solution, 2 times, bridge only for accessories...

 

all he has to do is to walk into radio riga technical dept and just ask for a contact with any of the technicans over 55-60.

this is peanuts for them.

just as a hint to what can be expected, here is what is being now built by a retired engineer from radio belgrade (ignore the language):
http://www.tubeaudiolab.co.yu/index.html

jean hiraga raved about his 6L6 PP amp in revue de son:http://www.tubeaudiolab.co.yu/hiragatest.html

 

Tube CAD simulation of the input 12AT7 Totem Pole Amplifier, with and without the input CAP:

Gain: 33.1db - 28.1db, decrease 5db, almost same as NFB

Z Output (Impedance?): 2.79k - 6.54k

Freq -3db high: 93.7khz - 166khz

Vth: 0.33v - 1.38v, apparentely the highest the better, whatever it means...

Listening impressions, obvious differences:

- More noise, before couldnt hear 1 meter away from the speaker, now can hear it up to 1 meter, aligned with the wizzer cone, if I raise my head I dont hear it even close to the speaker, probably not bad for tubes and 96db speakers...

- Frequency balance tilted down, apparent less highs, more bass...

- Less "damping", bass and precurssion not as sharp, like when you do a tweak wich limits high freq output, sound appears slower, less lively, but many times it is just less distortion...

Timbre didnt change significantely, midrange sounds very full and natural, silky highs with all the detail...

Suggestions, please...

 

I tried to find out if it uses a digital volume control, but couldnt...

The Linn is not perfect, but I dont hear it changing the sound significantely, and I "need" DAC and bass management for external sources too, without many boxes and cables, so it is the best compromise I could find...

 

Some of those amps look interesting. Have you listened to any of them? Are prices shown on the site, I can't tell!

 

Likely to be power supply linked. Zero NFB. Triode. SE. Cheap PSU. Equals noise.

Less Bandwidth. The designer probably saved money on the OPT knowing he could use NFB. If you want bandwidth in a SET my understanding is you need some very good iron. Could also be linked to the increase in output impedence and the amp's interaction with the reactive load your speaker presents - now that you have no feedback to protect it.

Increase in output impedence leading to lack of damping and loss of control. An underdamped loudspeaker is like a poor vented bass box. Slow and ponderous.

Is that worth the other limitations that are now ruthlessly exposed by the loss of the NFB loop?

Yep. Put all the bits back, Sell the amp to someone in Riga without a wife, and buy a decent set of amps designed to run zero NFB. Sorry but that's the obvious conclusion.

 

It was already withou NFB, before I removed this CAP, so most of your post is nothing more than childish, not relevant, "I told you so"...

If you read the CAD simulation you will see that bandwidth actually increased to almost double...

The only semi-valid comment you make is about less damping probably caused by impedance increase...

As for your suggestions, I will gladly accept your offer of a decent set of amps designed to run zero NFB...

The OPT specs look pretty good...

 

Hey. Do what you want Antonio - it's not my problem. I was merely pointing out what I know from experience. I'd love to know how the removal of a NFB loop increases bandwidth.

Amp designers typically build the best sounding amps they can to a budget. It is unlikely they will actually add components if they are not essential to the proper operation of that unit, as otherwise they can make something that sounds better for less money. Think about it. Or maybe don't . As I say - it's not my problem.

 

The removal of an input CAP increased bandwidth, not the removal of the NFB loop, read before you post...

 

Well it makes no difference if the amplifier itself no longer has sufficient bandwidth because of no feedback loop and a cheap OPT does it?

The two main issues with SET's are power supply noise and bandwidth limitations. Designers use NFB to get around those issues. Yours did. it's a cheap way to reduce those issues - the other methods are expensive - like using massive air gap output transformers and heavily overbuilt power supplies. Given that your amp is a hybrid switchable between ultra linear and triode, I very much doubt enough attention was paid to these design criteria for use without NFB.

You don't want to hear that of course. That's fine.