[jeffreybehr]

My hybrid poweramp, a c-j ET250S...



...has too much gain; I could do with maybe 10dB less.  Can I do that with a tube change?  I have a vague recollection (I know NOTHING about tube engineering) that the 6FQ7 is a possibility; I see that it's pin compatible.

[S Clark]

What about PCC88/7dj8?

[sfox7076]

Since it is indirectly heated, the 1 volt drop in heater voltage likely won’t change things very much. 

[musicdre]

in my experience there is no significant (if any) drop in gain from 7dj8 compared to 6dj8.   

7dj8s are often recommended as longer-lived replacements for 6dj8s in tube-eating preamps like audible illusions.

[Nick77]

Since it is indirectly heated, the 1 volt drop in heater voltage likely won’t change things very much.

I use PCC88 tubes and I do believe there is a drop in overall dB, but its fairly low as mentioned.

[avahifi]

In general, the closed loop gain of a vacuum tube preamp or power amp is set by the feedback circuits.  The tube open loop gain less the fixed feedback attenuation sets the closed loop gain and the amount of feedback.

Thus changing to a lower gain tube than the what the circuit was designed for does not lower the gain of the overall circuit.  It just decreases the feedback and increases overall harmonic distortion.  This is the reason why older units can eventually start to sound pretty muddy.  Aged tubes have less gain so feedback goes down and the THD goes up.

So, in general, don't second guess the amplifier’s designer unless you actually know what the circuit is doing.

If the device is a true no feedback design, running open loop, then changing a tube will change the overall gain, but then you better very carefully select matched tubes or the channel to channel balance will be all over the place.

Frank

[Photon46]

Out of curiosity, what do you mean by "the amp has too much gain." Do you have an issue with a mismatch between source or preamp because of too much gain or what?

[RPM123]

Your best option may be to try a set of these if you don't mind a 12db reduction.

https://www.parts-express.com/harrison-labs-12-db-rca-line-level-audio-attenuator-pair--266-244

[jeffreybehr]

Out of curiosity, what do you mean by "the amp has too much gain." Do you have an issue with a mismatch between source or preamp because of too much gain or what?

The problem I had was the use of a normal-too-high-gain poweramp with a highly sensitive speaker, that being a 96dB Serenity Super-7.. The poweramp is long gone; the S7s are back in my system, driven by Atma-Sphere M-60s.

[FullRangeMan]

Low gain? its the 6n1P:
https://www.gstube.com/catalog/?key=6n1p&submit=Find

[poseidonsvoice]

Jeff,

Can you confirm that you have now solved your problem since it looks like this old thread was resurrected? It looks like you have. I am not sure that it is/was clear to FRM.

FRM,

The mu or amplification factor of a 6922 and 6N1P are essentially the same, it is around 33 to 35. So the 6N1P is not a low gain version of the 6922. Moreover, there are much greater differences between the two tube types, particularly in the dynamic plate resistance. The output Z of the 6N1P can be up to 3 times higher. They are different tubes, with different operating characteristics and parameters.

Best,
Anand.

[Tyson]

Yeah, the best thing is to get a low gain amp if you have high efficiency speakers.  My current amps are pretty low gain - the Dennis Had Inspire MB12 monoblocks and the TAL Korneff 45.  I do have a higher gain amp on my upstairs speakers (Almarro a318b), but it's also quiet after I took it to my friend Mike to work his magic. 

Efficient speakers are great, but they will uncover a whole host of noise issues that are buried by most other speakers. 

[avahifi]

Note that the 6N1P tube pulls twice the heater current than the 6922 tubes which might cause problems for equipment not designed for that.

Frsnk

[FullRangeMan]

Hi Anand,
In this case try the 6CG7 gain=20:
http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6CG7.pdf

Also in the Russian stocks there is the 6n6p gain=22 very linear tube.
http://www.mif.pg.gda.pl/homepages/frank/sheets/113/6/6N6P.pdf

http://www.gstube.com/catalog/?key=6n6p&submit=Find

Do you mean say 6n1p is not a substitute in this CJ amp?
I ask why its a sub recommended in some Decware amps.
http://www.decware.com/newsite/SE34I.htm
A 6N2P is a higher gain input tube that's kind of fun to have since it will sound completely different than the stock 6N1P/6922 compliment.  When the option is selected, you get both the stock 6N1P and a 6N2P for each channel.

[jeffreybehr]

Jeffrey,
Can you confirm that you have now solved your problem since it looks as if this old thread was resurrected? It looks as if you have. I am not sure that it is/was clear to FRM.

...

Best, Anand.

Yes, problem solved by selling the amp.  I'm now back to using the Super-7s...
https://www.audiocircle.com/index.php?topic=141060.0
...and Atma-Sphere OTLs,  model M-60/3.3 Imp.  Altho A-S offers a tube-substitution plug that eliminates the Voltage-gain 'top' of the cascode and about 20dB of gain, I'm not using them; the '60s seem to have just the right slightly-below-average gain.



And WOW does this system sound fabulous.               

FWIW, I believe that poweramps, generally, have too much gain, which results in magnifying too much noise preceding them in the signal chain.

[FullRangeMan]

You was not using a preamp?

[jeffreybehr]

You was (sic) not using a preamp?

I was and I am.

[FullRangeMan]

I was and I am.

The preamp volume control didnt solved the prob?

[Steve]

FWIW, I believe that poweramps, generally, have too much gain, which results in magnifying too much noise preceding them in the signal chain.

Very wise words Jeff. Too much gain and noise/hum to consider. The preamplifier has to handle different inputs. Simply using a selector switch and volume control (transformer types as well) is just not optimum by any means. One either loses highs, bass, or both, ringing etc. 

We have two problems. The source only needs to typically supply 1 volt signal, even 0,5 volts is ok. The digital player typically has an analog stage with a gain of 2, or 6db, and is worth about $1.50. There is no need for it. The 2 volt standard is ridiculous, 1 volt is plenty, and eliminating the stage improves the musical experience. Who doesn't want that. Simply increase the volume control. That is what it is there for.

As Jeff correctly mentions, most of the time the amplifiers also have way too much gain. Design for less gain/stages.

The best solution, imo, that eliminates stages (and should improve fidelity) is to rid the digital player's 6db analog gain stage, as well as rid of the amplifier of a stage if possible. Use the proper preamplifier with selector, volume control; increasing the volume control's usable range.

My system has a modified cd player with 1 volt output (no analog stage of 6 db gain). My preamp has 20 db of gain. My monoblocks are only two stage, with 16 db of gain. My volume control is usually set around noon to 1 o'clock.

cheers

steve

[Elizabeth]

I have never understood the fail of CD players using professional standard of 2 volts, instead of consumer standard 0.5 volts. Then compounding the problem, most preamp manufacturers have never adjusted the gain to fix the problem.
What the should have done, was lower the gain of both amp and preamp, and raised the ouput of other devices, like phono preamps to 2 volt back in the mid 1980s.. would have solved the problem. 
I too have 'too much gain'. But I just accept it.