Tube Pre-amp (1 Viewer)

[Michael R Price]

I guess I'm in an inquisitive mood today...

Well, if a tubed piece of electronics can make your system sound that much better, isn't the ideal setup to have an all tubed system and live with the compromises? Does the preamp or the amplifier generate more distortion that we need to worry about? See, I'm not sure that these improvements are caused by the use of tubes intrinsically. Would a really good solid state preamp have a similar effect?

 

[Amir]

Hey! seems like there are some guys here that know a bit about tubes. Any suggestions for tube rolling for Conrad Johnson PV14L which is 6C4, or EC90 etc. tube. The goal is maybe a bit warmer, richer, heavier sound. Current system seems to be a bit bright a too much sibilance for my taste. Thank you..
I posted on the TubeAsylum but didn't get any reply.
By the way Michael, we live in the same town!
Regard
Amir

 

[Amir]

Michael, your point could be correct but I had an experience with my system that proved otherwise. I have a Denon reciver using it with Parasound amp and was not happy with is as a pre then I bought the CJ14L and for home theater I use the unity gain. That means it is not pass through but a buffer. to my astonishment the sound of Denon "improves" going through the CJ! Tube do "color" and I like the coloring!
Amir

PS. I use a pair of Rogue Magnum M120 now - still love the parasoud and have it!

 

[Chu Gai]

Well Yogi, discussions of phase errors/shifts certainly require going into a lot of detail. Just to touch upon one aspect one can have a phase shift that's linear phase. That amounts to basically a delay. So long as this shift is happening in both channels it's inaudible. A real life example of that is moving forward and back from the speaker. Audible issues can occur when it's non-linear and contained within a narrow band. But even that depends on a lot of things such as the signal's energy. That's something you might heard if the signals had many transients. Maybe someday we'll touch upon this more deeply. Personally though, I don't see this is as an issue to be concerned about.

BTW, Yogi, have any of the changes you've made resulted in an elimination of that hum? Now I'm gonna ask a real stupid question here. The parts you replaced...did you measure either their resistance and/or capacitance? I'll have to dig a bit into the spec's of what you've got there to get a handle as to what's going on.

Michael...

Would a really good solid state preamp have a similar effect?

Well if we define good by meaning a low output impedance and inaudible distortion...flat frequency response and all that, then I don't think you'd have better than a 50/50 chance of discerning it from a tube based unit with similar performace specifications.

Amir: assuming what you're hearing is not a result of the recording, have you taken a look at your room and/or speaker placements? Maybe you need a little less top end and a tone control would do the trick.

 

[Amir]

Chu, the speaker placement with Denon only and with CJ in the loop was the same. The character of the sound, the position of the voices (height) the sound staging, the debth and width of the sound stage changes drastically with the CJ. The biggest change to the system was adding the tube CJ adding the Rogue power amps instead of the Parasound enhanced the focus, made instruments "richer" in harmonics, a bettered the sound stage but to smaller extent than the CJ. I never did try to take out the CJ and see the effect. Maybe I will try it. But for now I rather listen than tweak.
Amir

 

[Yogi]

Chu the hum is almost gone now. The most significant difference came from shielding the transformer with mu-metal. Its a non issue now. I didnt measure the capacitance or resistance of any of the components. I just made sure they were of the same exact specification as the components I replaced with the exception of Caps that were rated at a higher working voltage. I am sure the resistances and capacitances of some of the components must be slightly different esp the resistance of the silver wire compared to Cu wire. Also the Cap leakage currents must be different. But in all the changes seemed to have affected the sound in a positive way, so I am happy. Also it is to be expected that some of these impedance values of various components should change other wise whats the point of changing components if all their measured values were to be the same. You would get the same sound before and after the change wouldn't you?

Michael, I dont know if I were to build a SS preamp with the same part quality that it would sound the same as the tube one I have now. I would expect them to be the same if tubes and SS devices had the same electrical characteristics. But they dont, I think. Also certain design criteria have to change in incorporating a SS device instead of a Tube device in the circuit. So that in itself would cause some difference in sound, I would think. I dont know enough about tubes to make a judgement.

Even with all things being equal, I think the tubes have more appeal since their sound can be changed by going to a different tube, when all you are doing is changing the FR of the circuit and perhaps getting some favourable coloration in a certain band of the freq spectrum that might appeal to you like rolling off the highs or boosting the mid band etc. For the eternal tweaker in me this is a big enough incentive to go with tubes, plus I like the glow of tubes in dark.

 

[Chu Gai]

Thank god that hum's gone Yogi. Nothing worse than throwning good money after bad. Kind of like bringin a girl home that used to work at the Chicken Ranch, buying her new clothes and thinkin that you're special, then finding out she's still works at the Ranch. No, it's not a personal story!
Well if you haven't thrown the replaced parts out and have the means to do so, it'd be informative to determine what their values were. An example. Electrolytic caps can and do lose their capacitance. That's a function of manufacturing, age, and heat. Quite often what happens Yogi, is that a change in a cap really does result in improved performance, but it's not really that the performance has improved rather that it's been restored. Perhaps an issue of semantics. Send them over to Brett. He just recently score a snazzy little multimeter with a few bells and whistles.

 

[Brett DiMichele]

Chu,

I will accept any and all capacitors but I would prefer if
someone sent me the following.. Jensen, Auricap,AudioCap,
Solen etc

 

[Yogi]

Brett, how about Benning, Jackon electrolytic and multicaps?

 

[Michael R Price]

Yeah, but these handheld multimeters only go up to 20uf or something so they don't help with electrolytics (unless Brett got a really good one). I got some cheap foreign made one that measures to 0.1mv precision, temperature, capacitance, and the gain (hFe) of transistors for $35. You need a fancy piece of equipment to measure big capacitors... also, I think a lot of big capacitors actually have more capacitance than their rating, (tolerance is +75/-10 %), so that even when they start to get old they have a decent amount of storage.

Sorry for asking all those questions, as I don't feel qualified to discuss the differences in various preamps (especially tube since I've never heard a tubed piece of equipment in my system, only an amplifier that seems to behave a lot like tubes). I hope to build an "X-BOSOZ" mostly Pass-designed Mosfet preamp this summer (along with fixing up my CD playera little). It's really simple and shouldn't cost more than $100 with standard quality parts (and no chassis ).

Brett, did you think about trying "standard" quality parts like MKP capacitors and 1% metal film or matched carbon comp[?] (the black ones, whatever they're called) resistors, before going to Solen, Vishay, Blackgate etc? I mean, those things are really expensive.

Hi Amir, good to see someone else from around here! I'm a kid from the local science-magnet school in Silver Spring (Montgomery Blair). I'm not surprised you found an improvement in getting a good buffer stage for the system... the output stage of your receiver might have some distortion driving the input stage of certain amplifiers, whereas it's easier to drive a buffer. I know that my Zen amp (known to be wimpy) is supposed to sound better with a preamp even over the output of a very good quality DAC.

 

[Chu Gai]

Well it really depends on the value of the components you want to measure. It's just my opinion, but when you're looking to sink as much in parts as the original thing cost, it just sounds like a good idea to have decent tools. Kind of like modifying a car. Gonna do it with ebay Chinese $20 wrenches or you gonna buy something good?
But I fail to see how the cost of replacing good components with more expensive good components is economical. Look you get the ones that have the temp probe and you can check your fridge, calibrate your oven, use the other features to diagnose a variety of houselhold appliances, etc. Get a Craftsman or a Fluke and you've got a lifetime warranty.

 

[Michael R Price]

Chu,

I think the value of the components are fine to measure close enough. Even the cheap multimeters are fairly accurate, mine is specified at +/- 0.8% for resistance and +/-4.0% for capacitance, which is good enough to be sure of the intended value (it was right on the mark in troubleshooting which parts got damaged when I had some amplifier trouble). And in many circuits the exact values are not so critical; supposedly (don't know from experience) the differences in quality with better components are from lower distortion, not tighter tolerances. But if it matters, I (by mistake actually) use 2% caps and 1% resistors. This amplifier schematic specified polyester type for some important signal path capacitors, so I got those... and the unimportant ones, I got 2% polypropylene. A little switching around was in order.

 

[Chu Gai]

i agree. certainly good enough, provide you're in range, to determine if something's amiss.
you see, my way of thinking when replacing things is
a) if it's defective
b) if I really know it'll make an improvement

The first can be easy to determine. The second is not so easy and certainly in the tweaking realm is frought with enormous speculation and legends.

The thing is, it's not so easy to determine when one of your components needs service and/or replacement. The natural tendency for many of us is to assume everything is fine. Now with something like a car, you might find that your gas mileage is suffering indicating something's not right. But how do we diagnose, or run a performance check on everything?

Take for example mirrors that gradually get dirty over time. It's so gradual that some people wind up buying a new unit instead of having it cleaned. Some things, with a bit of creativity, can be diagnosed. With CD players, we can burn test tones and use the multimeter to get a handle on whether there's an issue with the frequency response. Often when that occurs, it's what called coupling capacitors that are no longer at their specified value. If you know where they are, you could replace them yourself.

 

[Michael R Price]

"...b) if I really know it'll make an improvement..."

You nailed it. Who knows, I bet my stuff and most others isn't good enough to tell a difference from changing a passive component. But maybe if we use all good quality components, the sum of those differences would be worthwhile.

Think I can totally remove the muting transistors and coupling caps (470uf 50v electrolytic! what the heck?) from my player with no problem? There's probably 10% of the distortion in my electronics, right there! Not to mention the crapped out power supply. It's mod time.

I read once that the actual circuit of a product contributes about 1/3 to its sound quality; the power supply contributes another third, and mechanical construction and resonance contributes the other third. That's quite an idea... What do you think of that?

 

[Brett DiMichele]

Mike,

I bought a $300.00 Craftsman Professional Multimeter for
$45.00 brand new It measures pretty stiff cap values
and will measure up to 20Amps peak so yeah it's a fairly
STOUT multimeter.

The other nice thing is it measures surface temps useful
for seeing just how hot your amp is getting plus you can
measure the Duty Cycle of a Circuit or measure Frequency

Really the only thing it doesn't measure is Inductance...


As far as parts go.. I am replacing my crossover parts with
good caps and mills resistors. Really after I remove the
sub woofer from the crossover the only caps left to replace
are relativly small (well, compared to the sub's cap on the
XO that is..) so I can afford to get really good caps just
for peace of mind..

As for the parts in my tube amps.. I haven't thought much
about changing out parts.. the stock caps in the audio path
are ILLusion Audio Paper In Oil audio caps, the non critical
power caps are WinCap electrolytics.

 

[Chu Gai]

That's a mighty big maybe sticking it's hand in your wallet and playing with our wishes. However if your coupling caps are crap it will mess up your frequency response. That'd be the first place I'd look. But like I said, there are creative ways to monitor your player's performance. Call it an annual checkup!
I think all those thirds add up to 1! There's some merit to that. Wanna bet the 5 year warranty on the ES line also has superior components that probably will maintain their specs for 7 years? Today, I don't think it's that hard to design components that are technically 'transparent'. As to whether that transparency will stand the test of time is another matter. Personally, if I were of a mind to switch out capacitors X for Y, I'd not be consulting audio forums. I'd be calling up manufacturers and looking to speak to some patient technical person.

 

[Brett DiMichele]

No elecrolytic is going to last forever. In 20 years those
caps may all need replaced reguardless of how botique or
exotic they may be..

At least the resistors, recifiers and diodes will last

 

[Brett DiMichele]

I just wanted to let you guys know I checked my manual and
I can check Cap's up to 150uF. So basicaly anything mid or
tweeter related I can check.. But big woofer caps are out
of the question

 

[Craig Ball]

I think a tube amp will only sound as good as what's feeding it, So I recommend using a tube pre-amp as we'll, I just sold my whole 6.1 system to move to tubes, and I love it. Don't get me wrong I miss the movies, but 2 channel tubes can't be beat. IMHO. Oh by the way I'm using a Eico HF-85 Pre and Dynaco ST-70 Amp.

Craig

 

[Brett DiMichele]

Craig,

Of course that is your opinion. I drive my tubes with a S.S
Pre that sounds absolutely fantastic and that is my opinion.