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For the record - I am HOOKED on this amp and in not way do I mean to even hint anything of a negative tone with these postings.
I was hunting for a EL34 tube that is more "tuby" in sound. However do you know that moment when you listen to your stereo and realize - am I fighting the nature of this amp? The VTA ST-70 is one GREAT sounding amp. Ain't NOOOO complaints 'bout that! But what it is NOT is a vintage tube stereo. It is a very articulate well balanced, dynamic non boomy in the bass clean sounding modern tube amp stereo - period!
So am I fighting putting in the KT-66's. Thinking I may loose more of the midrange that I like. I've had other KT tubes, in vintage amps and did feel I lost some of that "tube" sound.
Am I wrong in trying to convert this amp into more of what my Sherwood sounds like (and I love this stereo exactly the way it is). Or should I embrace a different more modern tube sound.
charles
Follow Ups:
"what my Sherwood sounds like"
Many of the older integrated amps exhibit frequency response anomalies because of their tone controls and lower quality passive components. One good example is the Heath AA-151. When you eliminate that area of circuitry by moving to a system with a straight line preamp and power amp, the tone of the system changes markedly. It's a big improvement in my opinion, but obviously, some people prefer the "older" sound.
--------------------------
Buy Chinese. Bury freedom.
I heartily agree. I have 3 units. 1 stone stock and the others modified w/out tone controls, etc. They are excellent performers with extremely good transformers. I thought the HK group went overboard with that unit and all the other integrateds that they marketed afterward were far inferior. Cheers, Dak
Keep it and enjoy it. You have the best of both worlds.
(tho I'd wager you'll gravitate to the VtA over time.)
K
after honing in on EL-34 in the Will Vincent ST70 (trying at least a dozen different quads), I
upgraded to a vintage GZ34 rectifier that, while not adding the "tube" sound you're searching
for, boosted the overall performance to a new level.
So maybe playing with the rectifier tube might add what you are seeking?
"Once this was all Black Plasma and Imagination" -Michael McClure
Here's some brainstorming.
I have a set of circa 2004 JJ E34L that had a palpable quality, sweet, warmer with a fuller mid-bass region, and a little rolled off up top. Don't know what the current crop of JJ E34L sounds like.
I've also tried EH EL34, reissue GL KT77, JJ KT77, reissue Mullard EL34, and the newer Tung Sol EL34B. Out of these five, I think the Tung Sol EL34B is the most "vintage" sounding. I've not heard the Chinese EL34B.
With regard to the triode/ultralinear switches, if the triode mode results in too much roll-off for you, you might try experimenting with the EH 6CA7 running in triode mode. I suggest this possibility because my Cary SLI-80 sounds significantly less rolled off in triode mode with my set of 6550 vs. my set of KT88. Some difference in their construction and/or operation must be responsible for this, and the 6CA7 does have some fundamental differences from an EL34.
As some have alluded to in this thread, it might not be possible to change the amp's baseline character, which I would think is a result of the particular circuit topology and perhaps also the transistors. But, its baseline character plus certain parts changes could possibly make for an outcome that strikes a balance between the way it sounds now and the sound of your Sherwood.
If you decide to pursue a more vintage sound, then, as others have mentioned or alluded to, we're talking carbon comp resistors everywhere, and maybe even ceramic instead of mica for the small value capacitors.
For coupling capacitors, it's interesting to read through some of the online capacitor shootouts. From what I read, plus some of my own experiences, the SB Electronics 716P and the original Auricaps are warmer choices, but their availability is in question now. Other alternatives that might be worth trying include REL AudioCap Theta, Cardas Golden Ratio, or just Mylar capacitors.
Pick electrolytics that are not specified as "low ESR" and omit any polypropylene bypasses across them. If you have the extra electrolytics on the PCB, make sure they are not specified as "low ESR" or remove them entirely.
Here's a thought - IIRC, doesn't the amp have a polypropylene capacitor in parallel with one of the quad cap sections? Or is that on the 120? If it is there, try removing it. Speaking of the quad cap, do you have the traditional style (Swiss roll internal construction) or the newer one with the discrete, low ESR capacitors stuffed inside? Try the traditional style, maybe even replacing the 80/40/30/20 unit with a 30/20/20/20.
But, you probably know this already.
Sounds potentially like a lot of work and it's unfortunate that experimenting can get expensive. But, I don't think you can really go wrong no matter what route you decide to take.
I'll first try the GL KT-66 and then at a later date the TungSol EL34B. Then maybe tinkle with the more economical 12AU7 driver tube. I already have a vintage amp that I treasure and use frequently. Two very different amps. Two very different sound presentations. Enjoy!
I would like to make painfully clear and clarify something from previous post below. I never implied or mentioned the word "sterile". I however DID say I LIKE the sound of the amp exactly the way it is. All I am trying to do is tube roll wisely. Is it wise to replicate something I already have - a vintage amp. Or strap on a pair ($$) and go with a more modern tube amp sound.
Thank you all for your input and I will stop festering and just buy something already for the holidays.
charles
Don't economize on the 12AU7. It can make a real difference. The older Mullards are most likely to warm up the sound. There are others such as certain Brimars, but I wouldn't count on a Brimar to do the trick unless you are familiar with it. I saw a comment here about the "BIG tone' that 6sn7s can bring to the sound Q. I couldn't agree more but be careful choosing it,once again get suggestions/directions about which to try.
BTW I own a couple of Sherwoods, the rich vintage tube sound is what they could make, they would probably sound much like the current production amps available today.
Steve
Mullard 12AU7's and new production Tung Sol 6L6G's will give you more midrange magic than the GL KT66.
...try the octal board with the 6SN7s that have "big tone."The KT66 is a really retro-cool-looking tube, but from what I read I kind of doubt it will get you any closer to a vintage sound, in fact, the opposite may be more likely.
The Tung Sol EL34B might help. Don't overlook the JJ E34L. AND, I've read different commentaries all suggesting the JJ 6CA7 is warmer and rounder.
Eurotubes.com touts a well-considered burn-in and matching process for the JJs they sell. BOI AudioWorks also has JJ and they claim a burn-in and matching process. Antique Electronic Supply is supposedly using a new burn-in and matching procedure. You might be able to get two quads of these other choices for the price of one quad of GL KT66. Just some food for thought.
Edits: 10/20/15 10/20/15 10/20/15 10/20/15 10/20/15 10/20/15 10/20/15
Guessing it was a choice between metal and carbon, but don't see any info on the site.
Am I confusing the VTA with another kit?
Dynakitparts.com offers either metal or carbon resistors as an option for their PCBs.
.
is that you are hearing differences in the passive components (which have improved considerably over the years) and power supply stiffness as opposed to the tubes themselves.
Old caps, for example, trade resolution for apparent "smoothness".
Hi, my experience with the VTA70 driver, the same as used in Charles' amp, was that it's the least traditional tube sounding of any of the driver boards that I've had in the same amp or any of my other amps with even changing it to have carbon comp resistors and paper in oil capacitors. It's more of a modern/sterile tone. With the right speakers etc I could see it really hitting the spot.
Charles, you can try to up the bias a bit to 45ma etc and see if it fills out the sound before you buy more output tubes. The VTA70 biasing is on the conservative side and gives one some room to experiment.
"My OP question is am I trying to morph the sound into a vintage amp. As well as not taking the amp in the direction it was meant to go? Which BTW I have NO problem with.
I already have the Sherwood for that. Am I duplicating sound types?"
Your question is confusing. You seem to say you want the amp to sound like a vintage tube amp but "not taking it in the direction it was meant to go?" You have a Sherwood amp for that sound.
Well, if you mean by changing tubes you would make your ST70 sound like a Sherwood? I would say that would not happen since the Sherwood has either 7591 power tubes or 7189 tubes which don't really sound like the EL34. But if you want to change the character of the sound of your ST70 to a more vintage tube sound you should rebuild it with vintage type components. I have noticed that the "vintage" tube sound to be related to carbon comp resistors and mylar and electrolytic capacitors. Just swap out all your parts in your ST70 for those components and I believe you amp will give you that type of vintage tube sound. cheers, Dak
I suspect it will take more than parts to get vintage sound. Both the circuitry and power supply are better in his new amp as well as parts. If he wants Dynaco sound it might be better to rebuild an old Dynaco amp, perhaps a MK3 and try to use new parts as much like the old ones, Don't use modern film caps or metal film resistors.
of implementing switching for running in Triode mode. I have the switching option provided by VTA, and it does provide a different, "softer" character.
Your making it too hard on yourself! Just make the amp sound the way you like it. To find out, you have to try different tubes. That's what rolling is all about.
The Shuguang EL34B does have a nice rich midrange. Not much highs or lows though. If you want to keep that rich midrange but get better extension, you are probably looking at real Mullard xf2 from the Blackburn plant. JJ KT77 and EH 6CA7 are nice tubes but their midrange is definitely thinner than what your using (but more extended at both ends). Have not tried the GL KT77, but for what they cost you might as well spend a few dollars more and get real Mullards.
KT66 are a totally different animal. They have great extension at the frequency ends (especially on top--best treble for these types of output tubes) and a very linear, fast, and detailed midrange. Almost the opposite of what you are using. But before you right them off, you really should try them. They can provide greater detail and more "air" to the music. You will hear things that you might not with the EL34Bs. You can always add some warmth with the input and driver tubes. Maybe you like them, maybe not. Another tube to try is the 6L6gc. Similar to the KT66 but maybe a touch "tubbier".
Enjoy the roll!
> > Similar to the KT66 but maybe a touch "tubbier".
They are similar in operation but not in sound.
KT66 is very fast, articulate and in your face.
Brings the performance in the room.
6L6GC is warm, textured and laid back.
Lays the performance out before you.
Nothing similar in their sound at all.
KT66 is more a rock and classical tube.
6L6GC is more a vocals and jazz tube.
DanL
Charles;
What are you running in your ST-70 for coupling caps caps and input/driver tubes?
If you want more mid range bloom try some Mullard EL-34 and some Jensen PIO coupling caps.
Meat; It's the right thing to do. Romans 14:2
Caps are PIO and tubes are top notcht! GE 12AU7 drivers and Shanguan EL34s. These tubes are great sounding and I would argue an opposing point of view.My OP question is am I trying to morph the sound into a vintage amp. As well as not taking the amp in the direction it was meant to go? Which BTW I have NO problem with.
I already have the Sherwood for that. Am I duplicating sound types?
Edits: 10/19/15
You may have a hard time getting it to sound vintage without some tweaks to the board. I thought that the amp was a complete 180 from vintage sound.
Look up Kegger over at Audiokarma. He has a lot of experience/knowledge with VTA70 driver boards. My guess is that he'd have some things for you to try that will get you where you want to be.
Completely agree - he built a very nice tube amp which sounds SS - and no amount of tube rolling will fix that IMO.
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