Tube amp sounds very bright; what's up with that?

tygr

tygr

Audiophoole
My new to me ST70, recapped and with VTA driver board sounds a little too bright to me. What ever has happened to that "tube warmth" I was expecting? Could it be the new EH tubes?

I run it alone with just my Sony ES CD player with output level control and it's too bright. I run it with my Magi all tube preamp and Denon DVD player and it's still too bright for my tastes.

Any insight?
 
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Well, I can't help but I have to admit I'm interested in the post. I have a totally oem ST70. I installed new caps and purchased a VTA board but have not stuffed/installed the board, preferring to listen to the stock sound for a while. Based on your post, it sounds like I may leave it that way.

FWIW, I have found some "modern" tube equipment to be quite unpleasantly bright, as if the manufacturers were out to prove that they could make a tube amp that could be as unpleasant as a bad solid state design....;)
 
petercapo said:
What were you using before this Stereo 70 w/VTA mod and how did its relative brightness compare?

Any other changes to your system, or just the amp?
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I've been listening to my big Class D amp. No other changes to my system and the speakers I'm using are not overly bright, in fact they are very neutral.

The ST70 is definitely brighter than what I've been hearing.
 
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Audio Nirvana super 12s in large (5.6 cu. ft.) cabinets and 10ga. stranded copper wires.
 
One thing I have wondered about with all these mods that are popular for the Dynacos - there doesn't appear to be any DATA re them, just descriptive talk. I haven't seen any tests that show, for example, that the response of the amp/preamp is more accurate with whatever mod than it was with a stock amplifier with up-to-spec resisters/capacitors.

One would think it would be easy to do performance tests that would clearly show the amp's response with/without the mod but no one seems to provide that info...
 
I also thought that the VTA board always was on the brighter side myself. I guess one could consider it more modern voiced. I ending up liking the stock driver a lot more than it after doing Dave Gillespie's small tweaks which consist of changing out the tube rectifier for diodes, adding a 50ohm 10watt resistor to drop the voltage down and installing a dc blocking filter in the front of the amp.

MexicoMike, if you haven't read the below

http://www.audioregenesis.com/documents/ST-70 Base Line Testing.pdf

show's how good the original driver board is complete with measurements. makes one wonder if there's any real reason to change it out as long okay driver tubes are to be found. 6GH8a's seemed to sound okay to me as a sub.

The only mod board that I recall that offered any measurements in the documentation was Shannon Parks' Diytube one which I thought also sounded pretty good.
 
I've heard that certain types or brands of capacitors can contribute to any brightness, high midrange or lack of.

Not sure wire really plays into anything like brightness in standard power or having nothing fancy, but I have experimented with my Pioneer SA-8500 with a pair of Fisher STV series 15 inch speakers. I've used house wire, single strand, brown lamp cord, actual speaker wire of different gauge and have not heard any difference. Mind you, this is just me. :scratch2:
 
Yes the capacitors could cause the difference that your hearing, using some Russian PIO. caps mixed in combination
with other caps on the board can help settle down that brightness and give you that smoother tube sound.
This would be the film caps not the electrolytic's that I would try something different.
 
My first amplifier rebuild was a ST70 using the VTA board for 12au7 tubes. I used the Russian PIO caps(K40-9??) and pretty much whatever resistors that were recommended. I did this about 3 years ago, and I think the VTA board may have changed some since then.
I broke the amp in with a Sovtek 5ar4, new re-issued Mullard EL34's and RCA clear top 12au7's. It did not sound offensive in any way during the break in period to my ears. Soon thereafter I replaced the 5ar4 with a NOS Mullard, and the El34's with NOS Mullards as well. I forget what driver tubes I used on the VTA board, maybe a combination of telefunken phase splitters and a Sylvania gold brand variant for the front tube.
I would not describe my ST70 as "bright". If anything, it's pretty laid back and warm, "female vocals to die for".

I understand the power circuit has changed slightly since my version, but at a fast glance, it looked to be more for stability than sonics,

I would never have described my amp as "bright" even during the break in period.

If anything, I thought using the Russian PIO dulled the sound a little,

It's a decent amp, very musical and easy to use.

If your amp is "bright or brash" sounding, give it a week or two to break in.
 
If the VTA board is the version that uses 12AU7 tubes, I'd recommend trying some Mullard, Amperex or other Philips-made 12AU7s, Those tend to be about as "mellow" as a 12AU7 tube comes.

The output tubes have VERY LITTLE influence on the brightness of the amp, by comparison.

Regards,
Gordon.
 
Thanks for all the advice guys. I'm going to try some tube rolling first, just to see if that has some effect, then I'll fine tune the rolling and/or start looking elsewhere for a solution.
 
That Gillispie article is the best thing I have ever read re this subject. I think it clearly makes the point that amplifier "accuracy" and "sound preference" can be two very different things. It would seem from his supplied data that some of the popular mods for the amp are for the purpose of changing the sound to suit a particular taste/opinion rather than making the amplifier "better" in an objective way.

Nothing at all wrong with altering the sound to your personal preference but it seems to me that that should be clearly stated by the mod-makers as opposed to implying that the mod "fixes" some design problem that doesn't actually exist.
 
Not to forget the invention of tone-controls, a "mod" that can tune sound according
to ones tastes. Easier and faster that soldering caps and replacing tubes.
 
I'm just an audio dumb ass who can't really read schematics. I need layout drawings. But thanks for that battradio.
 
easy solution-try adjusting the speakers so they are not toed in directly at your listening position- 15 inchers are going to beam high freqs -so adjust.
 
Do you have the speakers hooked up to the 8 ohm taps?
Try switching to the 4 ohm connections. Trust me.
I had a similar issue, and this resulted in a rather dramatic improvement.
 
GordonW said:
If the VTA board is the version that uses 12AU7 tubes, I'd recommend trying some Mullard, Amperex or other Philips-made 12AU7s, Those tend to be about as "mellow" as a 12AU7 tube comes.

The output tubes have VERY LITTLE influence on the brightness of the amp, by comparison.

Regards,
Gordon.
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If that board uses 12AU7's, can you also substitute 12BH7A's (a common practice with Mac amps)?
I much prefer the 12BH7's in my MC60's.
 
Naptown Rob said:
Do you have the speakers hooked up to the 8 ohm taps?
Try switching to the 4 ohm connections. Trust me.
I had a similar issue, and this resulted in a rather dramatic improvement.
Click to expand...



Why did that seem to help?

Thanks Rob, meanwhile I've ordered a variety of center replacement tubes for now.
 
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