Coupling cap sound changes? (Dynaco ST-70)

[trisweb]

So my Dynaco updates/mods have been going great so far. I've upgraded all the important parts (selenium rectifier diode, can cap, electrolytic caps, etc.) and just recently got around to replacing the input coupling capacitors with the Sprague orange drop 716P caps. I moved up the capacitance slightly based on recommendations from Bob Latino found on a forum... 0.22 uF to replace the 0.1 uF and 0.1uF to replace the 0.05 uF.

I'm noticing a slight but very noticable change to the sound in the high end. Seems greatly bumped up in the treble. More airy, raspy almost. And the focus and imaging that I remember the amp having prior to the change has become sort of diffuse and difficult to image well. Female voices and midrange realism seems to be down. Clarity overall has definitely improved, but I'm thinking "at what cost?"

Is this because of the capacitance change possibly, or just the type/newness of the replacements? Or do I just need to give them time and burn 'em in?

Any experiences/advice/tips on this? Thanks.

 

[tube-a-lou]

Hi,
Give it time to burn in and see how it is, Orange Drops 716 are known for
there slight brightness in the high's, what kind of speakers are you using. All
systems and ears are different, so give it time, if not just change them, I heard
the Russians oil caps are good and there are others.

Tube

 

[bonsai]

The orange drops are probably fine for the .10 spots... If you really want to go with what Bob Latino advises then you probably want to go with the Russian PIO's in the .22 spots.

Or try some other PIO like Mundorf or something... Lots of debate on coupling caps on these forums and the one you got info from Bob on. Bottom line.. you may want to upgrade a bit from the orange drops in the .22 spots. Not intending to offend here. Just idea material if you think the sound is not quite right.

Good advice on the burn in... Can't hurt to give this some time before the de-solder and solder work if you do make some form of change.

 

[trisweb]

Great, thanks for the advice both of you. I'll let them burn in and see what happens. As it is, I'm certainly enjoying the sound... the clarity is pretty amazing.

@tube-a-lou, I'm using ADS L520 speakers, which already have sparkly tweeters, so I get to hear *everything* up there. Fun.

One last question - regardless of the cap type, are the increased values (.22/.10 to replace .10/.05) okay? How does that affect the sound?

 

[rage]

I'd inspect your solder joints and then give some burn in time.

odd that imaging is worse, that to me might be pointing to an issue.

 

[trisweb]

I think I should definitely check the connections in that case - off the top of my head, the left channel sounds "stronger" than the right, possibly why the imaging appears to be off. Is there anything in particular I should check for other than cold joints?

 

[dumptruck]

What's the preamp situation here? You might want to make sure you haven't unmasked a problem with the signal coming in.

 

[tube-a-lou]

Great, thanks for the advice both of you. I'll let them burn in and see what happens. As it is, I'm certainly enjoying the sound... the clarity is pretty amazing.

@tube-a-lou, I'm using ADS L520 speakers, which already have sparkly tweeters, so I get to hear *everything* up there. Fun.

One last question - regardless of the cap type, are the increased values (.22/.10 to replace .10/.05) okay? How does that affect the sound?

Those I heard are great speakers so there's lot's of detail there, Like
my Celestion 100's there made for tube stuff, ( Fisher, Scott) on solid
state sometimes they are a little bright because of the metal domes.
So I have to watch what I have upstream.

Tube

 

[trisweb]

dumptruck - the preamp is a Yamaha 7.1 receiver with pre-outs. It's clean and images well either on its own power (while of course being sterile and solid-state or with other amps on the same pre-outs. Not the ideal source, but I trust it for the most part.

tube - yes, the speakers reveal everything. Not metallic tweeters on 'em, but soft fabric dome. They're very dynamic and have extended range into the mids, I like them very much.

Generally the amp sounds very, very good with these - I can't complain too much. It's lost some midrange edge (much of which I'm guessing was just fuzziness allowing the sound to blend smoothly) in exchange for pretty incredible clarity all around.

I've got the VTA board (with Solen caps) half-built, so I will wait until that's complete and enjoy the amp until then. I'll give it a good long burn in, see how I like it after a few weeks, and then have a good comparison to the new driver board.

Also will do some reading/study on how these input circuits/coupling capacitors do their job. Always good to learn.

Thanks all.

 

[tube-a-lou]

Hi,
Watch out Solens are known to be bright as well, sorry but that the experience
I had with them and others as well. but hey try them out, that's what I did when
I put them in my Celestion SL6 speakers.

Tube

 

[analog addict]

Maybe I'm a little off base here....

...but do you even need coupling caps on inputs? I'm assuming you're talking about caps wired between your RCA jacks and the first stage/tube of the amp, right?

I thought that's only to prevent a DC voltage input, and if you trust your preamp, it's not a problem you would have to worry about. Plus for whatever reason it is adding another component in your signal path....:scratch2:

 

[bonsai]

I'd get the VTA built and get that in. That should be a big boost to the sound quality. If you have not put in the .22 coupling caps on the VTA then I'd think about what you are going to use for the 4 of these.

 

[trisweb]

Yep, that sounds like a plan. I think I will stick with the Solen caps that came with the board initially, then see how I like the sound. I'm comfortable replacing them later on if needed. That'll give me a good baseline for comparison anyway.

I resoldered some messy joints on my existing board... one wire had even come loose (from an original ancient solder joint) but it was just connected to an unused jack on the front tube port so even if it was hitting something it wouldn't have done much. Also resoldered three cap connections. If the sound changed from that at all, I don't know - it just be more burn-in, or my imagination, but things are sounding very slightly better in the imaging department.

It's got less than 12 hours on it with these caps, so I'll keep going.

This is good motivation to get the VTA board done Great, now where's all that time I left lying around, I know it's here somewhere...

 

[Heaviside]

Hi,
Give it time to burn in and see how it is, Orange Drops 716 are known for
there slight brightness in the high's, what kind of speakers are you using. All
systems and ears are different, so give it time, if not just change them, I heard
the Russians oil caps are good and there are others.

Tube

I have the Russian paper in oil (PIO) caps on my Latino/Dynaco ST-120. I bought them as an upgrade from Bob Latino when I built my kit about a year ago. They are a little difficult to deal with as they are large, have conductive metal cases, and you will need to insulate the leads. But it was worth the trouble, as I am very pleased with the sound.

http://www.google.com/imgres?imgurl...1&ndsp=24&ved=1t:429,r:2,s:0&biw=1362&bih=497

I do wonder about the longevity of the PIO caps as I imagine that the oil will eventually evaporate in a similar manner to what happens with electrolytics, but I figure that will be a headache for my son as I'll likely be deaf or dead by then. :yes:

Dan

 

[Bob01605]

Hi Dan,

Those Russian K-40Y PIO caps are sealed and the oil will never evaporate out of them. These caps were made for the Russian military. The last lot of 200 that I received all had a "1981" date marked on them. I have used over 2000 of these Russian K40-Y caps in the last 6 years. To my knowlege, only ONE has ever failed in use. I took one apart. It is sort of a "jelly roll" of aluminum foil and paper saturated with a thick oil. Photo below ..

To Trisweb > Re: Your orange drop caps not sounding right after they were first installed > All capacitors need some "break in" time before they sound their best. I am not exactly sure what happens during this break in time but I have a feeling that something happens on the molecular level inside the cap that cannot be fully explained.

Bob Latino

 

[Fran604g]

Hi Dan,

Those Russian K-40Y PIO caps are sealed and the oil will never evaporate out of them. These caps were made for the Russian military. The last lot of 200 that I received all had a "1981" date marked on them. I have used over 2000 of these Russian K40-Y caps in the last 6 years. To my knowlege, only ONE has ever failed in use. I took one apart. It is sort of a "jelly roll" of aluminum foil and paper saturated with a thick oil. Photo below ..

To Trisweb > Re: Your orange drop caps not sounding right after they were first installed > All capacitors need some "break in" time before they sound their best. I am not exactly sure what happens during this break in time but I have a feeling that something happens on the molecular level inside the cap that cannot be fully explained.

Bob Latino

Nice...I've wanted to see what is in those Russian caps, thanks. :thmbsp:

 

[jcmjrt]

If you like the increased clarity but are somehow missing something with the orange drops (which are decent caps and you should consider letting them break in well before making decisions), then you might want to go with the Russian oils as has been suggested but also buy some of the small Russian teflons at the same time and try bypassing the oil with a teflon - clarity and warmth are really nice. Oils and especially teflons do require a pretty good break in to get full benefit.

 

[Fran604g]

Lee at diytube suggested this to me for trying different combinations of coupling caps in my GSG:
http://glass-ware.stores.yahoo.net/ouseswandpcb.html

 

[Heaviside]

Hi Bob,

Thanks for the pictures--very interesting to see what's inside. And it's good to know they should last a long time.

By the way, we're getting a lot of enjoyment out of your amp.

Dan

 

[Fisherdude]

Just found this thread...a point to consider:

To the op: You didn't raise the capacitance "slightly", you raised it 100%-120%. And you changed the type of capacitor at the same time. I would assume there would be significant changes in sound. However, since you changed two things at the same time, there is no way of knowing whether the change in sound quality is due to the doubling of the capacitance, the change in capacitor type, or (probably) a combination of both, with no way of knowing which change contributed the most to the change in sound.

If you want to "roll" components, you need to make only one change at a time. That way, you'll be able to attribute any noticeable change in sound to the one thing that you did. Otherwise, you're just guessing.