Hello:
I just restored an ST70. It is articulate and detailed. Got rid of the tubby bottom end. I also use a SS rectifier which is a listening preference. The tube rectifier sounded like the amp had a head cold. I'm using KT77 tubes.
So now it is time to choose the dreaded coupling capacitors. two choices stand out. SGO EVO Mundorf or copper Audyn. Also was considering a West Cap NOS. Looking for something that is efficient, doesn't add much to the sound but delivers the detail I worked hard to find in this circuit.
Does anyone have experience with these? I have read a lot but this question requires experience Please be reasonable but what would be your suggestion? Throwing out metalized PP @ .50 cents and at the other end of the spectrum caps that cost more than my car! I have an 80 dollar budget.
Not looking for debate just advice. Thank you all for your help. Im sure your experiences will help bring me insight.
I just restored an ST70. It is articulate and detailed. Got rid of the tubby bottom end. I also use a SS rectifier which is a listening preference. The tube rectifier sounded like the amp had a head cold. I'm using KT77 tubes.
So now it is time to choose the dreaded coupling capacitors. two choices stand out. SGO EVO Mundorf or copper Audyn. Also was considering a West Cap NOS. Looking for something that is efficient, doesn't add much to the sound but delivers the detail I worked hard to find in this circuit.
Does anyone have experience with these? I have read a lot but this question requires experience Please be reasonable but what would be your suggestion? Throwing out metalized PP @ .50 cents and at the other end of the spectrum caps that cost more than my car! I have an 80 dollar budget.
Not looking for debate just advice. Thank you all for your help. Im sure your experiences will help bring me insight.
The Jantzen 0.1uF Z Superior caps fit really nicely into the space on the stock ST-70 board. The copper Audyn caps have leads that are a nightmare to work with, especially if you're trying to stuff them into a PC board.
The over abundance of feedback in the ST-70 will tend to swamp out nuances that might otherwise be more easily heard between these parts. Old stock capacitors would be my last choice.
The over abundance of feedback in the ST-70 will tend to swamp out nuances that might otherwise be more easily heard between these parts. Old stock capacitors would be my last choice.
Dont be taken in by the polypropylene part of metalised polypropylene they are definitely NOT up to the spec of polypropylene Film Foil especially for use in audio .
The problem is twofold though real film foil versions cost many times the price of the metalised versions and they are several times bigger for a given capacity but usually have working voltages of 1000V or more .
I have a 0.1mfd 1000V polypropylene film capacitor that's the same size as a 10 mfd metalised version .
The problem is twofold though real film foil versions cost many times the price of the metalised versions and they are several times bigger for a given capacity but usually have working voltages of 1000V or more .
I have a 0.1mfd 1000V polypropylene film capacitor that's the same size as a 10 mfd metalised version .
Yeah the feedback isn't an issue. I filtered the power better with some Polypropylene CBB 630V 4.7uf. More bypass than decoupling and I used a AVX corning cap and a matched within 1ohm 1K resistor. The cap from cathode to grid uses a Mundorf EVO. That loss of detail went away. So quiet there is no audible noise. LOL turned it on thought I broke something. What I'm looking for is a cap to complement this work. The amp is now detailed and articulate.
Any commercially made capacitor by a large recognized Factory from the usual large suppliers (think Mouser, etc.) will work fine there.
No need to spend $30 for a job which can be done exactly the same by a "normal" part.
That
Of course it´s your money so if that makes you feel better, please be my guest.
A cap is a cap is a cap and to boot a coupling cap is doing a very simple and easy job.
No need to spend $30 for a job which can be done exactly the same by a "normal" part.
That
cap you despise will sound exactly the same as those costing $20 to $260 ...
Of course it´s your money so if that makes you feel better, please be my guest.
A cap is a cap is a cap and to boot a coupling cap is doing a very simple and easy job.
Well stated !
Another issue is the grid resistors, 270k is too much for the chosen tube (kt77)
as they might loose control when hot. EL34 is the recommended tube in this amp.
While I generally disagree with that statement, the difference between capacitors inside the GNFB loop is quite negligible indeed.
0.1 uF 600Volt. As per schematics.
600Volt is needed as one of the caps will be at B+ during poweron
and at the same time have -Bias at the other side. One _could_
get away with 400Volt, hoping for margins "on your side" but why take
the risk ?
I have had several years experience playing with coupling caps. I have owned almost all of the hi-end (overpriced) caps and have settled on these 2 as my personal favorites.
Russian PIO 0.47uF 600V
Jupiter Condenser Copper Foil 0.47uF 600V
Riken 0.1uF 600V
I have 6 of each available. If you want to buy a pair, happy to help within your budget. If you don't like them, just return for paid price less shipping.
Pat
banpuku@mac.com
I've used nothing but Russian teflon coupling caps for 12 years. K72 or preferably FT-3, though very little difference. In low-part SE 2 stage circuits with no feedback the difference is quite audible to me at least. And because of the quality of these caps I generally prefer plate chokes to interstages. They are a certain size, so that has to be allowed for.
What is the opinion of PP vs PIO? There are Russian PIO caps that incorporate PT in the PIO cap as well.
K75-10 1000V 1.0uf 5% tol. PIO Hybrid capacitor → K75-10 PIO → Tubes-Store.com
K75-10 1000V 1.0uf 5% tol. PIO Hybrid capacitor → K75-10 PIO → Tubes-Store.com
A cap is not just a cap. I'm out, too many opinions not enough science. If a cap is a cap than why so many caps? WOW ever study boundary or grain issues with respect to frequency and impedance in a cap or why some caps are not rated for some jobs because of HF issues or impact relative to form factor? HUH im not in the right place.
Hey Cathodefollower,
The most important aspect is what impedance and capacitance does the coupling cap have after it (has to drive). If the stage impedance is big and miller capacitance is small like a cathode follower for example then the cap material is not that important and it won't color the sound. At least from my experience.
PS: the forum is called DIY Audio not PHD Audio
The most important aspect is what impedance and capacitance does the coupling cap have after it (has to drive). If the stage impedance is big and miller capacitance is small like a cathode follower for example then the cap material is not that important and it won't color the sound. At least from my experience.
PS: the forum is called DIY Audio not PHD Audio
I prefer the Russian PIOs, followed by Jupiter Condenser. I did have a pair of Duelund's top caps at the time (copper), but preferred the Russian's tonality and harmonics. Also, the Russian caps are built like tanks, I believe hermetically sealed in those metal containers. Really good stuff.