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Millett "Starving Student" hybrid amp - Page 468

post #7006 of 7031
Quote:
Originally Posted by tomb View Post

Signal goes through the cathode bypass, that's why signal-quality caps (Muse ES) are used.

 

Gotcha. Any comments on the C3/C5 Nichicon cap choice? And do you have any of those muse caps in 220 uF in stock?

 

Also, for the Wima capacitors, there is no polarity correct?

 

Thanks!

Nathan


Edited by Nathan P - 1/21/16 at 6:23am
post #7007 of 7031
Quote:
Originally Posted by Fishline View Post
 

In case anyone find this helpful, here's my project on mouser (grand total of $63):

http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=0b0ae93f48

​(Can mouser projects be shared like this?)

 

This is for the 12AU7 version.  It includes everything (case, heatsink, etc.) except wires, tubes, tube sockets, and the CISCO PSU.  It's basically the version as seen on Instructables:

http://www.instructables.com/id/Headphone-Hybrid-Tube-Amp-SSMH/

 

Some notes:

1. There is a smaller Hammond case that can be used, but the heatsink will occupy the entire top of the that case, so holes will need to be drilled on the heatsink for tubes to poke through if you go with the smaller case (~$4 cheaper).  The case has several color options (BK for black, RD for red, YL for yellow, etc.)

 

2. I put in the Alps RK097 pot/switch combination.  It's about the same price as the Alpha, but has the builtin switch.  Saves a separate switch and drilling another hole in the case for it.

Here's the one I just built using the smaller Hammond case.  Drilling the tube openings through the heatsink and have them lined up with those on the case was the biggest challenge (without proper tools-- with a drill press I'd imagine it would be _much_ easier).  The small size of the case also makes the p2p wiring more challenging, but manageable. This is using the ALPS RK097 pot with the integrated switch, so there's not a separate power switch.  

post #7008 of 7031
Very nice!
post #7009 of 7031
Quote:
Originally Posted by Fishline View Post
 

Here's the one I just built using the smaller Hammond case.  Drilling the tube openings through the heatsink and have them lined up with those on the case was the biggest challenge (without proper tools-- with a drill press I'd imagine it would be _much_ easier).  The small size of the case also makes the p2p wiring more challenging, but manageable. This is using the ALPS RK097 pot with the integrated switch, so there's not a separate power switch.  

 

That's very nicely done. I really like the tube sockets placed through the heat sink. Very cool.

post #7010 of 7031

So I have a couple of questions.

 

Firstly, what are the comparative advantages/disadvantages to the C7/8 bypass caps? I removed the cheap panasonics I had in there and honestly I think it sounds better. Would it be even better with some nice Muse ES caps in there? I do not need the extra gain by any means. I've already switched R16 and R17 out for 100kOhm resistors and at least now I can use the first 1/3 of the volume pot. Channel balance seems much improved but I still kind of thing there's a bit of imbalance. Probably the 20% tolerance pot I'm using or a combo of it and tube mismatch. I'm using GE 5963s I got unmatched from Ebay. I ordered a set of Sylvania 5963's that are matched to 10% to play with.

 

Regarding the volume pot, at what point should I consider using a lower impedance pot to sway the volume adjustment? Right now I've got 100k resistors and a 50k pot. Would 50k resistors and a 10k or 25k pot be a better combo as far as input impedance goes? How much does the input impedance matter? Even uncased the noise floor seems reasonable as long as I don't have something electronic sitting right next to it.

 

Thanks!

Nathan

post #7011 of 7031
@fallenangel Thanks! that's not original though. The idea was from post #1840 of this thread. There are similar build elsewhere as well. The tube sockets were mounted from below to the case. I had to use 1/2" #4 screws to mount the sockets.
post #7012 of 7031
Quote:
Originally Posted by Nathan P View Post
 

So I have a couple of questions.

 

Firstly, what are the comparative advantages/disadvantages to the C7/8 bypass caps? I removed the cheap panasonics I had in there and honestly I think it sounds better. Would it be even better with some nice Muse ES caps in there? I do not need the extra gain by any means. I've already switched R16 and R17 out for 100kOhm resistors and at least now I can use the first 1/3 of the volume pot. Channel balance seems much improved but I still kind of thing there's a bit of imbalance. Probably the 20% tolerance pot I'm using or a combo of it and tube mismatch. I'm using GE 5963s I got unmatched from Ebay. I ordered a set of Sylvania 5963's that are matched to 10% to play with.

 

Regarding the volume pot, at what point should I consider using a lower impedance pot to sway the volume adjustment? Right now I've got 100k resistors and a 50k pot. Would 50k resistors and a 10k or 25k pot be a better combo as far as input impedance goes? How much does the input impedance matter? Even uncased the noise floor seems reasonable as long as I don't have something electronic sitting right next to it.

 

Thanks!

Nathan

 

Yes, as stated in a previous post - the signal definitely goes through the cathode bypass caps.  So, "audio-quality" electrolytics are important, here.  Since the cathode bypass caps are optional in either case, I'm not surprised that you note the sound is better without "non-audio-quality" caps being used.

 

Yes, Muse ES caps will probably sound the best as cathode bypass.  I can't explain it, but if you use cathode bypass caps, it seems more often than not, bass frequencies become most critical.  For example, if the caps are not sized large enough, the use of a cathode bypass cap can actually decrease the bass.  For this reason, many "old-timer" tube designers go way overboard and spec something much, much larger than what we've suggested for C7/C8.  That usually happens because it's not a straightforward calculation to determine, so they go way overboard to ensure that bass frequencies are not lost ... just in case.  One very well known current amplifier designer has the exact philosophy I just described.

 

However, Dsavitsk made the calculation - based on real-world measurements - that 220uf was sufficient.  We have supplied these caps - Muse ES - with every kit that Beezar has sold or built and there has never been a complaint about lack of bass. :cool:

 

About the volume pot - This may seem strange and I can't go into the theoretical details, but changing the impedance of the volume pot is not going to have any effect on the overall volume adjustment, except for how it matches up with the input resistors.

post #7013 of 7031
Thanks for the info! I would have bought your kit but I'm on a shoestring budget here. I'm kind of sad that I didn't understand the importance of that cap beforehand. I'll find an excuse to make a mouser order and throw them in. wink.gif

In the meantime I'm enjoying the heck out of this thing and need to figure out a case for it. I have some nice tigre caspi and canary wood boards i could use, or, I have access to a 3D printer... Decisions decisions.
post #7014 of 7031

This is seriously a sickness. I needed to order a couple of things from Mouser so just for fun I ordered some WIMA MKP10 caps for the output bypass (To compare to the MKP2's I have in there now) and some Vishay-Roderstein MKT's to compare for fun as well. I have another board so I figure why not try some stuff out before I make another one. I can combine what I learn into one ultimate version. ;)

 

Question-what do C3 and C4 do and are they as important when it comes to sound as the output bypassing caps?

 

Thanks!

Nathan

post #7015 of 7031
Quote:
Originally Posted by Nathan P View Post
 

This is seriously a sickness. I needed to order a couple of things from Mouser so just for fun I ordered some WIMA MKP10 caps for the output bypass (To compare to the MKP2's I have in there now) and some Vishay-Roderstein MKT's to compare for fun as well. I have another board so I figure why not try some stuff out before I make another one. I can combine what I learn into one ultimate version. ;)

 

Question-what do C3 and C4 do and are they as important when it comes to sound as the output bypassing caps?

 

Thanks!

Nathan


Do you really mean C2 and C4 or C3 and C5?

 

C2 and C4 capacitively couple the tube output to the MOSFET.  Every bit of the signal passes through these caps.  So yes, audio quality is important.  Luckily, they don't have to be very big to pass all the bass frequencies needed (that RC circuit stuff again).  So, a good film cap such as the Wima MKP10 will do nicely.  We upsized those two caps in the Beezar SSMH kit from Pete's original 0.1uf to 0.22uf.  Again, this is in order to eke out every bass frequency that we can.  Strictly speaking, they're probably more important than the bypasses on the output. 

post #7016 of 7031
Quote:
Originally Posted by tomb View Post
 


Do you really mean C2 and C4 or C3 and C5?

 

C2 and C4 capacitively couple the tube output to the MOSFET.  Every bit of the signal passes through these caps.  So yes, audio quality is important.  Luckily, they don't have to be very big to pass all the bass frequencies needed (that RC circuit stuff again).  So, a good film cap such as the Wima MKP10 will do nicely.  We upsized those two caps in the Beezar SSMH kit from Pete's original 0.1uf to 0.22uf.  Again, this is in order to eke out every bass frequency that we can.  Strictly speaking, they're probably more important than the bypasses on the output. 

 

 

Sorry, meant C2 and C4. Good to know. I've got MKP2's on there now. I'm not super well versed in the differences between the different lines of Wima's caps but it seemed to have similar specs and I thought I needed something a bit more compact than the 10's for Fred's board layout. Looking at the board in the flesh it'd be pretty easy to bend leads to get things to fit if necessary.

post #7017 of 7031

Just as an FYI, I purchased some Beckman branded 5963's made by Sylvania and they sound killer in this amp.

post #7018 of 7031

OK - So finally finished my second build and I am much happier with it than my first.  I gave my first to a very good friend of mine and he is enjoying it to the fullest.

 

My second build is a refined version of my first and is made entirely on a small stripboard.

 

Pic of the stripboard design...

 

http://i.imgur.com/4DXSgQe.png

 

PM me if you want the DIYLC file.
 

Nearly finished board:

http://i.imgur.com/gwsAIU8.jpg

http://i.imgur.com/hdcHv2F.jpg

 

I added the contact plugs so I could completely remove the board for maintenance.

 

Here is the completed board mounted to the enclosure:

http://i.imgur.com/x93k7ay.jpg

http://i.imgur.com/j7Qv8z6.jpg

http://i.imgur.com/1cMam1C.jpg

 

And the completed amp

http://i.imgur.com/jr8i2Ym.jpg

http://i.imgur.com/Reec3zi.jpg

 

I added both an RCA as well as a 1/4" input

http://i.imgur.com/d9OsGCy.jpg

 

I tried to do the Constant Current Source mod but was unable to get it to work - I did, however, add 2 100KΩ trimpots to input for balance though I only had to make very minuscule adjustments.

 

It sounds great! Better than the Bravo Ocean I have.

post #7019 of 7031

Looks nice, I might even build my own amp if i have enough free time

post #7020 of 7031

Here another amp :)

Best regards mates!

 

Toni

 

 

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