DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 12 Aug 2020, 22:28

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 726 posts ]  Go to page Previous  1 ... 65, 66, 67, 68, 69, 70, 71 ... 73  Next
Author Message
PostPosted: 13 Apr 2020, 20:51 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4209
Location: Arizona, USA
Hi, On the question about the power transformer. Any power transformer with similar ratings will be fine. You can go to as high as 12 VAC on the heater winding (be sure it has at least 1.5-2.0 amps) and the regulator will take care of the bringing it down to 6 volts. Be aware that it will need to dissipate a lot of heat ....about 6 watts or so. My preferance if you use a 12 VAC winding is to rewire the tubes for 12 VDC and use a fixed resistor in about the 1-5 ohm range to bring the rectified DC down to what is needed. It will have to be a 10 watt resistor though and it will get pretty warm too. You will need to experiment with the value as the internal impedance of the transformer and rectifiers will alter the value. I would start with 5 ohms and work from there. In my power amp design I use an 11.0 or 10.9 VAC winding with a bridge and filter cap to get the 12 volts. No resistor is needed.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 13 Apr 2020, 21:23 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4209
Location: Arizona, USA
Hi Everyone. I noticed that the tube types were not given. They are unchanged from before but are...V1/2 and V3/4 are ECC803S and V5 can be either ECC802S or ECC801S. I used JJ standard ones. The gold pin ones were no better in sound or S/N. If you use others the precision of the response might vary a bit but would not be likely to be audible. A tube with different anode resistance (Ra) might tend to upset the very low bass a bit. Top end can be affected in some cases as well. When I measured some others (standard 12AX7s) the response at 20K was down 1 db. Adding a 100pf capacitor across the 43K resistor in the RIAA section brought it back up. Since most of us can't hear that it is probably a moot point. I do however feel that the extended top end would likely have positive effects in the 5K to 10 region that we can hear. Less phase shift, more linear behavior. Still I am a dedicated perfectionist and if I can measure or hear something then it ought to be fixed. How any of you would know that the capacitor was needed is unknown as most probably don't have the ability to do real time Bode plots and scopes to see them on. In any case the deviations are quite small and the preamp complies with the standard between the 50HZ and 15KHZ limits it specifies. I like things that cover the whole range though.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 14 Apr 2020, 01:44 
Offline

Joined: 03 Feb 2018, 00:47
Posts: 60
Location: Brisbane, Australia
Working on sourcing the right caps.
Bruce, putting your budget hat on, what are the minimum level of caps for the 1uF bypass caps that will not compromise the device too much? You specify "Audio grade", some are up to $27 each and I need 12 of them, which pretty much won't happen.
Will Mundorf EVO caps work? I can possibly stretch to these over a couple of pys.

https://www.soundlabsgroup.com.au/p/MU-EVO-1u0-450V/

Thanks,
Glenn.


Top
 Profile  
 
PostPosted: 14 Apr 2020, 04:46 
Offline

Joined: 04 May 2018, 05:06
Posts: 7
For what's it worth.

I used these for basically anything non electrolytic with the exception of the filter section.
http://www.jantzen-audio.com/cross-cap/

Was a little under €2 each (about 3,50 in Australian dollars I think)


Top
 Profile  
 
PostPosted: 14 Apr 2020, 05:21 
Offline

Joined: 03 Feb 2018, 00:47
Posts: 60
Location: Brisbane, Australia
Wow. That was a great comment.
https://speakerbug.com.au/index.php?rou ... uct_id=140 in Australia. Exactly what I was looking for.
Thanks.


Top
 Profile  
 
PostPosted: 14 Apr 2020, 09:05 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4209
Location: Arizona, USA
Hi, I use the Jantzen Cross-Caps most of the time. Others like Solen and Panasonic are fine too. The thing to avoid is cheap caps that have poor linearity and resonse in the audio range. I won't mention brands but several are out there that just don't do the job. The 2 coupling caps have a large influence on the "flavor" of the sound and should be good ones. I have used Russian K40Y-9s, Audyn Copper Caps, Jantzen Silver and Auricaps there. The K40s are nice because of the metal case which can be grounded when you need extra hum shielding. The others need to be as far away from the transformer as possible as they will pick it up. Hum is the biggest issue in building this preamp. Even a tiny amount picked up by the input stage will be amplified by as much as 60db.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 14 Apr 2020, 21:53 
Offline

Joined: 03 Feb 2018, 00:47
Posts: 60
Location: Brisbane, Australia
Ok. Shielded transformer ordered. Cross-caps ordered. K40-9 coupling caps ordered.

I need symmetry, but I recognise the need for the layout to suit the noise requirements. What is your opinion of the layout below?

Note that is not the transformer and it will be underneath in a shielded area, it is just there to show the position. My goal will be the primary power supply components in the left hand half with a steel shield/divider down the middle. The two rear valves will be the first amplification stage, closest to the input sockets, then the second stage in the middle, then the CF which should be the least susceptible to picking up noise and hum at the front.

Alternately, the first stage could be the right hand pair, furthest away from the power supply but then the front one would have a longer path to the sockets.

Power socket will be rear left, audio in and out rear right.

I'd like the valves across the front for aesthetics, but I think that would make pickup more of an issue.


Attachment:
Groovewatt layout.jpg

Cheers,
Glenn.

Edit: No need to answer, just went back through the forum conversation and lo and behold vary close layout to yours.


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



Top
 Profile  
 
PostPosted: 15 Apr 2020, 20:39 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4209
Location: Arizona, USA
Hi, The layout I used lends itself to the shortest connections between stages and good placement of components for less noise and hum pick up. I tried others but none were quite as suitable. In any build like a phono preamp the layout and grounding are super important. They are the keys to a quiet design or one that hums like crazy. Preamps like this one have about 60 db of gain in the low bass region. A sure way to find and amplify hum. One of my first attempts (about 10 years ago) was able to locate a wall wart at 5 feet. Great for checking for magnetic/emi fields , but horrible for listening to records. Something to also consider is the location of the mid stage coupling capacitors. Depending on brand they can find a hum source rather well too. The output ones are not much of an issue as the circuitry impedance there is rather low but should be kept away as much as is reasonable from hum souces.

The changes in the design that I just posted a few days ago help mitigate the sensitivity to pick up hum, but they can't compensate for a less than optimal layout or construction.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 15 Apr 2020, 21:11 
Offline

Joined: 03 Feb 2018, 00:47
Posts: 60
Location: Brisbane, Australia
Thanks Bruce. I have K40Y-9 coupling caps on their way. How do you ground the case on those?

I am working through a wiring plan on paper. If I can make it look neat I'll post it up for people to comment. I want to use tag strip and point to point as much as possible, otherwise my obsessively neat nature will force me to layout a pcb and get them made ;)
I bought dual section filter caps (JJ 100uF + 100uF), which makes my layout a bit more interesting, but in the power supply section it should be ok. I will have an extra 100uF unused, is there anywhere it could be used to advantage (like the first filter capacitor maybe)? Or is extra a bad thing?
Thanks again for everythig.
Glenn.


Top
 Profile  
 
PostPosted: 15 Apr 2020, 21:49 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4209
Location: Arizona, USA
Hi Everyone....A flash update that may save you a few $$. Something I just discovered and verified in three of my phono preamps. If you use the Edcor transformer.....You can eliminate the low voltage regulator and its resistors and adjust terminal capacitor and substitute a 1 ohm 10 watt resistor. It turns out that the transformer impedance and rectifier drop work out just about perfectly. You get between 5.8 and 6.1 VDC. The difference in S/N with or without the regulator is too small for me to measure accurately. I'll update the schematic shortly.

Trackhappy, I would probably put it on the second or third section. Putting more on the first section may make the rectifiers conduct for a shorter pulse and increase the ripple current flow (not voltage) and find its way into the ground circuit and show up as a higher peak at 180HZ (in the US) or 150HZ in other countries. I build all my phono preamps (not the commercial ones though) on perf board. I prefer the ones with solder tabs on the them. It makes it easier to secure the parts. You can ground the cases of the K40s by either soldering to them (they are steel) or with a circular wire or clamp.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 726 posts ]  Go to page Previous  1 ... 65, 66, 67, 68, 69, 70, 71 ... 73  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 10 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy