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 27 Oct 2020, 22:39

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 143 posts ]  Go to page Previous  1 ... 11, 12, 13, 14, 15  Next
Author Message
PostPosted: 19 Apr 2020, 13:23 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
Sucsessfully completed build and it sounds AWESOME. :up: The gain is quite high but no problem with that. I used 500k pot on the input so there is some room for regulation. PS is solid state for both heater and B+. Will post the fotos when the chassis and input selector are ready. Thank You All for sharing this project, it helped me pass those sad days doing something stimulating. :beerchug:


Top
 Profile  
 
PostPosted: 16 May 2020, 04:40 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
Greetings, i'm still working on finishing this preamp, currently i'm on opamp RIAA stage designed by Bruce http://diyaudioprojects.com/Chip/Opamp-Phono-Preamp/ that i like to add to this little wonder :P
Now i need some help: i have poor performance when using this preamp to drive TA2024 based SS amp, but it works like a charm with my other system. Looking at schematics i see that TA2024 has 2,2uF capacitor at input so it is connected in series with 0,68 uF that i use as output decoupling in this preamp ( Cc on schematic). Is this the reason of poor performance? I'm about to bypass input capacitor in TA2024 but input is biased at 2,4V dc for gain setting resistance so maybe it's better to increase both capacitors ( Cc on preamp out and TAs input capacitor) to 4,7uF so it will result in 2,3 uF of total capacitance? My skills are insufficient and so my English so please be patient... any help will be appreciated.
Here is datasheet of TA2024 http://www.wolfteck.com/assets/Tripath%20TA2024.pdf
Thank you.
Witek


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



Top
 Profile  
 
PostPosted: 16 May 2020, 13:37 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1698
Location: US Pacific Northwest
A couple of things to consider.

First, the cathode follower was not designed for a 12AT7. It was designed ONLY for a 12AU7. Make sure that is the tube in the cathode follower socket.

Second, your schematic indicates a 12AT7. If you are using this in the preamp stage, the gain will be about ≈21v/v or 26.5 dB with a unbypassed cathode and ≈33v/v or 30.4dB with a bypassed cathode. In either case, this is a tremendous amount of gain.

Your schematic of the TA2024 amp shows it wired for a gain of 12v/v or 21.6dB. So for one watt out into 8Ω you need 2.83v-rms output which means 236mV-rms input. The TA2024 amplifer is a relatively sensitive amplifier that would not normally be used with a moderate gain preamp of this type. My guess is that you are seriously overdriving the TA2024 amp with this preamp. I would try a 20dB pad between the two before you do anything else.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
PostPosted: 16 May 2020, 14:55 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
Thank You for response i have to specify what i mean by "poor performance": mid and high tones are very clean and stage is well rapresented, the problem is lack of body in the low freq range, percussion souds like cheap electronic drum machine: shallow and click sounding.
I know that cathode follower is designed for 12AU7 tube and i'll get one ASAP, but the 12AT7 tubes i have are probably at their end of life, i recovered them from an 60's Grundig reel to reel with years of use done and mechanics permanently damaged, so probably gain is far from what it should be... before trying with Ta2024 i used to listen this pre connected to my Technics ss amp and at pot set to 10 clock soud level was the same as other sources... If there is some measurment that i can do please let me know. I measured preamp frequency response with my pc soud card and Rightmark Audio Analyser and it is very good, i don't know how to measure TA2024 output because it works in brigded mode and negative output pin is not at ground potential...
Thanks again for helping, i really appreciate it.


Top
 Profile  
 
PostPosted: 16 May 2020, 18:11 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
Suncalc wrote:
I would try a 20dB pad between the two before you do anything else.

1k3 for series resistor and 150r for shunt are ok?


Top
 Profile  
 
PostPosted: 16 May 2020, 18:25 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1698
Location: US Pacific Northwest
Sounds reasonable.

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
PostPosted: 17 May 2020, 15:36 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
20dB pad did not solve the problem, it give me liberty to go up to the max with volume pot but the low freq was still missing, so i try to substitute crucial caps on ss PA and it worked. Changed power rail caps with elna 1000uF (the board originally was equipped with cheap chinese caps 470 uF measured esr 3,6 ohm!!) and decouplig caps (was 1uF electrolitic and 1uF MKP) with 2,2uF wima's. Now it's playig much better, better then i would expect for such cheapo amp. I really enjoyed doing this project and i would like to thank to the author Suncalc for sharing and help. And this is how it looks:


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



Last edited by Witek on 17 May 2020, 18:09, edited 3 times in total.

Top
 Profile  
 
PostPosted: 17 May 2020, 16:07 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
the main board:


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



Top
 Profile  
 
PostPosted: 17 May 2020, 16:08 
Offline

Joined: 05 Apr 2020, 10:39
Posts: 10
Location: Tuscany, Italy
RIAA stage: Thanks to Bruce


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



Top
 Profile  
 
PostPosted: 17 May 2020, 23:50 
Offline

Joined: 23 Feb 2017, 02:02
Posts: 677
https://www.electronicproducts.com/RC_F ... ator.aspx#
You will need to use a 1.8uF capacitor to allow cut off below 20hZ when feed into the op amp of 20k input impedance
Not 0.68uF

And if you put two 2.2uF in series you only get half the capacitance 1.1uF


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 143 posts ]  Go to page Previous  1 ... 11, 12, 13, 14, 15  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Majestic-12 [Bot] and 24 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