Go Back   Home > Forums > >

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Valve DAC from Linear Audio volume 13
Valve DAC from Linear Audio volume 13
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools
Old 5th March 2021, 07:08 PM   #1501
MarcelvdG is offline MarcelvdG  Netherlands
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
Yes, just replace it with a jumper.
  Reply With Quote
Old 5th March 2021, 08:08 PM   #1502
SonnyMarrow is online now SonnyMarrow  United States
diyAudio Member
 
Join Date: Dec 2016
Got the heatsink for the Maida tapped and drilled and got the standoffs figured out for the DAC and filter board.

The 9-pin connectors will be as close as possible to minimize that distance, then the XLR outputs will be right next to the filter outs.

I also added two standoffs/holes to the filter near the output transformers because they are heavy and to combat the flex. Since there is no solder mask, I put some paint and electrical tape around the holes so the standoffs don't touch the ground pour.
Attached Images
File Type: png maida.png (438.4 KB, 156 views)
File Type: png stacking.png (465.9 KB, 154 views)
File Type: png filtersupport.png (438.6 KB, 156 views)
  Reply With Quote
Old 6th March 2021, 07:55 PM   #1503
Mikky1975 is offline Mikky1975  Italy
diyAudio Member
 
Join Date: Sep 2020
Default Noise floor and things to take care of

Hallo,
I had very little time in the last few month but Iím now ready to (finally!) begin building the dac. Iím therefore re-reading all documentation and the thread.
Concerning noise floor, as measured by Marcel recently: how that can be improved? Low noise regulation? B+ regulation? Do good E88cc make a difference?
Iím asking just to better understand where to put my attention since Iíve not started yet.

Thanks,
Mirko
  Reply With Quote
Old 6th March 2021, 11:23 PM   #1504
SonnyMarrow is online now SonnyMarrow  United States
diyAudio Member
 
Join Date: Dec 2016
I can't say that any of it is necessary, but since this is an expensive project anyway, I went all-out and tried to minimize any noise, usually overpaying for over-spec'd parts just for my own satisfaction lol. Nothing crazy, Vishay RN/CMF resistors, WIMA, Kemet, etc. Every resistor is at least 1%, then the ones that are specified in the schematic to be 1%, I used 0.1%.

I'm using external PSUs for the -300V, the 6.3V, and a 5V for my USB thing. I'm also using this reg for the on-board 5V supply.

My case layout is also really geared towards separating power things from signal, and the signal ground connects to the chassis at one point using this circuit.

Hopefully the efforts aren't wasted. I won't have any way to measure the noise, so hopefully I just don't hear it.
  Reply With Quote
Old 7th March 2021, 09:30 PM   #1505
MarcelvdG is offline MarcelvdG  Netherlands
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
There are a couple of resistors that should be stable and shouldn't have too much 1/f noise, particularly the anode resistors and anode trimming potmeters (RV1 and RV2). I recommend using metal film for the resistors and cermet for the trimming potmeters.

E88CC valves with good matching between their halves could very well lead to a lower noise floor than E88CC valves with somewhat worse matching. If you can measure or record the noise, you could try various permutations of the E88CCs, trim the anode trimming potmeters every time and see if it makes any difference. I used old old stock E88CC's in random order, by the way.

Retrimming the anode trimming potmeters RV1 and RV2 every now and then definitely helps.

Crosstalk from the sigma-delta modulate to the voltage reference or to the clock that drives the lower E88CCs worsens the noise floor, but I don't know any way to reduce that further than it is already reduced. Reducing this crosstalk was the reason to go for a four-layer board with the analogue/mixed signal circuitry on the top, the digital stuff on the bottom and two planes in between. C5, C24, C25 and C34 are also there specifically to keep the crosstalk to a minimum.

For the raw DSD version, you could try different DSD rates and using the bit clock or the master clock.

Last edited by MarcelvdG; 7th March 2021 at 09:35 PM.
  Reply With Quote
Old 8th March 2021, 01:21 AM   #1506
SonnyMarrow is online now SonnyMarrow  United States
diyAudio Member
 
Join Date: Dec 2016
I bought the WaveIO, which has data, word clock, bit clock, master clock, Vin, and 5 GNDs. I think to connect to P9, it's:

data to pin 5
word clock to pin 11
bit clock to pin 9
master clock to nothing
Vin to pin 19 or 20
GND to pins 2, 4, 6, 8, 10?
  Reply With Quote
Old 8th March 2021, 01:56 AM   #1507
acg is offline acg  Australia
diyAudio Member
 
Join Date: Oct 2013
Location: Sunshine State
Quote:
Originally Posted by MarcelvdG View Post
There are a couple of resistors that should be stable and shouldn't have too much 1/f noise, particularly the anode resistors and anode trimming potmeters (RV1 and RV2). I recommend using metal film for the resistors and cermet for the trimming potmeters.
May be a waste of $$, but I have used Vishay Foil 1240W series trimpots in my build, simply because of their position at the anode and because they are less likely to wander than the cemets.
  Reply With Quote
Old 8th March 2021, 12:12 PM   #1508
Mikky1975 is offline Mikky1975  Italy
diyAudio Member
 
Join Date: Sep 2020
Thanks Marcel, acg, SonnyMarrow for the hints, already processed as per your suggestions

I don't seem to find a BOM for the B3 Lundahl filrters, apart from transformers and RM8 inductors suggested by Ray. Does anybody have the BOM handy?

Many thanks in advance for the support!

Mirko
  Reply With Quote
Old 8th March 2021, 12:26 PM   #1509
diyAchim is offline diyAchim
diyAudio Member
 
Join Date: Dec 2012
Re: trimpots - they need to be trimmable from above, otherwise this will be a PITA.

One turn trimmers for the tube balancing seem to me optimal in this position. With a multiturn trimmer it will not be easy to sweep, and sweeping gets you there!
  Reply With Quote
Old 8th March 2021, 06:39 PM   #1510
Mikky1975 is offline Mikky1975  Italy
diyAudio Member
 
Join Date: Sep 2020
Quote:
Originally Posted by acg View Post
May be a waste of $$, but I have used Vishay Foil 1240W series trimpots in my build, simply because of their position at the anode and because they are less likely to wander than the cemets.
I see Vishay 1240W are 1/4W, enough for what they have to dissipate?

Ciao,
Mirko
  Reply With Quote

Reply


Valve DAC from Linear Audio volume 13Hide this!Advertise here!
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
13.8V 80A Linear PS circuit design analysis for Ham Radio Use FJHookah Power Supplies 71 27th October 2019 02:52 PM
Is it tradition that we use linear PSUs for valve amps? Paul Uszak Power Supplies 9 2nd September 2016 10:58 PM
Audio Valve Eklipse volume pot value? Ki Choi Tubes / Valves 0 27th March 2015 05:22 PM
Londog Audio VDt1 Valve Output 24/192 DSD DAC mainscablesrus Mains Cables R Us 1 1st October 2013 06:52 PM
Audio Note DAC 2.1x valve DAC juancho Swap Meet 0 6th July 2005 09:16 PM


New To Site? Need Help?

All times are GMT. The time now is 12:47 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki