Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

#26 pre amp
#26 pre amp
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 Search this Thread
Old 15th January 2018, 07:52 PM   #4571
adam1016 is offline adam1016  United States
diyAudio Member
 
Join Date: Jan 2016
Location: Chicago, IL
Andy, euro21, and Rod,

Thanks so much for the feedback. For the B+ Power supply, would I be good using caps rated at 400V? In PSUDII, the cap spikes at 460V, but only at turn on for about a millisecond, so I'll still use the 450V on that one, but for the other 3, the max seems to be 320V. It's a lot easier and cheaper for me to source caps at 400V.

The other question I have is how to wire in the potentiometer and balance controls. I plan on using 4 Pots total, a coarse and fine pair for the volume, and one for each channel fine adjustment. Essentially, the idea is that I don't want to introduce any unnecessary resistance, and a balance pot would add half of its value at the midpoint. Is this actually something I need to worry about or can I just use a balanced pot? Also, where would I wire it in? I'm thinking at the output, but that leaves the issue about what to do about R8 in the schematic.
  Reply With Quote
Old 15th January 2018, 09:21 PM   #4572
euro21 is offline euro21  Hungary
diyAudio Member
 
Join Date: Sep 2004
Location: Budapest
#26 pre amp
With such high DCR chokes as 155J (1026 Ohm) the 200V output is on the border.
Use higher first capacitor (220nF) and higher bleeder resistor (100k), then output is just over 200V.

Spike on first capacitor???
Empty capacitor (at 0 sec) has virtually zero impedance (only ESR), so its voltage is rising upwards from 0V.

As you can see, the first capacitor peek voltage about 350V so use 450..620V polypropylene.
Attached Images
File Type: jpg 250VAC AZ1 cLCLC PSU.jpg (83.0 KB, 385 views)
  Reply With Quote
Old 16th January 2018, 06:25 PM   #4573
adam1016 is offline adam1016  United States
diyAudio Member
 
Join Date: Jan 2016
Location: Chicago, IL
Euro, Thanks so much for all the schematics, I've bought the parts mentioned in post 4568. I've decided to forgo the balance controls for now, and maybe put a small pot on each monoblock amp if necessary.

In terms of the volume pot, I need help deciding where to wire it, and what value pot to use. Across the output seems like it should work, but that brings in the issue of the relatively high gain of the 01A, which might cause clipping on higher voltage sources. I plan on using a stereo blue velvet, and am wondering where I should wire it in.
  Reply With Quote
Old 16th January 2018, 06:42 PM   #4574
euro21 is offline euro21  Hungary
diyAudio Member
 
Join Date: Sep 2004
Location: Budapest
#26 pre amp
If you use -relatively large value- potentiometer in the preamp, put in the input side.

Gyrator loaded preamp usually has low output impedance, so driving interconnect and power amp is mostly easy. If you use there volume control (except TVC/AVC), lost of majority of driving capacity.
  Reply With Quote
Old 16th January 2018, 06:51 PM   #4575
adam1016 is offline adam1016  United States
diyAudio Member
 
Join Date: Jan 2016
Location: Chicago, IL
Alright, I'm thinking 100K Blue velvet, as keeping it in the middle would be the 47K specified in the schematic. Would I keep the 47K in series, parallel, or not at all??
  Reply With Quote
Old 16th January 2018, 07:48 PM   #4576
euro21 is offline euro21  Hungary
diyAudio Member
 
Join Date: Sep 2004
Location: Budapest
#26 pre amp
Quote:
Originally Posted by adam1016 View Post
I plan on using 4 Pots total, a coarse and fine pair for the volume, and one for each channel fine adjustment.
Why?

IMHO balance is totally unnecessary. Completely uninteresting that sweet spot is in the "middle", or need to sit other position in the sofa.

Coarse and fine tuning separation also wasting of money.
Good (If I use potentiometer, regularly use Noble, TKD or black Alps -RK40- ones) potmeter cost is over 100 dollar.
Matching accuracy 0.2-1dB, attenuation 0...50dB.
If it's a "clicking" version, the steps about 2dB.
Value is indifferent, if you use 22k..200k range.

I don't understand why must use "fine tuning" if the amplifier stages gain is adjustable to equal.
  Reply With Quote
Old 17th January 2018, 03:33 AM   #4577
adam1016 is offline adam1016  United States
diyAudio Member
 
Join Date: Jan 2016
Location: Chicago, IL
True, I'll be able to adjust the gain on the monoblocks.

In terms of wiring, I've come up with the following:
Click the image to open in full size.
Is there anything I should look out for in terms of wiring/grounding/noise gotchas while building this amp?
  Reply With Quote
Old 17th January 2018, 07:33 AM   #4578
euro21 is offline euro21  Hungary
diyAudio Member
 
Join Date: Sep 2004
Location: Budapest
#26 pre amp
My version of 01a preamp.
The second picture is my #26 preamp grounding scheme.
Attached Images
File Type: jpg 01a gyrator loaded preamp.jpg (84.6 KB, 263 views)
File Type: jpg My[1].jpg (78.5 KB, 265 views)
  Reply With Quote
Old 17th January 2018, 12:38 PM   #4579
king4joy is offline king4joy  Hong Kong
diyAudio Member
 
Join Date: Apr 2011
With your first picture, there is a slight typing error.......the + side of the filament is open...

I think
  Reply With Quote
Old 17th January 2018, 03:24 PM   #4580
euro21 is offline euro21  Hungary
diyAudio Member
 
Join Date: Sep 2004
Location: Budapest
#26 pre amp
Quote:
Originally Posted by king4joy View Post
the + side of the filament is open...
There are no filament, so + side also missing. :-ppp

I haven't proper 4 element Spice model for 01a, so use 3 element (anode, grid, cathode) one.

The R12 (10R) represents the half filament, which is need for proper filament bias voltage.
  Reply With Quote

Reply


#26 pre ampHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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


New To Site? Need Help?

All times are GMT. The time now is 01:46 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki