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

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

My private blowtorch clone
My private blowtorch clone
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 6th April 2020, 09:28 PM   #1
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
Default My private blowtorch clone

In hommage to the great Joachim Gerhard, who generously shares his insights in his „My private ...“ threads, and of course also to John Curl, who came up with this line stage in the first place, I finally came around building my own version of it. So far nothing to write home about, however I tried a bunch of things and wanted to share my findings here, hope you like it!
(Trying to structure everything into individual posts, based on the topic)

Here in the middle my version. Slightly less beautiful and refined, I know…. But still trying to keep up with the original design! (To a loving father, every child looks most beautiful ;-))
It has the same 5 position input, but only one volume control (with LDRs), and the phase switch has a middle “zero” position that serves as output mute.
Attached Images
File Type: jpg ctc-love.jpg (16.6 KB, 434 views)
File Type: jpg bt1 in rack.jpg (177.3 KB, 439 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:30 PM   #2
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
Here is the backside. I used lots of Neutrik XLR and RCA connectors, and an industrial (M12) connector for the power.
Attached Images
File Type: jpg bt1 backside.jpg (137.0 KB, 437 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:31 PM   #3
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
The case is made from two aluminum sheets (top and bottom), held by side plates made from wood, and the front- and backplates also from aluminum. All metal sheets are 4mm thickness. Here is a picture showing the structure of the case.

Another picture shows how the top plate is recessed, by the thickness of the heatsinks mounted on top, to achieve a flat top surface. The heatsinks are SK105 from Fischer-Elektronik, with 15mm thickness.
Attached Images
File Type: jpg bt1 sidewall.jpg (94.5 KB, 432 views)
File Type: jpg bt1 recessed heatsink full view.jpg (247.8 KB, 422 views)
File Type: jpg bt1 recessed heatsink.jpg (134.6 KB, 102 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:33 PM   #4
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
The whole thing is powered with switchmode DCDC converters (+/- 48V and +/-12V, independent for both channels), and the input voltage is a 24V SMPS, hence no second case for the PSU. Attached are the pictures showing the power supplies.

On the right side, four DCDC converters take the input 24V to create the +/-48V for the amplifier. On the perfboard are some post-filters to reduce high frequency noise, and additional DCDC converters to convert the input 24V to +/-12V for the relays and servos.
They are all mounted to the bottom side of the case, to provide the necessary cooling. In operation they hardly heat up, so no problem there.
Attached Images
File Type: jpg bt1 onboard psu.jpg (272.3 KB, 269 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:36 PM   #5
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
Here a picture of the (partly stuffed) PCB I made (one per channel), indicating the different functional blocks.
Turns out the PCB was designed with a rather hot needle, so it looked quite different once I had finished debugging ;-)
(Sorry, I don’t think I will make these PCBs available, since the bug fixing part would be very frustrating to everybody – believe me I’ve been there ;-( )


Red (on the left): Input selection reed relays
Yellow: LDR-based attenuator
Blue: The actual amplifier circuit
Purple: Output phase selection
Green: Servo
Blue-green: Voltage regulators
Attached Images
File Type: jpg bt1 pcb.jpg (250.3 KB, 299 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:37 PM   #6
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
This shows the amplifier PCBs in the case, along with the input / output wiring and all the control leads for the relays and volume. The well-trained DIY eye will easily spot the additional cables, resistors, modifications, …. Took me quite some time to iron everything out…..
Attached Images
File Type: jpg bt1 amp inside.jpg (455.6 KB, 287 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:37 PM   #7
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
But what is that grey blob on top of the amplifier stage? It's a 3D printed heat spreader.... I wanted to put something to protect the JFETs from temperature differences, a simple copper foil would have done but we live in the 21st century, so I opted for something more rocket-sciency ;-)
The material I wanted is ceramics, but that would have been crazy expensive, so I settled for aluminum-filled nylon. Put some thermal grease on top of the transistors, and carefully slide it over them, fix with a screw.
Attached Images
File Type: jpg bt1 heat spreader.jpg (133.4 KB, 232 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:38 PM   #8
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
The power transistors (Fairchild FQA19N20 / FQA12P20) are mounted below the PCB. The second picture shows the “sandwich”, and the mounting screw is accessible through a hole in the PCB. I actually had enough space in the amplifier, but this was more of a challenge ;-)
The transistors are first mounted onto the metal plate with silicone pads, screws not fully tight. Then, the PCB is lowered onto the transistors and each lead of the eight transistors carefully inserted, then the PCB is fixed with some screws and distance pieces, finally the transistor mounting screws are tightened and then the solder joints made. That ensures least possible mechanical stress on the solder connections.
Attached Images
File Type: jpg bt1 mosfet mounting screw.jpg (159.7 KB, 169 views)
File Type: jpg bt1 mosfet mounting 2.jpg (242.9 KB, 156 views)
File Type: jpg bt1 mosfet mounting.jpg (224.9 KB, 150 views)
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:39 PM   #9
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
And, just as a side comment – I have never before built a line stage with 15dB gain, using 16 power transistors in TO247 package... ;-)))
__________________
Paradise documents are here: Link list
  Reply With Quote
Old 6th April 2020, 09:40 PM   #10
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
My private blowtorch clone
The MOSFETs were also matched, using a little test circuit sketched on the back of an envelope (literally ;-)), a little amplifier with the same bias current as in the final amplifier, with 0.5V RMS sinus input, measuring the output amplitude, and matching the transistors for output amplitude as close as possible, both N and P. Of course, the gate voltage needs to be adjusted, for every transistor to run at identical drain current.
Attached Images
File Type: jpg bt1 mosfet selection1.jpg (241.7 KB, 155 views)
File Type: jpg bt1 mosfet selection2.jpg (696.4 KB, 202 views)
__________________
Paradise documents are here: Link list
  Reply With Quote

Reply


My private blowtorch cloneHide 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Private messages Bonsai Forum Problems 26 24th May 2020 02:19 PM
When a Luxman clone is not a clone carlmart Solid State 68 3rd January 2020 09:16 AM
Generic Asian Clone driver board RE and Clone jacampb2 Car Audio 26 3rd July 2018 08:01 PM
FS: Drivers for JBL 250Ti clone (LE14, 108H clone, 104H-2 GordonW Swap Meet 10 20th May 2014 08:19 PM
Question regarding ProAc 2.5 Clone and Tempo 2 Clone zoooh Multi-Way 5 11th March 2003 08:19 PM


New To Site? Need Help?

All times are GMT. The time now is 08:35 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki