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

Instruments and Amps Everything that makes music, Especially including instrument amps.

Reducing Signal Voltage for FX Loop
Reducing Signal Voltage for FX Loop
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 October 2018, 03:45 PM   #31
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
Originally Posted by fozzy215 View Post
TBH, I wish I had such an interest when I was a kid, to pursue electronics as a career. But it's never too late to learn and I'm enjoying the process.
Well.I did When I was 16 I started studying Industrial Engineering and wanted a "peaceful noiseless" Hobby for fun, since I moved to Downtown Buenos Aires (think Downtown NY or London for comparison) from a rural City in the middle of the Pampas where I had enjoyed model plane building and flying, launching homemade rockets, wild stinking Chemistry experiments, etc. , much frowned upon by close neighbours, typical of living in the dense built core of a large City.

I was a big fan of the old Popular Mechanics magazine and built as many projects from it as I could, but most activities were noisy, foul smelling or needed machinery unsuitable to appartment life, so Electronics was both cool and inconspicuous.

But before the current Oriental onslaught, (we are talking 1969 on here) "whatever you made you could sell" so I started making and selling "color organs" (light show machines) to Discos, then Strobe lights (I was the first guy making them in Buenos Aires), my first Guitar product was a Treble Boost pedal (think the silicon version of Dallas Rangemaster) straight out of Popular Mechanics, then my first Bass amp: a Fet input Ampeg BT15 preamp clone driving a Motorola 100W amplifier, then a long string of Blackface Fender clones, from a Champ to Bassman 50 to Twin Reverb versions.

That started in 1969, it will be 50 years in the Profession next February, have already built and sold over 14000 amps and cabinets, (lost count around 2004) but my current customer database , started in 1999, holds some 8500 phone numbers.

Oh, and what happened with the University?
Actual manufacturing and selling took more and more of my time, plus I had to "adjust" my career to actual needs, so after 4 years of Industrial Engineering I switched career name and University and added 2 years of Electronics Engineering and then switched to 1 extra year of Business Administration.

So I donīt *really* have a Degree hanging from my wall although my formation was very solid and focused ... plus 50 years experience actually *doing* it.

In fact, former University pals, who persisted and got their degrees, generally donīt work "as Engineers", running actual production in some Industry, but do Administrative work, or are glorified salesmen ("Sales Engineers") or are registered "Expert Witnesses" at some Court or glorified Math or Physics teachers and so on.

If I had to do the same today, it would be all but impossible, who can beat *cheap* *cheap* Oriental Electronics, which to boot are rising in quality?
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
  Reply With Quote
Old 6th October 2018, 04:58 PM   #32
fozzy215 is offline fozzy215  United States
diyAudio Member
 
Join Date: May 2018
Location: Philadelphia, PA
Quote:
Originally Posted by JMFahey View Post
Well.I did When I was 16...
That's a pretty impressive resume. While it may seem impossible today, with the internet and social media you have access to a much larger market. Sure, the competition is proportionally just as big, but just look at all the "boutique" pedal companies out there now. It seems like there's hundreds of 'em making Tube Screamer clones. All it takes is a well known YouTuber to review your product and then boom - you're the next "big thing".

While it' easier said than done, so is the career path that you've managed for yourself.

While I'm in no position at the moment to do it, I've pondered the idea of starting an audio company. The pedal industry is completely saturated, but there will always be a market for tube amps. I guess it's easier entry to make pedals, which suggests why there's so many companies (likely most are just a dude and his wife) doing it. Most of the small amp companies seem to just make Fender/Marshall/whatever clones. I've seen very few that actually try to develope their own unique "sound". I guess whatever sells, right?
  Reply With Quote
Old 6th October 2018, 05:49 PM   #33
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by JMFahey View Post
If I had to do the same today, it would be all but impossible
What you have done is pretty amazing. You are Argentina's own Leo Fender mixed in with Hartley Peavey (from the days when he was an innovative manufacturer who made really good products.)

I know those once-amazing pampas that you grew up on, have mostly disappeared now too, just like the possibility of a simple and successful life as an electronics engineer.

The electronics engineers I knew all either changed careers, became (bad) managers, or became "field application engineers" for semiconductor manufacturers.

"Field application engineer" is management-speak for "underpaid person who drives around trying to sell our parts". I still have memories of one particular "Field application engineer" who would show up in a tight white shirt and tighter blue jeans, sit on the desks of single young engineers, flipping her hair casually and flirting with them like crazy in the attempt to get them to order semiconductors from the company she worked for.

I'm not sure whom I felt more sorry for - the "engineer" flirting to try to make a living, or the lonely engineers whose vulnerabilities she was trying to take advantage of.

-Gnobuddy
  Reply With Quote
Old 11th October 2018, 01:08 AM   #34
Max999 is offline Max999
diyAudio Member
 
Join Date: Jun 2017
I have been reading this thread with great interest. The way Soldano did the effects send is not really common I think.

I am interested in the output impedance of this circuit.
Is it the CF output impedance + the voltage divider output impedance or is the CF output impedance replaced by the voltage divider output impedance?

If it is the latter I wonder what would happen if the resistor to ground would be smaller then the CF output impedance ...

Hope you don't mind that I bring this up in your thread Fozzy2015
Attached Images
File Type: gif soldano fx loop send.gif (4.2 KB, 20 views)
  Reply With Quote
Old 11th October 2018, 02:11 AM   #35
fozzy215 is offline fozzy215  United States
diyAudio Member
 
Join Date: May 2018
Location: Philadelphia, PA
I don't mind at all! In fact, that very circuit was what originally inspired this thread. IMO, if you ignore the fact that it's DC coupled, it's not uncommon (most modern amps use AC coupled). In the SLO's instance, that particular CF is intergral to the preamp's tone, and IMO is a nifty way to drop the signal down to manageable levels. It's funny that it's often criticized - even suggesting Soldano "made a mistake". I recently saw a video of him talking about the SLO loop, and he indeed designed that way on purpose (obviously).

I don't know the exact answer to your question. I'm sure someone will chime in soon. My guess is it's 2.2k || impedance of CF.
  Reply With Quote
Old 11th October 2018, 02:18 AM   #36
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
The CF is "few K". This is in series with 100K, so we have 100+few K. Pessimistic, 103K.

The other path is 2.2K.

at most: 103K||2.2K = 2.154k
at least: 100K||2.2K = 2.153k

The CF impedance is nearly irrelevant.

Note that if *instead* we had come from the plate of a common cathode stage, Zout like 39K, it is 2.16k so not significantly different in impedance. (Apparently the distortion is different.)
  Reply With Quote
Old 11th October 2018, 04:13 PM   #37
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by PRR View Post
The other path is 2.2K.
There is also the extremely undersized 1 uF coupling capacitor to consider. At 80 Hz, it has an impedance of about 2k ohms, which has to be added to the output impedance of the CF + resistors, essentially doubling the output impedance of the entire send circuit.

Using a 10uF cap would have virtually eliminated this problem, and 10uF caps only cost pennies more than 1uF caps, worst case.

What a pity to double the send impedance simply by using an inadequate coupling cap!

-Gnobuddy
  Reply With Quote
Old 12th October 2018, 03:32 AM   #38
Max999 is offline Max999
diyAudio Member
 
Join Date: Jun 2017
So if we would make the 2.2K resistor 500 Ohms, the output impedance would be
103K || 500 Ohms = 497 Ohms PRR?

I saw the same Soldano clip Fozzy215. Maybe people don't like the loop because they try to use it with instrument level pedals. I called the design uncommon because I thought that most effects loop sends put the voltage divider before the CF, but I will look up some well known amp designs to check now. The DC coupled CF is undeed something that adds 2nd harmonic distortion, I have a feeling you are already familiar with this link The Valve Wizard

Cool that you spotted the too small cap Gnoboddy, I did not thought about it raising the output impedance, but since Soldano intended it to feed line level gear ( 10K-22K input impedance) I would also make it bigger to make the low end a tad more "transparant".

Does the 1M resistor serve a purpose?
  Reply With Quote
Old 12th October 2018, 07:58 PM   #39
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by Max999 View Post
So if we would make the 2.2K resistor 500 Ohms, the output impedance would be
103K || 500 Ohms = 497 Ohms PRR?
Plus/minus the usual 10% or more...none of these numbers is exact because of component tolerances. Fortunately, for audio electronics, we rarely care if things are as much as 10% off-spec. (With some exceptions, like high-order active filters.)

Quote:
Originally Posted by Max999 View Post
Does the 1M resistor serve a purpose?
Yes, it does! It's there to make sure the 1uF coupling cap has a path to ground, so it can finish charging up once the amp is powered on.

If you don't have that 1M resistor, the capacitor won't be able to charge. The left end of the cap is at a slight positive voltage, and when you plug the FX send into some other piece of gear, the input of that device provides a path to ground for the right end of the 1uF cap. So now the capacitor charges through the input of that external FX gear, and you hear a big "Thump!" through your speakers.

So the 1M is there to try to stop "thumps" when you plug the send signal into some external piece of gear.


-Gnobuddy
  Reply With Quote
Old 13th October 2018, 02:22 AM   #40
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Quote:
Originally Posted by Max999 View Post
So if we would make the 2.2K resistor 500 Ohms....
You have 1/4th the level.

At any "reasonable" impedance, Level is more important than exact impedance.

Most guitar-cord stuff will be 50K input or more. By the 10X rule, anything 5K or lower is "real low" source impedance, we don't need an exact number.
  Reply With Quote

Reply


Reducing Signal Voltage for FX LoopHide 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
Need help reducing voltage going to led JimBanville Parts 10 12th June 2015 08:10 PM
Reducing Signal Level Without Affecting Tone howe0168 Tubes / Valves 5 27th April 2013 04:57 PM
reducing voltage rtill Solid State 28 16th January 2009 01:45 PM
Reducing PSU Voltage hernanstafe Parts 1 9th March 2007 05:14 PM
reducing spdif signal level Sjef Digital Source 10 29th May 2005 04:24 PM


New To Site? Need Help?

All times are GMT. The time now is 09:44 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