preamp to handle peaks - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

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

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 12th June 2012, 12:55 AM   #1
emosms is offline emosms  Bulgaria
diyAudio Member
 
Join Date: Sep 2010
Default preamp to handle peaks

Hi
I want to build simple tube preamp for my guitar audio interface.
My guitar pickups have a really high output.
I enjoy the agresive tone and gain with overdrive, but it is pretty hard to set nice clean tone.
Cannot avoid the peaks that cause cracklings when I pluck the strings hard.
---
Consider smth. that can handle 3v, lets say 5v input signal peak...
Is it possible?
---
I would like to build it with 1pc 6n2p-ev. Military russian valve, low gain analog of 12ax7.
Do I have to keep high anode voltage, to achieve that?
Max anode voltage - 300v. I plan to power the unit with 9 v like the other effects, then use a transf to get +306 supply.
Then keep the voltage at anode 250-275?
---
Can you point me to some similar solution and schematics - to handle high peaks?
My first idea is to recreate the input stage of some classic guitar amp, the first valve only, then line out. I want to make the thing nice small and neat.
---
Pls, tell me if I would benefit to use input/output transf, especially the output transformer compared to simple voltage divider for line out.
Best Regards
  Reply With Quote
Old 12th June 2012, 01:08 AM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Guitar and instrument amplifier related questions belong in Instruments & Amps. Please see header at top of tubes/valves and I&A. Moving it should get you some useful input as well.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 12th June 2012, 11:57 AM   #3
diyAudio Member
 
Join Date: Apr 2010
You want to use a 12AU7 in the first position and bias it for -6V.
  Reply With Quote
Old 12th June 2012, 04:58 PM   #4
diyAudio Member
 
Loudthud's Avatar
 
Join Date: Nov 2007
Location: Near Dallas Texas USA
The best way to handle a signal that big is with a variable gain stage on the front end consisting of two or possibly three opamps. Follow that with a tube stage to add the warmth. An output transformer could be used for a line output, but finding one won't be easy.
  Reply With Quote
Old 12th June 2012, 05:59 PM   #5
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
Sounds like you need a Compressor !!

jer
  Reply With Quote
Old 12th June 2012, 06:27 PM   #6
diyAudio Member
 
chrispenycate's Avatar
 
Join Date: Aug 2006
Location: Geneva, Switzerland
There should be no problem getting a tube to handle the voltage (or quite a lot more) but running off nine volts and getting heater voltages (6.3 or 12.6 volts) and and anode (several hundred) seems inefficient. Why not start with a power supply (which will not, admittedly, be "small and neat", but needn't be enormous) with enough spare capacity to handle a few more tubes if you should decide to go that way?

But how are you going to handle the problem of the line out still being too peaky and dynamic? A clean preamp's basically going to reproduce what you put into it (normally higher level; this time perhaps not). If the input starts distorting (which it will do much more pleasantly than a transistor, definitely), clipping off the peaks, can you still refer to it as "clean"? You can do that with much lower anode voltages – 120-150 will work fine. And "line output" doesn't really mean that much, here; what were you intending to run it into? We tend to use different drive/impedance characteristics for going into instrument amps, PA/recording consoles or long cables.

Most standard tube guitar amps have pretty standard front ends, generally run at maximum gain, which would give you 50 0r 60 volts of signal from your five (it's easy enough to attenuate it, but did you want to go there in the first place?) Standard line level is only 0.775 volts RMS; you might be stepping down your guitar to reach it.
  Reply With Quote
Old 12th June 2012, 07:18 PM   #7
emosms is offline emosms  Bulgaria
diyAudio Member
 
Join Date: Sep 2010
Tried to simulate some schematic. Actually, lets say to handle ... +-10 volts from a really nasty hum. I coil tap my neck hum and I love it, but still too high output. Nice for gain, bad for clean if I hit hard. It is even parallel, when not tapped, but stili i get some craclkings.
I suspect, the problem is that the audio interface is USB powered, so at +5v supply it could easily distort and do that pretty bad.
Click the image to open in full size.
---
diagrams at RV1-max and min setting:
+-10v input. Is it ok that it clips one sided? is that pleasing soft clipping?
http://oi50.tinypic.com/1414fhx.jpg
http://oi48.tinypic.com/1ha17b.jpg
---
+-5v
http://oi48.tinypic.com/33116wj.jpg
http://oi47.tinypic.com/24busnq.jpg
---
+-3.5 no clipping at max gain
http://oi50.tinypic.com/x9eet.jpg
---
Could I have the valve compress the signal? I see the gain is lower when it clips, and if it is not harsh clipping, maybe it is ok. Not sure if this clipping sounds like a clean sound, but half the wave is compressed a bit.
---
Abt the peaks and the next stage - I will simply turn it down from the line out pot. I will also try to play with it as a bass gtr direct box for to mixer (consider adding a balanced out) so I will keep the gain pot - smth like "sensitivity"
---
Abt compressor - dont really like compressors, it really ruins it. I have never had a good compressor, only guitar rig simulation, but sounds unnatural. Mby will try some for bass or for recording and mixing - dont understand that matter.
What if I use a lower gain tube like 6DJ8/ECC88, it has a gain 33.
---
I will look for that opamp solution, but my hopes are that simple dbl_triode solution can handle and "compress" it and if there is some clipping - it would sound nice like a bit sparkled still clean tone. How to set it so that it compresses a bit naturally?
p.s.
got new graphics, set the overal gain to 3 at max. it starts clipping really soft at 5.5 v) the at +-10v the upper half has a gain bit more than 1.5, the lower less than 3, no clip
At gain pot to min the gain is 2 at 1v. at 10v it is a bit over 1.0 for the uper half and 2.0 the lower (no clip)

Last edited by emosms; 12th June 2012 at 07:47 PM.
  Reply With Quote
Old 12th June 2012, 09:39 PM   #8
emosms is offline emosms  Bulgaria
diyAudio Member
 
Join Date: Sep 2010
12au7 seems to work
have some doubts it could be substituted with 6n1p
but no compression, peak comes, peak goes throug. Dont know if I let double less signal to the next stage.
or apply some variable gain opamp, but mby after the valve.
or some simple optical compressor set at high threshold. have no idea about it and if the LDR and led parts are critical

Last edited by emosms; 12th June 2012 at 09:43 PM.
  Reply With Quote
Old 13th June 2012, 09:07 AM   #9
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
A good compressor will allow you to set the knee at a very high threshold so that only the very tips of the peaks get compressed with out messing with the dynamics of the overall signal.

It is common practice to over do it and have it to start sounding bland with no dynamics at all.

This is commonly built into some bass amps as well (namely Peavey) to help maintain a clean tone without clipping the power amp.

FWIW

jer
  Reply With Quote
Old 13th June 2012, 06:19 PM   #10
diyAudio Member
 
chrispenycate's Avatar
 
Join Date: Aug 2006
Location: Geneva, Switzerland
Personally, I much prefer symmetrical clipping, and I would set the anode of your first section to half rail, then bias the cathode follower to that – despite bootstrapping, I can see no reason to go down as low as 1kΩ on a tube grid. And remember, while a cathode follower brings down the output impedance, it can only current drive in one direction. The tube can pull the output up pretty fast, but the 100k resistor can only take so much current going down. (One reason to run on a slightly lower HT voltage, so you can centre the output on a smaller cathode resistor.) Anyway, your average DI box will take up the slack.

If you want soft clipping it's actually easier to use semiconductors somewhere the voltage is around the three or four RMS (X3 for peak to peak, though with guitar waveforms) a few diodes in series with resistors round them, cheaper the diodes, better they work (I'd draw a picture, but haven't got anything I can import directly onto this site yet).
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Resonance Peaks NTSBuilding Multi-Way 7 4th February 2010 10:16 PM
Where are peaks and nulls most offensive valleyman Full Range 3 21st November 2008 06:00 PM
Notch filter for FR peaks help! Vikash Multi-Way 11 9th December 2006 12:58 AM
100 – 3000Hz, 95+ dB, without peaks?! rick57 Multi-Way 25 27th March 2006 02:49 AM
Powered sub peaks MichaelJHuman Multi-Way 0 10th September 2005 12:39 AM


New To Site? Need Help?

All times are GMT. The time now is 07:53 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2