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.

Suggestions for a Medium Gain Guitar Amp Topology...
Suggestions for a Medium Gain Guitar Amp Topology...
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 1st February 2018, 02:29 PM   #11
flysig is offline flysig  United States
diyAudio Member
 
Join Date: Apr 2009
I've been working on a similar project, also with a cathodyne phase splitter. After poking around the web, a 6SN7 push-pull power output stage gets good mention for tone. V+ around 250V.

For the output transformer, 6k primary resistance was found to be very good sounding, even though on paper something around 20k makes more sense. The Hammond 125A has lots of taps so you can experiment with different impedances.

The 12BH7 is another tube which gets pretty good reviews in low wattage guitar amps.

I haven't come across anything on low wattage amps which indicates pentodes have superior tone. All of these amps are using preamp tubes, not small power tubes. Thus these tubes are really aimed at voltage amplification rather than driving lots of current. Maybe that's why triodes are ok too in low wattage applications.

Using a power soak on your regular amp is not a bad option. The Weber Micro Mass does a good job on my 15W Fender Super Champ XD.

With low wattage you can never get to that point of interaction between guitar and amp which only happens at high volumes.

Last edited by flysig; 1st February 2018 at 02:52 PM.
  Reply With Quote
Old 1st February 2018, 03:34 PM   #12
tristanc is offline tristanc  United Kingdom
diyAudio Member
 
Join Date: Dec 2015
Location: Oxford
Suggestions for a Medium Gain Guitar Amp Topology...
Quote:
Originally Posted by jcarr View Post
Have you considered a similar concept as this project by Tristan Collins?

Merlin High Gain Preamp + Firefly Output Tristan Collins
Quote:
Originally Posted by Gnobuddy View Post
Interestingly, Mr. Collins doesn't actually say that he liked his creation!

(Though he does say he disliked it's predecessor, a Firefly.)
Quote:
Originally Posted by jcarr View Post
The living-room amp that Mr. Collins declares his liking for is the N5X to AX84 HO, but it is a 5-watt design.

N5X to AX84 HO build Tristan Collins
Wow, someone reads my site!

I ended up having three builds with very similar preamps (basically the High Octane but converted to Merlin's High Gain) but with differing tone stacks or power amp sections - self split, EL84/6V6 and EL34.

Of the builds I'd recommend the Merlin High Gain Preamp + Firefly Output. I think I may have hit the sweet spot with that one, perhaps by accident. Gain down and Master up you get the power amp distortion and it is surprisingly loud. Go the other way and it is, well, as Merlin says, High Gain.

At home I play the firefly and EL84 builds through a Tayden 12" True Brit at living room / neighbour friend levels (terrace house...).

All the bits are available from Barry at AmpMaker + an enclosure from BlueBell Audio.
  Reply With Quote
Old 1st February 2018, 04:03 PM   #13
Rootz is offline Rootz
diyAudio Member
 
Join Date: Jan 2010
As I see it you've got roughly two options:
- Reactive load and re-amplifying;
- Pre amp distortion;

I see no way to get cone breakup and distortion without annoying your neighbours. That breakup is however part of the sound of a cracked Marshall through 1 or 2 4x12 cabinets. Those amps push the speakers beyond their linear range. Furthermore the amps themselves distort on multiple levels: power supply sag, OT saturation, preamp, phase inverter, power tubes reaching saturation, blocking distortion. I probably forget some mechanisms.

Those old amps with very moderate gain clean up very easy. Very good amps when you just want to use the volume control of your guitar and maybe a boost pedal to push the amp over the edge distortion wise. Not so good for full on metal though.

I have neighbours and a pair of ears which need to be handled with care. So I've build a reactive load for my bigger amps. I based the load on my 4x12 with greenbacks. Same impedance peak at 110 Hz and the same rising impedance toward the higher frequencies. I don't know how to compensate for back emf produced by the cone movement and haven't investigated the influence on the behaviour of the amp. Nevertheless, many people were utterly impressed when hearing the load and it performed way, way better than the Hotplate and Ultimate Attenuator I had back then. Playing the amp flat-out through it is hard on the amp though, but so is playing flat-out through speakers. Output valves replaced every 6 to 12 months (frequent player/usage).

Later I build a complete pedalboard with some commercial and mostly home build pedals. Totally different sound. Not as lively or organic I'd say, but very portable and versatile.

Now a AC4 with your speaker is never going to sound like a 100 Watt Marshall. It's got its own sound and will sound steller with some overdrive pedal or a vintage fuzz in front of it.
  Reply With Quote
Old 1st February 2018, 05:46 PM   #14
tristanc is offline tristanc  United Kingdom
diyAudio Member
 
Join Date: Dec 2015
Location: Oxford
Suggestions for a Medium Gain Guitar Amp Topology...
Quote:
Originally Posted by LeftHandFool View Post
Good evening all,
Ideally, I'm trying to get an amp that'll comfortably do 'crunch', and clean up with the volume pot, with extra gain on hand (or perhaps at foot) for the gratuitous twiddly bits.

For the output stage, I'm looking to go <4W. Because I already have some, the first choice is to try the EF86 out, either push pull, or dual single-ended.
In the event of push-pull, I'm leaning towards a cathodyne phase inverter, simply because I haven't tried one before.

Any other suggestions are also welcome. As a project, it's still at the conceptual stage thus far.
The chassis I'll be using is currently punched for 5 noval sockets, but there's room for at least 2 more. HT+ will be around 320V.
Thinking about it - a cathode biased PP or SE with VVR for the PA might fit the bill?

AmpMaker's N5X is an ideal platform to start from for a PA in that case. My N5X build turned in to the Merlin High Gain preamp through tweaking, but with the Power control on 0 you are definitely getting PA distortion at low-volume levels if that is what you're after. And the difference between EL84 and 6V6 is noticeable. Loads of options.

T
  Reply With Quote
Old 1st February 2018, 07:22 PM   #15
LeftHandFool is offline LeftHandFool  United Kingdom
diyAudio Member
 
Join Date: Oct 2017
Location: Carlisle, UK
Quote:
Originally Posted by tristanc View Post
Thinking about it - a cathode biased PP or SE with VVR for the PA might fit the bill?

AmpMaker's N5X is an ideal platform to start from for a PA in that case. My N5X build turned in to the Merlin High Gain preamp through tweaking, but with the Power control on 0 you are definitely getting PA distortion at low-volume levels if that is what you're after. And the difference between EL84 and 6V6 is noticeable. Loads of options.

T
Hi Tristan, thanks for the input. I dig your Firefly amp, I've had my eye on it for a while now. I've been on and off thinking about a project like this for a fews years, I thought there'd be a lot more 1-2W circuits out there but there's not much. I'm starting to think there may be good reason for that .

I actually tried the Ampmaker VVR on my 18 Watt clone a year or two back but wasn't that impressed with it's performance. I think I've tried and failed with power scaling and attenuation at this point; I was looking to go down something similar to your Firefly route.
However, given the advice I've had here, and the fact that you weren't too smitten with the Firefly I'm starting to reconsider. Biting the bullet and accepting a little more preamp gain seems the sensible route. After all, there's no substitute for genuine power and ear crushing volume...

What was it about the Firefly you didn't like?

Matt.
__________________
www.falderguitars.com
  Reply With Quote
Old 1st February 2018, 08:01 PM   #16
Gnobuddy is online now Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by LeftHandFool View Post
Biting the bullet and accepting a little more preamp gain seems the sensible route.
I think many people found fly-powered power amp sections were too limiting, weak and buzzy when overdriven, and too quiet for clean tones.

My best compromise so far is a watt or two in the power amp (enough for good clean tone at living-room volumes), but generate the distortion in the preamp - and use a pentode in the preamp.

One way to look at it: if your preamp chain ends in a pentode, what is the topological difference between it, and a power amp? Say your preamp is triode -> triode -> pentode; how different is that really from a Fender Champ, except micro-powered?

Push-pull requires a little more thought, but is also do-able. Have a phase splitter driving two (small signal) pentodes as usual, with resistive anode loads (rather than an output transformer). Feed those two out-of-phase anode signals into a long-tailed-pair / differential amplifier to combine them together (mathematically identical to what the output transformer does). The output of your long-tailed-pair pseudo-transformer is now equivalent to the output of a push-pull power amp.

The difference between EL84 and 6V6 sound was mentioned; I agree, and I believe part of that is the fact that one is a true pentode with 3 grids, while the other is a beam tetrode.

Beam tetrodes tend to generate a lot more second harmonic distortion than pentodes; pentodes tend to generate a lot more third harmonic distortion than beam tetrodes.

To my ears, beam tetrodes are usually more likely to "sing" or "shimmer", while pentodes are more likely to "growl".

Note that there are small-signal pentodes (like the EF86 or 6AK5), and also small-signal beam tetrodes, though they were rarely advertised as such.

For example, if you take a magnifying lens and look at the "pentode" inside a 6JW8, you find there are only four grid support rods visible: only enough for two grids. The "pentode" is actually a beam tetrode, though the datasheet says "pentode".

I'm assuming the Phillips patent on pentodes had expired by the time these tubes were being manufactured, which allowed the manufacturer to call them "pentodes" even though they were actually something quite different.

-Gnobuddy
  Reply With Quote
Old 1st February 2018, 09:00 PM   #17
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


YouTube
  Reply With Quote
Old 1st February 2018, 09:19 PM   #18
LeftHandFool is offline LeftHandFool  United Kingdom
diyAudio Member
 
Join Date: Oct 2017
Location: Carlisle, UK
Quote:
Originally Posted by Gnobuddy View Post

My best compromise so far is a watt or two in the power amp (enough for good clean tone at living-room volumes), but generate the distortion in the preamp - and use a pentode in the preamp.

One way to look at it: if your preamp chain ends in a pentode, what is the topological difference between it, and a power amp? Say your preamp is triode -> triode -> pentode; how different is that really from a Fender Champ, except micro-powered?...

-Gnobuddy
Thanks Chief, that's a lot of useful information to ponder...

The 6V6 is the Beam Tetrode, yes? IIRC Morgan Jones expeains the differences, so I'll re-read tomorrow. From memory, the Tetrode added a screen between grid and anode, while the Pentode went one further, but there were copyright issues which caused some valves to be 'mismarketed', shall we say .
As an aside, I used to have a Roost 100W head, which ran on a quartet of KT77's, the KT standing for Kinkless Tetrode, as they went some way to fixing the awkward kink in the grid curves?

From my side of the pond, the 6V6 is a pesky American 'tube', I don't think I've ever owned an amp which uses them. Perhaps now is the time to try... They'd be overpowered for this application, would they not? Datasheets for breakfast tomorrow.

RE your first post, feeding a Pentode Triodes; I'm looking at using the two halves of an ECC83 to drive an EF86. The first gain stage will be standard, cool biased, with a switchable second gain stage with a more focused/filtered topology to push the mids. Perhaps not a million miles from the Marshall Super Lead.

Hopefully I'll have some rudimentary circuits drawn before the weekend is out.

Thanks again,

Matt.
__________________
www.falderguitars.com
  Reply With Quote
Old 1st February 2018, 09:25 PM   #19
LeftHandFool is offline LeftHandFool  United Kingdom
diyAudio Member
 
Join Date: Oct 2017
Location: Carlisle, UK
Snip! Posted the same reply twice.
__________________
www.falderguitars.com

Last edited by LeftHandFool; 1st February 2018 at 09:28 PM. Reason: Idiocy.
  Reply With Quote
Old 1st February 2018, 09:48 PM   #20
zenelectro is offline zenelectro  Australia
diyAudio Member
 
zenelectro's Avatar
 
Join Date: Sep 2009
Quote:
Originally Posted by Printer2 View Post
An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


YouTube
A couple of things:

a/ That schematic is copyright information
b/ It's a great sounding amp

I would take the front end of an '800 (2203) with master vol and marry it to the 1W back end.

cheers

Terry
  Reply With Quote

Reply


Suggestions for a Medium Gain Guitar Amp Topology...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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Variable Gain Control Topology JFace Tubes / Valves 16 2nd March 2015 08:33 AM
Advice: medium power bass guitar amp/speakers dizmayed Instruments and Amps 7 30th June 2011 06:48 AM
Medium power Class D battery bass guitar amp SEclassA Class D 5 14th December 2010 11:01 AM
high gain 2nd order high pass active filter topology sreten Solid State 21 23rd March 2006 01:26 AM
DIY preamp design - gain topology, IC vs. discrete, OPA627 vs. Zen... ? dorkus Pass Labs 18 10th July 2001 05:26 AM


New To Site? Need Help?

All times are GMT. The time now is 05:42 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