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 Post subject: Re: Guitar amplifier ?
PostPosted: 05 May 2018, 08:39 
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Location: Chilliwack, BC
The only exception to the rule is a bass guitar amp - there you want a LOT of clean power and get any effects from pedals.

/me used to play bass :D

Cheers!

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 Post subject: Re: Guitar amplifier ?
PostPosted: 05 May 2018, 14:20 
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Joined: 26 Dec 2016, 03:46
Posts: 194
Location: Bayarea
Yeh, we are talking mainly about guitar amp, Never even look into bass amp. One thing for sure people don't want a lot of distortion with bass.

My experience in design guitar amps are limited to tubes, but my experience in designing hifi amp is mainly SS. I am getting into tube hifi amp in the near future, I have a rough design, but it's at least two design down the line, doubt I'll get to it this year. In my experience, design hifi amp and guitar amp cannot be more different. Popular guitar amps are mostly tube amps. Majority of the design evolves from the Fender 59 Bassman. High gain ones just stack more stages.

People can design guitar amps with very little knowledge of electronics. Totally different from designing hifi amp. Hifi amps are all theory, then simulation to optimize before even lay the first glass. I can speak for SS amp, it's much much harder to design than guitar amps.


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 Post subject: Re: Guitar amplifier ?
PostPosted: 05 May 2018, 23:18 
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Joined: 09 Oct 2012, 19:43
Posts: 335
Location: Vancouver Canada
I always thought starting with a clean amp and if distortion is wanted for sound it is an effect that is added. The signal is distorted while still in the pre-amp stage where signal levels are standardized prior to the necessary current supply stages for driving the spkrs. Yes the result is a distorted version of the original signal but not the result of over-driving the amp and speakers to the point of distortion, short life span, and sometimes sparks. So the sound desired is achieved and the amp runs within it's design parameters. At least until the refreshments start.
A quick search reveals: (also i suppose the ideal freq any dedicated amp should have)
Table of Bass Frequencies
Fundamentals Harmonics To
4-string Bass 41Hz-392Hz ~4kHz-5kHz
5-string Bass 31Hz-392Hz ~4kHz-5kHz
6-string Bass 31Hz-523Hz ~4kHz-5kHz

Guitar Frequency Range (80 - 5K)
80 to 1..2K Fundamentals
1.2K to 5K Upper Harmonics

I'm not taking a stand of distortion levels as with SS .01THD @ rated PWR is common and tubes run on distortion but that is a slight difference compared to a distortion petal being stomped into the tune.


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 Post subject: Re: Guitar amplifier ?
PostPosted: 06 May 2018, 01:01 
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Joined: 26 Dec 2016, 03:46
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Location: Bayarea
I can assure you theory really is useless for guitar amp. I experimented designing two different filter circuits that give exactly the same output waveform in simulation both amplitude and phase. I build both to compare the sound, it cannot be more different.

You don't look at frequency response to design guitar amp....unless it's really off.

You don't design a clean undistorted amp and add effect. If that works, all you need a a pedal board. It's nothing this simple. In cascade high gain amp, people put control in which stage to overdrive. AND to me, the best result is overdrive the output stage. This is where power scaling I was talking about. An amp that you can adjust the output power, you always drive at the optimal level, then adjust the output power for the venue.

Guitar amp is a completely different animal. When comes to hifi low THD amps, I can talk theory with you until the cows come home, I learned and used them all. You can design a high end hifi amp on paper and simulation and get very close result on pcb first time through. You have to get your hands dirty in designing guitar amp.

In most case, designing guitar amp is a whole lot easier. You don't need a lot of knowledge, any joe blow can tinker with a guitar amp. But it's hard for me in the sense you really need to go on a performance to judge. I don't play anymore, I sure as hell not willing to haul amps around to play in gigs. So it's hard for me to judge the amp. For musicians, all they need is some very basic knowledge of electronics and they can start modifying amps. That's what I did in 1978. Hell, I though now that I really go deep into electronics, I can do better.......WRONG, other than designing the power scaling using MOSFET ( electronics), I have no more advantage than 1978, in fact, disadvantage as I don't go out and play anymore. And even the MOSFET power scaling is no better than the stupid way I did putting in an extra transformer to power the preamp stage and filaments, then put a variac to vary the voltage of the +B and grid bias of the power tube.


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 Post subject: Re: Guitar amplifier ?
PostPosted: 06 May 2018, 22:13 
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Joined: 09 Oct 2012, 19:43
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Location: Vancouver Canada
I'll certainly admit to seeing variacs on stage and knowing a few people who would do anything just to hear a totally over-driven amp. Just just in case it had that desired sound. Guess it was the HiFi'er in me coming out.


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 Post subject: Re: Guitar amplifier ?
PostPosted: 06 May 2018, 23:14 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
It's hard to sepearate.... when I was hired as a designer for CK Amps, I had to take a learning curve. So I hung out at a local guitar shop for months and LISTENED... not only to amps, but every person there. Then I brought in designs and they were honest in their opinion. I guess it took over a year of this for them to eventually quiz me and declare me at least a guitar amp tech :D

Cheers!

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* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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 Post subject: Re: Guitar amplifier ?
PostPosted: 07 May 2018, 00:53 
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Joined: 26 Dec 2016, 03:46
Posts: 194
Location: Bayarea
Geek wrote:
It's hard to sepearate.... when I was hired as a designer for CK Amps, I had to take a learning curve. So I hung out at a local guitar shop for months and LISTENED... not only to amps, but every person there. Then I brought in designs and they were honest in their opinion. I guess it took over a year of this for them to eventually quiz me and declare me at least a guitar amp tech :D

Cheers!


What is CK amps? I have not been to Guitar Center for like a decade already, really don't know the new brands anymore. Which model you design?

I designed two amps and stopped a few years back. As I mentioned before, I don't play and I really don't know people as I quit 39 years ago. I have no one to give me feedback. I use the chassis of a Marshall JCM900 combo and a KMD combo as the platform, took out everything including the power and output transformer and put in my own circuits. I like them a lot, both with power scaling, channel switching. After that, I just put in the closet and there is stayed for all these years. I turn to hifi amp design as it requires much more theoretical knowledge. I can design the whole amp on paper, simulate before laying down the first pcb. It pretty much came out one time through. Hifi amp is one I can enjoy everyday. I watch tv with the stereo and I love every minute of it.

Guitar amp is very sensitive to component values particularly in the tone circuit. Slight change in values can make a different amp. That is so subjective. Like you said, you took the time to go to the music store and have people listen to it to make a judgement for the design. If I am 30 years younger, I might have a lot of fun doing that. But then, I have to work!!!

One thing, I don't believe in the fuzz of choosing components, like carbon comp resistors, film caps, brand of tubes etc. I made it a point to use all metal film resistors, all ceramic caps except the large 0.1uF 600V cap which I did not have at the time, so I use the old Fender orange drop. I make it a point to go on ebay to buy the cheapest Shinghan tubes and not matching anything. Result were great. I use Classic Tone Bandmaster OPT for both my amps because of the small size ( hopefully it starts to saturate sooner) instead of the bigger Marshall style OPT. All in all, I am very happy.

I use Warehouse Speakers, no complains, I don't like JBL, Emenince, not even Celestion that much.


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 Post subject: Re: Guitar amplifier ?
PostPosted: 07 May 2018, 01:03 
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Joined: 26 Dec 2016, 03:46
Posts: 194
Location: Bayarea
laurie54 wrote:
I'll certainly admit to seeing variacs on stage and knowing a few people who would do anything just to hear a totally over-driven amp. Just just in case it had that desired sound. Guess it was the HiFi'er in me coming out.


It really does not work just put a variac on the AC line of the amp, as you turn it down, the voltage of the filament and the preamp drops also. It does not sound good. I discover this in 1973 when I came to US from HK, I shipped my Marshall Plexi 100W over from HK, it was 220V, I accidentally plugged into the 110V, it's a lot softer, but the sound changed...not in a good way. That gave me the idea of power the filament and preamp separately with constant voltage, then the variac on the +B and grid of the power tubes only, that was heavenly. I should have patented that in 1978, but I was a starving student, I moved on to electronics and dropped music all together.

It's the modification of my Twin Reverb that got me into electronics, I was so into electronics that I quit music in 1979 and never look back. I had my full career as an EE and manager of EE. It's only after I retired that I came back full circle and design two of the guitar amps. I found out London Power came out with power scaling in the 90s using MOSFET to vary the voltage of the output stage and they sell the kits. I am pretty sure I did it earlier in 1978. I designed both amps using MOSFET as source follower to drive the +B of the power tube, then an inverted amp to drive the grid bias. Exactly the same idea as variac before.

I am still very passionate in electronics, designing hifi power amp is my pass time, much better than cross word puzzles!!! :D


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 Post subject: Re: Guitar amplifier ?
PostPosted: 07 May 2018, 02:11 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Yungman wrote:
What is CK amps? I have not been to Guitar Center for like a decade already, really don't know the new brands anymore. Which model you design?


Heh, we didn't last that long as I live in the **wrong** province for boutique amps :(

The best known one we sold was Roctal :smoking:


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_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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 Post subject: Re: Guitar amplifier ?
PostPosted: 07 May 2018, 02:51 
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Joined: 26 Dec 2016, 03:46
Posts: 194
Location: Bayarea
It's not easy to make money in music electronics. So many boutique amps and guitar company gone under. Very little money to be made, it's not like have a good design and you have it made. Marketing is everything. I used to talk to a guitar pickup maker name D. Allen, profit margin is very thin. Consider the cost of making the chassis, cabinet, the speaker. those are the most expensive items. Then the cheap musicians want to pay very little. You can't compete with the large companies like Fender that out source to Mexico. When volume is high, things are a whole lot cheaper. If you sell even 50 amps, you likely have to hand build everything, it takes days to build one amp!!! How can you survive? Cost over $2000 to have a booth in the show to do demo. If it's not because of Carlos Santana, Mesa likely would not be around. I remember D Allen spent so much time traveling to get endorsement from musicians.

That's why I did not pursue guitar amp. I put in a lot more effort in hifi amp because I enjoy it, I use it hours a day. I am not trying to market it, just for the fun of it. When comes to high end audio amps, it's the same thing, no money in the market. Volume is so low, how can people make a living unless you have the big name. It cost me $800 to build one amp, I already have all the pcb and pretty well chassis design already, it will take me like a week to build one on my own. So if I can sell 100 a year, $5000 each, I have to hire people, form a company, rent, what's left? How long it takes to build up the reputation, how many shows I have to go?


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