Please help in improving the sound of a gain channel.

[Alan0354]

I have been working on a Gain channel. My hearing is getting confused!!!! It sounded grainy and the lower string sounded like farting. Please give me some pointer to improve the sound. I did a video, #1 is a pedal that I think is sounding better. #2 is my amp. Here is the schematic:





And here is the video:

Gain 2nd try - YouTube

Please give me some suggestion to improve the sound, it got bud kicked by a tiny pedal!!!!

Thanks

[J M Fahey]

1) WHERE are you plugging your pedal and gain channel?
In a guitar amp input?
Pedals are DESIGNED to be used that way, and are equalized accordingly; your gain channel is not a pedal but meant to drive a power amp.
That alone makes the comparison you are making not very fair.

2) FWIW the pedal incorporates some pre distortion bass cut, to lower mud and farting, yours does not.
Anyway itīs like a thousand others, in this case 2 "Fender gain stages" driving a Marshall cathode follower tone stack driver, nothing new under the Sun.
If you cut bass to make it tighter, it will morph into a JCM800.
As a rough description, consider it similar to a JCM800 preamp with more Bass, it certainly sounds like that.

FWIW the first half sounds tighter but "muffled buzzy" , if that means something to you, the second one is slightly more natural and sounds like the guitar notes are accompanied by a higher octave.
jm2c

[Alan0354]

Thanks for the reply. I use a A/B switch to route the guitar to either the gain channel or the pedal to the clean channel of the same amp, so the power section and PI section is common.

I know this is same type of circuit in many many other amps like Soldano Atomic 16 etal. I just want to fool around and get the feel of what affecting what. I know when I started out, I had 10uF cathode cap on the second stage parallel to R6, I eliminated that. I get back some high frequency gain by adding a 1uF cap on the third stage parallel with R11. That tighten it some already. It's the farting that I can't stand.

I intentionally adjust the pedal to sound similar to the sound of the amp to show the pedal has a tighter sound on the low string and smoother on the upper strings. The amp almost have a little of the cracking sound. Any suggestion?

[g1]

What makes you think the amp should sound better than the pedal?

[Chuck H]

First, you write like my doctor. Take some time, will ya? No one should have to decipher runes and gliphs as an added effort.

There are other things I might do differently too, but here's a start:

[Alan0354]

Thanks. I notice yours and all the other schematics in this configurations try to cut as much bass as possible before the tone stack. I definitely try that tomorrow.

[J M Fahey]

Yes.
Rather than before the tone stack, the trick is before the distortion stage.
FWIW classic Distortion pedals (MXR Dist+ , Tube Screamer, RAT, tons others) *heavily* cut bass, below 300Hz most of them
Thatīs why "cheap silicon" manages to sound quite well.
And all of them cut treble, in various amounts afterwards.
So donīt be surprised for finding Pedals "quite good", theyīve been running this race for almost 40 years now.
The really buzzy ones are older (Fuzz Face, Vox Distortion Booster, Big Muff, etc.) and unbearable if used into a clean channel.

[Chuck H]

Yes.
Rather than before the tone stack, the trick is before the distortion stage.
FWIW classic Distortion pedals (MXR Dist+ , Tube Screamer, RAT, tons others) *heavily* cut bass, below 300Hz most of them
Thatīs why "cheap silicon" manages to sound quite well.
And all of them cut treble, in various amounts afterwards.
So donīt be surprised for finding Pedals "quite good", theyīve been running this race for almost 40 years now.
The really buzzy ones are older (Fuzz Face, Vox Distortion Booster, Big Muff, etc.) and unbearable if used into a clean channel.

Nice rundown of some oft not learned tonal rules and standards that players from back in the day are aware of, but modern players don't seem to grasp. Indeed the old D-boxes sounded best when they were used for both added clipping AND overdriving the amp into more clipping. Thereby masking the uglies of the silicootie distortion. This is something we (old guy guitarists) learned because we used and tweaked with a relative paucity of options for tone.

Cutting bass before the clipping stages is done because clipping the LF too much causes a lack of definition and dynamics creating a more horn like effect. Remember that most of the actual signal voltage coming from an electric guitar is in the LF and guitar amp voicing compensates for this. Likewise, HF isn't cut early because failing to clip it would mean a failure to generate the upper harmonics we all love. So we clip the HF early for the harmics and then dial down the HF later to keep the tone from getting too thin or harsh. So, LF is gradually introduced through the amp and HF is gradually reduced through the amp. This just seems to be the tonal preferences we (players in general) have landed on.

[Alan0354]

Wow, this is insightful. I am really schooled.

No wonder I saw people putting high pass filters in the chain to enhance the highs. Good example is they use a 1M resistor in series with the 1M volume pot after the first stage, then put a 470pF across the 1M resistor to pass the highs through.

So 300Hz is the magic number cutting LF?

They should have a button of "Double like". "Like" cannot describe enough.

[Chuck H]

Just to make it extra clear I'd like to point out two scenarios that send the issue home.

1) Modern ultra high gain amps generate A LOT of preamp distortion. As noted there are usually a lot of high pass circuits early in these amps. They still let enough lows through so that they can be well amplified after the clipping stages. If you look at these designs you'll see that the tone stack is always at the end of the clipping stages. That's how these amps produce so much gain AND bottom end for that grindy V-notch EQ wanker tone with the low B string guitars.

2) A regularly repeated thread here is where a new builder makes a Fender copy and then complains that it's too farty and doesn't have enough bass. Well... Those designs run A LOT of LF through the preamp. BF designs have the tone stack right after the input triode. These amps are usually combo's so they're small, open backed cabinets. Add to that the tendency for guitar players to want more bass than they need. The amp sounds great run clean with single coils and the bass knob on 8 with the volume on 3. So then pushing a humbucker into the input the amp is clipping with the volume on 2. But now the guy wants some overdrive so he cranks it up to 7, 8 or 10. Remember the bass knob is still at 8. At that point it's hard to discern if the bass knob is doing much because it just adds flab. It sounds like it might be warming up the tone a little but it's not really adding much other than flab. But WE WANT MORE BASS so we leave it up and write a post because the amp doesn't sound "right". The way to handle this is to set the amp up for the amount of volume and clipping we want and then advance the bass knob until we hear it getting flabby. Then back it off a little. That's it! That's all the clear, defined bass the amp can make. Turning up the bass knob after that won't get you anywhere. Experienced players know this and you can look at their amp settings as proof. If you want more bass your only option is to get bassier speakers.

[pdf64]

I've got a hunch that the standard BF arrangement limits bass due the coupling via the B+.
Consider that for the fx channel, 3 cascading gain stages share the same node, and that's not particularly well de-coupling from upstream.
When I've tried arrangements with better de-coupling, the tone seems more bottom heavy but to prove the point I need to rig up an AB switch.

'So 300Hz is the magic number cutting LF?'
I think that the tubescreamer high pass breakpoint is 720Hz.
There's a great analysis of it on geofex http://www.geofex.com/Article_Folder...ch/tsxfram.htm
Pete

[J M Fahey]

FWIW hereīs what I made already THIRTY years ago, following those unwritten rules.
All SS.

Preamp?: a humble RC4558 (later replaced by a TL072)

Gain stage with active Presence control > switchable passive mid notch (frequency chosen by ear until clean sound was sparkling/Fendery ) > gain stage with active volume (so it would be easy to slam it rail to rail) > Marshally tone stack > tone compensated Master Volume, also adjusted by ear to avoid buzzyness at low volumes .
EDIT: I forgot, the gain control goes to 20
Not kidding: "9" is "10" and "10" is "20" , thereīs a HUGE gain jump in the last 10% of the pot. (remember itīs active), it practically leaves the second op amp open loop for lots of shriek , harmonics and wild distortion.

Power amp? a classic simple 100W amp, 2 x 2N3055H outputs with +/-42V rails, with mixed (current/voltage) feedback to make damping ~ 1, what I had measured in my earlier Tube Fender clones.

This guys plugs his generic guitar straight into it

So itīs just a very simple SS amp, not more complex than, say, a Marshall Lead 12, tweaked to death by ear, onstage and live, which is the sound that counts.

I sold *thousands* of them, in the 80's and early 90's and most are still around.

[JoeM]

That's really cool. And NO tubes!

[Justin Thomas]

Is it too late to answer the "best SS amp you ever heard" thread? Not MY style or tone, but that is a damn good sounding and touch responsive amp, even with that "generic" guitar! :P I just wish I understood the beginning when he was talking... Did I miss anything there?

Thamks to everyone here for the info about the Fender fart - I've helped a few customers with that, simply having them dial the bass back under heavy overdrive, and reminding them that that is why there are bass players! Though it actually helps my loud bass playing too!

[Alan0354]

I've got a hunch that the standard BF arrangement limits bass due the coupling via the B+.
Consider that for the fx channel, 3 cascading gain stages share the same node, and that's not particularly well de-coupling from upstream.
When I've tried arrangements with better de-coupling, the tone seems more bottom heavy but to prove the point I need to rig up an AB switch.

'So 300Hz is the magic number cutting LF?'
I think that the tubescreamer high pass breakpoint is 720Hz.
There's a great analysis of it on geofex Tube Screamer Frame Definition
Pete

I use separate resistors to decouple the first two stages from the third. Each with their own 20uF filtering cap. So hopefully coupling through +B does not happen.

I did some experiment and the high pass in the stages before the tone stack helps. The thing is I do like the more gritty sound with the heavier bass, but I just don't like the farting on the lower strings. I really want to see whether I can balance that.


I have a few question of the preamp tube:

1) What is the effect of raising or lowering the plate current?
2) What is the effect of raising or lowering the plate voltage?
3) What is the effect of symmetrical and asymmetrical clipping?

thanks