Treble peaker squealing

[Mr.Death]

 Hi, I added an attenuator/treble peaker to V1A and I'm getting a high pitched squealing sound, not sure if it would be called oscillaton? I added this before the stock bright cap which is on a switch from the factory. When I switch off the stock bright cap the squealing goes away. I think I made an error along the way. I added a schematic. Amp is a Traynor YBA3. Thanks.

[ac427v]

Thanks for the schematic. But I need to also see V2 to understand how your mod connects. Can you send another JPEG?

[Mr.Death]

Thanks for the schematic. But I need to also see V2 to understand how your mod connects. Can you send another JPEG?

I will later tonight.  At work currently. 

[HotBluePlates]

I added an attenuator/treble peaker to V1A and I'm getting a high pitched squealing sound I'm getting a high pitched squealing sound ...

How about just removing the added resistor/capacitor?

I'm a little curious why these parts are needed, when the tube-stage prior has bass-reduction via its cathode bypass cap, and the Volume control already has a bright cap.

[Mr.Death]

I added an attenuator/treble peaker to V1A and I'm getting a high pitched squealing sound I'm getting a high pitched squealing sound ...

How about just removing the added resistor/capacitor?

I'm a little curious why these parts are needed, when the tube-stage prior has bass-reduction via its cathode bypass cap, and the Volume control already has a bright cap.

Im modelling this after a Marshall JCM800 which has both the attenuator and bright caps.

[Mr.Death]

I see I have some homework to do. Thanks for your knowledge thus far.

[Mr.Death]

Looking at the soldano SLO it has the same attenuator /peaker before the gain pot. Like what I have tried. I guess Im missing something here. New to this so go easy on me. Lol. Thanks again.

[Mr.Death]

Im modelling this after a Marshall JCM800 which has both the attenuator and bright caps.

JCM800 Preamp schematic

The JCM800 has these parts (and channel-mix resistors) after the Volume control, not before.  It would seem your schematic shows the added parts in the wrong place.

I also didn't see the 2nd channel present in your schematic.  The "treble peaker" is a capacitor across a channel-mix resistor in the JCM800.  If there are not 2 channels, and so you're not mixing 2 channels, you cannot add this "peaker cap" because it doesn't have the other circuit-parts needed for it to do its job.

The schematic you posted is for the plexi, not the JCM800. The JCM800 has the attenuator/peaker where I added them.

[Mr.Death]

JCM800

[Willabe]

Mr. Death?  Come on.

Your not looking at this right. You have to look at the whole preamp, all the preamp stages strung together.

That SLO has what 4 preamp stages? So he had to start stripping the bass out from the 1st stage output. Because it's very high gain and it will get muddy sounding real quick. 

[Willabe]

JCM800

That Traynor amp would have to be pretty much gutted to build a JCM800 out of it. And that's a lot to gut, including treble and bass expander circuits, redoing the power tubes screen supply, move the cathode follower further down the preamp, etc.

I'd leave that amp alone, other than change the power tube to something more common.

Sell it to someone who will use it as is and use the money to buy a Marshall JCM800 or parts to build 1.

[pdf64]

Jcm800 is a product range, dozens of models, plexi is the front panel material used in the 60s, again on dozens of models.

Neither JCM800 or plexi adequately identifies a particular amp design.
Please be more specific, refer to actual model codes and schematic dates, dates being essential as model code designs could change drastically   

[Mr.Death]

JCM800

That Traynor amp would have to be pretty much gutted to build a JCM800 out of it. And that's a lot to gut, including treble and bass expander circuits, redoing the power tubes screen supply, move the cathode follower further down the preamp, etc.

I'd leave that amp alone, other than change the power tube to something more common.

Sell it to someone who will use it as is and use the money to buy a Marshall JCM800 or parts to build 1.

Dude, you have no idea what I have done to the amp thus far. Lots of the things you have mentioned I have done. Ill figure this out on my own. Sell the amp????? Not a chance. As it is the amp sounds fantastic, just looking to tweak it.

[Mr.Death]

Jcm800 is a product range, dozens of models, plexi is the front panel material used in the 60s, again on dozens of models.

Neither JCM800 or plexi adequately identifies a particular amp design.
Please be more specific, refer to actual model codes and schematic dates, dates being essential as model code designs could change drastically

Ummm, I posted the schematic I was referring to for the JCM800 with the attenuatot/peaker.

[pdf64]

Hi, I added an attenuator/treble peaker to V1A and I'm getting a high pitched squealing sound, not sure if it would be called oscillaton? I added this before the stock bright cap which is on a switch from the factory. When I switch off the stock bright cap the squealing goes away. I think I made an error along the way. I added a schematic. Amp is a Traynor YBA3. Thanks.

Per se, the treble peaker / bright cap are unlikely to cause oscillation.
Bad design, layout and lead dress are far more likely.
So what's your design, layout and lead dress?

[Willabe]

Dude, you have no idea what I have done to the amp thus far.

1st off, my name is not Dude.

Too late, you already trashed a good a good amp.

[HotBluePlates]

The schematic you posted is for the plexi, not the JCM800. The JCM800 has the attenuator/peaker where I added them.

Thanks for the correction!  I was mislead by the wrong-name for the file (which had "JCM800") and didn't pay attention that it did not have the Hi channel cascade into the Lo channel inputs.

I just deleted my post to avoid confusion for others.

Per se, the treble peaker / bright cap are unlikely to cause oscillation.
Bad design, layout and lead dress are far more likely.

Now that I'm looking at the correct schematic, I see that your schematic matched that of the circuit you wished to copy.

That being the case, I agree with pdf64 that this might be a layout issue leading to oscillation.  So what's your layout?

[Mr.Death]

Lead dress was the issue. Cleaned up some wiring, works as it should. Thanks.

[HotBluePlates]

Lead dress was the issue. Cleaned up some wiring, works as it should.

Awesome!!  Glad you got it sorted out.

[GlideOn]

JCM800

That Traynor amp would have to be pretty much gutted to build a JCM800 out of it. And that's a lot to gut, including treble and bass expander circuits, redoing the power tubes screen supply, move the cathode follower further down the preamp, etc.

I'd leave that amp alone, other than change the power tube to something more common.

Sell it to someone who will use it as is and use the money to buy a Marshall JCM800 or parts to build 1.

The JMP is not a very complicated circuit and there's ample room inside and out of the YBA3 to accommodate.

People such as myself do it all the time to their YBA1s and because it has extremely stout transformers, not only stands up to Marshalls but even surpasses.

It's certainly a worthwhile thing to do.

In fact, OP could use the extra controls logical good use, such as:

Treble Expander - NFB Control
Bass Expander - Resonance Control
Bass Boost - V2 Cap

DM if you need any help.

FYI: Shielded wiring really helps when you're adding more gain.

[Willabe]

It's certainly a worthwhile thing to do.

At the expense of wreaking a perfectly good amp.

You want to build a Marshall, fine, but don't wreak a nice Traynor. If the amp was already trashed, beat up, then ok, but not 1 that's in pretty good shape to great shape. 

There's plenty of Marshall's out there, we don't need to convert other good amps to be another Marshall.

[GlideOn]

It's certainly a worthwhile thing to do.

At the expense of wreaking a perfectly good amp.

You want to build a Marshall, fine, but don't wreak a nice Traynor. If the amp was already trashed, beat up, then ok, but not 1 that's in pretty good shape to great shape. 

There's plenty of Marshall's out there, we don't need to convert other good amps to be another Marshall.

It's 2025 and these amps are 50+ years old and are fairly common, not terribly valuable collector's items. Most if not all of them are going to need work to keep them working so they are by definition not going to be stock after the fact.

It's really getting tiresome seeing these kinds of takes.

Really, what's it to you? Do you have stock in the company or something? Whatever happened to "live and let live?"

It's his amp, he can and should do whatever he wants with it and as a fellow Traynor owner I will only encourage never discourage him to fully realize the possibilities of this/these platforms.

Stock they are reather decent sounding, but nothing to write home about. Pete and crew in all of their wisdom designed these to be rental and bass amps that were/are damn near bulletproof.

They are glorious sandboxes. They are handsome heads with durable chassis and huge, monstrous transformers bolted to them. Inside is a generic turret board that was placed inside a variety of YBA models of the era. To me, it represents a world of possibilities and potential.

Please feel free to do whatever you want with this OP and nevermind the naysayers, ever.

I have spoken. 

[Willabe]

It's really getting tiresome seeing these kinds of takes.

Really, what's it to you? Do you have stock in the company or something? Whatever happened to "live and let live?"

Apparently you've been told this before as it's a sore spot for you.   

I already said what it is to me.

And I don't appreciate your smug and snarky attitude. Your response is totally unnecessary and unwarranted, 1st strike, I'll be watching how you treat the other members here. You need to change your tone when you post a response.

You need to remember your a guest here, you don't run the place and to be a little respectful to other members.

It's 2025 and these amps are 50+ years old and are fairly common, not terribly valuable collector's items. Most if not all of them are going to need work to keep them working so they are by definition not going to be stock after the fact.

You seem to think you got it all figured out. Yes, I know these things. But their not the point. Still doesn't mean they should be gutted if their in decent to good condition.

And what your saying goes against your "Whatever happened to "live and let live?"

I have spoken. 

You won't have spoken for long here if you keep up with the snarky, smug and smart aleck attitude. You'll be gliding on out of here quick.