HRM tonestack losses

[JD0x0]

For my next build, I'd like to try a different style tonestack for the HRM circuit. I plan on using a modified version of a Hiwatt tonestack, but the losses from the loading of the tonestack are larger on the Hiwatt stack. A slight loss in output doesn't really concern me, as you can easily compensate by setting the overdrive volume higher, but I am concerned about other effects of the increased loading. For example, I'd like to avoid 'congestion' or excessive compression.

I've attached a pic. As you can see, the losses aren't massive, but the difference is fairly significant. Of course, there's way to compensate for this.. I could run a LND150 as a buffer to reduce losses, or just move the tonestack to get driven off of V2a, so V2b acts as a recovery stage, but I'd like to see what others think, before I start adding complexity and modifying the circuit further.

UntitledTonestack.png

[JayB]

If you got an extra triode, wire two triodes in parallel which will cut the output impedance in half and still retain its character.

[JD0x0]

If you got an extra triode, wire two triodes in parallel which will cut the output impedance in half and still retain its character.

Yeah that'd about halve the output impedance, if I'm not mistaken.. Someone correct me if I'm wrong, but I think an LND150 could be used as a buffer, and apparently it wont saturate as a tube would, so it should keep the tone a bit more consistent compared to a tube CF.

I actually didn't find that was really necessary, though. The amp seems to work great as is. I was worried it might be a bit to compressed, but the amp is extremely dynamic, IMO. Part of that may be the increased filtering I used on the screens and PI, the amp as a whole is very punchy and dynamic.

[10thTx]

Just a thought to consider ………………

This has become my favorite OD channel "tone stack" in the D-inspired amps I've built. Turning down the treble and bass pot gives a pseudo "midboost" tone. Turning them up, midscoops the tone. And there is enough gain to not worry about loss with the tone stack for what I am wanting.

With respect, 10thtx

[JD0x0]

Just a thought to consider ………………

This has become my favorite OD channel "tone stack" in the D-inspired amps I've built. Turning down the treble and bass pot gives a pseudo "midboost" tone. Turning them up, midscoops the tone. And there is enough gain to not worry about loss with the tone stack for what I am wanting.

With respect, 10thtx

The Bax/James stacks are really cool and seem versatile. The Hiwatt style stack I used here can be used much to the same effect, but it has a mid frequency band, too, which gives the mid sweep a really big range. You can get a narrower scoop by cutting the mid control rather than pushing the Treble and bass controls. It's also a bit more efficient than the James. I havent tried the Bax with an ODS, but this HW stack has quickly become my favorite.. It really should have the controls user accessible, as it's such an effective tonestack, it'd be a complete waste to have it on 'set and forget' trimmers on the inside of the amp like a typical HRM.

Untitled.png

[fred.violleau]

I built an HRM two years ago with the tone stack in the front of the amp. I thought it would be great to be able to tweak it. I also added a bypass switch to test the difference in the overdrive. I realized that the tone stack induces a significant gain loss, compared to the bypassed circuit. And second the tone stack is not versatile enough to get different usable settings. I am interested though in trying something different, so I might give this tone stack a try. Does It imply more gain loss than the usual HRM tone stack?

Cheers,

Fred.

[JD0x0]

Yeah, this setup definitely has more losses than a standard HRM, if it's plate driven, as you can see from the modeled EQ's in the OP. I reduced the 100k/1Meg voltage divider on the output of the tonestack to try to compensate slightly. Really, all it seems to amount to for the most part, is you need to compensate with the Drive master volume slightly to make up for the losses.

[norburybrook]

are you guys bypassing the main tonestack though when you're making these 'judgements'?

IMHO, the HRM OD is meant to have the main tonestack bypassed(PAB) to sound like it's meant to.




M

[JD0x0]

are you guys bypassing the main tonestack though when you're making these 'judgements'?

IMHO, the HRM OD is meant to have the main tonestack bypassed(PAB) to sound like it's meant to.




M

This amp has switchable PAB on both channels, so you can pick and choose how you want to use it. Obviously, the first tone stack is scooping some mids, and on the normal HRM you're also scooping mids at the HRM. Together, I could see how this may provide too much mid cut. This stack, can actually dial in a mid 'hump' so unlike the typical HRM, you can counteract the first tonestack's midscoop that way, and then use the PAB as a fat boost when you defeat the clean stack, you lose the mid cut, and just have the 'hump' from the OD eq. This is roughly what the EQ would look like mids dimed, treble: 3, Bass: 5

PRM.png

Of course, you don't have to use it like that, either. I intended the amp to be flexible and usable with/without PAB on the OD depending on how the user sees fit.

[fred.violleau]

are you guys bypassing the main tonestack though when you're making these 'judgements'?

IMHO, the HRM OD is meant to have the main tonestack bypassed(PAB) to sound like it's meant to.




M

Marcus, good question, I will have to check how it is implemented!

Fred.