What's the purpose of R105 in the Hot Rod Deluxe 2 tone stack?

[freefrog]

Hi again Alga,

I've took the same road several years ago... the HRD is probably the amp that I've modified the most - with a variable success and less rewards than with my other amps, sadly and FWIW.

Mine currently includes three additional switches and a new "variable NFB" pot on the back pannel... I'll share with you a depiction of the related mods ASAP.

Regarding the BassMan voicing, I've tweaked the drive channel in a way that I find satisfying and that I'll explain you later.

Regarding the clean channel, I'm still not totally satisfied but I've found that [a resistor (ideally a trim pot) in series with a cap] parallel to R9 is a good way to "tune" the tone. It's even possible to implement a "contour" control there. Again, more later about that.



Now, I'd find difficult to recommend a mod as a first step: if you "blackface" the tone stack without altering the rest of the circuit, you might find the clean channel too dark and thumpy... if you do a second mod to correct that, the "honk" might come back...


A problem with this amp is that its stock EQ has been designed to match the Tweed style 1x12 cab and its resonance: even if the circuit is tweaked to approximate a Blackface, it won't sound like an open 1x12 or 2x12...

Here is the frequency response of my uber-modified HRD upon the curve of a "real" Fender Twin Reverb RI: this time, the frequency response has been captured through a direct box between power amp and cab:



BTW, the green and pink lines under the frequency response translate the distortion generated: it's something to keep in mind, since a same EQing with a different distortion curve doesn't sound the same at all.

In this case, the HRD distorts less because I've fitted it with a 12AY7 in V1 (the Twin has still its stock 12AX7's). But the result is similar.

In fact, these curves are close enough to make my HRD "Twin" sounding... but only through the cab of the Twin. Once played through its own cab, it returns to its HRD sonic footprint...

Now, it's true that with lits imited value, size & weight + its solid 40w of power, the HRD remains a good amp for live sessions - reasons why I often take mine on stage.

Hope to be useful. See you later!

[alga]

Hi again Alga,

I've took the same road several years ago... the HRD is probably the amp that I've modified the most - with a variable success and less rewards than with my other amps, sadly and FWIW.

Mine currently includes three additional switches and a new "variable NFB" pot on the back pannel... I'll share with you a depiction of the related mods ASAP.

Regarding the BassMan voicing, I've tweaked the drive channel in a way that I find satisfying and that I'll explain you later.

Regarding the clean channel, I'm still not totally satisfied but I've found that [a resistor (ideally a trim pot) in series with a cap] parallel to R9 is a good way to "tune" the tone. It's even possible to implement a "contour" control there. Again, more later about that.



Now, I'd find difficult to recommend a mod as a first step: if you "blackface" the tone stack without altering the rest of the circuit, you might find the clean channel too dark and thumpy... if you do a second mod to correct that, the "honk" might come back...


A problem with this amp is that its stock EQ has been designed to match the Tweed style 1x12 cab and its resonance: even if the circuit is tweaked to approximate a Blackface, it won't sound like an open 1x12 or 2x12...

Here is the frequency response of my uber-modified HRD upon the curve of a "real" Fender Twin Reverb RI: this time, the frequency response has been captured through a direct box between power amp and cab:

[ATTACH=CONFIG]48562[/ATTACH]

BTW, the green and pink lines under the frequency response translate the distortion generated: it's something to keep in mind, since a same EQing with a different distortion curve doesn't sound the same at all.

In this case, the HRD distorts less because I've fitted it with a 12AY7 in V1 (the Twin has still its stock 12AX7's). But the result is similar.

In fact, these curves are close enough to make my HRD "Twin" sounding... but only through the cab of the Twin. Once played through its own cab, it returns to its HRD sonic footprint...

Now, it's true that with lits imited value, size & weight + its solid 40w of power, the HRD remains a good amp for live sessions - reasons why I often take mine on stage.

Hope to be useful. See you later!

Freefrog

Woao! I´m so excited. Interesting we have practically the same goal to achieve with this amp. We have the same tube (12AY7) in the V1. We both soldered a jumper across the mid pot and also changed C1, lot of things in common looking for our goal.

I tried to blackface the amp and happend exactly what you describe. Too dark (lot of high frequencys lost) not cutting well in a band situation, and too much thump due to change the R12 from 130k (carbon comp) to 100k (metal film).

Very eager to know details about your mods, especially for the attenuation you invented for tamig the strong high mids in R9 and how did tweaked the drive channel. I guess changing C23 C11 and putting a 12DW7 in the V2.

[freefrog]

Freefrog

Woao! I´m so excited. Interesting we have practically the same goal to achieve with this amp. We have the same tube (12AY7) in the V1. We both soldered a jumper across the mid pot and also changed C1, lot of things in common looking for our goal.

I tried to blackface the amp and happend exactly what you describe. Too dark (lot of high frequencys lost) not cutting well in a band situation, and too much thump due to change the R12 from 130k (carbon comp) to 100k (metal film).

Very eager to know details about your mods, especially for the attenuation you invented for tamig the strong high mids in R9 and how did tweaked the drive channel. I guess changing C23 C11 and putting a 12DW7 in the V2.

Hi again alga,

I've still to write a diary of the mods done on my HRD: it would be useless to describe these changes one by one, since they work as a whole...

IF you want to avoid a long tedious (and always risky) mod session on your amp, the simplest thing to do might be to replace R9 with a 1,5nF cap in series with a 100k resistor (exactly like in the stock drive channel). It would give a tighter/brigther clean tone, close to the clean channel in the Blues Deluxe RI (which involves even lower value caps, since it is fitted with a 10n followed by a 100k resistor, itseif plugged in a 750pF cap... in this case, the bright cap is another 750pF, switchable, over the 100k resistor).

If ever you notice some "blocking" distortion, put a resistor of a few hundreds of k between the output of this network and the ground, just like in the BDRI.

Of course, it would look more "professional" to swap directly C18 for a 1,5nF cap, but leaving it as it is and putting it in series with another 1,5nF cap would give practically the same result (since 22nF in series with 1.5nF = 1.4nF)... and it would allow to do that mod without pulling out the whole PCB (which is a pain in the @§§).

Regarding the drive channel, don't waste your time with C11 & C23: I've changed these ones then came back to the stock value.

Instead, you might try to tweak the gain and its bandwidth because that's where is the real main problem with this channel IMHO. Here is what I've done for that:

-C8 replaced with a 1k to 1,8k resistor paralleled with the 1µ cap (I migth have reduced R17 but since I've tried various cathode caps, it was simpler for me to add a resistor directly next to C8).
-C9 = 1k in series with 1.2k paralleled itself with the second switchable cathode cap (22µ).
-R21: 1k (if memory serves me. Not sure on this one but that's probably what I've done, in order to obtain a global cathode resistor value recalling the usual 820 Ohm).

Useful tool if you want to adjust these components to your taste:

https://www.ampbooks.com/mobile/ampl...or/calculator/

Oh, and...

-R19 value halved. Done with a second resistor of the same value than the stock one, in parallel with it.



All these tweaks can be done with some careful "pig tailing" if necessary. It doesn't look nice but it avoids to hurt the frail tracks of such a flimsy PCB...

"More later"... :-)

EDIT -

Below is the response of the modified clean channel in my HRD, vs the EQing of the stock preamp, captured from the FX loop output. Settings were the same: all controls at noon, volume @ 1 or 2/12.



I add the response of the whole amp (captured through a DI box between amp and cab) when it's excited by a polyphonic signal, in drive mode (yellow channel), compared to the response of a Bassman, normal channel, same settings.



Again, "more later", if time permits - in the meantime, alga, I've tried to send you a PM: check your mailbox. :-)

[freefrog]

Regarding the drive channel, don't waste your time with C11 & C23: I've changed these ones then came back to the stock value.

Instead, you might try to tweak the gain and its bandwidth because that's where is the real main problem with this channel IMHO. Here is what I've done for that:

-C8 replaced with a 1k to 1,8k resistor paralleled with the 1µ cap (I migth have reduced R17 but since I've tried various cathode caps, it was simpler for me to add a resistor directly next to C8).
-C9 = 1k in series with 1.2k paralleled itself with the second switchable cathode cap (22µ).
-R21: 1k (if memory serves me. Not sure on this one but that's probably what I've done, in order to obtain a global cathode resistor value recalling the usual 820 Ohm).

Useful tool if you want to adjust these components to your taste:

https://www.ampbooks.com/mobile/ampl...or/calculator/

Oh, and...

-R19 value halved. Done with a second resistor of the same value than the stock one, in parallel with it.

My bad, I've apparently mixed up my notes with those regarding another amp... :-/

Here is EXACTLY what I've done with the Drive channels - V2 being a 12AX7...

-C8 swapped for a 1k resistor in series with a 1µ cap (polarized).
-C9 replaced by a 1k resistor in series with [a 1µ cap parallel with (a 1k resistor in series with a 100nF cap)]. It forms a “stepped” cathode cap…
-R21: 820 Ohm (1.5k makes it sound too grainy and thin with the 12AY7 that I've put in V1)
-R19 value halved.

Master cranked and gain under 4/12 = clean on the verge of breakup, on the two channels.

Gain full up and master lowered= a decent approximation of cranked classic Fender amps.

The "more drive" channel distorts hardly more than the other... but my goal was precisely to make the two channels comparable in gain (and volume) with different voicings. Now, the yellow channel recalls a Bassman while the red channel is somewhere between a cranked Deluxe Reverb and a Marshall.

These change don't pretend to make sense without the other mods done to the amp (blackfaced EQ and a few coupling caps changed elsewhere in the circuit + the mods mentioned above, among others).

FWIW...

[freefrog]

Well...

Alga has sent me two PM, twice: I’ve replied three times and have completed my PM’s with some indications above.

He hasn’t replied to these various messages and posts that I had wrote for him despite of my busy planning.

I hope that all is right for my interlocutor,. A few words from him would be appreciated…


ANYWAY:

Not yet enough time to write a complete diary about the mods done to my HRD.

I’ll just post below the frequency analysis of this customized amp, miked by a SM57:



white and green lines = clean channel of the stock model, when I’ve got it in 2010.
Yellow line = the clean channel of the same amps fed by the same testing signal through the same mic and recorder, nowadays, after the 15 or 20 mods that I’ve kept.
Red line = a Fender Twin Reverb (65 RI) in the same conditions.

I've played the modified HRD on stage at gig levels more than once : it's still not a Blackface (nor even a Tweed) but at least, I've got rid of the boomy farty bass and peaky high mids in favor of some nice sparkle... FWIW, before possible further explanations if it has any interest for some other musician and IF time permits. :-)

[alga]

Well...

Alga has sent me two PM, twice: I’ve replied three times and have completed my PM’s with some indications above.

He hasn’t replied to these various messages and posts that I had wrote for him despite of my busy planning.

I hope that all is right for my interlocutor,. A few words from him would be appreciated…


ANYWAY:

Not yet enough time to write a complete diary about the mods done to my HRD.

I’ll just post below the frequency analysis of this customized amp, miked by a SM57:

[ATTACH=CONFIG]48718[/ATTACH]

white and green lines = clean channel of the stock model, when I’ve got it in 2010.
Yellow line = the clean channel of the same amps fed by the same testing signal through the same mic and recorder, nowadays, after the 15 or 20 mods that I’ve kept.
Red line = a Fender Twin Reverb (65 RI) in the same conditions.

I've played the modified HRD on stage at gig levels more than once : it's still not a Blackface (nor even a Tweed) but at least, I've got rid of the boomy farty bass and peaky high mids in favor of some nice sparkle... FWIW, before possible further explanations if it has any interest for some other musician and IF time permits. :-)

Hello Freefrog

Yes, shame on me I sent you a repeated PM learning how to use the PM on this forum. Sorry for that my friend. I have to say a big THANKS for all your support. I appreciate you replied so fast despite your busy planning. Fortunately and thanks god I´m ok.

With your guidance I´m pretty sure I´ll achieve my goal with this amp (get rid of the overkill high mids on the clean channel) and get closer to a blackface sound type.

Would like to know what do you or others think will be the difference between achieving this by using a EQ pedal in the fx loop of the amp and by using a dedicated and designed network for that?

Best regards and eternally thanks

[alga]

Well...

Alga has sent me two PM, twice: I’ve replied three times and have completed my PM’s with some indications above.

He hasn’t replied to these various messages and posts that I had wrote for him despite of my busy planning.

I hope that all is right for my interlocutor,. A few words from him would be appreciated…


ANYWAY:

Not yet enough time to write a complete diary about the mods done to my HRD.

I’ll just post below the frequency analysis of this customized amp, miked by a SM57:

[ATTACH=CONFIG]48718[/ATTACH]

white and green lines = clean channel of the stock model, when I’ve got it in 2010.
Yellow line = the clean channel of the same amps fed by the same testing signal through the same mic and recorder, nowadays, after the 15 or 20 mods that I’ve kept.
Red line = a Fender Twin Reverb (65 RI) in the same conditions.

I've played the modified HRD on stage at gig levels more than once : it's still not a Blackface (nor even a Tweed) but at least, I've got rid of the boomy farty bass and peaky high mids in favor of some nice sparkle... FWIW, before possible further explanations if it has any interest for some other musician and IF time permits. :-)

Hello Freefrog

Yes, shame on me I sent you a repeated PM learning how to use the PM on this forum. Sorry for that my friend. I have to say a big THANKS for all your support. I appreciate you replied so fast despite your busy planning. Fortunately and thanks god I´m ok.

With your guidance I´m pretty sure I´ll achieve my goal with this amp (get rid of the overkill high mids on the clean channel) and get closer to a blackface sound type.

Would like to know what do you or others think will be the difference between achieving this by using a EQ pedal in the fx loop of the amp and by using a dedicated and designed circuit network for that?

Best regards and eternally thanks

[freefrog]

Hi alga,

No worries: I was just wondering if you had encountered a problem, with your amp or with anything else. It's reassuring to know that all is right for you.

Taking your time to reply is/was a good idea IMHO: that's what I should do too... instead of thinking out loud in too long posts, that I must correct once my memories refreshed. :-))

An EQ in the loop is certainly a good alternative solution, avoiding repeated mod sessions as well as the related risks for the amp (and for the user, potentially). Now, it's not a magical cure since it won't necessarily correct the basic character of an amp... but will quickly tend to sound fake iwith some settings - IME: YMMV.

More later and/or in PM's (I reply before and after my working days so my free time for that remains limited).