#124 CAP QUESTION

[martin manning]

Both the mid and bass pots are wired as variable resistors so the larger values can replicate the effect of the smaller values. The Skyliner's 500k bass pot with a 10k tail does a better job of spreading out the effect of the bass control at low frequencies.

[Sven]

Thanks for a confirmation on the schematics. All right, now it is clear! It is always good to get a confirmation (isn't it)... So, it shall be ¨#124 schematics 1984¨ and also it shall be 2x 100 uF capacitors for a total of 50 uF for the first stage in the Power supply section of this 50 Watt amp.

ALSO IMPORTANT, since we have that excellent opportunity of having member BLUESFENDERMANBLUES, an expert, on this thread, I shall use this occasion to ask him whether his schematics for an active FX PARALLEL LOOP based on some MESA idea - it is in DUMBLE FILES section - named CLAUS-ULATOR III ver. 1 dated May 3, 2013, is the FINAL workable solution that I could include into this build of #124 Dumble clone? I see not much (or any) use of a serial FX loop, thus if this is indeed a final and useful PARALLEL FX LOOP solution, I would be glad to get a confirmation from the ¨master builder¨ that the schematics is OK and could proceed to build it... Thanks in advance...

Since I shall use 2x EL34 for the output valves, it is important to know if there should be some difference of values (resistors, caps and such...) for those output valves as opposed to the 6L6 type used in the standard Dumble amplifier? I once red somewhare here on this forum, some years ago, that GRID RESISTORS going into each output valve should be different if instead of 6L6's one uses EL34's. Is that so, and what is the new resistor value for EL34 in this schematics? All the best and thanks again to nice people who care to respond and keep this exchange going towards a better result in actual build...

[martin manning]

...I shall use this occasion to ask him whether his schematics for an active FX PARALLEL LOOP based on some MESA idea...

He says as much here: http://ampgarage.com/forum/viewtopic.ph ... highlight=

...I shall use 2x EL34 for the output valves, it is important to know if there should be some difference of values (resistors, caps and such...) for those output valves as opposed to the 6L6 type used in the standard Dumble amplifier?

Be sure to connect the suppressor grids to the cathodes (pin 1 to pin 8, and don't use pin 1 as a tie point for the g1 resistor). 1k screen resistors are recommended for EL34 as opposed to the 470R shown in the layouts.

[TUBEDUDE]

Has anyone tried tying the supressor grid to the raw bias voltage, instead of the cathode. I think Garnet amps did this and claimed more stable, bullet resistant operation.

[bluesfendermanblues]

interesting. what about the different mid pot value, surely that has a big effect on the tone? also no master bright cap, I've found the master bright cap to have a significant effect on the overall tone, obviously dependent on value

so you can switch between the two different caps and slope resistors combinations but use the same mid pot.....which mid pot do you use, 250 or 100k?


Marcus

Don't get too confused with pot values.

The only one you should really be concerned about is the treble pot, since it has a 'fixed' value in the circuit - its kind of a mixer. And also the treble pot is usually a linear.

The bass pot and the mid pot are logaitmic and if you use alpha pots they provide 15% of their total resistance at 12 o'clock/noon. That means a 100k log at noon is 15k and a 250k is 40k at noon.

Here's a tip for you: Put your ohm meter at the input and mid logs and you will see that they are in fact quite similar in real life playing situations.

When you've build the amp - and played it in for about 100 hours - try and measure the ohm values at your favorite settings.

My personal sweet spots are:
#102 clone with skyliner,
mid pot :28,4k (measured from center log to ground) and
Bass pot: 80-120k (measuered from center log to ground).

​Classic amp
mid pot: 19k ​(measured from center log to ground) and
basspot: 34k. (measured from center log to ground) and

So you see I'm not above 100k on the middle pot - so IMO it doesn't matter for me whether I have a 100k or 250k mid pot. What I do like is to have the sweet spot not too far from 12 o'clock so I can adjust the amp around the sweet spot.

But each to his own.

[bluesfendermanblues]

Thanks for a confirmation on the schematics. All right, now it is clear! It is always good to get a confirmation (isn't it)... So, it shall be ¨#124 schematics 1984¨ and also it shall be 2x 100 uF capacitors for a total of 50 uF for the first stage in the Power supply section of this 50 Watt amp.

ALSO IMPORTANT, since we have that excellent opportunity of having member BLUESFENDERMANBLUES, an expert, on this thread, I shall use this occasion to ask him whether his schematics for an active FX PARALLEL LOOP based on some MESA idea - it is in DUMBLE FILES section - named CLAUS-ULATOR III ver. 1 dated May 3, 2013, is the FINAL workable solution that I could include into this build of #124 Dumble clone? I see not much (or any) use of a serial FX loop, thus if this is indeed a final and useful PARALLEL FX LOOP solution, I would be glad to get a confirmation from the ¨master builder¨ that the schematics is OK and could proceed to build it... Thanks in advance...

Since I shall use 2x EL34 for the output valves, it is important to know if there should be some difference of values (resistors, caps and such...) for those output valves as opposed to the 6L6 type used in the standard Dumble amplifier? I once red somewhare here on this forum, some years ago, that GRID RESISTORS going into each output valve should be different if instead of 6L6's one uses EL34's. Is that so, and what is the new resistor value for EL34 in this schematics? All the best and thanks again to nice people who care to respond and keep this exchange going towards a better result in actual build...

Thanks for the kind words!

Having experimented a lot with the loop, I've come full circle and must admit I prefer the sound of the original serial loop.

However, In the latest incarnation of my loop experiments, adding a pot in parallel with the loop, I believe is the most respectful (towards Mr. D) way to implement a parallel function and it preserves the Dumble tone. However, there's no right or wrong... let your ears decide.

[Sven]

However, In the latest incarnation of my loop experiments, adding a pot in parallel with the loop, I believe is the most respectful (towards Mr. D) way to implement a parallel function and it preserves the Dumble tone. However, there's no right or wrong... let your ears decide.

Your schematics that I see as the latest is the one I mentioned, named Claus-ulator III, dated May 3,2013. Is that the latest incarnation of loop experiments, or perhaps, very likely, there might be something newer since year 2013? In other words, what is ¨latest incarnation¨ scheme? I would actually like to implement it in this build as an active PARALLEL FX LOOP (NO NEED FOR PARALLEL/SERIAL SWITCH, ONLY PARALLEL I OK). WHICH SCHEMATICS IS THAT? Thanks.



P. S. It is a special subject as to which FX loop is better, but I think that parallel loop is the one and the only that is good and useful since I cannot think that whole valve amp sound goes through a transistor pedal and than one thinks that one has a ¨pure valve sound¨ while there is a serial section with 100% who knows what kind of IC or transistor garbage from a guitar pedal... while parallel loop is much more pure valve sound. Many other advantages as well...

[bluesfendermanblues]

............P. S. It is a special subject as to which FX loop is better, but I think that parallel loop is the one and the only that is good and useful since I cannot think that whole valve amp sound goes through a transistor pedal and than one thinks that one has a ¨pure valve sound¨ while there is a serial section with 100% who knows what kind of IC or transistor garbage from a guitar pedal... while parallel loop is much more pure valve sound. Many other advantages as well...

Let you ears decide my friend!

Don't form an opinion until you have listened carefully to the differences.

E.g.there's a general consensus that tubes are warm and that transistors and ICs are cold. However, it's probably the other way around since well build transistor circuits are warm and tube gear emphasizes the top end of the sound spectrum with nice overtones.

The NEVE preamps/mixers that everybody are heralding are pure 60's transistor technology (with great transformers) and the sound is not 'transistor' or cold. Its quite warm. Modern Fender and Peavey amps use a lot of tubes, but to me they sound rather cold and uninspiring.

Don't factor out gear just because it uses transistors and don't think gear is warm just because it uses a tube.

[Sven]

I have spent my life with NEVE consoles... I am a professional Sound Engineer, Producer etc., so I know quite a lot about sound and transistor NEVE equipment etc. However, GUITAR PEDALS are NOT designed by Mr. Rupert Neve, rest assured of that... nor do they sound even closely as good as NEVE equipment (on the other hand, they do not cost as much as NEVE equipment). But, that is a long story...

ANYWAY... there was my question about Claus-ulator III ... is that your final scheme of PARALLEL FX LOOP, dated May 3, 2013. or is there some newer scheme that I did not find here? What do you have for us if we wish to make built-in PARALLEL FX LOOP in 124 Dumble clone? Thanks.

[norburybrook]

Sven, me too as a session musician and producer. Don't use them that often anymore due to budgets being cut and the general state of the industry. Mostly mixing in the box nowadays.


Interesting thread. thanks for the wise words Bluesfendermanblues ,I've got a #102 and a bluemaster so I'm going to do the #124 EXACTLY as it was, with the classic stack etc.... I can always 'update it' if I don't like it. It will be interesting to hear how it sounds , I'm sure it wont be a million ,miles away from #102 but I'm curious all the same.


Marcus

[bluesfendermanblues]

I have spent my life with NEVE consoles... I am a professional Sound Engineer, Producer etc., so I know quite a lot about sound and transistor NEVE equipment etc. However, GUITAR PEDALS are NOT designed by Mr. Rupert Neve, rest assured of that... nor do they sound even closely as good as NEVE equipment (on the other hand, they do not cost as much as NEVE equipment). But, that is a long story...

.

Respect for your background.

[bluesfendermanblues]

I have spent my life with NEVE consoles... I am a professional Sound Engineer, Producer etc., so I know quite a lot about sound and transistor NEVE equipment etc. However, GUITAR PEDALS are NOT designed by Mr. Rupert Neve, rest assured of that... nor do they sound even closely as good as NEVE equipment (on the other hand, they do not cost as much as NEVE equipment). But, that is a long story...

ANYWAY... there was my question about Claus-ulator III ... is that your final scheme of PARALLEL FX LOOP, dated May 3, 2013. or is there some newer scheme that I did not find here? What do you have for us if we wish to make built-in PARALLEL FX LOOP in 124 Dumble clone? Thanks.

The best version IMO is the simple dumbleator with an added 25k pot:
http://ampgarage.com/forum/viewtopic.php?t=21205

I'm very interested in knowing what you think, once you get it build.

[Sven]

Thanks, much appreciated... yes, that is the PARALLEL FX LOOP that I have already drawn into my AutoCAD drawing that I am working on for the schematics of the amp. My expertize is indeed in Sound (Sound Engineer, Producer, Musician, Composer, Arranger...) much more than in valve amps (although I do have a BSEE degree, Electrical Engineer). In these matters regarding valve amps those my other qualifications are NOT of much value when it comes down to actually MAKING an amplifier... it is rather expertise of A NUMBER OF EXCELLENT FELLOWS HERE ON THIS FORUM that is perhaps going to be my saving grace, as well as of my friends here who are going to help me. All the best and thanks again (it is nice to get confirmation)... Sven

As for the CAPACITOR question, I am still undecided: If a 100 W Dumble amp has a total of 150 uF capacitance in the first section of Power supply, what should be capacitance of a 50 Watt version of that amplifier, half of that (75 uF) or one third of that (50 uF) or somewhat more than half of that (100 uF)? As a fellow up in this thread stated, THERE IS NO PRECEDENCE FOR A 50 WATT AMP. What really changes with smaller or larger capacitance? I used to know that some years ago, but I forgot it (if I ever actually knew it, I wander, ha, ha, ha...).

[norburybrook]

Sven, you've got me thinking the same thing

I've decided to get a pair of 100uf and stick them in to replace the (expensive) 220's I have there now. At this stage it's an easy swap.

My reasons are; I have a 50w #102 with 220's so I'm curious to try this #124 with less filtering.

Also, looking at the 50w 3rd gen amp it's a low plate amp with 100k slope just like the #124 so not a million miles away.


anyway, we've got two #124 threads going consecutively here will be interesting to compare notes as we go along

Marcus

[martin manning]

I like that plan, since you can easily clip in another 50uF (net) and compare back-to-back. Seems like HAD eventually decided that 2x 220uF was enough for a 100W amp. It will be good to hear your impression upon hearing the difference between 50uF and 100uF in your 50W.