Changing caps to get a more transparent, sparkly, rich CLEAN

[andyhardy]

Here is a carr slant 6 hand drawn schem. Might help

[PaisleyTube]

Joost: what speaker(s) are you using?

The Slant differs in many, many ways; powersupply-nodes (voltages), phase-inverter values, reverb-mix-resistor, etc., bright-cap/volume-control-configuration.

Don't know which values you did use in your 124-type amp but I would 1st look at:
- speaker/cabinet
- treble-cap/bright-cap
- bright-cap across MV
- tailoring pi and neg.feedback

This Slant looks more like a tweaked VibroluxReverb than a Dumble imo.

Have fun, greez from Chris @ Vleuten

[diagrammatiks]

Whoops nevermind. The Carr is fixed or cathode bias switchable.
The Marshall is fixed and cathode biased.

I'll leave the schem up though. it's coo.

I've been meaning to breadboard this circuit.

[img1320]http://drtube.com/schematics/marshall/4001m88.gif[/img]

[glasman]

Here would be a few things I would try if wanting more sparkle in the amp.

- A few OD 715's or 716's in selected spots. (ie Output coupler for clean section, input cap for PI section). 715s are much faster than PS series so be care, not too many spoil the broth.

- Silver mica for treble cap
- Polyprop for mid cap
- 1W CF or CC for slope and maybe even the plate resistors. I always find they add a little something to the top end when used as plate resistors.
- Silver mica for bright caps and master control (a 47pf does wonders on a master control).

My comments on the E-cap versus film power supply debate.

Polyprops in the power supply, got to be kidding. Been there done that, the lack of ESR really kills the feel, bloom and organic nature of the amp. Part of the sonic appeal of crappy e-caps is there effect on the recovery time of the power supply stages.

If a person wants to experiment with PP caps, I would suggest anding a 1 to 10 ohm resistor in the ground leg to simulate a little ESR.

If I were building a bass amp, I might look for extremely low ESR caps and build an extremely stiff power supply as I llike punch in the low end. But in that case you would be looking at 5000uf+ filtering on the two supply rails.

[Joost]

Thanks for the replies everyone. Today, with the help of Erwin we tweaked the phase inverter and it made a lot of difference. we also tried to different tubes and a different slope resistor and a different mid-cap. I also changed the bass cap from a 6PS to a xicon. We also were able to really dial in the phase inverter with a signal generator. All in all I am already very close to where I want this amp to be now. I will do some more experiments Erwin suggested for the fun of it. But I am even more pleased with this amp now than I already was. It is a very gratifying and cool project. With the overall flexibility of a buffered effects loop and a cool overdrive channel, I wouldn't trade this amp for any Carr right now.

as for speakers, I am using a combination of scumback M75 and H75. Ian tested it tonight and thought the amp was amazing and very inspiring, he kept playing it.

[llemtt]

I think that at this point I'd be a little cautious...
In terms of measurable characteristics the ESL and ESR of a film cap is much lower any electrolytic capacitor. I haven't seen published numbers for Solen but Mundorf lists 9mohm..
An electrolytic capacitor has on average around 250-400mohm ESR...

ok but you have still to explain how 9mohm instead 400mohm (are you talking milli-ohms??) make a more sparkling clean sound...

that's what's all about



@glasman

can you please argument capacitors specs in terms of "faster" or "slower"?

thanks

[BobW]

Some of the electrolytic cap parameters such as ESR and ESL are typically measured at 100kHz, so you can't really use these numbers as a direct comparison from one cap to another. My day job as a switchmode power supply design engineer (among others), has told me over the 25+ years that you can't always rely on the data sheets alone. You also have to trust your ears when building amplifiers.

[glasman]

I think that at this point I'd be a little cautious...
In terms of measurable characteristics the ESL and ESR of a film cap is much lower any electrolytic capacitor. I haven't seen published numbers for Solen but Mundorf lists 9mohm..
An electrolytic capacitor has on average around 250-400mohm ESR...

ok but you have still to explain how 9mohm instead 400mohm (are you talking milli-ohms??) make a more sparkling clean sound...

that's what's all about



@glasman

can you please argument capacitors specs in terms of "faster" or "slower"?

thanks

I use the terms Fast and Slow to describe the response of the caps. I use a Quadtech 1730T LCR Meter to measure caps. When measuring I look at ESR, Q and Dissipation. Dissipation and Q are related to one another (D= 1/Q).

In the typical polyster cap (say a Mallory 150 or PS series) the value of Q will be in the 250 to 300 range. For a polyprop cap, the values will be in the 4000 to 6000 range.

Experience has shown me that the higher the Q the brighter the cap and edginess they impart on the sound. This is especially true in the case of metallized polyprop caps.

Gary

[M Fowler]

Carr amps use Solen Fast caps so apparently some designs can sound very good using them.

[glasman]

Carr amps use Solen Fast caps so apparently some designs can sound very good using them.

The comments in my last post were based on signal path caps only.

Solens are normally used in power supplies. They have few caps that could be used in the direct signal path. I think .1uf is the smallest cap they make.

I will give a positive comment, the solens will probably NEVER have to be replaced in a power supply applications due to their polyprop construction.

In the right amp, solens would be useful in the power supply and bypass capacitor locations.

Gary

[llemtt]

Thank you Gary

I am aware of ESR but I never think in terms of Q or D (aka DF)

but actually D = 1/Q = ESR/Xc or Q = Xc/ESR

so all that is needed to describe the behavior of a capacitor at a certain frequency is C and ESR

DF is a measure of energy dissipated by the capacitor (or if you prefer energy not converted into useful work) the lower the Q the higher the energy wasted the lower the effectiveness of the capacitor -> equivalent to a resistance put in series with it (so published equations make sense...)

using high Q, or equivalently low ESR, caps in power supply account for increased effectiveness of filtering; being aware of the frequencies of your interest you can obtain the same results with a slightly higher capacitance

in your experience does a better filtered, some also say "stiffer", power supply improves the clean sound?

cheers
teo