Inductor in Dumble SSS amps

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mabruk
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Inductor in Dumble SSS amps

Post by mabruk »

There is an inductor at the Hi-Low filters section of SSS Dumble amps. Does anyone really know what is the job of that component?
I have been testing it and could find no difference at all either with or without the inductor.

How many other components are in Dumble amps to just pay for them and doing nothing ?
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martin manning
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Re: Inductor in Dumble SSS amps

Post by martin manning »

That inductor has been discussed at length here, and it does nothing as shown. Of course, there is always the possibility that it's location in the schematic is misunderstood. AFAIK, that is the only component that doesn't seem to have any purpose in any Dumble amp.
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M Fowler
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Re: Inductor in Dumble SSS amps

Post by M Fowler »

People say the SSS was derived from the Ampeg SVT which has an inductor in the mid range circuit.

Like Martin states is seems the SSS is lacking the circuit for the ,900H inductor.
mabruk
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Re: Inductor in Dumble SSS amps

Post by mabruk »

I know Ampeg circuits from the seventies or even before that were using one or more inductors in their EQ circuits but in those cases
they had a specific and useful job to do.

I don´t think that one is the only component doing nothing in SSS amps since you have three, 3 complete double triode valves dedicated just to the reverb circuit.
And I will give you details. The first triode of those six is amplifying a signal taken just from the volumen pot wiper and loading it with the miller capacitance
of one more triode. That signal could be taken from the plate of the same triode (even directly from the final dry CF cathode) which has already been amplified, and go directly to the 1M dwell pot by means of a small capacity of about 500p and a series resistor if needed. In this case and thanks to the much less plate (or cathode) resistance, compare to the grid one, the dry signal will remain practically unaffected.

Then, instead of using two complete valves to do the mix you can attenuate and easily buffer the dry signal with just one more low value resistor at the dry CF cathode - as a voltage divider of around 30dB - and a cap in order to have a "send" output for a proper FXloop. Then the rest of the job from the "return" to the PI (reverb mix included) will be perfectly accomplished by using the two triodes already saved. That type of mix at lesser levels is more efficient than the original with two CFs at high signal levels. In the case of the reverb driver it is ok to do it with a valve instead of solid state but only due to practical reasons since an extra and proper power supply should be needed in such a case.

That way you will already have exactly the same jobs done with one whole valve less and no need at all for a Dumbleator.
Last edited by mabruk on Thu Sep 28, 2017 12:34 pm, edited 1 time in total.
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martin manning
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Re: Inductor in Dumble SSS amps

Post by martin manning »

What you describe may be a more efficient way to get a similar result, but in the original I don't think replacing any of the components with a wire would result in no effect at all as is the case with the inductor in the filter circuit.
mabruk
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Re: Inductor in Dumble SSS amps

Post by mabruk »

martin manning wrote: Wed Sep 27, 2017 10:11 am What you describe may be a more efficient way to get a similar result, but in the original I don't think replacing any of the components with a wire would result in no effect at all as is the case with the inductor in the filter circuit.
The inductor I say has a value of 1H or less and is connected in series to the plate of a triode through a 100k res. and 10n cap. also in series.
At the other side there is another 10n cap. and a res. of 470k value. So at a frequency of interest, say 1khz, and according to XL = 2piFL = around 5k ohms. which can fall within the 100k resistor tolerance.

Apart from that I have done different tests both using analog simulators and a real amp as well, noting absolutely no difference at all with or without the inductor. And not only myself but there were 4 more different guitar players doing the tests.

I said to use a piece of wire instead of the inductor in order to mean that the 100k resistor should remain connected to the rest of the circuit after removing the inductor or just not using it.

There are other things that I commented before like why using an external unit like a Dumbleator (about 1k dollars more to spend) just to do a simple job that can be easily implemented inside the amp. It is more since the fact of taking outside a piece of shielded wire - even if it is just one meter length - from the amp to the other unit without using any form of buffering will be enough to cause important high frequency losses. IMHO I can see no seriousness at all in these types of designs.

When I see Fender, Marshall, Ampeg or similar amps and read and analyze their circuits, I enjoy learning from them. But all the opposite happens with most of these extremely expensive boutique amps that I have to change their circuits because many of them lack even common sense. I have been doing it for long time and also design amps as a hobby so I will also make mistakes, of course, but they will be surely different from the ones I see here so often, and thanks to this forum.
Last edited by mabruk on Wed Sep 27, 2017 10:47 pm, edited 2 times in total.
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martin manning
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Re: Inductor in Dumble SSS amps

Post by martin manning »

The filter circuit has been simulated and tested with and without the inductor before by myself and others here, with the same result as you found.

What's the value of a boutique amp? More than the sum of its parts almost by definition, and the premium is not anything you can calculate using electronic formulae!
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M Fowler
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Re: Inductor in Dumble SSS amps

Post by M Fowler »

Ceriatone uses a large inductor unknown name and it is 0.39H - 0.39H per Nik.
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martin manning
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Re: Inductor in Dumble SSS amps

Post by martin manning »

The logical conclusion there is that it is not in the location shown in the schematics posted here. I'm sure there are some here who know the details, but they aren't talking.
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Re: Inductor in Dumble SSS amps

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mabruk
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Re: Inductor in Dumble SSS amps

Post by mabruk »

martin manning wrote: Wed Sep 27, 2017 10:37 pm The logical conclusion there is that it is not in the location shown in the schematics posted here. I'm sure there are some here who know the details, but they aren't talking.
I don`t think it is even important since any inductor within an EQ circuit implies a rather narrow action due to the high or at least significant "Q" introduced by this component, which is not of much use in guitar amps. It could be ok when acting together with others, like in a graphic equalizer that could be placed outside or even inside the amplifier. I remember however some Gibson guitars that were made including an inductor just in series with different capacitors that could be selected with a switch in order to vary the point where the mid notch was applied. That way the guitar could be connected to any amp with a flat or near flat response. The same could be made inside any amp instead but I think the fact of using active components anyway (not practical at all inside guitars) the EQ and voicing options needed could be easily implemented with just capacitors and resistors.

All in all I mean that inductors are ok in order to make important EQ correction with minimum signal losses. Even that, they should be tamed with an adequate amount of resistance either implicit or not to control "Q". Inside amps we have many options to do similar corrections with RC components only. It is true that it will imply to wear an important amount of signal out that later could however be easily recovered.
mabruk
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Re: Inductor in Dumble SSS amps

Post by mabruk »

martin manning wrote: Wed Sep 27, 2017 10:37 pm The logical conclusion there is that it is not in the location shown in the schematics posted here. I'm sure there are some here who know the details, but they aren't talking.
I had a few of these SSS clones and all of them had the inductor located in the place we know. They were brought to me in order to change the FXloop and make it opeative, other to just being repaired. So I had chances to deeply revise the whole circuit. The ones I saw were known as 50w Texas Flood and the owners told me that they were exact copies of the originals except for a small variation made in the Jazz/Rock Switch. i saw it in fact and looked rather tricky to me, they had called Jazz to what originally was the Rock position and then inserted resistors of 15k and 68k at the bottom of bass and middle pots respectively for the new Rock state. So just increasing mids, lows and, on the way, leaving the middle pot practically not operational and rather limited the other one.

Curiously, I was trying and playing the guitar with this amp plus some other friends of mine as well. And all of us, specially my friends who were professional musicians, noted an
important amount of compression when playing the amp. Then I still wonder what could be the reason for that.
Another thing is that despite of being only a 50w amp (I measured no more than 38watts before clipping) with 2 x 6L6GC (7851 in reality) It had a 12AT7 working as the typical power CFs to drive the final valves, which could be probably unnecessary.

Anyway the filtering was rather light (50uF for the first one and 22uF for all the rest) and the resistors in the positive rail were rather small as well (1k8, 4k7 and 1k) from screens to PI and preamp nodes. So I am not sure if that could be the reason for such a compression. The rest of the amp was also the same to what we are used to see in these forums.

I would like to know if someone else have noted said compression and have an idea of what could be the reason. I had no more chances to experiment.
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erwin_ve
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Re: Inductor in Dumble SSS amps

Post by erwin_ve »

I haven't build or played the sss.
But feedbackloops can cause compression at certain frequencies.
Driving a cathode follower hard can also add a fair amount of compression.
Mark
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Re: Inductor in Dumble SSS amps

Post by Mark »

I did a search of the SSS amp circuits and I didn't find one with the inductor. Is there a circuit diagram on TAG?
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martin manning
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Re: Inductor in Dumble SSS amps

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