Parallel loop - for ampgarage users only :-D

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mshowson
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Re: Parallel loop - for ampgarage users only :-D

Post by mshowson » Wed Aug 03, 2011 1:47 am

Thanks for the reply. So with the built in d'lator, the preferred method for supplying the plates of the send/return tube is to decouple from the main B+ rail with a resistor and filter, to pin 1, decouple again with resistor and filter to pin 6, and land all grounds for the circuit to say, the mounting screw for the buffer tube.
Do I understand this correctly?
Much appreciate the help...Mark H

mshowson
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D'lator built in hum

Post by mshowson » Thu Aug 04, 2011 1:15 am

Finally banished the hum.
Moved each ground one by one to a common star at the 12ax socket.
little or no improvement until I moved the cathode resistor/bypass cap on pin 8 to the new star.
The hum must have been coming through there as I had them grounded to a different point on the chassis.
I never fail to be humbled by the ground hum ghost...especially when I think I understand the whole thing..
Thanks kindly for the fix, Mark H.

bluesfendermanblues
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Re: Parallel loop - for ampgarage users only :-D

Post by bluesfendermanblues » Thu Aug 04, 2011 5:14 pm

mshowson wrote:Thanks for the reply. So with the built in d'lator, the preferred method for supplying the plates of the send/return tube is to decouple from the main B+ rail with a resistor and filter, to pin 1, decouple again with resistor and filter to pin 6, and land all grounds for the circuit to say, the mounting screw for the buffer tube.
Do I understand this correctly?
Much appreciate the help...Mark H
Exactly. Thats the way to do it.
Diva or not? - Respect for Mr. D's work....)

bluesfendermanblues
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Re: D'lator built in hum

Post by bluesfendermanblues » Thu Aug 04, 2011 5:31 pm

mshowson wrote:Finally banished the hum.
Moved each ground one by one to a common star at the 12ax socket.
little or no improvement until I moved the cathode resistor/bypass cap on pin 8 to the new star.
The hum must have been coming through there as I had them grounded to a different point on the chassis.
I never fail to be humbled by the ground hum ghost...especially when I think I understand the whole thing..
Thanks kindly for the fix, Mark H.
Great you solved it.

Aiken and Dumble are the masters of grounding layout in guitar amps.

All the preamp stuff gets grounded close to the input jack.
The loop, PI, Screen and cathode of the power tubes gets separate grounding points close to their physical location because they draw a lot of current that might cause hum downatream if you dont follow the Dumble layout.

Btw have recently build a couple of fender tweed clones, using the Dumble grounding layout. Result? Totally hum free Amps ! :)
Diva or not? - Respect for Mr. D's work....)

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greiswig
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Re: Parallel loop - for ampgarage users only :-D

Post by greiswig » Sun Nov 27, 2011 7:33 pm

I built one of KOC's series-parallel loops (without the 20db switch) into a little aluminum box that I attached to the chassis on my build. I prefer parallel mode because I use a rackmount TC effects unit, and running the loop in series (adjusting the wet mix with the TC's mix control) it seems to lose some of the impact that the parallel mode has.

However, there is something else that this loop in parallel mode lacks. It's difficult to describe, but even with just a short cable in the loop there is a noticeable affect on the sound, and it isn't what I would call "smoothing" or positive. More like the sound getting veiled. It's pretty subtle, so it doesn't bother me for the most part...but then again perfectionism is kind of the name of the game here, isn't it?

The one thing that I do really like about the series Dumbleator is the ability to use the return as the overall volume...having played with that on another build recently, I definitely hear advantages to running the amps MV up pretty high, then using the return to control volume. Can't do that with my loop, for sure.

So...I'm wondering what the chief architectural differences are between KOC's "Ultimate effects loop" and this series-parallel Dumbleator? For those of you who have heard Claus's design, is it uncolored or does it color in a good way?
-g

John_P_WI
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Re: Parallel loop - for ampgarage users only :-D

Post by John_P_WI » Sun Nov 27, 2011 10:26 pm

There is some discussion about the KOC loop here:

http://ampgarage.com/forum/viewtopic.ph ... ht=oconnor

bluesfendermanblues
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Re: Parallel loop - for ampgarage users only :-D

Post by bluesfendermanblues » Sun Nov 27, 2011 10:30 pm

Hi G,

I only use the Dumbleator loop in serial mode. I also missed that certain 'something' when running the loop in parallel.

In order to not ruin the tone with my cheap effects units (Boss SE50 or SE70), I use a Suhr Minimix II that 'convert' my effects to parallel operation in the Dumbleator loop. -Just like (Scott) Dogear suggested. I guess the minimix is not necessary if you have a 2290, which has an internal analog mixer.
Diva or not? - Respect for Mr. D's work....)

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David Root
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Re: Parallel loop - for ampgarage users only :-D

Post by David Root » Tue Nov 29, 2011 1:00 am

I used the TUT all-tube loop in one high gain amp, it worked fine. KOC recommended the 12AT7 in it and that's what I used. It is a bit more complex than is really needed IMHO and I haven't used it since.

In my four pre-tube D-builds I use Normster's series buffered loop, which is a stripped down Dumbleator, because it fits in the chassis and on the main board with minimal space issues, and sounds good. I like it with a 12AT7 too. It is nice to use the Return pot as an MV, no doubt about it. Normster's loop is in the Dumble Files if those of you not already familiar with it are interested.

The Claus-umbulator is also good, and has a series/parallel option too. Would fit in a four-pre D-chassis OK I think. Slightly more complex than Normster's, and is also in the Files I think.

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Tonegeek
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Re: Parallel loop - for ampgarage users only :-D

Post by Tonegeek » Wed Dec 14, 2011 2:50 am

In parallel mode, what does the 220k resistor do that goes vertically from the recovery output to the 500p, 220k, .47Uf junction? It looks to me like it would cause feedback.
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bluesfendermanblues
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Re: Parallel loop - for ampgarage users only :-D

Post by bluesfendermanblues » Wed Dec 14, 2011 7:23 am

Tonegeek wrote:In parallel mode, what does the 220k resistor do that goes vertically from the recovery output to the 500p, 220k, .47Uf junction? It looks to me like it would cause feedback.
It creates the artificial "0" connecting point..... like in a mixer. Theoretically, if you wanted to add more effects units in parallel, you could expand the system with more send and return jacks plus send and return pots and inject these to the "0" point. And that way build a larger effects mixer and still retain your initial preamp tone.

Anyway like I wrote in a post above I prefer the dumblator in serial mode WITH a Suhr minimix II for running (my cheap boss se 50 or se 70) the effects in parallel.

The parallel mode is working fine and transparent, but the serial mode (with suhr minimix if you dont have a 2290) gives that certain compression and rightious highend roll off.
Diva or not? - Respect for Mr. D's work....)

bluescaster
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Re: Parallel loop - for ampgarage users only :-D

Post by bluescaster » Wed Jan 04, 2012 10:03 am

Hi, and happy new year !

According to http://aikenamps.com/FeedbackAmp.htm and wanted to just use parallel loop i ask myself if this would be ok ?

[IMG:800:328]http://img812.imageshack.us/img812/2496/myloop.jpg[/img]
By bluescaster at 2012-01-04

The 220K between master pot and V1 grid reduce the gain of the stage to 1. No need of 2 x 10M for local feedback.

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jelle
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Re: Parallel loop - for ampgarage users only :-D

Post by jelle » Wed Jan 04, 2012 2:09 pm

Why would you want to limit the gain of the recovery stage to 1?

bluescaster
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Re: Parallel loop - for ampgarage users only :-D

Post by bluescaster » Wed Jan 04, 2012 2:13 pm

Hi, cause i want to keep the same signal level as when the loop is bypass.

tictac
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Re: Parallel loop - for ampgarage users only :-D

Post by tictac » Thu Jan 05, 2012 5:48 am

Then why do you need a gain stage at the return? You could simply passively mix the effects return and the dry signal and use one less gain stage.

TT

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angelodp
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Nice

Post by angelodp » Fri Feb 21, 2014 8:57 pm

Just finished the adjustments to a S/P Dlator I built. It now matches the most current schematic and works quite well. Will post pics soon. Its a stand alone.

Thanks

Ange

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