Question about newly finished D-Lite. FIXED... or?

[Svempan]

Thanks for your suggestions

Please come with more !!!

[dogears]

Mu suggestions are part of a well researched system. Most of what I posted converts your non Dumble values to the accepted standards that appear in almost all ODS amps. Do them all to establish a baseline from and then tweak from there.

Equalizing is the same as saying get the same voltage drop on each cap. So we are on the same page. I use 270K and it works for me. I have seem only 1 Dumble with 220K and maybe 2 dozen with 270K.

They all have the 150K FET load on the end of the string...

Let us know how it turns out! Good luck.

...Raise V1a grid to 33K.
Change the bypass on V1a and V1b to 4.7uf.
...

Is the input gain pot linear? Linear pot there will give the impression of no headroom.....

Thans for all the tips!

Raising V1a grid resistor is a good suggestion. After checking for faulty components I will probably try that.

I’ve already tried changing the bypass capacitor on V1a and V1b to 4.7uf

I guess you mean the Volume pot with "the input gain pot". It's not linear. The distortion doesn't change at all in different positions off this pot. With the Master Volume at full, the distortion is the same at any position on the Volume pot, from just audible to when the rest of the amp starts to distorts.

By the way: The distortion sounds almost as it does in some amps when the Volume control is all the way down, but there’s still a little sound . If you’ve tested many, especially vintage amps, you probably have heard this.
One thought now hits me: I haven’t checked the 1M grounding resistor on the control grid of V1a. Could it be that the grid is loaded in som bad way?... I will check.

...Change the silver mica 390pf on the V1b grid resistor to a 500pf ceramic.
Change the treble cap to a 330pf ceramic.
Replace the .0012uf on bass pot with a .001uf. Type doesn't matter.
Try lower CL2 cap. Maybe .02 PS series.
Reduce the negative feedback resistor to a 4.7k
Replace PI plates with 110K/120K
Replace output grids with 5.1K
Replace screen resistors with 500ohm
Lower the choke replacement resistor to a 330ohm
Raise the main cap equalizing resistors to 270k
Raise the 1K dropping resistor to a 2.2K
Lower the FET simulator to 150K
Possibly go back to the 22K/2.2K dropping as well...

I see these suggestions as modifications. Mainly not as fixing for the problem. What do you think?

Regarding the feedback resistor, I will probably lower that. I like the sound with more negative feedback. This is a good place for tweaking, especially when using the amp at higher sound levels.

Regarding the values of the dropping resistors: As I see it, the exact values is not as important as what B+ voltages it will be with the respective resistor. The power transformer in this amp gives rather low voltage so I have tweaked the resistors to values that give the B+ voltages I want to the pre amp.

The FET simulator resistor surprises me in any case. My intuition says that it should be removed totally. I don’t see the reason for it (other than discharge the filter caps when the Stand By is off). Please correct me if I’m wrong. The distortion problem should definitely not be there without the resistor and probably not with values from there down to 150 k.

Your "Raise the main cap equalizing resistors to 270k" makes me think that there's something i don't know or yet understand. For me the reason for theese resistors (the two 220 k in parallell with the two main filter caps) ONLY is to get the same voltage drop over the two caps. I wonder what you mean with equalizing resistors?

I’m grateful for your suggestions, so please excuse that I’m questioning some of them .

[Svempan]

Nice clean build!
I have a D'Lite 44.
I am no expert on these amps but I guess I wasn't expecting chimey Fender cleans on this amp.
I can keep it pretty clean until I get it up there loud.

Especially if you have the volume dimed and turn the gain up on the master.
It seems to go into saturation pretty easily on my amp.
Isn't this typical of this amp?

BTW, where did you get your relay PCB's?

Thanks for your nice comment .

I do think there should be a clean sound in this amp att least comparable to, for example a Fender Vibrolux Reverb.

The relay PCBs come from Brown Note as the kit does.

[stelligan]

Svempan,

Some others here may scoff at this, but I can experience a sort of "input distortion" as you describe on nearly every amp I've ever owned. And this style amp seems to be very sensitive to that effect. It is usually with my guitar volumes up near max. I play 12's on my Gibson scale length guitars with an unwound 20 on my G string at standard pitch. I play 11's on my Fender style guitars. I use extremely stiff and hard picks. I think sometimes I just bark too much into an amp. Experimenting with pickup height on your guitars and rolling the volumes back may also help. I have found, through much experimentation, that my problem with that sound was too much energy going in. I swapped the 1M resistor on my input jack to a 470K on one of my builds and that helped a ton. Seems I remember stories of Stevie Ray Vaughn and Jimi Hendrix going for those old cheap coiled cords into their amps because the straight, high tech ones "pass too much electricity". Try some things on the outards with picking techniques and volume controls before you yank too much of the innards out of your pretty build. Let the amp do the work. Just my 2 cents.......

[johan]

Hi everyone
"Svempan" is building this one for me. If there's a problem I'm sure you and he can sort it out.
SJ, no hurry. Take your time and get it right. See you next saturday

BTW, did you get the 4-8-16 taps to work with 6L6's?

Any more suggestions?

/ Johan

PS SJ! Telia email has been down today. Talk to you later...

[Svempan]

Mu suggestions are part of a well researched system. Most of what I posted converts your non Dumble values to the accepted standards that appear in almost all ODS amps. Do them all to establish a baseline from and then tweak from there...

Dogears,

Thank you very much. I DO appreciate your suggestions and that you took your time to write them down to me .

I'm a tube amp tech that basically repairs, make services and modifies tube amplifiers for musical instruments. I have done that for many years, but I absolutely don't regard myself as an amp designer and my experience of the ODS design is small and mostly theoretical.

As I understand it your suggestions come from experience from many ODS style amps, so it would be stupid of me not to listen to them...

I've also studied all the ODS-101 schematics which I guess you have had some influence in.

By the way: I also hope that my English isn't too bad .

[Svempan]

...Some others here may scoff at this, but I can experience a sort of "input distortion" as you describe on nearly every amp I've ever owned. And this style amp seems to be very sensitive to that effect...
... I swapped the 1M resistor on my input jack to a 470K on one of my builds and that helped a ton. Seems I remember stories of Stevie Ray Vaughn and Jimi Hendrix going for those old cheap coiled cords into their amps because the straight, high tech ones "pass too much electricity". Try some things on the outards with picking techniques and volume controls before you yank too much of the innards out of your pretty build. Let the amp do the work. Just my 2 cents.......

Stelligan,

This amp is not meant for me. Johan, the owner, seems to have a lighter picking technique than me, but I still think that this distortion shouldn’t occur like this.

You may be right that the first gain stage distorts like this also in other amps with higher output guitars and hard picking, but I think it’s a little too much in this amp.

Swapping the input grid to ground resistor to 470 k seem as a good suggestion. If I don’t find any faulty parts I will try that.

[Svempan]

...SJ, no hurry. Take your time and get it right. See you next saturday

BTW, did you get the 4-8-16 taps to work with 6L6's?

Thanks. I will work on the amp this weekend.

Yes, I did get the 4-8-16 taps to work with the 6L6's. The transformer has taps on the primary for both 4000 and 8000 primary impedance. Now it's wired for 4000 ohms primary with 4, 8 or 16 ohms on the secondary (speaker output).

[johan]

GREAT! Then I can wire the cab for 16 ohm. Just got my new speaker cables incl internal wiring for the speakers.

If you think it distorts with "normal" attack something must be wrong. Hope it's not too much of a trouble for you. Sorry the build took longer than expected.

(sätt upp det som "utbildning" i deklarationen )

[Svempan]

If you think it distorts with "normal" attack something must be wrong. Hope it's not too much of a trouble for you. Sorry the build took longer than expected.

Don't worry. I will fix this. But maybe you will not get the amp before next saturday.

And please don't be sorry! I like this work very much. Problems makes you to learn new things...

[Normster]

Just to be clear about the distortion, are you talking about the bass notes farting out when you really dig in to low notes? (Almost sounds like a bad speaker.) If so, I've experienced this with nearly every Dumble style amp I've ever built. With only 1M/22k loading the grid of V1a, it's probably too easy to overload the first stage. I think it's also part of what makes the amp so touch sensitive. It may also be aggrevated by the lower plate voltage. (A Vibroverb runs about 220V on the plates, about 25V higher than Dumble.)

I sounds like you've done a good job of isolating the problem to the first gain stage. Now it should be relatively simple to tweak for a bit less gain by reducing the size of the bypass cap, attenuating the input, or raising the headroom of the first stage. Assuming you don't find any faulty components, my vote would be to first try a 5uF bypass cap with 33k grid resistor. If that moves you in the right direction, just tweak from there.

Of course, this is all just speculation. I'm just a "layout" guy, not an EE. I rely on guys like Scott, Gil, Moss, Bob-I, et al for my engineering expertise.

[Svempan]

Just to be clear about the distortion, are you talking about the bass notes farting out when you really dig in to low notes? (Almost sounds like a bad speaker.) If so, I've experienced this with nearly every Dumble style amp I've ever built. With only 1M/22k loading the grid of V1a, it's probably too easy to overload the first stage...

Normster,

Your right in your description of the distortion. That’s exactly how I hear it.

Also interesting that you've experienced this with nearly every Dumble style amp you've built .
One of my own amps (I call it "Clean King" and have told about it hear on Amp Garage before), which has a design influensed by Steel String Singer with EF86s in the preamp, doesn't have this uggly distortion.

Se my next reply for more information on Johan's D-Lite.

[Svempan]

OK. Now I've done some things and am satisfied for now .

I've done most of dogears' suggestions except the ones in the power supply. I've also changed the first tube to a NOS GE 5751.

I also tried different values on the FET simulator resistor and also tried without this resistor. The problematic distortion this thread is about is worse with this resistor, and even worse with 150k than with 220k. As I couldn't(?) hear any advantages in the sound with this resistor, I removed it.

The Gibson SG I mostly have tested the amp with before has PRS McCarty pickups. Now when I've played more with some of my Strats and with my '66 Gibson 335 I've really realized how much higher the SG's output is.

Now when I play with Strats or with the 335 I don't hear any of the ugly distortion in question, even when I really dig in to low notes.

I also think that the sound is better now after the mods suggested by dogears. Thank you!

The changes I've done to get me satisfied is:
- Raised V1a grid resistor to 33K.
- Changed the bypass caps on V1a and V1b to 4.7uf.
- Changed the silver mica 390pf on the V1b grid resistor to a 470pf ceramic.
- Changed the treble cap to a 330pf ceramic.
- Replaced the 0.0012uF on bass pot with a 0.001uF ceramic.
- Changed V1 to a 5751.
- Reduced the negative feedback resistor to a 4.7k.
- Replaced screen resistors with 470ohm.
- Took the FET simulator resistor away.

Regarding the choke replacement resistor I want to discuss that with Johan (among other things). I think the sound is rather good now with the 500ohm resistor and the 470ohm screen grid resistors. Personally I think I would preferred a choke, but this will be one of the things Johan and I have to discuss. But we will discuss SOUND, not the technical stuff...

Johan! Using this resistor instead of a choke is called "the Robben Ford mod". The sound gets a little more compressed and could maybe be described as a little smoother.

For you who are interested, the voltages on the tubes is now as follows:
V1a plate: 200V
V1a cathode: 2.3V
V1b plate: 208V
V1b cathode: 2.2V

V2a plate: 240V
V2a cathode: 2.0V
V2b plate: 240V
V2b cathode: 2.0V

V3a plate: 311V
V3a cathode: 60V
V3a grid: 37V
V3b plate: 296V
V3b cathode: 60V
V3b grid: 39V

V4 and V5 plate: 418V
V4 and V5 screen grid: 416V
Bias -45V gives approximately 27mA cathode current per tube when idling.

I will send the amp to Johan in the beginning of next week. Then we will meet next Saturday on a tone party with a couple of other guitarist friends. I look forward to hear Johan’s comments then .

[Structo]

I reevaluated my D'Lite 44 today and it has pretty good cleans up until the output tubes saturate.
I mean this thing can bark!

It's all stock at this moment.
I may be getting some low order parasitics but it's hard to tell if it's my speakers or the combo the head is sitting on that has a reverb pan in it.

[dogears]

Svempam,

Good to hear it is better! I'd strongly urge that you change the string to 22K/2.2K. The V2 voltage is way too high for sweet OD. If you like 200V on V1, the new string should keep it around there, but lower V2 alot. Try the 220K FET simulator again once the string is in. Let me know!