DGT 15

These are the things that keep the over thinker up at night ; )

Overthinking for sure!! But that's what the lifetime "gear quest" is, right? I mean, if we stopped overthinking we'd be happy with the first couple of guitars and amps we bought, and play them forever.
 
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The Russian military power tubes sound subtly more like the DG30 to me, than the JJs do. He might be right tho- a hotter V1 tube could cause the same thing. Who knows.

I wonder if the 15 has the huge transformers the 30 does?
 
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So, a DG15 with the Russian NOS military power tubes seems like a real option here, DG agrees they get it closer to the DG30. So now I may be back in the market for one...
 
So, a DG15 with the Russian NOS military power tubes seems like a real option here, DG agrees they get it closer to the DG30. So now I may be back in the market for one...

Great to hear. I fell into a batch of those a few years back. It’s all I use… strong midrange and clean! My amp is shipping today so mid next week! Here we go!
 
Great to hear. I fell into a batch of those a few years back. It’s all I use… strong midrange and clean! My amp is shipping today so mid next week! Here we go!

Be sure to give us a before/after comparison of the JJs/Russian tubes! Very interested! I like everything about the DG15, except that slight lack of clarity that is obviously present in the DG30. In David's video, you can here the Russian tubes help that... he never did do a DG30 vs a DG15-with-Russian-tubes... that would be very telling.

I can afford the 30, it's not about the money. It's about the volume. I know it's got a MV but I don't really know how well it works, I've never seen anyone really demo that feature of the 30.
 
Be sure to give us a before/after comparison of the JJs/Russian tubes! Very interested! I like everything about the DG15, except that slight lack of clarity that is obviously present in the DG30. In David's video, you can here the Russian tubes help that... he never did do a DG30 vs a DG15-with-Russian-tubes... that would be very telling.

I can afford the 30, it's not about the money. It's about the volume. I know it's got a MV but I don't really know how well it works, I've never seen anyone really demo that feature of the 30.

I’m an amp builder as well… already wondering about increasing the plate voltage to the DGT30 spec.
 
I’m an amp builder as well… already wondering about increasing the plate voltage to the DGT30 spec.

Well that's interesting... I have a feeling that IS what the big difference is in these 2 amps, especially since the 15 is rated for EL84s and the 30 is specifically rated for 7189s.... I'm guessing the 7189s, in the same circuit, would give a little more headroom than EL84s, due to their higher plate rating... and that's what it sounds like in the Grissom video... that would match my experience in the EL84 amps I have owned (and tried 7189s in)
 
Well that's interesting... I have a feeling that IS what the big difference is in these 2 amps, especially since the 15 is rated for EL84s and the 30 is specifically rated for 7189s.... I'm guessing the 7189s, in the same circuit, would give a little more headroom than EL84s, due to their higher plate rating... and that's what it sounds like in the Grissom video... that would match my experience in the EL84 amps I have owned (and tried 7189s in)

Well, I doubt that that change was to improve tone, but to make tube swaps easier.
 
Well, put in an order for a set of the 7189’s this morning. Don’t get me wrong, I’m very happy with the amp as-is, I just like to try different things! They really aren’t that expensive, I think about $70 with shipping, which is a steal for NOS power tubes.
 
Well that's interesting... I have a feeling that IS what the big difference is in these 2 amps
I’m going to guess there are other differences.

This is a gut shot of one of PRS’ other CAD amps, the HXDA. However, the DG30 is built the same way: hand wired with mil-spec tag boards, chassis mounted tubes instead of circuit board mounted, thick, welded aluminum chassis, etc.

People often disagree about whether this stuff factors into amp tone. I believe it contributes to a more transparent tone.

Even Mesa's Randall Smith has said on a video that he believes hand wired amps sound different, but that he prefers to have the consistency that's possible with circuit board amps. That's fine, it's a conscious decision by one of the masters of the circuit board amp.

Maybe someone will share what the DGT15's innards look like.

I don't have shots of my DG30's internal wiring, and I'm far too lazy to take the amp apart to take a pic, sorry.

VmDRI9E.jpg


As to how close the 7189s bring the 15 to the 30's tone, based on the video Grissom demo'd, I really don't think it matters all that much. They still sound different to me.

Again, different doesn't equal better or worse. It only means they don't sound the same.

I’m an amp builder as well… already wondering about increasing the plate voltage to the DGT30 spec.
Both Doug Sewell and Grissom have said that the DG30 will literally melt the power tubes without the dual fans. So if you're moving a DGT 15 to the DG30 spec, you might want to be extra careful.
 
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Both Doug Sewell and Grissom have said that the DG30 will literally melt the power tubes without the dual fans. So if you're moving a DGT 15 to the DG30 spec, you might want to be extra careful.

Well that's interesting!
 
Well that's interesting!
It is! PRS also recommends giving the head at least a foot of air space in front and behind the amp, so the fans can operate most efficiently.

The DG30 also has a grille cloth that can be seen through in certain light, so the fans can best draw air over the power tubes. For whatever reason, I can't see through the grille on the HXDA or my Mesas, though the Lone Star also has a fan for the power tubes.

The only other amp heads I've owned that I could see through the grille cloth to the tubes were my Two-Rocks, though they didn't have fans, at least not the kind with propellers (I was a fan ;)).
 
It is! PRS also recommends giving the head at least a foot of air space in front and behind the amp, so the fans can operate most efficiently.

The DG30 also has a grille cloth that can be seen through in certain light, so the fans can best draw air over the power tubes. For whatever reason, I can't see through the grille on the HXDA or my Mesas, though the Lone Star also has a fan for the power tubes.

The only other amp heads I've owned that I could see through the grille cloth to the tubes were my Two-Rocks, though they didn't have fans, at least not the kind with propellers (I was a fan ;)).

The only other amp I've owned with a cooling fan was the Genz Benz Black Pearl (one of the few pieces of gear I wish I still had- it was awesome), also running EL84s very hot. It was more of a Matchless/Badcat/AC30 thing.
 
The only other amp I've owned with a cooling fan was the Genz Benz Black Pearl (one of the few pieces of gear I wish I still had- it was awesome), also running EL84s very hot. It was more of a Matchless/Badcat/AC30 thing.
I appreciate it when an amp designer says, "Know what? This thing is gonna run hot. Let's prolong the life of the components by putting in a cooling fan," as long as the fan isn't loud. In the cases of both the DG30 and Lone Star, the fans are very quiet.
 
Well, back home from a week's vacation and the 7189's were waiting for me. Comparing quick recordings of each indeed produces differences I would call mild, which was pretty much as expected, although I do prefer the 7189's. Perhaps a hair less saturation than the stock JJ's with the master wide open, and the EQ analyzer indicates a slight cut in the 150-250Hz and a little more in the sub 100Hz and 400Hz-3K but repeated tests are showing only about 1-2 dB difference at most. Overall it's a slight clarity improvement similar to what one might do with some EQ in the mixing stage (except the sub-100Hz).

DG's video shows that the 15 tends to have a little more gain at the same preamp settings, so I think there's a case to be made to run the gain a hair lower on the 15, even with the 7189's.
 
Well, back home from a week's vacation and the 7189's were waiting for me. Comparing quick recordings of each indeed produces differences I would call mild, which was pretty much as expected, although I do prefer the 7189's. Perhaps a hair less saturation than the stock JJ's with the master wide open, and the EQ analyzer indicates a slight cut in the 150-250Hz and a little more in the sub 100Hz and 400Hz-3K but repeated tests are showing only about 1-2 dB difference at most. Overall it's a slight clarity improvement similar to what one might do with some EQ in the mixing stage (except the sub-100Hz).
Because standard EL84s are to be avoided in the DG30, I can't make a comparison without risking damage to my amp, so it's interesting to read about how the tubes sound different in the 15, even if the difference is small.

Based on your measurements, I'd definitely expect a little less low-mid mud, with midrange lift adding some clarity, so your description seems right on.

THD, clipping and other distortion artifacts also affect the character and feel of the amp, so it seems there might be a combination of factors at work beyond frequency response that affect the clarity when the tubes are swapped, especially because the 7189s are run so hot in the 30W.
 
Les, I have looked up what THD is on more than one occasion. If I have ever understood it, it didn’t stick. Can you give a simple explanation of what is meant by THD?

Sad thing is, I even have a THD Univalve amp, and I still can’t remember.
 
Les, I have looked up what THD is on more than one occasion. If I have ever understood it, it didn’t stick. Can you give a simple explanation of what is meant by THD?

Sad thing is, I even have a THD Univalve amp, and I still can’t remember.
THD = Total Harmonic Distortion. It's one measurement of how much the signal is distorted as it runs through an amp or other circuit; there are other measurements as well.

I'm sure I'm oversimplifying here, and our electrical engineering friends can correct me, but these are the basics as I understand them:

Distortion is undesirable in hi fi (or most recording equipment), where you want the signal to be reproduced as closely to the original signal as possible. However, as you can imagine, it's. often desirable in guitar amplifiers.

A high fidelity amp has very little harmonic distortion, usually below a tenth of a percent, and in the case of the high end stuff, significantly lower.

A "clean" tube amp, on the other hand, often has as much as 10% THD without even cranking the gain. The distortion artifacts add the familiar "amp sound" to what's running through it, though the speakers have their own distortion. So the amp is throwing out added harmonics to the signal, and that can be pleasing to the ear.

Hi fi people often discuss the even-order harmonic distortion accentuated by tube gear vs the odd-order harmonic distortion produced by solid state gear, as a reason they prefer tube gear. However, with hi fi and recording gear the distortion is so low that solid state gear is just fine, and I don't find solid state recording or hi fi gear irritating to listen to.

Guitar amps, with their high levels of distortion are probably a different story.
 
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