JimL11
1000+ Head-Fier
Cool! Hopefully this means more people will build it. Note that they did not contact me before making this available, and I don't make any money from this.
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Stax SRM-T1 Repair, Re-Cap, Mod
- Thread starter spaceace1014
- Start date
I wrote that blog, Jim, and I'm not making money from it either. I just wanted to let you know what I did based on your suggestions.
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JimL11
1000+ Head-Fier
Ah, thanks! As you might have guessed, I don't read German.
Actually I have 
Part 4 went online yesterday: STAX Vacuum Tube Driver [Teil 4 - ECC99 Tube Swap]
CSS mod and ECC99 tubes go hand in hand just fine, I like it a lot!
CSS mod and ECC99 tubes go hand in hand just fine, I like it a lot!
- Joined
- Jan 15, 2015
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Just joined the T1 club and found this thread...
@Firschi - did you also post in English anywhere?!
My T1 arrived with no manual - is there a PDF version to be found somewhere?
How about maintenance docs / manual, for if/when maintenance is required? Schematics, instructions, anything.....
armani006
Member of the Trade: DIY cable maker
The Stax 006tII amplifier was upgraded using a CCS-Mode board from Dominik - @Firchi. The board was purchased from him and simply installed.
I note as a minus of upgrade - High frequencies have become sharper. At all levels, both on instruments and on slaps, cod and hissing sounds.
When playing the guitar in instrumental music, the nail strike on the strings became very sharp, somehow unnatural, just like a plastic blow
nails on plastic strings. The plates and jingle of the triangle also became sharper and more accented. Wind instruments also sound sharper. With a long listening, it is tiring. It is comfortable to listen quietly only.
In the middle frequencies, everything is better. As a plus of upgrade I count that the voices have become more accentuated. Compositions with good emphasis on vocals, they became more vivid, no matter female or male. The voice became intimate, close in sound to the listener. Very good effect.
As well as the plus - Percussion, the bass has become more defined, more emphasized. There was no more weight or amplitude in it, it just became clear, faceted, more punched.
The scene has become a little wider, the volume in the sound is more felt. Find out more the location of the tools.
In general, a distinctive digital signature appeared in the sound. The tube sound began to wander less. The original amplifier sounds soft, somewhere warmer
and just more veiled. With the upgrade, everything began to sound sharper and digital. For those who feed the amplifier from a good DAC without sharpness
such a sound would probably be a good combination. But if you have a sharp Delta-sigma DAC in the sound and need to be softened, then it probably will not work.
Probably this CCS-Mode modernized amplifier is closer to a transistor Amp, although it remains a tube amp in fact.
Now I’m thinking more about taking a multi-bit DAC. It would have approached this amplifier better than delta sigma.
The sound comes from the PC to the DAC via optics -192 / 24bit, the Audio-GD NFB28 DAC with the Saber 9018, Neotech Up-OCC copper interconnect cables.
Headphones SR-L500 + Custom mode leather Pads 2.5 cm thickness.
P.S.
after few month I've got R2R DAC it is Denafrips Ares II, now sound is more elastic and smooth. High sharpness from D/S dac has gone.. Now I really enjoy this duet R2R and CCSmodded Stax amp.
I note as a minus of upgrade - High frequencies have become sharper. At all levels, both on instruments and on slaps, cod and hissing sounds.
When playing the guitar in instrumental music, the nail strike on the strings became very sharp, somehow unnatural, just like a plastic blow
nails on plastic strings. The plates and jingle of the triangle also became sharper and more accented. Wind instruments also sound sharper. With a long listening, it is tiring. It is comfortable to listen quietly only.
In the middle frequencies, everything is better. As a plus of upgrade I count that the voices have become more accentuated. Compositions with good emphasis on vocals, they became more vivid, no matter female or male. The voice became intimate, close in sound to the listener. Very good effect.
As well as the plus - Percussion, the bass has become more defined, more emphasized. There was no more weight or amplitude in it, it just became clear, faceted, more punched.
The scene has become a little wider, the volume in the sound is more felt. Find out more the location of the tools.
In general, a distinctive digital signature appeared in the sound. The tube sound began to wander less. The original amplifier sounds soft, somewhere warmer
and just more veiled. With the upgrade, everything began to sound sharper and digital. For those who feed the amplifier from a good DAC without sharpness
such a sound would probably be a good combination. But if you have a sharp Delta-sigma DAC in the sound and need to be softened, then it probably will not work.
Probably this CCS-Mode modernized amplifier is closer to a transistor Amp, although it remains a tube amp in fact.
Now I’m thinking more about taking a multi-bit DAC. It would have approached this amplifier better than delta sigma.
The sound comes from the PC to the DAC via optics -192 / 24bit, the Audio-GD NFB28 DAC with the Saber 9018, Neotech Up-OCC copper interconnect cables.
Headphones SR-L500 + Custom mode leather Pads 2.5 cm thickness.
P.S.
after few month I've got R2R DAC it is Denafrips Ares II, now sound is more elastic and smooth. High sharpness from D/S dac has gone.. Now I really enjoy this duet R2R and CCSmodded Stax amp.
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armani006
Member of the Trade: DIY cable maker
I want to add to my previous post - now Stax headphones sound more close to HEDDs sound, not the same but closer. I owned HEDDs but sold because of weight and uncomfortably. Everything sounds more clear and I hear more room, more wider sound stage. Only one regret that hard rock music sounds more painful because of sharp trebles. But instrumental music now is fantastic. Only after hours of testing I can fix it. I think modded amp became more transparent, it has higher -dB resolution and shows clearly how DAC sounds. Before this mode I didn't hear big differences between DACs. The amp gives less of his own impact to the sound. I think now to buy multibit DAC.
Didn't like delta-sigma at all. I know this cus I compare Stax amp to the HEEDs headphones drive by the same Audio-GD. Now they both sound more equal as before modding.
Didn't like delta-sigma at all. I know this cus I compare Stax amp to the HEEDs headphones drive by the same Audio-GD. Now they both sound more equal as before modding.
JimL11
1000+ Head-Fier
The Stax SRM-006 is basically the same circuit as the SRM-T1, other than transistor substitutions as old types became obsolete. Back when Kevin Gilmore wrote up his triode electrostatic amplifier he commented that the T1 "is actually a really good unit, but..as it gets louder and louder, the sound becomes more restricted, and...the amount of high-frequency energy slowly disappears."
I believe the reason for this is that the output tube plate resistors suck up the majority of the signal current by Ohms law, V = IR. The plate resistors have to have a lower impedance than the headphone, in order to supply enough current to drive the headphones, but that also means that it burns up the majority of signal current as heat. The current demands are most severe at low frequencies due to the bulk of music power being in the low and low-middle ranges (roughly half of the power being at 250 Hz and below, depending on the type of music), and at high frequencies, because electrostatic headphones, which resemble capacitors, need relatively high currents to drive the voltage swings.
The constant current load mod replaces the resistors with a circuit that is very high impedance at audio frequencies, but allows enough current flow to drive the headphones. This basically eliminates the signal current wastage of the plate resistor, allowing the output tubes to supply more than double the amount of current to the headphones, while decreasing the overall load on the tubes, which also decreases distortion. Thus, the high frequency signals are stronger, as is the bass, resulting in the difference in sound signature you hear. I believe it is more faithful to the source, but it may or may not be more pleasant to hear. I think the mod is sonically pretty transparent. The reason I believe this to be the case is that the same mod, applied to the old Stax all-tube SRX circuit, is the basis for the SRX Plus circuit. A number of critical listeners have heard that amp, and none of them have ever complained of any solid-state dryness or sharpness to the sound.
I believe the reason for this is that the output tube plate resistors suck up the majority of the signal current by Ohms law, V = IR. The plate resistors have to have a lower impedance than the headphone, in order to supply enough current to drive the headphones, but that also means that it burns up the majority of signal current as heat. The current demands are most severe at low frequencies due to the bulk of music power being in the low and low-middle ranges (roughly half of the power being at 250 Hz and below, depending on the type of music), and at high frequencies, because electrostatic headphones, which resemble capacitors, need relatively high currents to drive the voltage swings.
The constant current load mod replaces the resistors with a circuit that is very high impedance at audio frequencies, but allows enough current flow to drive the headphones. This basically eliminates the signal current wastage of the plate resistor, allowing the output tubes to supply more than double the amount of current to the headphones, while decreasing the overall load on the tubes, which also decreases distortion. Thus, the high frequency signals are stronger, as is the bass, resulting in the difference in sound signature you hear. I believe it is more faithful to the source, but it may or may not be more pleasant to hear. I think the mod is sonically pretty transparent. The reason I believe this to be the case is that the same mod, applied to the old Stax all-tube SRX circuit, is the basis for the SRX Plus circuit. A number of critical listeners have heard that amp, and none of them have ever complained of any solid-state dryness or sharpness to the sound.
armani006
Member of the Trade: DIY cable maker
Perfect explanation Jim, same as I thought.. I like the amp is more transparent. I enjoy it.
It could be interesting to measure it as Amir from audiosciencereview.com do this..
Can't say if it sounds dry and sharp as solid-state amp, but higher sharpness in sound in compare to original amp comes from your explanation above, so it's noticeably and it is loss of original sound signature for those who prefer original sound.
For me personally it is good to have more transparent amp. Think that this CCS-mode is "must have" for those who don't care about originality of Stax.
It could be interesting to measure it as Amir from audiosciencereview.com do this..
Unfortunately I don't have solid-state amp to make A/B comparison, so have no idea what to think about this. May be someone can explain or already did this.
Can't say if it sounds dry and sharp as solid-state amp, but higher sharpness in sound in compare to original amp comes from your explanation above, so it's noticeably and it is loss of original sound signature for those who prefer original sound.
For me personally it is good to have more transparent amp. Think that this CCS-mode is "must have" for those who don't care about originality of Stax.
armani006
Member of the Trade: DIY cable maker
Jim. any ideas how to improve power section of amp? I mean power transformer, is it any better variants on market?
Krassi
100+ Head-Fier
Wow thats really interesting and since i am german i dondt need any translation.
I got a very nice condition t1 from a yahoo japan auction and also shot me some nos toshiba tubes for it.
its very interesting what can be modified on that amp!
I got a very nice condition t1 from a yahoo japan auction and also shot me some nos toshiba tubes for it.
its very interesting what can be modified on that amp!
armani006
Member of the Trade: DIY cable maker
Ask @Firschi to assist you. (He is also available here https://www.prof-x.de/forum/viewtopic.php?f=4&t=480&sid=6fdece4f19de7aa48f4c3d2e9e291281&start=120)
Jim, any ideas how to improve power section of amp? I mean power transformer, is it any better variants on market?
Krassi
100+ Head-Fier
Thanks for the Tip.. i already read the full post there and i actually will
I will pm him. Sounds really crazy what can be done with a t1
I will pm him. Sounds really crazy what can be done with a t1
armani006
Member of the Trade: DIY cable maker
this is actually a huge improvement and "must have" option, I feel this effect only after a week of testing. It's difficult to fix it fast manner but lately - sound control, deep bass responce, wide sound stage.. ask Dominik, you should have it and make feedback here ))
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