I realized I should have put this thread here in the tube section.
I simply cannot afford this product I want. I'm wondering if there is anyone I could pay to help me design a clone of this? Or if there is a DIY product on the Forum like this with plans I could build one from? If you scroll down the page you can see a photo with the top off.
DECWARE all tube gain stage / purist preamp model ZSTAGE
I simply cannot afford this product I want. I'm wondering if there is anyone I could pay to help me design a clone of this? Or if there is a DIY product on the Forum like this with plans I could build one from? If you scroll down the page you can see a photo with the top off.
DECWARE all tube gain stage / purist preamp model ZSTAGE
Please take a look at the Akido line amps:-
GlassWare Line Stage & Headphone Amplifiers Kits and PCBs
Depending on the tubes used, the gain ranges from 8x to 45x.
I am in the process of building a line stage for a SE amp using 12AX7s. The pcb is very high quality.
GlassWare Line Stage & Headphone Amplifiers Kits and PCBs
Depending on the tubes used, the gain ranges from 8x to 45x.
I am in the process of building a line stage for a SE amp using 12AX7s. The pcb is very high quality.
The price isn’t bad for tube gear. Source all the parts and some machining on the case and you’ll easily be at $200. Unless of course you live in China.
Possibly both. It started out just wanting to add some tube warm without any sound degradation. Now I found my new amps have a 7K input impedance, so I may need gain now as well.
I wish I knew how to get the parts list for a Decware Zstage. I do NOT need a case, which should be a lot of the cost of a Zstage.
The schematic, with parts values, are at the kit link posted earlier. See post #2.
I'm not aware that the input impedance of an amp has any relation to whether or not you need gain. As far as I know it's related to the output level of your source and the input sensitivity of the amp. Many modern sources (CD players, DATs, for instance) have an output of 2v. Most SS amps can be driven to full power by less than that. So a so-called "passive preamp", which is nothing but a simple volume control, can be used and no gain is really needed.
What is the input sensitivity of your amp? What sources are you using?
Keep in mind that, ideally, you want the output impedance of a preamp to be ~10% of the input impedance of your amp. That would be 700 ohms, in your case, which is very low and in line with a typical SS preamp.
On the page about the prebuilt version, they claim it's under 1k, but they don't give an actual figure. My technical understanding is limited but I question whether it's that low considering the tubes it uses.
I forget the actual formula but I believe it's related to the plate resistance of the tube. Each section of the 12AU7 has a plate resistance of 6.5k.
I would think that you would need to put a cathode follower between it and the amp in order for it to be under 1k. I've seen schematics of one of the Decware amp kits, posted on their website, that had several errors in it, so I'm skeptical.
Perhaps some of the more technically gifted people here could comment on the actual output impedance.
Not sure why this particular preamp appeals to you, but I think I'd look elsewhere.
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When I first looked at the pic of the unit I thought something was missing . . . the tubes. Then I noticed that it seems to have single 12AU7 whose top is protruding through the front panel.
Since it's stereo and only has one dual triode, then each channel uses a single section whose plate resistance is 6.5k.
Edit: I thought the kit showed the sections in parallel, but I was mistaken.
The manual for the prebuilt one also indicates that it has adjustable gain. It shows an illustration of a knob that allows for continuous adjustment "from 0 to 5 volts or more". Yet, if you look at the pic, the only pot shown is on the input.
So there seems to be a disconnect between what is pictured and what they claim to be selling. And this is not a new product, the date on the manual is Jan 2011. Errors such as this on a company's website, IMO, shows a severe lack of attention to detail.
Since it's stereo and only has one dual triode, then each channel uses a single section whose plate resistance is 6.5k.
Edit: I thought the kit showed the sections in parallel, but I was mistaken.
The manual for the prebuilt one also indicates that it has adjustable gain. It shows an illustration of a knob that allows for continuous adjustment "from 0 to 5 volts or more". Yet, if you look at the pic, the only pot shown is on the input.
So there seems to be a disconnect between what is pictured and what they claim to be selling. And this is not a new product, the date on the manual is Jan 2011. Errors such as this on a company's website, IMO, shows a severe lack of attention to detail.
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I can tell you why the decware tube gain stage appeals to me. I read where my icepower amplifiers need 5 volts to be driven to full power rating. Their advertising claims say this makes music sound better because it increases the voltage to 5 volts output, and that is what got my attention. That is the only reason I'm stuck on this product, but after reading what some of you more technical guys have said, I'm not sure it's not way overblown in price and something really simple. But if this is so I don't understand the 6-month wait. That tells me the product is really great and sought-after, but I don't know if it's what I need or not now. I may be saying input impedance, when I mean to say input sensitivity. There are a lot of threads about input rating on the icepower asp1000, needing good voltage to drive it. But I am so technically challenged! I know this is the DIY forum, and I can build and design the hell out of a pair of speakers. I'm lost on electronics outside of passive crossovers though. Everything that was mentioned in the post above, regarding the technical details of the decware went right over my head mostly.
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Please allow me to try again to explain what I'm trying to do and what I need. I have a computer with USB out to a topping D90. I've Been Told using the volume control on the D90 will give me poor sound, compared to using it as a standalone DAC. I need a simple way to control volume to my icepower asp1000 amplifiers. So it seems I need more voltage than the D90 is going to put out. So I assume I need a preamplifier, voltage gain stage, or maybe something else I'm not aware of. Using icepower amps will not get me for the warm side of things so I considered using tubes to do this volume control with. But I am so lost! I've never used amplifier that require something special for a preamp before.
I've copied and pasted the below from another thread. This is the kind of information I'm finding. This is what I'm concerned with and asking about.
"I've read that the ASPs have very low input impedance, 7kOhms, so that could be a problem when hooking it up with a pre-amplifier.
Especially if you are using a tube pre-amp.
I think, and I'm really not an expert on electronics, that it should have at least a 100kOmh input. No?
One way to solve this problem, at least that is what I've heard, is to use a direct-coupled, balanced, dual FET input stage (input buffer).
The
I saw a post once @ DIYAudio regarding a project for a balanced dual FET input stage... Do you have any knowledge on the subject? Would anybody recommend the use of such a input stage on ASP 1000"
"I've read that the ASPs have very low input impedance, 7kOhms, so that could be a problem when hooking it up with a pre-amplifier.
Especially if you are using a tube pre-amp.
I think, and I'm really not an expert on electronics, that it should have at least a 100kOmh input. No?
One way to solve this problem, at least that is what I've heard, is to use a direct-coupled, balanced, dual FET input stage (input buffer).
The
I saw a post once @ DIYAudio regarding a project for a balanced dual FET input stage... Do you have any knowledge on the subject? Would anybody recommend the use of such a input stage on ASP 1000"
Here is a post from another similar thread.
"Because of the relative low input impedance of amp you need low output impedance driver. You can use pre-amp with low output impedance or imo best solution TVC (transformer volume control). .
I faced the same issue with L15D Pro modules which have 3.3kOhm input impedance. Also tried resistance devider in front, which reduces gain but also affects audio quality. So a potmeter (passive Pre) will not work (high output impedance compared to the low input impedance of amp).
I tried several active pre-amps designs (tubes, Fets for very low output impedance) but was not satisfied. Then I decided to use step-down transformers because they will lower the output impedance by square times voltage division (I.e. voltage divided by 2 means impedance lowered 4 times). I ordered Sowter attenuators type 9150 which gives steps of -10 dB. Well, this works! Great sound not affected by attenuation as with potmeter"
"Because of the relative low input impedance of amp you need low output impedance driver. You can use pre-amp with low output impedance or imo best solution TVC (transformer volume control). .
I faced the same issue with L15D Pro modules which have 3.3kOhm input impedance. Also tried resistance devider in front, which reduces gain but also affects audio quality. So a potmeter (passive Pre) will not work (high output impedance compared to the low input impedance of amp).
I tried several active pre-amps designs (tubes, Fets for very low output impedance) but was not satisfied. Then I decided to use step-down transformers because they will lower the output impedance by square times voltage division (I.e. voltage divided by 2 means impedance lowered 4 times). I ordered Sowter attenuators type 9150 which gives steps of -10 dB. Well, this works! Great sound not affected by attenuation as with potmeter"
You can use a MOSFET as a source follower as a buffer on the output of a tube preamp. That way the tube doesn't have to try to drive the low input impedance of the solid state power amp.
You could also use a tube as a cathode follower but you will get lower output impedance from a MOSFET source follower, and the MOSFET of course does not need a heater supply.
You could also use a tube as a cathode follower but you will get lower output impedance from a MOSFET source follower, and the MOSFET of course does not need a heater supply.
And I also read this below in quotations. On another thread I read where people are talking about using professional direct interface boxes. This is getting crazy. I just need a few recommendations for the best solution without degrading sound quality. Unless I'm mistaken, I'm needing high output impedance from a preamp. Somewhere around 100k. Will input buffers do this for me, or are they just to lower the volume? Can I use a stepped volume control, or is that only used to lower the volume? Or do I need to Simply by the correct balanced output preamp?
"It is unfortunate that the ICEPower 1000ASP has such a low input impedance (I believe it is 10K, not that it matters). You can build a buffer and place it in front of the Icepower to raise its input impedance...thats what a Jeff Rowland 501 has, and a hefty price tag...."
"It is unfortunate that the ICEPower 1000ASP has such a low input impedance (I believe it is 10K, not that it matters). You can build a buffer and place it in front of the Icepower to raise its input impedance...thats what a Jeff Rowland 501 has, and a hefty price tag...."
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Slightly under 3V RMS actually.
D90 is capable of producing 4V RMS on its XLR outputs, and ASP1000 can be used in the balanced mode too - you don't really need any gain in that case, just the quad audio taper pot (or stepped attenuator) and four source/cathode followers.
If you opt for keeping the non-balanced configuration, you'll need 2-3x gain. That's not easy to do in a sane way with just the tubes.
I know what a stepped attenuator is, but what is a quad audio taper pot ? Is this just another type of attenuator? So please let me ask for simplicity's sake. The way you are suggesting me run this, is my DAC wide open on its volume. Then use and attenuator all the way down to zero for no sound, and simply turn it up for my master volume. Is this correct?
And when you mention four source/cathode followers, are these something that adds tubes for the warmth and tube rolling I wanted to try? Or something else? Thanks for your patience.
I appreciate you letting me in on the specs of the D90 on the balanced outputs. I will definitely be going balanced. Someone sent me a link for a Gold Point stepped attenuator, but it was almost $600. I buy a preamp first. So so let me ask, there are a million stepped attenuator at every price point on the net. Do you know if any reasonably priced, say no more than $300 attenuators which will not hurt my sound quality and are balanced? Ready to purchase, and this is why I'm asking such Direct questions. Thank you so much for the help.
And when you mention four source/cathode followers, are these something that adds tubes for the warmth and tube rolling I wanted to try? Or something else? Thanks for your patience.
I appreciate you letting me in on the specs of the D90 on the balanced outputs. I will definitely be going balanced. Someone sent me a link for a Gold Point stepped attenuator, but it was almost $600. I buy a preamp first. So so let me ask, there are a million stepped attenuator at every price point on the net. Do you know if any reasonably priced, say no more than $300 attenuators which will not hurt my sound quality and are balanced? Ready to purchase, and this is why I'm asking such Direct questions. Thank you so much for the help.
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