I'd like to lower the gain of an AE-3 DJH preamp to something in the neighborhood of 10 dB. Is it possible to do this without adversely affecting the sound?
My ASL amps have an input sensitivity of 1.0 v. I want to have good volume control over low listening levels. I'm afraid any preamp with more than 10 dB will force me to stay under 9 o'clock on the volume knob.
This is a FAQ. Preamp gain, especially tube preamp gain, is far too high for line sources when the speakers are of average (say 88 db) efficiency. The cure is to put resistance at the amplifier input. The easy way to determine the amount needed is to put a potentiometer (volume control) in the line and measure the amount of resistance required to make the preamp volume control usable. Any tech can do this for you. I got especially peeved when I had the amp and preamp from the same manufacturer and the same series (CJ in my case) and the mismatch was horrid. A switch and a few resisters at the power amp input is the fix which the manufacturer should provide.
The manufacturer or a modifier can do it internally/elegantly.
I like this idea. I sent a message to Cary and AES to find out what they recommend. I'm waiting to hear from them.
A switch and a few resisters at the power amp input is the fix which the manufacturer should provide.
When preamps offer switchable gain, is it usually a voltage divider design?
Along with Rothwell and Endler, I found Harrison Labs. The Endlers use Yaego metal film resistors which are about the cheapest resistors you can get. This doesn't instill confidence that they're transparent. Rothwell and Harrison don't say what they use.
I'll wait to hear from Cary to find out what they say. The gain of the AE-3 DJH is 20 dB which is definitely high... especially for me since I've been using passive preamps the past year.
Bob, I completely agree with you, but Kevin at Upscale assured me that he's never had a problem mating an AE-3 DJH with amps that have less than 1v input sensitivity. My DAC has an output of 1.8v which is less than your average 2v. My speakers are 87 dB inefficient, so that may help tame the gain as well. I don't have the AE-3 in my possession, so this may be a moot exercise, but I'm preparing myself for the worse case scenario.
I built my own balanced attenuators for the input side of a tube preamp using Vishay resistors from Partsconnexion. I was able to try a few combinations first then zero in on the level of reduction that worked best. I also tried the Endlers, which were ok, but not as good as the ones I made. You could easily build them inside the preamp, and that way you would only have to reduce gain at one of the inputs. I would stick with the least amount of attenuation that works for you, since I believe that attenuation reduces dynamics.
I would second Mitch2 both on building own with the least attenuation that works and on reducing gain at individual inputs. The second point may be more important on older equipment where phono/tuner outputs are lower than on the digital source. Can make a big difference in "listenability". If not here someone at the diyaudio.com will tell what value to use. It's pretty easy to diy and you can pick the parts. Good luck.
Since your preamp uses 6SN7s and you say you are comfortable with DIY, you might want to try something similar to the modification I made to my Supratek Chenin preamp. I built two adapters that let me use 7193 (aka 2C22) single triodes instead of 6SN7s. They are half the gain of a 6SN7, cost $5-10 each, look pretty cool with their dual top caps, and IMHO sound much better. I have detailed the modification on the last page of the "Preamp Deal of the Century" thread if you are interested.
Here are a couple of links; http://www.play-hookey.com/dc_theory/voltage_divider.html and http://www.goldpt.com/mods.html
I built external dividers since I wasn't sure whether I was going to keep that particular preamp (which I didn't), but if you are happy with your system and your preamp, I still recommend internally constructing the dividers, or as Goldpoint calls them; "preattenuation circuits." I can send pictures of my balanced dividers to you if you e-mail me privately.
Ait, I appreciate you pointing this out to me. Your mod sounds very intriguing. You know a lot more about tubes and circuits than I do. After reading your description, I see there's very little in the way of actual changes (just two wires if I'm not mistaken), but I have to wonder if your instructions translate to the AE-3. I'm a bit leery of changing the circuit. I might revisit this another day, but for now I'd like to try something less risky.
Mitch2, thanks for those links. I figured it was a voltage divider. I'll email you for pics and values you used.
I used to own the DJH preamp with 2 different SS poweramps (Linn Klout and Pass Labs Aleph 30) and its 20 db gain had me clipping the amps at 11 o'clock. I sold it because it had little volume control adjustment, even if it did sound awesome.
This preamp was designed for use with the Sixpacs. I think it would also work with the earlier Rocket 88 (non R). I liked the DJH pre a lot but feel it still won't work with the new Superamp 2 that I now own. I would call Cary's tech suport (same for AES), and ask about a recommended mod for it. 919-355-0010 They are up on this design.
Hi Mjcmt, I've been emailing with Gerald Walsh at AES. He said they can reduce the gain to 10 dB. I'm considering it. It's only $125. But I know I could build attenuators for a fraction of that price (probably using better resistors), so that's my dilemma.
AES has been tough to communicate with. Most of my questions have gone unanswered. I'd rather not deal with that (whether it's attitude or being too busy I don't know). I can easily build my own attenuators. According to Goldpoint's website, I need 68.1K and 46.4K resistors to reduce the gain by -10 dB when dealing with an input impedance of 100K. I'll use Texas Components TX2575 resistors. I don't think there's anything more transparent available.
Thanks for all your replies. I appreciate your help.
It is funny that you have had problems with Cary (AES). Every time I called Cary and told the receptionist I wanted to talk to someone about an AES product technical support I got transfer immediately. He would look up the schematic and have an answer. One time he didn't have an answer and put me on hold for a very short time while he spoke to Dennis Hadd for an answer. I'm really impressed. (The only time I couldn't get transfered was at lunch from 12-1 EST)
Mjcmt, I appreciate your info. I've been emailing with Gerald at AES, but his replies have been intermittent and sparse. I haven't tried to call. Maybe I should have done that, but he seems either too busy to answer my questions or not interested in supplying information that doesn't directly lead to a service fee. From my perspective, I think it's a fair question to ask if resistors will be added to the signal path to reduce the gain or if the original circuit will be modified. If I sell the unit, I need to disclose any changes to the buyer.
At this point, I think my best option is to use in-line attenuators and keep the unit in stock form. I have a hunch Cary's mod would be the same thing, but tucked inside the chassis. If I use attenuators, I can change them at any point in time. A mod will be permanent.
Ask them what to do. They really will help if you call and they will recommend what mod to do inside the chassis if you want to do it. They are a bit slow on emails, but are a great source of knowledge if you call.
I just bought a pair of Rothwell attenuators with -10 dB which is perfect for my situation. I think it's the right thing to do given that I can change the attenuation myself at any point in time. Thanks again, Mark
Mboldda1, I recently bought the Goldenjack attenuators from Iain in the UK (the -14dB version), and they allowed me to do away with my preamp and the set of ICs. They are very transparent, and allowed me to maximize the use of my DACT attenuator on my CDP. Highly recommended!