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    ST70 or ST120?

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    sailor

    Posts : 269
    Join date : 2011-04-04

    ST70 or ST120?

    Post by sailor on Tue Aug 30, 2011 3:42 pm

    I have 2 sets of speakers. One is 99 db/1 watt the other is a set of maggie MGIIIa's that I have owned forever. About 83db/1 watt on a good day. My new amp would be used with the first speakers but I would like to have the option to use them with the Maggies. I know I will need the 12au7 driver board no matter which amp I choose. I also know that the 70 is not enough power to make the Maggies happy. I have hooked an old stereo 70 to them and they wanted more power. I also know from the stereo 70 that I had that The first speakers need as low a gain as is possible otherwise I may have a volume problem. I am using a transcendent sound preamp.
    Ok here is what I would like: The ST-120 with KT-120 tubes and the low gain driver board. Will it work? Is the gain higher at a given volume setting between the 70 and the 120. Also is there a gain difference at a given volume setting between EL34, KT88 and KT120's in the same amp. I'll probably buy this amp before the first of the year.


    pmit2188

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    Join date : 2011-08-13
    Age : 59
    Location : Michigan,USA

    Re: ST70 or ST120?

    Post by pmit2188 on Tue Aug 30, 2011 4:56 pm

    I don't have an answer for you but it would be nice to here from you if you decide to get the st-120. I just built the st-120 (kt88s) and am very pleased with it driving my Paradigm Studio 60s (89-92db). I'm currently using my preout on my receiver but am thinking about building a preamp and have been looking at Transcendent. It would be nice to know how your combination sounds if you add the st-120


    Last edited by pmit2188 on Tue Aug 30, 2011 5:00 pm; edited 1 time in total (Reason for editing : new info)

    Bob Latino
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    Re: ST70 or ST120?

    Post by Bob Latino on Tue Aug 30, 2011 7:08 pm

    It's tough to get ONE amp that will satisfy both 99 dB speakers and 83 dB speakers. The ST-70 with either the standard gain or lower gain board is not enough power to drive 83 dB speakers.

    What I would recommend in your situation is the ST-120 with the standard gain board and the stepped attenuator. The ST-120 would have enough power to driver your Maggie MGIIIa's to fairly loud volumes. With the 99 dB speakers you can then use the attenuator on the ST-120 as a master gain control. With your 99 dB speakers, set the attenuator at half volume and then use a preamp to drive the speakers. The use of the attenuator (in effect) lowers the gain of the amp and would require much more input from the preamp for a given volume level.

    Bob


    Last edited by Bob Latino on Tue Aug 30, 2011 8:50 pm; edited 1 time in total

    mantha3

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    Re: ST70 or ST120?

    Post by mantha3 on Tue Aug 30, 2011 8:22 pm

    I have the ST-120 with the stepped attenuator and it is awsome. If you go with a pre amp then you can just put the attenuator at the final step which is by-pass. Excellent! I love the CD player direct to the amp!!!

    sailor

    Posts : 269
    Join date : 2011-04-04

    Re: ST70 or ST120?

    Post by sailor on Tue Aug 30, 2011 10:20 pm


    Bob, too simple, the perfect solution, Thanks. Is the gain, at a set volume, about the same for all of the tubes? Also I have a ladder type stepped attenuator, how much clearance is there in that area? It's probably less than an inch longer.
    pmit2188, I have had the preamp for 8 years. I don't know how it compares with tubes 4 hifi's preamps. That would best be answered by them. If you go to tubes4HIFI's preamp site you will see that they will build the transcendent sound amp for you for $100, $599 total. I would also do all of the upgrades they show. They need to be done. If you build it yourself do the upgrades. Use the stepped volume. It is a no frills preamp. Not at all slow and tubbee. Sound wise, It is very very fast and detailed. It can't make a bad amp sound better. But it will let a great amp like yours sound as great as it can. Again ask tubes4hifi for there opinion, I want to buy one of there amps in the near future and want to stay on there good side.

    Bob Latino
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    Re: ST70 or ST120?

    Post by Bob Latino on Wed Aug 31, 2011 6:09 am

    There is not much room in the stereo/mono slot area for an attenuator. If you have an attenuator already you could try to fit it in but most attenuators made today will be too large for that area. The gain with the VTA standard gain (12AT7) driver board will be higher at any set volume level than the volume with the lower gain (12AU7/12BH7) driver board. The amp will achieve full power with either driver board but it will take more preamp drive level from your preamp to do so with the lower gain board.

    As has been mentioned before, the attenuator allows you to use any high level signal source directly into the ST-70/ST-120 - BUT - people forget that the attenuator may also be used WITH A PREAMP as a "master level control" to alter the gain of the ST-70/ST-120.

    Bob

    sailor

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    Re: ST70 or ST120?

    Post by sailor on Thu Sep 01, 2011 9:22 pm

    Actually it was the output tube gain at a given input I was not sure about IE: KT88 to KT120. Now another question. I used calipers to measure the ladder stepped volume control and it measures just under 1.5 inches Will that fit in 120 chassis. I know it would be tight. Also it would be the side of the resistors [insulated] so the would not need much clearance. Also 2 inches long, but I don't think that would be the problem.

    Bob Latino
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    Re: ST70 or ST120?

    Post by Bob Latino on Thu Sep 01, 2011 9:46 pm

    A KT120 with the same bias settings gave about 8 % more power than KT88's in the M-125 monoblocks. I am pretty sure that KT120's in the ST-120 will have a similar power gain over KT88 output tubes. IMHO you probably won't notice any real gain in power using KT120's over the KT88's when playing the amp.

    A stepped attenuator with a diameter of 1.5 inches is too large to fit into the stereo/mono area. You will be banging into the left channel input jack. The attenuators that I use are 7/8 inch in diameter and fit the stereo/mono area OK with very little room to spare.

    Bob

    sailor

    Posts : 269
    Join date : 2011-04-04

    Re: ST70 or ST120?

    Post by sailor on Fri Sep 02, 2011 9:11 am

    Thanks for the info Bob.

    sailor

    Posts : 269
    Join date : 2011-04-04

    Re: ST70 or ST120?

    Post by sailor on Fri Sep 02, 2011 6:23 pm

    One last question. The driver boards, I assume that the low and high gain pc boards are the same. Just some of the resistors and 3 tubes are different. Is this correct?

    Bob Latino
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    Re: ST70 or ST120?

    Post by Bob Latino on Fri Sep 02, 2011 6:42 pm

    sailor wrote:One last question. The driver boards, I assume that the low and high gain pc boards are the same. Just some of the resistors and 3 tubes are different. Is this correct?

    Yes - the "two" boards are exactly the same board but there are 16 resistors that are different from the standard gain board to the lower gain board. Eight resistors on each channel. Yes - the three tube are different also. Three 12AT7 tubes on the standard gain board and three 12BH7 or 12AU7 tubes on the lower gain board.

    Bob

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